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aeolid – A nudibranch sea slug of the suborder Aeolidina.

allopatric – Organisms, especially related, occurring in separate non-overlapping geographical areas.

annulate – A form that carries rings-shaped segments.

anterior – The front or towards the front.

anti-feedant – Organic compound possessed by an animal or plant that deters or inhibits feeding by a predator.

anus – The external opening at the end of the alimentary canal through which solid waste matter (faeces) is expelled.

aperture – Relating to a shell it is the single large terminal orifice through which the head, foot and mantle is extruded.

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

apical – The region at a tip or apex.

aposematic – A warning signal by colouration or markings to warn potential predators that the bearer should be avoided.

arborescent – repeatedly branched, bushy or tree-like.

axial – Refers to the direction of shell sculpture that is roughly parallel to the coiling axis.

autotomy – A process by which an animal deliberately casts off part or parts of its body as a defensive action – cerata or sections of the mantle in the case of sea slugs.

Batesian mimicry – A phenomenon in which non-harmful species have evolved to mimic the appearance of a species that is harmful to potential predators.

benthic – Relating to the bottom of a body of water. A benthic organism lives on or in the substrate.

bifid – Split or cleft into two parts – forked.

bifurcate – To divide into two branches or forks.

bilobed – Having two lobes.

bipinnate – With reference to the gill – having small side branches arising on two sides of the main stem (like a feather).

bivalves – An aquatic class of molluscs (Bivalvia) having two shells (valves) 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.

branchia – Refers to the gill.

branchial pocket – A cavity on the dorsal midline of a dorid’s body into which the gills can be retracted. May be situated from halfway back to very close to the posterior end depending on species.

buccal – Referring to the mouth or mouth cavity.

carnivorous – Refers to an organism that eats organisms of the animal kingdom.

caruncle – Elevated ridge or lobe between or anterior to the rhinophores in some armininid nudibranchs. Has a presumed sensory function.

caryophyllidia – Microscopic spicule bearing tubercles on the mantle surface of some discodorids. Of unknown function but postulated to be sensory.

caudal – Of or like or relating to the tail.

cephalic – In or related to the head.

cerata – (singular ceras) Finger-like processes arising in groups from the notum of aeolid and some armininid nudibranch sea slugs and containing diverticula of the digestive gland. They function in respiration, digestion and (in aeolids) defence. The term is also used for the similar-looking processes in some sacoglossans but they are not morphological related.

cerebral ganglion – A ganglion is group or cluster of nerve cell bodies. In sea slugs the cerebral ganglion in the head region is the closest structure they have to a brain.

chemosensory – able to detect chemicals.

chitin – A fibrous organic compound consisting of polysaccharides for support or protection.

chloroplasts – The plastid organelles within a plant cell that contain chlorophyll and conducts the process of photosynthesis.

cilia – (singular cilium) Fine hair-like organelles. There are two types; motile, that beat with a lash-like stroke and non-motile, that serve in a sensory capacity.

cladobranchs – A clade or group within the Nudibranchia order that possess a branched digestive gland.

clavus – The distal portion of the nudibranch rhinophore, above the stalk. It is often enlarged, carrying lamellae, papillae or other embellishments to increase surface area.

club – As for clavus.

cnidarians – Animals that belong to the phylum Cnidaria the distinguishing feature being cnidocytes, specialised cells that they use mainly for capturing prey. Examples include jellyfish, anemones, hydroids and corals.

cnidophages – Specialised cells that store the sequestered nematocysts (kleptocnides) in the cnidosac.

cnidosac – A small sac at the apex of each ceras of most aeolids in which functional undischarged nematocysts, acquired from the cnidarian prey, are stored for defensive use.

columella – The pillar forming the central axis of the shell around which the whorls spiral.

columellar lip – Inner lip of the shell aperture.

conspecific – Referring to organisms that belong to the same species.

contract – To shorten. Compare with retract.

corallivorous – To feed upon corals.

crenulated – Finely notched or corrugated – relating to the edge of a shell.

cruciform – Having the shape of a cross.

cryptic – Body camouflaged to resemble part of the natural microhabitat; or possessing secretive behaviour. May also refer to species being thus far unrecognised as a separate species, being hidden and undescribed amongst others.

