Cephalopoda Glossary

Richard E. Young, Michael Vecchione, and Katharina M. Mangold (1922-2003)


Abdominal septum - See mantle septum.

Aboral - Away from or opposite the mouth.

Abyssal - The great depths of the ocean (See Cephalopod Ocean Habitats).

Accessory gland complex - The glandular complex in cirrates that forms sperm packets and is a counterpart of the spermatophore-forming complex of other cephalopods.

Acetabulum - See sucker.

Adult - A female that has mature eggs (these are frequently stored in the oviducts), or a male that has produced spermatophores (these are stored in Needham's sac).

Afferent nerve - Nerve carrying impulses toward the brain or specific ganglia.

Afferent vein - Vein carrying blood toward an organ.

Anal flaps (= anal valves) - Small flaps on the lateral sides of the anus (See Digestive System Terminology).

Anterior - Toward the head end.

Anterior salivary glands - Glands on or in the buccal mass that aid in preliminary digestion (see: Digestive System Terminology).

Antitragus - Knob that projects inward from the posterior surface of the central depression of the funnel lock of some squids (mostly chiroteuthids and mastigoteuthids) (see: Funnel lock).

Apomorphic - Derived from a more ancestral condition. Loosely considered the "advanced" condition.

Areolar spots - Circular spots, generally light colored but often with complex pigmentation and of unknown function that occur in lines along the aboral surfaces of some arms and portions of the head in some opisthoteuthid cirrates.

Arm - One of the circumoral appendages of cephalopods. In decapodiforms each member of the fourth pair of arms is modified to form a tentacle.

Arm formula - The relative sizes of arms arranged according to their length. The largest arm is indicated first and the shortest last. An example arm formula is IV>III=II>I. Here arm IV is the largest, followed by arm III which is the same size as arm II and both are larger than arm I.

Armature of the arms - The grappling structures on the oral surfaces the arms and tentacles, including both suckers and hooks (see: Arm Armature).

A-seriation - Type of cusp arrangement on the rachadian tooth of the radula: multiple cusps seem to move laterally when viewing successive rachadian teeth from adjacent rows.

Autotomy plane - Plane through an arm of an octopod that is predisposed to break when the arm is autotomized.

Bactritida - Fossil taxon that existed about 428 - 216 million years ago and is thought to be the ancestral stock of the Ammonoidea and Coleoidea.

Basal shelf - See cirrate shell terminology.

Basic tentacular clubs - The basic types of club present in the Decapodiformes (see: Basic decapodiform clubs).

Bathypelagic - The deep pelagic region of the ocean (see Cephalopod Ocean Habitats).

Beak - One of the two chitinous jaws of cephalopods. The dorsal mandible is the "upper" beak and it inserts within the lower beak to cut tissue with a sissors-like action (see: Beak Terminology & Measurements).

Beak shoulder - A region of the beak between the jaw-edge extension (jee) and wing in the lower mandible and the jee the lateral wall in the upper mandible. The shoulder is complex and understanding its structure is important in mastering beak identification and evolution.

Belemnoidea - A fossil taxon that is thought to be the sister group of the Coleoidea. Belemnoids are distinguished by the presence of hook-like structures on the arms rather than suckers.

Benthopelagic - A free-swiming animal that lives just above the ocean floor but rarely rests on the ocean floor.

Bilateral Symmetry - The symmetry exhibited by an organism or an organ if only one plane can divide the structure or animal into two halves that are mirror images of one another.

Bioluminescence - The production of light by living organisms, sometimes called "living light." The light is produced as a product of a chemical reaction that generally takes place in complex organs called photophores or light organs.

Branchial canal - A large opening at the base of each gill lamella and between the primary afferent and efferent blood vessels of the gill (see: Gill Morphology). A branchial canal is absent in Nautilus, sepioid decapodiforms and cirrate octopods.

Brachial crown - The combination of arms and tentacles that surround the mouth (see: Brachial & Buccal Crown Terminology).

Brachial lobe of the brain - The anterior-most part of the brain located ventral to the esophagus. The large axial nerve cords that run down the centers of the arms connect to this lobe. The proper name is "anterior subesophageal mass." In octopods this lobe is fused with the rest of the subesophageal mass while in decapodiforms and Vampyroteuthis it is separate from the remaining brain (see Brain Terminology).

Branchial gland - Elongate gland adjacent to and paralleling the gill where the gill attaches to the mantle wall.

Branchial heart - A pulsating gland at the base of the gill and through which the afferent blood to the gills flows. It contributes to the blood flow through the gill but also is the site of hemocyanin (the blood respiratory pigment) synthesis.

Brachial photophores - Photophores located on the arms.

Brachial pillar - A very narrow and elongate anterior region of the head between the eyes and the base of the brachial crown. A branchial pillar is especially well developed in many young cranchiid squid.

Brain - Medial portion of the central nervous system. It includes the subesophageal and supraesophageal masses but generally does not include the large optic lobes (see Brain Terminology).

Brooding - Incubation of eggs by the parent. A characteristic feature of incirrate octopods but also found in some squid (e.g., Gonatidae).

Buccal connective - Muscular membrane that runs from the buccal support to the base of the adjacent arm. The position of the connective on the fourth arms was recognized in the early 20th century as an important character in interpreting phylogenetic relationships among decapodiforms (see: Brachial & Buccal Crown Terminology).

Buccal crown - Umbrella-like structure that surrounds the mouth and is surrounded by the brachial crown. It consists of buccal supports and the buccal membrane. The buccal crown is present in most decapodiforms but absent from all octopodiforms (see: Brachial & Buccal Crown Terminology).

Buccal mass - Muscular bulb at the beginning of the digestive system that contains the mouth, beaks, radula and various glands (see: Digestive System Terminology).

Buccal membrane - The muscular membrane that connects the buccal supports and together with the supports, forms the buccal crown. The pigmentation of the buccal membrane often differs from that of the adjacent oral surfaces of the arms (see: Brachial & Buccal Crown Terminology).

