• ACLEIOPROCT. Nudibranchs with the anus located on the right side of the body but quite dorsally, between the cerata emerging from the right side of the digestive gland and those from the left side. Opposite: Cleioproct.
  • ADAPICAL. Close to the apex.
  • AFF. Latin abbreviation “affinis” meaning “similar, but not identical”.
  • ALOCTONE. Species that originated and evolved in a different place than it is found.
  • ANTIDEPREDANT. That prevents predation. It refers to defensive substances.
  • ANULLATE or RINGED. Means “provided with rings”, generally refers to rhinophores.
  • APEX. Latin word that indicates the upper end of an organ.
  • APICAL. Relative to apex.
  • ARBORESCENT. Branched like a tree, shaped like a tree.
  • ARMINACEANS. Members of the Arminidae family, characterized by the lack of rhinophoric sheaths and by having a branched liver gland, gills under the mantle and anus in a lateral position.
  • AUTOCHTONE. Species native to the place where it lives.
  • AUTOTOMY. When an organism voluntarily detaches parts of its body to distract predators during an attack.


  • BENTONIC. Organisms that live linked to the seabed.
  • BIODIVERSITY. Variety of animal and plant species in their environment.
  • BIPINNATE. Primary and secondary branches of the rachis.
  • BRANCH or GILL. Respiratory organ of aquatic animals. In dorid nudibranchs, they are usually arranged dorsally around the anus.
  • BRANCHIAL. Related to the GILL.
  • BRANCHIAL APPENDICES. Branched structures with respiratory functions, typical of dendronotaceans.
  • BRANCHIAL LEAF. Each of the units that make up the BRANCH or GILL.
  • BUCCAL MASS. Muscular organ within the mouth that houses the jaws and manipulates the radula.


  • CARYOPHYLLIC. Relative to tubercles surrounded by spicules, typical of the notum of some Doridaceans.
  • CARNIVORE. That feeds on other animals.
  • CARUNCLE. Sensory organ, similar to a chicken crest, located between the rhinophores of the nudibranchs of the Janolidae family.
  • CEPHALIC VEIL. Anterior extension that, in some nudibranchs, widens the sensory area of ​​the head. It may have digitiform or branched tentacles.
  • CERA. Elongated papilla with respiratory function that contains diverticula of the hepatic gland and that appears, in very variable numbers, on the back of some nudibranchs. They also tend to have a defensive function.
  • CERATA. Plural form of CERA. Colloquially, “cerata” is used for singular, with the plural “ceratas”.
  • CHITIN. Organic substance that is part of the composition of radular teeth.
  • CHITINOUS. Formed by chitin.
  • CLEIOPROCT. Nudibranchs in which the anus is in a lateral position, surrounded by the cerata that emanate from the anterior part of the left lobe of the digestive gland. Opposite: Acleioproct.
  • CNIDOCYTES or CNIDOBLASTS or NEMATOCYTES. Stinging cells found on the tips or cerata in nudibranchs. These stinging cells are not made by the nudibranch, but by the species that it feeds upon. A cnidocyte fires a structure that contains the toxin, from a characteristic subcellular organelle called a cnidocyst.
  • CNIDOCYSTS or CNIDA or NEMATOCYST. Cellular organelles in the form of stinging capsules present in the tentacles of cnidarians, with the ability to shoot a microscopic harpoon that injects venom as a defense method.
  • CNIDOSACS. Small cavities located at the end of the cerata where the cnidocytes are stored without being triggered.
  • COMENSALISM. Symbiotic association in which one part benefits from the other, which does not obtain advantages, but does not suffer any harm.
  • CONGENERIC. Relating to several species belonging to the same genus.
  • CONSPECIFIC. Relating to several specimens belonging to the same species.
  • CONTRACTIBLE. That can shrink or contract.
  • CORALYGEN. Biocenosis of hard substrate characterized by a sciaphillyc environment (in low light) where encrusting red algae and corals are found, species capable of fixing calcium carbonate from water.
  • COSMOPOLITAN. Term defining a species with a worldwide geographical distribution.
  • CRYPTIC. Coloring patterns that favor camouflage with the medium. It is also said of morphologically very similar -but genetically different- species.
  • CRYPTOBRANCH. Doridacean nudibranchs that can completely retract the gills inside the body.
  • CTENIDIUM (plural CTENIDIA). Synonym of “BRANCH” or “GILL”. Some aquatic gastropods possess one ctenidium known as monopectinate and others have a pair of ctenidia known as bipectinate.
  • CUSP. Small indentation at the margin of a radular tooth.


