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Nudibranch Glossary

Definitions of terms relating to heterobranchs.


aeolid - A nudibranch belonging to the major group (suborder) Aeolidina.
annulate - A shape that consists of rings or ring-like segments.
- Toward the front of the body.
aperture - The single large terminal orifice of a shell through which the head-foot is extruded.
apertural sinus - Recurved notch in margin of aperture of a shell.

apex - Narrow first formed part of shell, typically bearing a protoconch (the tip of the spire).

apical - Relating to the tip or apex.

autotomy - A defensive behaviour in which an animal deliberately casts off part of its body (usually the mantle or cerata).
axial - Describes direction of shell sculpture that is more or less parallel to the coiling axis.
benthic - Refers to an organism living on or in the substrate.

bifid - Divided by a deep cleft into two parts.
bipinnate - With small side branches arising on two sides of the main stem or axis (refers to the gill).

bivalves - An exclusively aquatic class of molluscs that has two shells that are typically symmetrical along the hinge line and feed by siphoning and filtering particles from the water.
body whorl - One complete spiral turn of a univalve shell.
branchial pocket - A cavity in the posterior midline of a dorid’s body into which the gills can be retracted.
buccal - Referring to the mouth or mouth cavity.
carnivorous - Literally a meat-eater; but in this context relates to a nudibranch feeding on a diet of animal material (e.g. sponges, bryozoans, bristle worms, cnidarians, or sea squirts).
caryophyllidia - Specialised spiculose tubercles on the mantle surface of some cryptobranch dorids.
cerata - (singular ceras) Finger-like processes arising in groups from the notum of aeolid and zephyrinid nudibranchs and containing diverticula of the digestive gland. Function in respiration, digestion and (in aeolids) in defense.

caruncle - Elevated ridge or lobe with presumed sensory function.

caudal - Relating to the tail.

chloroplasts - The plastid within a plant cell that contains chlorophyll and is the site of photosynthesis.
- Fine hair-like organelles that beat with a lash-like stroke.

clavus - The distal portion of the rhinophore above the stalk. It is often expanded and ornamented with lamellae or papillae.

club - See clavus.
cnidosac - A small cavity at the apex of each ceras of aeolids in which unexploded nematocysts aquired from the cnidarian food are stored.
columella - The pillar forming the central axis of the shell around which the whorls spiral of a shell.
columellar lip - Inner lip of aperture of a shell.
crenulate - Finely notched; regularly indented.
cryptic - Body camouflaged to resemble part of the microhabitat; or possessing secretive behaviour.
cryptobranch gill - Gills of dorid nudibranchs which can be retracted completely into a branchial pocket below the notum.
distal - That section of an organ or appendage which is most remote from the point of attachment to the body.
digestive diverticulum - A branch of the digestive gland within a ceras.
dorid - Nudibranchs with a circle of gills surrounding the anus in the midline towards the rear of the body, belonging to the major group (suborder) Doridina.
dorsal - The top surface of the animal.
dorsum - (= notum) The exposed back or top surface of a nudibranch mantle.
endemic - A species that is restricted to one or few localities in its distribution.

epiphytic - Referring to organisms living on the surface of a plant.

filament - A slender thread-like process.
foot - The large muscle mass on which gastropods move.
fusiform - Spindle shaped.
gill - (= branchia) The respiratory organ. Either in the form of single leaflets (hence pinnate) or with side branches (bipinnate or tripinnate).

gizzard - A modified region of the gut used for masticating food.

habitat - The natural environment in which an organism lives.
herbivorous - Feeding on plant material (e.g. seaweed, encrusting microalgae).
hermaphrodite - Bisexual; an individual possessing functional male and female reproductive organs and capable of producing both sperm and eggs.
hyponotum - The under surface of the mantle.
in situ - Refers to the natural environment of an animal.
incised - A deep etching or mark on the shell surface.

infaunal - Living within the substrate.
infrapallial lobe - Posterior fold of body enclosing shell of cephalaspideans.
inner lip - Inner margin of aperture overlying columellar of a shell.

intertidal - The area of foreshore that lies between high tide (when it is covered by water) and low tide (when it is exposed to the air).
intraspecific variation - Refers to natural variation in one or more charcters between individuals of the same species.
involute - Refers to the spire of the shell of the family Bullidae, which is sunk below the level of the apex.
jaws - Thickened, horny plates within the buccal cavity.
lamellate - (= perfoliate) Rhinophores bearing plates on the posterior face of the stalk or clavus.

lappets - Muscular plates or extensions associated with the mouth.
last whorl - The last most recently formed whorl of gastropod shell.