cryptobranchs – An unnatural grouping of dorid nudibranchs that can completely withdraw their gill into a branchial pocket below the notum – crypto = hidden.

ctenidium – Respiratory organ located in mantle cavity or pallial groove. Believed to be homologous to the sea slug’s gill.

cutaneous – Relating to or affecting the skin.

deimatic behaviour – A rapid startle display designed to intimidate and warn off predators.

dendritic – branching, tree-like

detorsion – A developmental process whereby the sea slugs reverse much of the torsion that most gastropods undergo to adapt to living in a shell with a single aperture.

diffusion – A passive process of movement of a substance (including gases) from an area of high concentration to an area of low concentration – e.g. through the thin cell walls of a gill.

digestive diverticulum – A branch or lobe of the digestive gland usually located within a ceras.

digitiform – Of finger-like appearance

distal – The part which is situated away from the point of attachment or origin or a central point – opposite to proximal.

dorid – Nudibranchs with a circle of gills surrounding the anus, or an arc of gills just anterior to the anus, in the midline located in the posterior-half of the body. They are grouped in the suborder Doridoidea.

dorsal – The upper surface or back of an animal.

dorsolateral – Referring to a region that is at the sides or edges of the top surface.

dorsum – Refers to the upper (top) surface of the sea slug mantle = notum

endemic – Referring to a species that is native and restricted to a certain locality in its geographic distribution.

enrolled – Rolled up like a cylinder or tube but with a lateral groove.

epibont – An organism that lives on the surface of another living organism and is harmless to that organism (not a parasite).

epiphytic – A term borrowed from botany meaning, in this context only, plant or sessile animal growth attached and living on animal or plant but not as a parasite.

epithelium – Most often used to describe the skin tissue of an animal but also refers to the outer lining of organs and the also the lining of internal cavities.

extra-branchial – Describing structural processes located in close proximity to the gill. Believed to provide some protection.

extra-rhinophoral – Describing structural processes located in close proximity to the rhinophores. Believed to provide some protection.

filament – A slender thread-like process.

foot – The large ventral muscle mass being the organ of locomotion for gastropods.

fusiform – Spindle-shaped.

gastropod – A taxonomic class of molluscs including the sea slugs that if there is a shell present is most always only one.

genus – (plural genera) A taxonomic rank between family and species. A genus will contain one or more species that will share the first part of their name – the genus.

gill – (= branchia) The respiratory organ enabling gaseous exchange with the water environment. The term may also be applied to a wide variety of different structures performing the function. These are referred to as secondary gills.

gizzard – A modified muscular region of the gut used for masticating food, sometimes with grinding plates.

habitat – The type of natural environment in which an organism lives and is characterised by both physical and biological aspects.

haemocoel – the primary body cavity of molluscs in which the internal organs are bathed in haemolymph (= blood) – an open circulation.

haemolymph – The circulatory fluid of the sea slugs that contains blood and lymph fluid combined. There are no blood cells.

Hancock’s organ – A bilateral chemosensory organ located anteriorly between the headships and foot. Found in the majority of the shelled sea slugs.

headshield – An adaption of the head where it is widened to assist the sea slug to push through the substrate but preventing

herbivorous – Describing an animal that feeds on plant material such as algae.

hermaphrodite – Describes an organism possessing both male and female functional reproductive organs and capable of producing both sperm and eggs. All sea slugs are hermaphrodite.

holotype – The single physical example (rarely an illustration) of an organism, known to have been used when the species was formally described – the type specimen.

homologous – Usually referring to organs of different taxa that are similar in position, structure and evolutionary origin but not necessarily in function.

hyponotum – The under surface of the mantle. Sometimes referring to the area between the underside of the mantle and the foot (the hyponotum groove).