  • DENDRONOTACEAN. Nudibranch member of the parvorden Dendronotida, with rhinophores surrounded by a sheath, and anus in a median lateral position.
  • DESCRIPTION. Written declaration of the taxonomic characters of a specimen of a taxon.
  • DIGESTIVE GLAND. Synonym of liver gland. Gland that produces and secretes digestive juices.
  • DIGITATION. Finger-like projection of the body.
  • DIMORPHISM. Which has two forms.
  • DISTAL. Relative to the end of some organ, the most distant part of the body.
  • DISTRIBUTION. Geographical extension of the habitat of a species.
  • DORID o DORIDACEAN. Nudibranch belonging to the Doridina suborder, characterized by a broad foot, a “notum” or thick and fleshy mantle, with two sensory projections called rhinophores and a retractable or contractile branchial plume located at the back, surrounding the anus.
  • DORSUM or NOTUM. Upper body of a nudibranch.
  • DORSAL. Relative to DORSUM. Opposite to the VENTRAL part that is where the foot is.


  • ECOLOGY. Term coined by the German biologist Ernst Haeckel in 1866, referring to the science that studies the relationships of living beings with their environment. Since the 70s it also means “protection of the environment”.
  • ECOLOGICAL NICHE. Set of activities and relationships that each species has developed in its own habitat.
  • ENDEMIC. Species typical of a specific habitat or geographic area.
  • EOLIDACEAN. Nudibranch member of the parvorder Aeolidida, with cerata on the back and without rhinophoric sheaths.
  • EPIBIONT. An organism that lives on the surface of another living organism.


  • FAMILY. Taxonomic rank; group of various GENERA that have a large number of common characters.
  • FOLIATE. Leaf-like structure, applied to some nudibranchs.
  • FOOT. Muscular part of the ventral zone of the mollusc. It is the organ responsible for locomotion and sometimes (in some carnivorous species) to capture preys.
  • FOULING. Layer of animal and vegetal organisms that grow on the surface of objects submerged in water (docks, boats, buoys, etc.).


  • GENUS (plural “GENERA“). Taxonomic rank; group of morphologically similar species.
  • GILL. Respiratory organ of aquatic animals. In dorid nudibranchs, they are usually arranged dorsally around the anus.
  • GONAD. Genital gland in which male or female gametes are formed.


  • HABITAT. Natural environment in which animal and plant species live and develop. The group of organisms that inhabit a habitat is called “community”.
  • HEPATOPANCREAS. Gland that secretes digestive juices and other substances useful for the metabolism of nudibranchs. Synonym of digestive gland.
  • HERMAPHRODITE. An organism that has both male and female reproductive organs. All nudibranchs are hermaphrodites.
  • HYPONOTUM. Area of the body located under the MANTLE or NOTUM, next to the foot.
  • HOLOTYPE. Original specimen designated as the owner of a species, deposited in a recognized museum.


