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Glossary of Terms


Abdomen the posterior section of the body, behind the thorax or the cephalothorax
Acoelomate any organism that lacks a cavity between the body wall and the digestive tract
Adductor muscle a muscle whose function is to close a bivalved shell or carapace e.g. as in ostracods, bivalved molluscs
Antenna one of a pair of jointed feelers on head of various arthropods
Antennule small antenna or feeler, especially the first pair of antennae in Crustacea
Anterior towards the front, usually the head end (opposite to posterior)
Appendage a limb or other process extending from the body, usually articulated
Asymmetrical not symmetrical
Basal relating to, located at, or forming a base
Benthic living on the seabed
Bifid divided into two parts
Bilateral symmetry a basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other along the midline
Bioluminescence production of light by living organisms, this ability occurs in many different organisms, both plants and animals
Biramous in the Crustacea, it describes the condition in which appendages are divided into two segmented branches: exopodite and endopodite, these branches arise from a basal segment called the basipodite
Birefringent the resolution or splitting of a light wave into two unequally reflected or transmitted waves by an optically anisotropic medium such as calcite or quartz
Bisexual reproduction an animal that has the reproductive organs of both sexes
Bract siphosomal element, usually containing much mesoglea, with a protective or buoyancy function
Brood chamber a chamber used to incubate eggs, or young
Buoyant capable of keeping a body afloat
Calcareous of, containing, or like calcium carbonate
Calyptope planktonic larval stage following the nauplius in euphausiid crustaceans
Carapace in the Crustacea it describes a fold of the exoskeleton of the head that extends back over the thorax and may be fused with a few or all of the thoracic segments. It may also extend laterally to protect the sides of the body
Carnivore an animal that eats other animals
Carotenoid any of a group of red and yellow pigments
Globule a small spherical body
Caudal referring to the tail
Caudal rami literally, tail branches
Cephalosome first segment of the prosome (head and thorax of copepods); bears mouthparts (crustaceans)
Cephalothorax fused head and thoracic body segments often covered by a carapace dorsally and laterally (crustacean)
Chaeta bristles protruding from pockets in the body wall
Chelae the pincerlike organ or claw terminating certain limbs of crustaceans
Chelate claw-like or pincer-like; bearing chela or claws
Cheliped either of the pair of appendages bearing a chela
Chitin a tough, protective, semitransparent substance, forming the principal component of the exoskeleton
Chitinous composed of chitin
Cilia minute hairlike organelles, identical in structure to flagella, which line the surfaces of certain cells and beat in rhythmic waves, providing locomotion to ciliate protozoans and moving liquids along internal epithelial tissue in animals
Ciliary relating to cilia projecting from the surface of a cell 
Cirri a filament or slender appendage serving as a foot, tentacle, barbel, etc.
Coelenterate the animal phyla Cnidaria and Ctenophora collectively
Coelenteron the single body cavity of a coelenterate
Coelom the body cavity of higher metazoans, between the body wall and intestine, lined with a mesodermal epithelium
Compress to condense, shorten, or abbreviate
Compound eye the eye of most insects and some crustaceans, which is composed of many light-sensitive elements, each having its own refractive system and each forming a portion of an image
Coxa proximal segment of pereiopods of crustacea; may be expanded and plate-like in some forms
Coxal plate coxae of pereiopods laterally expanded into flattened lamellar structures extending freely (as plates) to overhang the coxa-basis hinge of the leg
Cytoplasm the cell substance between the cell membrane and the nucleus, containing the cytosol, organelles, cytoskeleton, and various particles
Dactyl last (distal) segment of the endopodite of crustacean appendages
Dactylozooid a kind of zooid of Siphonophora which has an elongated or even vermiform body, with one tentacle, but no mouth
Denticle small tooth-like process
Detritivore an organism that feeds on and breaks down dead plant or animal matter, returning essential nutrients to the ecosystem
Detritus dead material derived from biota
Diapause resting phase in the life history in which metabolic activity is low, and periods of adverse environmental conditions can be tolerated
Diel vertical migration refers to a pattern of movement that some organisms living in the ocean's photic zone undertake each day, travelling to the surface during the night to feed, then descending to darker, safer depths during the day
Dinoflagellate any of numerous chiefly marine plankton of the phylum Dinoflagellata, usually having two flagella, one in a groove around the body and the other extending from its centre
Diploblastic having two germ layers, the ectoderm and endoderm, as in the embryos of sponges and coelenterates


situated away from the point of attachment or origin or a central point especially of the body
Dorsal upper surface
Dorsoventral plane pertaining to the dorsal and ventral aspects of the body; extending from the dorsal to the ventral side
Ectoderm the outer germ layer in the embryo of a metazoan
Endite extensions of some basal segments of the endopodite of crustacean appendages that project medially (towards the midline of the animal)
Endoderm the innermost body tissue that derives from this layer, as the gut lining
Endopodite inner branch of a biramous crustacean appendage
Endopod the inner or medial branch of a two-branched crustacean leg or appendage