ICZN – International Commission on Zoological Nomenclature, acts as adviser and arbiter for the zoological community by generating and disseminating information on the correct use of the scientific names of animals. The ICZN is responsible for producing the International Code of Zoological Nomenclature – a set of rules for the naming of animals and the resolution of nomenclatural problems.

in situ – Refers to when the animal is situated in its natural environment.

incised – A deep etching or mark on the surface of a shell.

infaunal – Refers to an animal that lives within the substrate e.g. burrowing.

infrapallial lobe – A posterior fold of the body enclosing the posterior end of the shell in cephalaspideans.

intertidal – The area of foreshore lying between high tide (when it is covered by water) and low tide (when it is exposed to the air).

intraspecific variation – Refers to the natural variation found in one or more features between individuals of the same species.

invertebrate – Animals without and do not develop a vertebral column.

involute – Describes the spire of a shell that is sunk below the level of the apex.

jaws – In sea slugs refers to the thickened, horny plates within the buccal cavity for gripping prey.

junior homonym – In biology – refers most usually to the more recent of two identical names that refer to different organisms and is therefore invalid.

kleptocnides – “Stolen stinging cells”, the term used for the sequestered nematocysts once stored in the nudibranch’s cnidosac.

kleptoplasts – Chloroplasts that are sequestered through the agal diet of certain sacoglossans and then maintained by the host to temporarily continue photosynthesis for its benefit.

kleptoplasty – The behaviour (theft) of taking undigested chloroplasts from a food source. They are then used for temporary photosynthesis.

lamellae – (singular lamella) A thin layer, membrane or plate of tissue.

lamellate – (= perfoliate) A term used to describe the structure of some rhinophores that bear plates or leaflets on the clavus that are either horizontal or vertical.

lappets – The muscular plates or fleshy extensions associated with the mouth. Often sensory for close proximity food location.

larvae – (singular larva) The juvenile stage of an animal prior to its undergoing metamorphosis into an adult. Its form can be completely different to the adult.

last whorl – The body or last, most recently formed whorl of the gastropod shell terminating in the aperture.

lateral – Positional term relating to of, at or towards the side.

lecithotrophic – Refers to the type of development in which larvae utilise only the reserves of yolk in the egg to nourish themselves Generally a free-swimming, non-feeding, short duration larval stage.

limaciform – slug-shaped.

mantle – The organ surrounding the viscera of molluscs and secreting the shell. In those sea slugs without a shell it develops into the layer that covers the body – the notum.

mantle margin – The outermost edge of the mantle.

mantle skirt – The expanded edges of the mantle in the shell-less sea slugs.

medial – Positional term relating to of, at or towards the middle or midline. Opposite to lateral.

metamorphosis – A biological process whereby an animal develops by undergoing a significant physical and abrupt change in body structure often accompanied by a change in habitat, diet and behaviour.

metapodium – A posterior lobe or extension of the foot. It bears the operculum when present.

molecular sequencing – The process of determining the order of nucleotides in an animals DNA to obtain a genetic profile. RNA sequencing reflects the sequences that are actively expressed in the cells.

monophyletic – Refers to a group composed of a collection of organisms, including the most recent common ancestor of all those organisms and all the descendants of that most recent common ancestor. Such groupings often referred to as a clade.

morphology – The structure and form of organisms (the anatomy) without regard to function.

Mullerian mimicry – A form of biological resemblance in which two or more unrelated noxious, or dangerous, organisms exhibit closely similar warning systems, such as the same pattern of bright colours.

nematocyst – The specialised stinging cell of the Cnidaria (a minute capsule with a coiled thread that rapidly unwinds on discharge) to capture prey or act in defence. Present in hydroids, sea anemones, corals, etc. the food of aeolid nudibranchs. They separate the nematocysts from the remainder of the hydroid tissues and pass them, undischarged, through the digestive diverticulum in the cerata to the cnidosac at the tip where they are stored to be used for the aeolid’s own defence.

nocturnal – Active at night only.

notum – Refers to the upper (top) surface of the sea slug mantle = dorsum

noxious – Usually used to describe something not as dangerous as toxic but still harmful and often distasteful as well.

nudibranch – Correctly used only for those sea slugs that are members of the order Nudibranchia. Incorrectly used in much popular literature to refer to all the sea slugs.

obligate – In relation to feeding, indicates that the animal requires that particular food to survive.

octocorals – Corals with 8-fold symmetry – soft corals, gorgonians & sea pens.

odontophore – The “cartilaginous” projection in the mouth that supports the molluscan radula.

oophagous – Relates to the eating of eggs.