Buccal suckers - Small but normal suckers that are present on the oral surface of the buccal supports of some decapodiforms (bathyteuthid families, some loliginids and some sepiids) (see: Brachial & Buccal Crown Terminology).

Buccal support (= buccal lappet) - One of six to eight, large muscular flaps of the buccal crown that surround the mouth. The supports are connected by the buccal membrane. The buccal supports are thought to be homologous with the inner ring of tentacles that surround the mouth of Nautilus (see: Brachial & Buccal Crown Terminology) .

Buoyancy (neutral, positive, negative) - The tendency to float in seawater. A neutrally buoyant object does not rise or sink but maintains its position in the water; a positively buoyant object will rise and a negatively buoyant object will sink.

Bursa copulatrix - A spermatophore receptacle found in some sepiolids and consisting of folded glandular epithelium of the lining of the mantle cavity just anterior to the oviduct opening.

Caecal sac - The sac-like, thin-walled posterior portion of the caecum that lacks the internal, ciliated leaflets characteristic of the anterior portion of the caecum (See Digestive System Terminology).

Caecum - Region of the digestive tract of all cephalopods between the stomach and intestine. It is the primary site of food absorption (See Digestive System Terminology).

Calcareous - Composed of calcium carbonate (CaCO3)

Calamus - The conical papilla of the end-organ of the hectocotylus in many incirrate octopods. It is located at the distal termination of the sperm groove and usually lies adjacent to the last arm sucker.

Cambrian Period - Oldest period of the modern (Phanerozoic) geological timescale (see: Geological Timescale).

Cement body - Structure in the spermatophore that allows adhesion of the discharged spermatophore to a female (see: Spermatophore Terminology).

Carpal sucker - Suckers in the locking apparatus at the base of the club (see: Tentacle Terminology).

Carpal knobs - Knobs in the locking apparatus at the base of the club (see: Tentacle Terminology).

Carpus - The "wrist" of the club that carries the carpal locking-apparatus (see: Tentacle Terminology).

Carpal locking-apparatus (= proximal locking-apparatus) - The region at the base of the tentacular club which has small suckers and knobs. The carpal suckers and knobs of one tentacle can adhere to their counterparts on the opposite tentacle which, thereby, holds the clubs together at their bases (see: Tentacle Terminology).

Cartilaginous tubercles - Rigid cartilagenous spines, with one or several cusps, in the skin of certain squids and octopods.

Cephalic cartilage - Cartilage surrounding the posterior part of the brain of cephalopods and generally encompasing the statocysts. Anteriorly the cartilage thins into facia making a well-defined limit difficult to establish. The cartilage has a large central foramen through which the esophagus passes and minor foramina for nerves and blood vessels.

Cephalic vein - Large vein that drains the head and lies on the ventral surface of the visceral sac, along side or dorsal to the intestine. The cephalic vein terminates by dividing into the two vena cavae, each of which passes through the "kidney" (nephridium), the branchial heart and into the gill.

Character state - A particular condition of a taxonomic character. For example, the character "sucker" may include the two states: sucker with a horny ring or sucker without a horny ring.

Chemotactile - Refers to chemical and touch sensitivity.

Chitin - A mucopolysaccharide that is the major component of the cuticle (exoskeleton) of arthropods and a major component of the gladius and beaks of cephalopods (also found in many other phyla).

Chorion - A tough secreted membrane that surrounds the egg.

Chromatophore - A pigment cell. In cephalopods the chromatophore is part of an organ composed of numerous cells including many slender muscle cells. Under nervous control, the muscles rapidly expand and flatten the pigment cell which spreads the pigment over a relatively broad area (see: Cephalopod Chromatophore).

Circularis muscle - A circular muscle found in the suckers of most sepioids and loliginids that surrounds the sucker at the base of the horny ring.

Cirrate male reproductive system - The male reproductive tract of cirrates does not make typical spermatophores. As a result, the tract differs greatly from that of other coleoid cephalopods (see: Cirrate Male Reproductive Tract).

Cirrate octopod measurements - Measurements used in describing cirrates differ somewhat from other cephalopods (see: Cirrate Measurements).

Cirrate shell - The cirrate shell differs greatly in shape and thickness from all other cephalopod shells and has its own set of terms to describe it (see: Cirrate Shell Terminology).

Cirri - Muscular, conical structures that arise from the sides of the arms of some octopodiforms. Cirri are homologous with trabeculae of decapodiform arms and tentacles.

Clade - A monophyletic group. That is, a group whose members share a closer common ancestor with one another than with members of any other group. Stated another way, a monophyletic group is a group of taxa that share a common ancestor and the group includes all descendent taxa of that ancestor.

Cladistics - A method of phylogenetic classification that relies on the relative sequence of origin for grouping taxa. Cladistic methodology relies on a series of rules, paramount of which is determining which character states are "derived" (i.e., apomorphic) and which are "ancestral" (plesiomorphic) then basing relationships only on the shared derived states.

Class - High-level taxon (see: Classification Terminology).

Club - See "Tentacular club."

Coelom - An internal body cavity of mesodermal orgin that is lined by an epithelium. Cephalopods have two coeloms, the visceropericardial coelom and the nephridial coelom (see: Visceropercardial coelom).

Collar - Muscular structure extending from the nuchal cartilage to the funnel that forms a one-way valve that lets water enter the mantle cavity but closes as the mantle contracts thereby forcing exhalent water out through the funnel.

Color filters (in photophores) - Structures that alter the color of bioluminescent light (see: Photophore terminology).

Continental slope - The relatively steep slope of a continent beyond the shelf (See Ocean Habitats).

Continental shelf - The relatively shallow (ca. less than 180m) ledge that surrounds continents (See Ocean Habitats).

Conus (= primary conus) - The cup or cone-shaped posterior end of the gladius of some cephalopods. It is not formed by the infolding of the vanes (see: Gladius Terminology).

Conus field - Lateral portions of the gladius that are continuous posteriorly with the primary conus or its remnant and laterally with the edges of the vanes (see: Gladius Terminology).

Cornea - Smooth, thin, turgid, transparent skin without muscles that covers the eyes to protect the eye lenses of incirrate octopods and some decapodiforms (see: Corneas & Eyelids).