Epibenthos organisms living on the surface of the seabed or in the water column just above the bottom
Epidermis the outermost living layer of an animal, usually composed of one or more layers of cells
Epipelagic of or pertaining to the stratum of the oceanic zone where enough light is present for photosynthesis to occur, generally at depths of 0 - 200 m (656 ft)
Epipodite extensions of some basal segments of crustacean appendages that project towards the outside
Euphotic zone the uppermost layer of a body of water that receives sufficient light for photosynthesis and the growth of phytoplankton
Exopodite outer branch of a biramous crustacean appendage
Exoskeleton a hard outer structure, such as the shell of an insect or crustacean, that provides protection or support for an organism
Exumbrella convex surface of the bell of a medusa (jellyfish)
Filter feeders animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure
Flagellum a long, lashlike appendage serving as an organ of locomotion
Foliose with many leaves; having leaf-like lobes
Furcilia post-calyptope stage in the life cycle of euphausiid crustaceans
Fuse to combine or unite
Gastrozooid feeding polyp, situated on the siphosome, bearing a tentacle usually with several tentilla
Geniculate having kneelike joints or bends
Genital of, pertaining to, or noting reproduction
Gill the respiratory organ of most aquatic animals that breathe water to obtain oxygen, consisting of a filamentous structure of vascular membranes across which dissolved gases are exchanged
Gonad a sex gland in which gametes are produced; an ovary or testis
Gonophore a structure bearing or consisting of a reproductive organ or part, such as a reproductive polyp or bud in a hydroid colony
Gonozooid sexual stage of salps (planktonic tunicates)
Graze to feed
Gymnoplean tagmosis prosome-urosome boundary located posterior to fifth pedigerous somite
Herbivore an animal that mainly feeds on plants
Hermaphrodite an organism having both male and female reproductive organs in a single individual
Heterotrophic capable of utilizing only organic materials as a source of food
Holoplankton organisms that spend their entire life in the water column, often called permanent plankton
Host a living animal or plant from which a parasite obtains nutrition
Ischium first (proximal) segment of the endopod of crustacean thoracic appendages
Lappets lobes of the bell margin of jellyfish (Scyphozoa) medusae formed by scalloping
Larvae the young of any invertebrate animal
Lateral pertaining to, or on, the side
Locomotion the act or power of moving from place to place
Macrozooplankton zooplankters between 2 and 20 mm in length
Mandible a crushing or biting mouth appendage of a crustacean
Marsupium brood pouch found on the ventral surface of the thorax of female peracarid crustaceans, formed from plate-like extensions of the coxa of thoracic limbs (oostegites)
Manubrium tube bearing the mouth hanging down from the under surface of a medusa
Maxilla paired mouthparts of crustaceans located anteriorly to the mandibles
Maxilliped 1, 2 or 3 pairs of thoracic appendages of crustaceans adapted for assisting in feeding
Medusa a saucer-shaped or dome-shaped, free-swimming jellyfish
Megazooplankton zooplankters greater than 20 mm in length
Membranous thin and flattened like a membrane
Meroplankton organisms that only spend part of their life cycle in the water column e.g. eggs and larvae, often called temporary plankton
Merus second segment of the endopod of crustacean thoracic appendages
Mesoglea the noncellular, gelatinous material between the inner and outer body walls of a coelenterate
Mesopelagic of, pertaining to, or living in the ocean at a depth of between 180 m (600 ft) and 900 m (3000 ft)
Mesozooplankton zooplankton between 200 µm and 2 mm in length
Metamorphic pertaining to or characterized by change of form, or metamorphosis
Metamorphosis a profound change in form from one stage to the next in the life history of an organism
Metanauplius a larval crustacean in a stage following the nauplius, and having about seven pairs of appendages
Metasome thoracic segments in copepod crustaceans
Metatroph requiring dead organic matter for food
Microzooplankton zooplankton less than 200 µm in length
Moults periodic shedding of the cuticle
Natatory formed or adapted for swimming
Nauplii a larval form with three pairs of appendages and a single median eye, occurring usually as the first stage of development after leaving the egg
Nauplius early planktonic larval stage of crustaceans
Nectophore swimming bell
Nematocyst an organ in Cnidarians consisting of a minute capsule containing an ejectable thread that causes a sting
Neritic living in coastal waters i.e. the shallow water over the continental shelf
Neuston organisms that live at the very surface of the sea
Omnivore an omnivorous animal
Omnivorous eating both animal and plant foods
Ovigerous bearing eggs
Ovisac an egg-containing capsule
Paedomorphosis development of sexual maturity in an otherwise juvenile body
Palp an elongated, often segmented appendage usually found near the mouth in invertebrate organisms such as mollusks, crustaceans, and insects, the functions of which include sensation, locomotion, and feeding
Papillae one of certain small protuberances concerned with the senses of touch, taste, and smell
Parapodia one of the unjointed rudimentary limbs or processes of locomotion of many worms, as annelids
Parasite an organism that lives on or in an organism of another species, known as the host, from the body of which it obtains nutriment
Parasitic of, pertaining to, or characteristic of parasites
Parthenogenesis a form of reproduction in which the egg develops into a new individual without fertilisation
Pedigerous bearing or having feet or legs