  • ICHTHYOTOXIC. Literally, toxic to fish. Some nudibranchs secrete substances with these properties.
  • ICZN. Acronym of International Commission on Zoological Nomenclature.
  • INCERTAE SEDIS. Latin expression used in taxonomy to indicate the inability to exactly place a taxon within a classification scheme.
  • INFRALITTORAL. Seafloor area below the tidal level, in which marine phanerogams and photophilic algae survive. In the Mediterranean it reaches down to about 40 meters deep.
  • INTER-SPECIFIC. Relating to the relationships between two or more species.
  • INTERTIDAL. Coastal range between low tide level and high tide level.
  • INTRA-SPECIFIC. Related to morphological variability within the same species.


  • JUVENILE. Stage of development between egg hatching and the subadult stage. The separation criteria between the larval and juvenile stages is not well defined.


  • KLEPTOCNIDY. Mechanism by which a nudibranch ingests the cnidocysts or stinging cells of the cnidarians from which it feeds to take them to their appendages so that they become a defensive system as if they were stinging cells of its own.
  • KLEPTOPLASTY or KLEPTOPLASTIDY. Symbiotic phenomenon whereby plastids, notably chloroplasts from algae, are sequestered by host organisms. The word is derived from Kleptes (κλέπτης) which is Greek for thief. The alga is eaten normally and partially digested, leaving the plastid intact. The plastids are maintained within the host, temporarily continuing photosynthesis and benefiting the predator. The term was coined in 1990 to describe chloroplast symbiosis. Present in most sacoglossans.


  • LABIATE. Related to the lip, usually external.
  • LAMELLA / LAMELLAE. Thin tissue layer with sensory function, sometimes also with respiratory function. Frequent in the rhinophores.
  • LARVA. Stage of development that goes from egg hatching to the juvenile stage. The separation criteria between the larval and juvenile stages is not well defined.
  • LECITOTROPHIC DEVELOPMENT. Veliger larvae that feed on the embryonic yolk, with a short planktonic phase, because they settle in a time lapse from a few hours to 2-3 days. They have a limited dispersal capacity.
  • LESSEPSIAN. Species that has migrated from the Red Sea to the Mediterranean Sea through the Suez Canal. The name derives from the designer of the Suez Canal: Ferdinand de Lesseps.
  • LIP ARMOR. Chitinous layer that covers the buccal lip.
  • LIVER GLAND. Synonym of digestive gland.
  • LOBULATE. Indicates prominent, rounded projections; generally refers to the margin of the nudibranch mantle.


  • MACARONESIA. Biogeographic region formed by the archipelagos of the central eastern Atlantic: Azores, Madeira, Salvagem, Canarias and Cape Verde.
  • MALACOLOGIA. Branch of Zoology that studies mollusks.
  • MARGIN (of NOTUM). Lateral projection more or less evident around the body of some nudibranchs.
  • METAMORPHOSIS. All the transformations of form and structure that some animals undergo, such as most nudibranchs.
  • MIMETISM or MIMICRY. The ability of a species to go unnoticed in its habitat and deceive, with its physical appearance, a possible predator.
  • MONOPECTINATE. With only one GILL or BRANCH.
  • MONOPHILETIC GROUP. When all the organisms included in the group have evolved from a common ancestral population, and all the descendants of this ancestor are included in it.
  • MORPH. Synonym with “FORM”.
  • MORPHOLOGY. Study of the shapes and structures of animals.
  • MOUTH. Opening through which the animal is fed.
  • MUCRON. Apex of the rhinophores of some nudibranch species.
  • MUTUALISM. Symbiosis in which two organisms mutually benefit from the cohabitation situation.


  • N. SP. Abbreviation for “new species”.
  • NEOTYPE. The nominal species of a genus, when there is a need to objectively define the nominal taxon and there are reasons to believe that the holotype has been lost.
  • NEPHRIDIUM. Excretory organ that eliminates metabolic residues from the animal’s body.
  • NOMEN DUBIUM. Latin term meaning “dubious name”.
  • NOMEN INQUIRENDUM. Latin term indicating that the name requires verification.
  • BINOMIAL NOMENCLATURE. Taxonomic management system applied by Linnaeus to name living things. Each species is uniquely identified by a name written in italics and composed of the binomial: Genus (the initial always in uppercase) and species (always in lowercase).
  • NOTAL. Related to NOTUM.
  • NOTUM. Synonym of “DORSUM”.