Counterillumination - - The production of bioluminescent light by an animal to conceal its silhouette against the downwelling light. The process can allow an aninmal to become virtually invisible under dim directional light.

Crest of hectocotylus - In loliginids a protective membrane on the hectocotylized arm can fuse with the adjacent suckerless papillae (former sucker stalks) to form a crest on the dorsal or ventral margins such that the original form of the papillae is obscured.

Cretaceous - The last period of the Mesozoic Era (see:  Geological Timescale).

Crop - Expansion (i.e. a broading or a side pocket) of the esophagus for storing food. Present in Nautilus and most octopodiforms (see: Digestive System Terminology).

Ctenoglossan radula - Radula in which the lateral teeth are multicuspid.

Cupped coil - The peculiar posterior end of the histioteuthis gladius that is rolled into a coil.

Cusp- A point or projection on a tooth of the radula or on a cartilagenous tubercule in the skin.

Cuttlebone - Predominately calcareous internal shell of sepiids (cuttlefish). It is composed of many chambers and functions primarily as a buoyancy organ. The cuttlebone is homologous with the phragmocone of Spirula, Nautilus and many fossil cephalopods.

Dactylus - The narrow, distal portion of the tentacular club of most decapodiforms. In squids the dactylus is usually characterized by the ventral expansion of the club and the absence of a dorsal protective membrane (see: Tentacle Terminology).

Decapodiformes - Higher-level taxon (superorder) that includes the squid and cuttlefish.

Demersal - Living close to the ocean floor.

Demibranch - A half-gill formed from all the primary gill lamellae on one side of the gill.

Diel vertical migration - Vertical animal migration during twilight. Many mesopelagic animals migrate at sunrise from near-surface waters to spend the day at greater depths then return to shallow depths at sunset where they spend the night. Some animals migrate vertically over 1000 m others migrate less than 100 m.

Distal - Situated away from the point of origin or attachment. For example, the arm tip is the distal end of the arm.

Distal oviduct - The "distal oviduct" is an extension of the oviducal gland in octopods that often has the same general appearance as the oviduct proximal to the oviducal gland.

Doratopsis - Peculiar paralarval stage of the Chiroteuthidae. The paralarva is very slender and can reach a large size (see: Doratopsis Stage).

Dorsal - Toward the uppermost surface of a cephalopod, opposite the ventral surface where the funnel is located.

Dorsal mantle cavity - Dorsal portion of the mantle cavity that completely surrounds the viscera in octopods. In decapodiforms and Vampyroteuthis the viscera are fused to the mantle and shell dorsally and the mantle cavity lies lateral and ventral to the viscera.

Efferent vein - vein carrying blood away from an organ.

Efferent nerve - nerve carring impulses away from the brain or specific ganglia.

Egg mass - A large number of eggs encapsulated in a gelatinous matrix or a large number of such structures that are attached together. The egg mass of an oceanic squid can be a large, fragile gelatinous ball carrying many thousands of eggs. In contrast, the egg mass of a neritic squid (loliginid) can be composed of very tough capsules each carrying several hundred eggs with many capsules attached together at their bases and to the substrate to form an egg mass.

Ejaculatory apparatus - Portion of the spermatophore involved in the eversion of the sperm mass (see: Spermatophore Terminology).

End organ (of hectocotylus) - The tip of the hectocotylus in incirrate octopods consisting of a calamus and ligula presumably for manipulating the spermatophore during copulation.

Epipelagic zone -  The upper pelagic zone of the ocean (see: Ocean Habitats).

Epithelial pigmentation - The pigmentation that is contained in epithelial cells which are unable to change their shape. Color in most cephalopods, however, is due to pigment granules that are contained in specialized organs, the chromatophore organs, that can change shape rapidly under nervous control. See chromatophores.

Esophagus - The portion of the digestive tract between the buccal mass and the stomach. Often a portion of the esophagus is expanded to form a crop for food storage (see: Digestive System Terminology).

Eye pore - Small pore just anterior to the cornea in some decapodiforms. The pore is the remnant of the large eye opening of oegopsids and connects fluid between the lens and the cornea with the exterior environment.

Eyes - Eyes are the primary sensory organs of cephalopods and are usually large and positioned within the head. However some species have small eyes and some have eyes on stalks (see: Eye size and position).

Eyelid sinus - Indentation, often complex, of the anterior margin of the eyelid (see: Corneas & Eyelids).

Family - The taxon rank above genus (see: Classification Terminology).

Fin angle - The angle between the longitudinal axis of the mantle and the posterior border of one fin.

Fin attachment - A fin attaches to the shell, the mantle, the opposite fin or some combination of these (see: Fin Attachment).

Fin cartilage - Cartilage associated with the fins of all fin-bearing cephalopods (see: Fin Attachment).

Fin length - This measurement varies in different major taxa (see: Fin Shapes and Sizes).

Fin lobe - The portion of a fin that extends anteriorly from the fin's anterior point of attachment or posteriorly from the fin's posterior point of attachment. This is often called the "free" lobe (see: Composite Squid).

Fin position - Fins are located anterior to the termination of the muscular mantle (subterminal position) or mostly posterior to it (terminal position) or somewhere inbetween (see more on: Fin position).

Fin shapes - Fins are classified, somewhat arbitrarily, by their shape as Sagittate, Rhomboid, Circular/Elliptical, Lanceolate, Ear-shaped, Lobate, Ribbed or skirt-like (see: Fin Shapes and Sizes).

Fins - The pair of muscular "wings" used in swimming and located along the dorsolateral surface of the mantle, usually in its posterior half .

Foot - See: Molluscan foot.

Foveola - Transverse membranous fold of skin that forms a pocket in the funnel grove of ommastrephid squids.

Free fin lobe - The portion of a fin that extends anteriorly from the fin's anterior point of attachment or posteriorly from the fin's posterior point of attachment.

Funnel (= siphon) - The ventral, muscular tube through which water is expelled from the mantle cavity. The funnel is thought to have evolved from the molluscan foot.