Pelagic living in the water column
Pereiopod walking leg (swimming leg of copepods); located under the cephalothorax or metasome of crustaceans
Periphery the external boundary of any surface or area
Photophore light-producing organ
Photosynthetsis the process by which phytoplankton make carbohydrates from carbon dioxide and water, using energy captured from sunlight by chlorophyll, and releasing oxygen as a byproduct
Phytoplankton plankton consisting of free-floating algae, protists, and cyanobacteria, phytoplankton form the beginning of the food chain for aquatic animals and fix large amounts of carbon, which would otherwise be released as carbon dioxide
Pigmentation coloration with or deposition of pigment (a coloring matter or substance)
Pleopod swimming leg located under the abdomen or urosome of crustaceans, often called swimmerets
Pleosome anterior 3 segments of pleon bearing biramous pleopods
Pleura abdominal segments of crustaceans
Pleurobranchiae gills that arise from the lateral walls of the thorax in decapod crustaceans
Pluteus larval stage of echinoid or ophiuroid echinoderms
Pneumatophores a gas-filled sac serving as a float in some colonial marine hydrozoans, such as the Portuguese man-of-war
Podobranchiae gills that arise from the coxae of thoracic appendages in euphausiid and decapod crustacean
Podoplean tagmosis prosome-urosome boundary located posterior to fourth pedigerous somite
Polyp a sedentary type of animal form characterized by a more or less fixed base, columnar body, and free end with mouth and tentacles, esp. as applied to coelenterates
Posterior towards the tail, behind; opposite to anterior
Propodus fourth (penultimate) segment of the endopodite of the crustacean limb
Prosome anterior part of the body in some invertebrates
Prostomium anterior, pre-segmental region of the body, anterior to mouth, may bear eyes, antennae and palps, and encloses part of the brain
Prototroch a preoral circlet of cilia of a trochophore larva
Protozoan any of a diverse group of eukaryotes, of the kingdom Protista, that are primarily unicellular, existing singly or aggregating into colonies, are usually nonphotosynthetic, and are often classified further into phyla according to their capacity for and means of motility, as by pseudopods, flagella, or cilia
Radially symmetrical animals which are symmetrical in 2 or more planes e.g. a sea urchin
Rostrum prolongation of the anterior portion of the carapace that projects beyond the head, usually between the eyes; found in Crustacea
Scavengers an animal or other organism that feeds on dead organic matter
Scyphistoma a stage in the life cycle of a jellyfish or other scyphozoan when it is fixed in place and reproduces asexually to produce free-swimming medusae
Segmentation the subdivision of an organism or of an organ into more or less equivalent parts
Segments a clearly differentiated subdivision of an organism or part, such as a metamere
Sessile eye an eye attached by the base
Setae solid bristle-like structure found in Chaetognatha, that are used for locomotion, in Arthropoda, hollow bristles containing living tissue, which extend from appendages
Setose bearing bristles (setae)
Solitary living habitually alone or in pairs
Somite one member of a series of paired segments into which the thickened dorsal zone of mesoderm is divided
Spawning to deposit eggs, produce spawn
Spine a stiff, pointed process or appendage on an animal
Stalked eye an eye attached to a stem or projection
Statocyst an organ found in many invertebrate animals that is used to orientate the body in space i.e. for balance
Subchelate prehensile gnathopods the claw-bearing and grasping limbs of amphipods for processing food
Subumbrella concave or undersurface of the bell of a medusa (jellyfish)
Suspension feeders animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure
Symbiotic the living together of two dissimilar organisms, as in mutualism, commensalism, amensalism, or parasitism
Symbiotically the living together of two dissimilar organisms, as in mutualism, commensalism, amensalism, or parasitism
Telson posterior projection of the terminal abdominal segment of crustaceans, particularly malacostracans. Along with the uropods it forms a tail fan
Tentacle any of various slender, flexible processes or appendages in animals, esp. invertebrates, that serve as organs of touch, prehension, etc.; feeler
Thermocline region of relatively sharp temperature change in the water column, the depth of the thermocline varies seasonally in temperate seas
Thoracic of, relating to, or situated in or near the thorax
Thorax the portion of the body between the head and the abdomen
Tintinnid ciliates of the choreotrich taxon Tintinnida, distinguished by vase-shaped shells called loricae, which are mostly protein but may incorporate minute pieces of minerals
Uniramous in arthropods, an unbranched appendage. In crustaceans the exopodite is often lacking in walking legs
Uropod last of a pair of abdominal appendages in malacostracan crustaceans, they are usually broad and flat and form a tail fan with the telson
Urosome abdomen of copepods, though may be used for abdominal segments bearing uropods in other crustaceans
Urosomal pertaining to the abdomen of copepods, though may be used for abdominal segments bearing uropods in other crustaceans
Velum inward projection of the margin of the bell of hydrozoan medusae
Ventral lower surface (opposite to dorsal)
Vertical migration refers to a pattern of movement that some organisms living in the ocean's photic zone undertake each day, travelling to the surface during the night to feed, then descending to darker, safer depths during the day
Zooid an organic cell or organized body that has independent movement within a living organism, especially a motile gamete such as a spermatozoon