operculum – A horny or calciferous plate that partially or completely closes the aperture on retraction into the shell of most (not all) shelled molluscs.

opisthobranch – No longer a valid term although sometimes now used informally to refer to all the sea slug types. It was previously used to describe members of the subclass Opisthobranchia, now an invalid taxon being non-monophyletic.

oral tentacles – Pair of tactile and chemosensory tentacles (or flaps) around the mouth; used for close proximity food location and recognition.

oral veil – A membranous extension of the head above the mouth sometimes with well-developed sensory projections.

osphradium – A chemosensory organ of some molluscs associated with the respiratory ctenidium and believed to monitor the water quality within the mantle cavity. Of the sea slugs only the primitive shelled species have an osphradium located in the mantle cavity anterior to the gill.

outer lip – Outer edge of aperture of a shell.

ovivore – Feeds upon eggs.

pallial – Relating to the mantle.

palmate – Shaped like a hand with processes that are extended like fingers.

papilla – (plural papillae) A small, delicate, finger-like projection.

papillate – bearing papillae

parapodia – (singular parapodium) Thin flap-like lateral extensions of the foot in Cephalaspidea, Sacoglossa, Anaspidea and Thecosomata sea slugs that wrap up over the sides of the shell or body that may or may not meet in the midline. They may be used for body protection, respiration, plastid “farming” or swimming.

paratype – A specimen of an organism that helps define what the scientific name of a species actually represents, but is not the holotype. Specifically, in zoological nomenclature, a paratype is officially defined as “Each specimen of a type series other than the holotype.”, where the type series are the specimens cited in the original publication of the new species.

pedal – Relating to the foot.

pelagic – Passively drifting or floating in the sea including on the sea surface, with currents or winds.

perfoliate – = lamellate

pericardium – Sac-like structure enclosing the heart.

periostracum – The protective outermost layer of gastropod and bivalve shells. It may vary from thin and transparent to thick and horny or fibrous.

phanerobranch – An unnatural grouping of dorid nudibranchs that can contract their gill but not withdraw it into a pocket below the notum so that it is always visible – phanero = visible or to show.

phylogenetic – The evolutionary development and therefore the history of a species or a species trait. Also applied to higher taxons.

pinnate – Having side branches – resembling a feather.

planktotrophic – Refers to the type of development in which free-swimming larvae spend a considerable time feeding and growing in the plankton before settlement and metamorphosis into the adult.

plicate – Folded, corrugated or twisted – producing a larger surface area.

porostomes – Members of a group of dorid nudibranchs that lack a radula and feed suctorially – the radula-less dorids.

posterior – The rear or towards the rear.

predator – An animal that feeds upon another.

prey – An animal upon which another animal feeds.

propodial – Referring to features of the anterior part of the foot.

propodium – The anterior part of the foot.

prosobranchs – Snails of the Prosobranchia – literally gill in front (of the heart).

protoconch – Larval shell of a gastropod. Smallest spiral tip of a shell, if not lost through damage.

proximal – The part which is situated closer to the point of attachment or centre of the body – opposite to distal.

pustule – A small, conical or rounded swelling on the notum. Technically, should describe such a protuberance that is filled with a fluid or thicker compound. While pustule should not = tubercle the terms are often used interchangeably.

radula – A flexible, chitinous ribbon of small teeth contained within the buccal cavity used for feeding by, rasping at, cutting away pieces of, puncturing or pulling in prey. Combination, arrangement and shape of the teeth is useful in delineating species etc.

remnant – A part that is left of the original whole. Refers to organs or structures that are reduced through evolutionary development.

respiration – Process of gaseous exchange between an organism and the environment.

reticulum – Intersection of lines or structural parts forming at network-like pattern. (adj: reticulate)

retract – To pull back inside. Compare with contract.

rhinophoral pocket – A cavity into which the rhinophore of a dorid nudibranch can be withdrawn.

rhinophoral sheath – A  sleeve, raised above the mantle surface of dendronotoid nudibranchs, surrounding the base of a rhinophore and into which the rhinophore can be contracted for protection.

rhinophores – Paired chemo-sensory tentacles located anteriorly on the mantle or on the head, of most sea slugs.

sculpture – Texture of and any embellishment on the surface of a shell.