Funnel groove - Depression on the posteroventral surface of the head in which the funnel lies. Most distinct in some squids.

Funnel-mantle locking-apparatus - This locking mechanism between the funnel and mantle can, depending on its form, either limit all movement between the funnel and mantle (a true lock) or, also, allow anterior-posterior slippage which may assist jet propulsion. See Mantle locking-apparatus. The funnel lock - The funnel component consists of two structures (generally cartilagenous) located on the posterolateral corners of the  (see: Funnel lock). The mantle lock - The mantle components (often cartilagenous, sometimes fibrous) lie on the inner surface of the mantle opposite their funnel counterparts. The location of the funnel lock mandates that the mantle lock be close the anterior mantle margin. However, how close depends both on its function and evolutionary history (see: Mantle lock).

Funnel organ - The glandular structures on the internal dorsal and ventral surfaces of the funnel.

Funnel retractor muscles - Muscles (often large) that attach to the corners of the funnel and run posteriorly to attach to the sides of the shell sac (generally near the base of the gills) or, in a some species, insert on the mantle wall.

Funnel valve - Semicircular muscular flap extending from and continuous with the posterodorsal funnel wall. The funnel valve apparently acts as a one-way valve to prevent inspiration of water through the funnel when mantle expansion draws in water to pass over the gills for respiration. A funnel valve in absent in octopods and some squids.

Genus - The taxon below the family level and above the species level (see: Classification Terminology).

Gill - Primary organ for the exchange of respiratory gases between blood and sea water (see: Gill Morphology).

Gill lamella (=primary lamella) - Complex gill leaflet that extends perpendicular to the axis of the gill and contains the respiratory epithelium. The lamella contains further subdivisions, the secondary and tertiary lamellae. In octopods the number of lamellae is a taxonomic character.

Gladius - The chitinous remnant of the shell in many decapodiforms and Vampyroteuthis. It is generally feather-shaped and lies in the dorsal mid-line of the body along the full length of the mantle. The gladius lies within the shell sac which secretes it (see: Gladius Terminology).

GL - Gladius length. Sometimes used as a measure of the body (=mantle) length when direct of measurement of the mantle is unreliable (usually due to deformation).

Half-orange gills - Gills of some cirrate octopods with broad primary lamellae whose arrangement looks similar to half of an orange.

Hatchling - Young cephalopod that has just hatched from the egg.

Head-mantle fusion - The head and mantle are fused in a variety of cephalpods. The dorsal fusion of the head and mantle occurs in all Octopodiformes and in many Sepioidea but is uncommon in Oegopsida and absent in myopsida. Much less common is the ventral fusion at the position of the funnel/mantle locking apparatus (see: Dorsal Head-Mantle Fusion).

Hectocotylus - The modified arm in males used for transferring spermatophores to the female. In incirrates the hectocotylus is one member of arm pair III while in decapodiforms frequently one or both members of arm pair IV are modified. Many species of coleoid cephalopods lack a hectocotylus.

Heterodont radula - Radula with more than one cusp on the rhachidian tooth and, usually, the first lateral tooth (see: Radula).

"Histioteuthid-club" - Club with a peculiar structure found only in the Histioteuthidae and Psychroteuthidae (see: “Histioteuthid-club” Structure).

Homodont radula - Radula with a single cusp on all teeth (see: Radula).

Holotype - The single specimen designated to represent a species name. It is an international standard of reference that provides objectivity for the species name.

Hook - Horny structure that looks like a single claw and is derived from the inner sucker ring in some decapodiforms. Hooks may be found on the arms and/or tentacular clubs of squid. The relative advantage of hooks vs toothed rings is uncertain (see: Hook Terminology).

Horizontal arm septa - Septa, extending the length of the arm (i.e., parallel to the arm axis), that roughly divides the arm into oral and aboral regions. This feature is a characteristic of the arms of cirrate octopods and the incirrate octopods of the family Bolitaenidae. The functional significance is unknown.

Horny rings of suckers - Suckers of decapodiforms have two types of hard, horny rings. One, the inner ring, lies around the inner walls of the acetabulum and often bears teeth. The other, the outer ring, is composed of numerous platelets and lies on the surface of the infundibulum.

Inferior frontal lobe system - A system of lobes in octopod brains: the paired posterior buccal, lateral inferior frontal and subfrontal lobes, and the single median inferior frontal lobe. They form a functional unit concerned with the chemotactile information from the arms and its use.

Infundibilum - See sucker.

Ink sac - Organ composed of a gland that secretes ink, a sac that stores ink and a duct that connects it to the rectum. The ink sac generally appears black from the outside although it may be covered by silvery tissue in some species.

Integument- Skin.

Intertidal - The region of the shoreline between highest and lowest tides (see: (See Cephalopod Ocean Habitats)).

Invertebrate - An animal without a backbone. Refers to the wide variety of groups that lie outside of the vertebrates such as jellyfish, spiders, octopods and worms.

Juvenile - Life history stage between the paralarval and subadult stages

Jet propulsion - This is the typical method of fast swimming in cephalopods (see more here: Jet Propulsion).

Keel (club) - A muscular vane that extends dorsally from the aboral surface of the tentacular club of many species (see: Tentacle Terminology).

Lateral - Away from the midline.

Lateral funnel adductor muscles - Muscles that support the lateral attachment of the funnel to the head (see:  Lateral Funnel Adductor).

Lateral membranes of arms IV - See Tentacular sheath.

Lateral-line analogue - Sensory structure analogous to the lateral-line of fishes. The lateral-line analogue, which senses vibrations transmitted by the seawater, is located along a series of lines on the dorsal surface of the head with some sensory cells extending onto the bases of the arms.

Lense (in photophores) - Structure in a photophore that can focus or disperse bioluminescent light (see: Photophore Terminology).

Leucophores - Reflective cells in the skin of some cephalopods containing numerous refractive granules on stalks that together produce a scattered reflection of ambient light (see more here: Leucophores).

Light organ - See "photophore."

Light guides - Structures in a photophores that direct light via internal reflection (see: Photophore Terminology).