lateral - Relating to the side.
larvae (singular: lava) - The juvenile stage of an animal prior to its undergoing metamorphosis into an adult. Its form can be completely different to the adult.
lecithotrophic - Relates to the type of development in which larvae utilise only the reserves of yolk in the egg to nourish themselves.





mantle - The organ secreting the shell of molluscs. It develops into the layer that covers the body in heterobranchs without a shell.
margin - The outer edge of the mantle.

medial - Towards the middle or midline.
metamorphosis - A biological process whereby an animal develops by undergoing a physical and abrupt change in form often accompanied by a change in habitat and behaviour.
metapodium – Posterior extension of the mantle.
nekton - Permanently floating at the surface of the ocean.
nematocyst - The stinging organ of the Cnidaria (a microscopic capsule with a coiled thread that rapidly unwinds on discharge). Present in hydroids, sea anemones, corals, etc. Aeolid nudibranchs separate the nematocysts from the remainder of the hydroid tissues and pass them, unexpoded, through the digestive diverticulum in the cerata to the cnidosac at the tip where they are used for the aeolid’s own defense.

nocturnal - Active at night.
notum - (= dorsum) The exposed back or top surface of a nudibranch mantle.
nudibranch - Technically a member of the order Nudibranchia of the subclass heterobranchia (sea slugs). Equivalent of heterobranch in much popular literature.

operculum - A horny or calciferous plate that partially or completely closes the aperture
on retraction into the shell.
heterobranch - Technically a member of the subclass Gastropoda (includes bubble snails, sea hares, sea butterflies, caddis slugs, sap-sucking slugs and side-gilled slugs as well as nudibranchs).
oral tentacle - Tentacle (or flap) around the mouth; used for food location and recognition.
oral veil - A membranous extension of the head above the mouth.
outer lip - Outer edge of aperture of a shell.

palmate - Having a shape in the likeness of a hand with the fingers extended.
papilla - (plural papillae) A small, delicate, finger-like projection.
parapodia - Flap-like extensions from the sides of the foot in cephalaspidean, sacoglossan and thecosomatous heterobranchs. They enclose the body and can be used for swimming.
pelagic - Passively drifting or floating at the sea surface; drifting with currents or winds.

pericardium - Sac-like structure enclosing the heart.
periostracum - The horny outermost layer of gastropod and bivalve shells.
phanerobranch gill - Gills of dorid nudibranchs that cannot be withdrawn into a branchial pocket beneath the notum. They can only be contracted into a tight group above the notum.
pinnate - Bearing side branches; branched as to resemble a feather.
planktotrophic - Relates to the type of development in which larvae actively feed on micro-organisms to nourish themselves while they are in the plankton.

plicate - Folded.
posterior - Towards the rear of the body.

propodial - Located at the anterior part of the foot.
protoconch - Larval shell of a gastropod. Smallest spiral tip of a shell.
pustule - (= tubercle) A low, conical, rounded or uneven swelling on the notum.
radula - A flexible, cuticularised feeding organ contained within the buccal cavity; bears numerous minute teeth.

respiration - Exchange of gases between the environment and the organism.
reticulum - Network; any reticulated system or structure.
rhinophore - Sensory tentacle on the head, or anterior section of the mantle, of heterobranchs.
rhinophoral pocket - The cavity into which the rhinophore of a dorid nudibranch can be withdrawn.
rhinophoral sheath - Upstanding flange from the antero-lateral part of the mantle (of dendronotoid nudibranchs) into which the rhinophore can be contracted.
sculpture - Surface structure and ornamentation on shell surface.

siphon - Elongation of mantle edge to form a tube for water flow.
shell - The molluscan shell is a calcareous exoskeleton which encloses, supports and protects the soft parts of the animal. It is formed, repaired and maintained by the mantle. In heterobranchs it may be reduced, internal or completely lost in the adult.
spawn - Mass of eggs embedded in transparent jelly.
spicule - A minute rod or star-shaped thickening in the mantle; spicules can be interwoven in a sponge-like fashion to give a protective texture to the mantle.
spire - The visible part of all the whorls except the last (shell body) whorl.
striate - Marked with fine grooves.
subapical - Section below the apex or tip.
substrate - The type of sea floor on which a benthic organism lives and grows.

symbiosis - Describes a close and often long term interaction between different species usually where both organisms benefit.
tentacle - Projecting sensory appendage associated with the head or mouth.
tripinnate - With small side branches arising from three sides of the main stem or axis (refers to the gill).
truncate - shortened abruptly, squared off.

uniseriate - In relation to the arrangement of teeth in the radula where there is a single tooth in each row.
ventral - The underside of the animal.
viscera - The soft interior organs of the body.
whorl - One complete spiral turn of a univalve shell.

zooxanthellae - Symbiotic dinoflagellates in many cnidarians.


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