secondary gills – Structures that perform gaseous exchange (respiration) for an animal but not homologous with the true gill.

secondary metabolites – Organic compounds that are produced by, but are not directly involved or required in the normal growth, development or reproduction of an organism.

sessile – Refers to animals that are predominantly immobile, living a fixed existence. Some have a motile larval stage.

shell – A calcareous structure that acts as an exoskeleton (in most cases) to support and protect the soft vulnerable body parts. In sea slugs the shell may be external, reduced, internal, a remnant or completely lost in the adult.

sinus – A sac or cavity in any organ or tissue.

siphon – A tubular extension of the mantle to facilitate water flow into or out of the mantle cavity. Also a verb to describe the action of that water flow.

siphonophores – Cnidarian animals belonging to the Siphonophorae (such as bluebottles), some of which are preyed upon by Glaucus nudibranchs.

slugivore – Feeds on sea slugs.

spatulate – Refers to the wide flattened shape of the anterior portion of the body of some sea slugs.

spawn – Refers to the grouping of laid eggs as a – string, coil or mass fixed in a transparent jelly.

speciation – The evolutionary process of producing new species.

species – A level of biological classification comprising related organisms that share common characteristics and are capable of interbreeding to produce fertile offspring.

speciose – Rich in species.

spicule – A minute calcareous rod or other shaped body in the mantle to give a protective or supportive texture to the mantle.

spire – The visible part of a shell – all the whorls excepting the last or body whorl.

spongivore – Feeds upon sponges.

stalk – Usually a term used to describe the base portion of a rhinophore that supports the sensory clavus.

statocyst – A small organ of balance and orientation.

striate – Marked with fine grooves.

subapical – Referring to the portion below the apex or tip.

submarginal – Adjacent to or just inside of the edge or margin.

substrate – The surface upon which an organism is attached or moves across I.e. lives upon.

symbiosis – Describes a close and often long term interaction between two or more different species usually where both organisms benefit.

sympatric – Organisms, especially related, that occupy the same geographical location without loss of identity from interbreeding.

synonymDifferent scientific names of the same taxonomic rank that pertain to that same taxon. Only one of them is considered valid the others being superseded.

synonymized – Where a species may have more than one name and those considered invalid are identified and “brought into synonymy” with the name considered valid.

synthesise – The act of creating something by combining two or more components. In biology, the creation of an organic compound.

taxon – A taxonomic group of any rank, such as a species, family, or class.

taxonomist – A biologist that studies, names, defines and and groups organisms into categories (taxons).

taxonomy – Concerned with the classification of organisms into a hierarchy or scheme of classification.

tentacle – Protruding sensory appendage most often on the head or around the mouth but also of the anterior portion of the foot – usually paired – left and right.

torsion – The rotation by 180 degrees of the visceral mass in an anticlockwise direction during gastropod development to suit living in a shell with a single aperture.

toxic – containing or being poisonous – capable of causing serious debilitation or even death.

translucent – Semitransparent, allowing light to pass through but not detailed shapes.

tripinnate – Refers to a gill that has a main stem and primary and secondary branches.

truncate – Having the appearance of being shortened by removal of the end thus looking blunt or cut off.

tubercle – Short rounded projections above the surface usually on the mantle but can also refer to similar projections on rhinophores and cerata.

type location – The geographical location from where the holotype (type specimen) was collected.

type species – The species on which a genus is based and with which the genus name remains associated during any taxonomic revision.

uniseriate – Describing an arrangement of teeth in the radula where there is only a single tooth in each row.

vascularised – refers to a tissue or structure that has circulatory vessels throughout.

velar tentacles – A term used to describe the processes projecting from the oral veil in some sea slugs. These have a sensory ability.

veliger – Larva of molluscs. Named derived from the characteristic ciliated, bilobed velum used for swimming and feeding.

ventral – The lower surface or underside of an animal.

viscera – The soft internal organs of the animals body.

whorl – One complete spiral turn of a univalve shell. Also one turn of an egg spiral.

zooxanthellae – Symbiotic single-celled dinoflagellates, that photosynthesize, found in many cnidarian animals. Taken up and utilised symbiotically by some aeolid nudibranchs that prey on the cnidarians.