Ligula - The portion of the sucker-free end-organ of the hectocotylus of many incirrate octopods that is generally elongate and longitudinally grooved. The ligula in octopodids is often spatulate in shape with transverse ridges. Spermatophores transferred along the sperm groove of the hectocotylus presumably enter the ligula which assists in their transfer to the female. Details of the use of the ligula are unknown.

Lips - Two concentric muscular, glandular rings of skin that surround the mouth and beaks.

Living chamber - Largest and most recently formed chamber of the Nautilus shell (also refers to numerous shells of fossil cephalopods) in which the animal resides.

Locking-apparatus of tentacular stalk - Continuation of the carpal locking apparatus down the oral face of the tentacular stalk.

Mantle - A fold of the body wall that covers the visceral region and encloses a space between the viscera and the mantle called the mantle cavity. In coleoid cephalopods the mantle generally contains strong muscles that can expell water from the mantle cavity to provide thrust for locomotion (= jet propulsion).

Mantle cavity - Space enclosed by the mantle. In cephalopods the mantle cavity contains the visceral sac, gills, anus, openings of the gonoducts, nephridial pores and various muscles and septa.

Mantle locking-apparatus - The mantle component (usually fibrous) of the structure that "locks" the mantle to the funnel. This lock, depending on its form, can either restrict all movement between the funnel and mantle or allow just an anterior/posterior slippage (see: Funnel/mantle Locking Apparatus).

Mantle length (ML) - The standard measure of length in coleoid cephalopods. In decapodiforms ML is measured along the dorsal midline from the mantle margin to the posterior tip of the body, excluding long tails. In octopodiforms ML is measured from a line joining the midpoint of the eyes rather than the anterior mantle margin since the latter is obscured by the head/mantle fusion.

Mantle (= abdominal) septum - A anteroposterior septum that connects the mantle wall with the visceral sac along the midline in the ventral mantle cavity. The ventral mantle artery runs along the anterior end of this septum.

Manus - The proximal, broad portion of the tentacular club. In squids the manus is generally equally expanded on both lateral margins and often includes enlarged suckers (see: Tentacle Terminology).

Mature - In cephalopods this term refers to sexual maturity which is determined for females by the presence of ova (mature eggs) free in the coelom or oviducts, and for males by the presence of spermatophores in Needham's sac.

Medial - Toward the midline.

Mesopelagic Zone - The middle-depth zone of the pelagic realm of the ocean (see: Cephalopod Ocean Habitats).

ML - Abreviation for Mantle Length, the standard length measurement for cephalopods.

Modal fishing depth - The single depth at which a midwater trawl spent the greatest amount of time during a particular tow. This is the depth at which cephalopods caught were most likely to have come from.

Mollusca - One of the major invertebrate phyla. Some of the common molluscs are snails and clams. The Cephalopoda is a class within the Mollusca

Molluscan foot - A major structure in molluscan morphology. In gastropods the foot is the muscular sole that the animal crawls with. In cephalopods the funnel, and possibly the arms and tentacles are derived from the molluscan foot. The evolutionary origin of the latter is still uncertain. They may represent outgrowths of the head (favored by anatomical evidence: nerve connections) or modifications of the molluscan foot that have migrated around the mouth (favored by embryological evidence: migration of arm primordia).

Monophyletic group - A group (taxon) that shares a common ancestor.

Myopsida - A high-level taxon (order) within the Decapodiformes. In recent classification, the Myopsida (contains the family Loliginidae) have been considered the sister group of the Oegopsida and the two groups together composed the Teuthoidea (squids). In contrast, at the beginning of the 20th century, the Myopsida included the Loliginidae and the Sepioidea (cuttlefish and relatives) and the presence of a cornea covering the eye lens defined the group. At present the phylogenetic relationships within the Decapodiformes are unresolved and the correct classification of myopsids is in limbo.

Neck - The region separating the posterior end of the cephalic cartilage and the collar. Only those cephalopods with elongate heads (e.g., chiroteuthids) have distinct necks.

Needham's sac - In males, the large storage sac for spermatophores that is an expanded region of the genital duct at the base of the penis.

Nephridial coelom - The cavity of the renal sac. It connects with the exterior via the renal pore and with the visceropericardial coelom via a pair of slender ducts from the latter.

Neritic - The region of the ocean that overlies the continental shelf (see: Cephalopod Ocean Habitats).

Nominal species - A species that is based on a type. A properly named species but not necessarily a valid species.

Nidamental glands - Large glandular structures found in decapodiforms and Nautilus that lie in and open directly into the mantle cavity. The glands are composed of numerous lamellae that are involved in secretion of egg cases or the jelly of egg masses.

Nuchal - Formerly a term generally relating to the posterior region of the head, now more restricted. See: Nuchal region.

Nuchal cartilage - See: Nuchal locking-apparatus.

Nuchal crest - See: Occipital crest.

Nuchal folds - See: Occipital folds.

Nuchal locking-apparatus - A cartilagenous locking structure in decapodiforms located middorsally just posterior to the head. It is composed of the nuchal cartilage, which forms an attachment site for collar and head retractor muscles, and a cartilage on the mantle that underlies the gladius. The apparatus helps keeps the head and mantle aligned dorsally during mantle contractions.

Nuchal membrane - See: Occipital membrane.

Nuchal organ - Small sensory organ with photoreceptor-like sensory cells that is located in the nuchal region of, apparently, all coleoid cephalopods.

Nuchal region - The posterodorsal region of the head and the area immediately posterior to it.

Occipital - Posterior region of the head in decapodiform cephalopods.

Occipital crest - Prominent transverse ridge in most decapodiforms that extends across the dorsal and along the lateral surfaces of the head at its posterior end (see: Occipital Region Terminology).

Occipital folds - Fixed folds of the head integument that adjoin the nuchal crest posteriorly and are perpendicular to it. The function of the folds is uncertain (see: Occipital Region Terminology).

Occipital membrane - A membrane connecting the main occipital folds at their posterior ends (see: Occipital Region Terminology).

Oegopsida - A high-level taxon (order) within the Decapodiformes. In recent classification, the Oegopsida (oceanic squids) has been considered the sister group of the Myopsida and the two groups together composed the Teuthoidea (squids). At present the monophyletic nature of the Oegopsida and the relationship between this taxon and the Myopsida are unresolved.

Olfactory organ - A chemosensory organ present on the head or neck in all coleoid cephalopods. The olfactory organ is thought to be the homologue of the rhinophore of Nautilus.

Ontogenetic descent - The progressively descent into a deeper-water habitat as a cephalopod grows older and larger. This distribution pattern is a particularly common in many pelagic cranchiid squids.

Opening/closing trawl - A trawl whose mouth is open during fishing at depth but is closed during descent and retrieval.

Optic lobes of brain - Large lobes of the brain associated with the eyes. In octopods and some squids the optic lobes may be separated from the rest of the brain by an optic stalk of varying length. In Octopus the optic lobes contain 92 million cells compared with only 42 million in the main central mass of the brain (J. Young, 1963) (see: Brain Terminology).

Optic nerve bundles - Large nerve bundles that run from the optic lobe to the eye.

Optic sinus - See "Eyelid sinus."

Oral - Toward or on the side of the mouth.

Order - The taxonomic catageory above the family level (see: Classification Terminology).

Outer statocyst capsule - Capsule in octopodiforms that is embedded in the cephalic cartilage and contains the statocyst capsule.

Oviduct - Female gonoduct. The oviduct conducts eggs from the visceropericardial coelom, that holds the ovary, to the exterior and is often used to store eggs. In some argonautoid octopods eggs are fertilized and undergo either partial (Argonauta ) or complete (Ocythoe) embryonic development within the oviduct.

Oviducal gland - Gland surrounding the end of the primary oviduct and responsible for secreting some of the external coatings over spawned eggs or, in incirrates, the cement at the base of the chorion stalk . In octopods it also acts as a spermatheca, and is located around the apparent middle of the oviduct. However, the "distal oviduct" is actually an extension of the oviducal gland.

Paralarva - First free-living, cephalopod life-history stage that is found in the near-surface plankton and that differs in both morphology and vertical distribution from older juveniles. Links to paralarvae on Tree-of-Life pages can be found here.

Pelagic - The region of the ocean away from the ocean floor (see: Cephalopod Ocean Habitats).

Penis - The long, muscular end of the male gonoduct that assists in transfering spermatophores to the female. Apparently, in species with a hectocotylus, the penis transfers spermatophores to the hectocotylus which in turn transfers them to the female. In species without a hectocotylus, the penis is often greatly elongate, capable of extending beyond the mantle cavity and can, apparently, transfer spermatophores directly to the female.

Photocytes - Cells in photophores that produce bioluminsecence (see: Photophore terminology).

Photophore - Organ that produces bioluminescence or "living light." Photophores are often complex with various color filters, reflectors, light guides, lenses and chromatophores surrounding the site of light production, the photogenic region. The name of specific photophores often reflects their position on the animal. For example, the branchial photophore is at the base of the gill, the anal photophore lies at the side of the anus (see: Photophore terminology).

Photophore location - Photophores are found in nearly any location in some squid. However, certain locations are the most common (see: Photophore Locations).

Photosensitive vesicles - Non-image forming light-receptive organs located inside the cephalic cartilage in squid and on the stellate ganglion in octopods. They perform a variety of function.

Phylum - Taxonomic level above "Class" (see: Classification Terminology).

Polarize - To determine the direction of evolution. That is to determine which state is "primitive" (plesiomorphic) and which is "advanced" (apomorphic).

Polarity - The direction of evolution. That is, one state is "primitive" (plesiomorphic) and another is "advanced" (apomorphic).

Posterior - Toward the closed end of the mantle, away from the head and arms.

Posterior buccal lobe (= inferior frontal lobe in squid) - A fused pair of lobes that are the anterior-most lobes of the supraesophageal mass of the brain of decapodiforms but is incorporated into the anterior portion of the supraesophageal mass behind the superior buccal lobes in most octopodiforms.

Posterior lip glands - Large glands surrounding the buccal mass just posterior to the lips. They are especially well-developed in stauroteuthid cirrates.

Posterior salivary glands - Glands generally located just posterior to the head whose secretion travels via a duct into the buccal mass.

Primary conus - A more primitive type of conus (see: Gladius Terminology).

Protective membranes - Membranes, generally supported by trabeculae, that form lateral borders along the oral surfaces of the arms and tentacular clubs in decapodiforms.

Proximal - Situated toward the point of origin or attachment. For example, the proximal end of the arm is the basal end of the arm.

Proximal and distal fields - Some male opisthoteuthid cirrates have enlarged suckers located proximally on the arms (proximal fields) and/or distally on the arms (distal fields).

Pseudomorph - A mass of ink and mucous that roughly has the dimensions of the cephalopod that secreted it (see: Pseudomorph Function).

Recent - Refers to an organism that is living or has lived within the past 10,000 years or to an object formed or to events within the past 10,000 years (see: Geological Timescale).

Reflectors (in photophores) - Structures in a photophore that reflects bioluminscence (see: Photophore terminology).

Radula - A toothed ribbon that lies in the buccal mass and that aids in movement of food into the esophagus (see more here: Radula).

Renal appendages - Structures that form the nephridium (=kidney). The renal appendages are outpocketings of the veins within the renal sac (primarily the venae cavae) that are covered with renal epithelium. The The renal sac communicates with the mantle cavity via the nephridial pore.

Rhachis - Central axis of the gladius, often thickened, that typically extends the full length of the gladius and sometimes called the median field (see: Gladius Terminology).

Rostrum (gladius) - Portion of the gladius that extends posteriorly or posterodorsally from the conus. A distnct rostrum is found only in the Onychoteuthidae, Ancistrocheiridae, Lampadioteuthinae and Vampyroteuthidae (see: Gladius Terminology).

Saddle - The region of the shell of cirrates connecting the lateral wings.

Saddle-shaped - The shape of the shell with an elongate central region (saddle proper) and broad wings found in cirroteuthid cirrates.

Sagittate fins - The most common fin-shape in squids with anterior free fin-lobes, a relatively sharp lateral angle and posterior elongation. See fin shapes.

Scales and tubercules - The skin of the mantle contains scales, tubercules and warts in various species (see: Mantle Armature).

Secondary conus - A conical region at the posterior end of the gladius that is formed by an inrolling and fusion of the vanes. The ventral line of fusion is usually apparent. The secondary conus may be rather short or over half the gladius length (see: Gladius Terminology).

Secondary eyelid - An eyelid that covers the ventral part of the cornea (see more here: Secondary Eyelid).

Secondary fin - A non-muscular fin-shaped structure found in some chiroteuthids, located posterior to the true or primary fin. The secondary fin may act as a buoyancy organ.

Secondary web - Web that extends from each arm to the primary web in some incirrate octopods. Separation of the arm from the primary web seems to be associated with feeding and/or defense (bell and baloon balloon postures) but the function is not well understood (see: Primary and Secondary Webs).

Semelparous - A reproductive strategy in which females spawn once then die. Sometimes called terminal or "big-bang" spawners. Many cephalopods are semelparous but many are not.

Semicrescent plate (arm suckers) - A semicrescent plate on the proximal margin of the inner sucker arm rings of the loliginid squid Uroteuthis.

Sepioid gills - Gills of some cirrate octopods that look superficially like gills of sepioids.

Sepioidea - A high-level taxon within the Decapodiformes. Typically this taxa includes the Sepiidae, Idiosepiidae, Sepiolidae, Spirulidae, Sepiadariidae but the monophyletic nature of the group has been questioned. At present the phylogenetic relationships within the Decapodiformes are unresolved and the classification is in limbo.

Shell sac - The sac that secretes the shell in the Coleoidea. The sac is composed of ectodermal epithelium that invaginates during embryonic development to form an internal sac.

Side pockets - Pockets formed by small membranous folds of integument lateral to the foveola in the funnel groove in ommastrephid and thysanoteuthid squids.

Siphonophore - A colonial, usually pelagic hydrozoan (Phylum Cnidaria). Siphonophores often form elongate colonies many meters in length and can extend large numbers of long, slender tentacles outward to capture passing animals. Large siphonophores in mesopelagic waters are especially dangerous traps to many fishes, squids and shrimps.

Siphuncle - The tube-like extension of the body wall, coelom and an external covering tube that penetrates the phragmocone and regulates gas exchange into the phragmocone chambers.

Species - Populations of animals that interbreed or are potentially capable of interbreeding in nature. Considerable debate exists over the general definition of a species and how the theoretical definition should be applied in practice. With regard to the latter problem, in cephalopods species are generally defined by distinct morphological traits not exhibited by any other species. This practice is valid if interbreeding is not occuring. However the amount of interbreeding (i.e., hybridization) that actually occurs in nature and contributes to or diminishes speciation is virtually unknown in cephalopods.

Sperm mass - The coiled rope of sperm that lies within the spermatophore or spermatangia (see: Spermatophore Terminology).

Spermatangia - Discharged spermatophore which consists of the sperm mass surrounded by a membrane (the inner tunic) with the cement gland at one end (see: Spermatophore Terminology).

Spermathecae - Specialized sperm-storage structures found in the skin of some female decapodiforms or as pockets of the oviducal gland in octopods.

Spermatophore - A packet of sperm that is formed by the male and passed to the female during mating. In most coleoids, this packet is very complex and contains a "rope" of sperm (= sperm mass), an ejaculatory apparatus and a cement body. Except for the sperm, the entire structure is non-cellular and consists of a complex architecture of secreted material (see: Spermatophore Terminology).

Squid - Common name given to members of the Teuthoidea and some members of the Sepiolidae.

Squid - general terminology - Diagramatic drawing with external features labeled (see: Composite Squid).

Stalk of tentacle - Region of the tentacle proximal to the club (see: Tentacle Terminology).

Stalked eyes - See: Eye position and size.

Statocyst - A sense-organ that detects gravity, angular accelerations and low-frequency sound. The statocyst is embedded within the cephalic cartlage and contains the statolith.

Stellate ganglion - Major ganglion of the peripherial nervous system of neocoleoid cephalopods that controls nerves to the mantle muscles.

Stomach - A muscular organ of the digestive system where primary digestion occurs. The stomach is generally lined with cuticular ridges to aid in grinding food, and is supplied with digestive enzymes from the digestive gland. The stomach may be greatly expandable in size and serve as a storage area until food can be fully processed (see: Digestive System Terminology).

Stylet - Remnant of the molluscan shell in incirrate octopods. It is generally a slender, pointed rod tightly surrounded by the shell sac and buried in the mantle muscle on either side of the mantle.

Subadult - Stage at which all of the characters that typically define the species are present. The subadult stage follows the Juvenile Stage and precedes the Adult Stage. A subadult stage is defined in cephalopods since the adult phase is frequently abbreviated.

Subequal - Nearly equal. Generally refers to the length of the arms when these appear to be approximately the same length. Arm lengths cannot be measured very accurately due to variation in their states of contraction.

Sucker - Muscular suction-cup on the arms and tentacles and occasionally on the buccal supports. The sucker consists of a cup-shaped portion, the acetabulum, and a flat, distal ring, the infundibulum, that contacts the substrate. Suckers of decapodiforms contain horny rings that often bear teeth or sometimes form hooks.

Sucker series - The longitudinal rows of suckers on the arms or tentacles of decapodiforms. Series (= longitudinal rows) contrasts with rows (= transverse rows) in describing sucker arrangement. In octopodiforms, sucker "series" is generally synonymous with "rows", the "longitudinal" component of the term is implied. Suckers can form distinct, regular series or indistinct, irregular series.

Sucker stalk - The structure between the sucker and the arm. In octopods it is a cyclindrical structure about the same width as the sucker and in decapodiforms it is constricted into a conical pillar.

Sucker teeth - Teeth on the inner horny sucker rings of some decapodiforms.

Superior buccal lobes - Lobes of the central nervous system that sit atop the esophagus where the latter enters the buccal mass in decapodiforms but are the anterior-most lobes of the supraesophageal mass of the brain of octopodiforms (see: Brain Terminology).

Superocular cirri - Muscular structures that can be raised or lowered above the eyes of octopodids but are apparent even when lowered.

Suprabrachial commissure - Nerve commissure that passes dorsal to the esophagus in most octopodiforms and connects the right and left anterior subesophageal masses of the brain.

Swimbladder - Gas-filled structure found in the dorsal region of the pelagic octopods, Ocythoe, Tremoctopus and Haliphron.

Synonym - One of two or more names applied to the same taxon. For example a synonym of the Cephalopoda is the Siphonopoda.

Systematics - The classification of organisms into hierarchial groups based on phylogenetic relationships.

Tail - Posterior narrow extension of the body posterior to the fins. The end of the fins and the beginning of the tail often overlap. An operational definition for point of demarcation for the purposes of measurement is: The point where a hypothetical line, continuous with the broad posterior edge of the fin, crosses the midline of the body (see: Fin Position).

Taxa, taxon - A taxonomic group of any rank. A taxonomic unit.

Tentacles - Modified 4th pair of appendages in decapodiforms that are capable of considerable extension and contraction. Although the tentacles are derived evolutionarily from the 4th pair of arms, the term, "arms IV" is reserved for the subsequent arm pair, the ventral arms, which are evolutionarily the 5th pair of arms. Each tentacle consist of a proximal stalk usually devoid of suckers, and a distal club armed with suckers and occasionally hooks (see: Composite Squid).

Tentacle absence - Tentacles can be absent because the species lacks tentacles, they are accidentally lost during capture, or they are naturally lost at sexual maturity (see photograph here: Tentacle Absence in Cephalopods).

Tentacle pads - Poorly understood and complex pad-like photophores that are found on the tentacular stalks of some chiroteuthidids.

Tentacle pocket - A pocket that surrounds the base of each tentacle and provides some room for tentacle retraction or contraction. The pocket is absent or weakly developed in oegopsid squids and most strongly developed in sepiids.

Tentacular club - The terminal, usually expanded part of the tentacle which bears suckers and/or hooks (see: Tentacular club terminology).

Tentacular retractor muscles - Muscles that result in the coiling of the tentacle when retracted in contrast with those muscles that result in shortening (contraction) of the tentacle.

Tentacular sheath - This is an alternative term for the lateral keel of arm IV. The keels of arms IV are offset laterally and often enlarged to fully or partially conceal, protect or encase the adjacent tentacles. The latter function is most fully developed in the chiroteuthids and mastigoteuthids (see: Brachial & Buccal Crown Terminology).

Terminal fins - Fins that extend to the posterior end of the body.

Terminal pad (tentacular club) - A circlet or disc of small suckers at the tip of the tentacular club. The pad of one club can adhere to the pad of the other club which holds the clubs together at their tips (see: Tentacular club terminology).

Terminal fins - Fins with more than 50% of their length posterior to the muscular mantle. These fins, therefore, are at the "terminal" or posterior end of the body and are generally suported by an elongate secondary conus of the gladius.

Terminal organ - A term often used for the penis in the Octopoda.

Teuthoidea - The higher taxon that includes all squid-like decapodiforms. The monophyly of this taxon is questionable.

Trabeculae - Muscular cones or flaps that support the protective membranes on the arms and tentacular clubs in decapodiforms. These are thought to be homologous with the cirri of the octopodiformes.

Tragus - Particular inward projecting knob in the funnel locking-apparatus of some squids. It is the knob found on the medial surface of the central depression (see:  Funnel lock).

Truncate teeth - Teeth on the inner horny of rings of decapodiform suckers that do not terminate in a point but rather a broad, flat tip.

Tubercules - Structures with one or more cusps just beneath the surface epithelium. Tubercules may be cartilagenous, fibrous or of other structure and may be confined to the integument or extend deeper.

Vanes (= wings; lateral fields) - Broad, lateral portions of the gladius that arise from the rachis (see: Gladius Terminology).

Ventral - Toward the lower surface of the animal (i.e., the side on which the funnel is located).

Ventral eyelid - An eyelid that can cover much of the cornea from a ventral position in many sepioids (see: secondary eyelid).

Ventral shield - The optically modified ventral mantle of heteroteuthins that usually projects anteriorly beneath the head.

Vesicular tissue - Tissues found in some decapodiforms that contain numberous vesicles filled with water that usually contains ammonium chloride. The vesicles may be concentrated in certain structures (e.g., the ventral arms) or scattered throughout the animal. The light solution in the vesicles provide buoyant lift.

Visceral nucleus - A concentration of digestive organs that sometimes includes reproductive organs as well. In cranchiid squids the visceral nucleus is especially distinct: the small, spindle-shaped digestive gland contains the ink sac and is adjacent to the stomach and caecum and associated structures (eg, digestive gland duct appendages, renal appendages). In most cephalopods the concentration of these structures is not so extensive but whenever a concentration exists, a visceral nucleus is present.

Visceral sac - The body posterior to the head surrounded by the mantle. The body wall in this region that incases the viscera is usually rather thin-walled, hence the name "visceral sac." The visceral sac is also called the "visceral dome."

Visceropericardial coelom - See "Coelom.

Water pores - One or two pairs of pores in the integument of the head that communicate with extensive spaces at the bases of arms on some pelagic argonautoid octopods.

Web - Muscular membrane that extends between the arms of many octopodiforms but is reduced or absent in most decapodiforms.

Web nodules - Muscular rods embedded in the web of some cirrate octopods.

White body - Amorphous organ near the optic lobes that forms white blood cells.

Wings (shell) - Lateral limbs of the shell of cirrate octopods

About This Page

University of Hawaii, Honolulu, HI, USA

National Museum of Natural History, Washington, D. C. , USA

Katharina M. Mangold (1922-2003)
Laboratoire Arago, Banyuls-Sur-Mer, France

Page: Tree of Life Cephalopoda Glossary Authored by Richard E. Young, Michael Vecchione, and Katharina M. Mangold (1922-2003). The TEXT of this page is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

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