  • OPISTHOBRANCH. Gastropod mollusk characterized by having the gills located behind the heart, among other anatomical features, such as the loss of the shell after metamorphosis (in most cases) and the detorsion of the internal organs of the body. Actually the use of this term is declining, as it is no longer valid taxonomically.
  • ORAL. Related to the mouth.
  • ORAL TENTACLES. Elongated tactile-type processes located on the sides of the mouth.
  • OVOTESTIS. Male and female gonads, typical of opisthobranchs.


  • PALEAL CAVITY. Cavity located between the edge of the mantle and the foot of gastropods in which various organs, including respiratory organs, are located. Nudibranchs lack it.
  • PALPS. Digitiform extensions of the body, more or less developed and with tactile function, located in the anterior part of the foot (propodial palps) and / or around the mouth (oral palps) according to the species.
  • PAPILLA. Small fleshy tubercle, generally conical in shape.
  • PAPILLOSE. Covered with papillae.
  • PARAPHILETIC GROUP. When all the organisms included in the group have evolved from a common ancestral population, but not all the descendants of this ancestor are included in it.
  • PARASITE. Organism that lives taking advantage of another living being.
  • PELAGIC. Organism that lives on the open seas, either swimming or floating.
  • PERICARDIUM. Area surrounding the heart.
  • PHANEROBRANCH. Doridacean nudibranchs that can NOT fully retract the gills within the body.
  • PHOTOPHILE. Organism that needs or tolerates total illumination.
  • PHYTOPLANKTON. Complex of plant microscopic organisms that are the food of many aquatic animals.
  • PLANKTON. Complex of microscopic, vegetable (phytoplankton) and animal (zooplankton) organisms, which coexist in the water column and are the food of many aquatic animals.
  • PLANCTOTROPHIC DEVELOPMENT. Veliger larvae that feed on plankton, with a long planktonic phase that can last several weeks. They have great dispersal capacity.
  • PLEUROPROCT. When the anus is located on one side of the body.
  • POLYMORPHISM. It occurs when in a population of the same species there are two or more clearly differentiated phenotypes, that is, there is more than one form or phase. Animals must live in the same area and reproduce among themselves indiscriminately.
  • POLYPHYLETIC GROUP. Group that does not include the most recent common ancestor of all its members; It is constituted by the artificial union of scattered branches of the evolutionary tree and, generally, is due to errors in the parentive interpretation, the criterion used for the classification of living beings.
  • POSTERIOR. Relative to the rear part of the animal, where the tail is.
  • PREY. An animal that serves as food to another animal.
  • PROPODIAL. In the anterior area of ​​the foot.
  • PSEUDOBRANCH. Epidermal structures (laminae, appendages, etc.) with respiratory function, present in some nudibranchs (e.g. in the genus Doto).


  • RADULA. Organ located in the pharynx, in the form of a ribbon covered with curved chitinous teeth, with the function of scraping food from the substrate.
  • RACHIDIAN TOOTH. The central tooth of the radula.
  • RACHIS. Axis of a branchial leaf or a rhinophore.
  • RETICULATE. A pattern of straight lines or ridges that intersect at angles.
  • RETRACTILE. Trait by which an animal can shrink and hide sensitive organs within the body when disturbed.
  • RINGED. Means “provided with rings”, generally refers to rhinophores.
  • RHINOPHORE. Chemo-sensory tentacle disposed on the head of the nudibranchs. The rhinophores can be smooth, ringed, lamellate, verrucose, wrinkled, etc.
  • RODS. Thin structures of the labial armor.


  • SCYOPHYLLIC. Environment protected from sunlight or an organism that avoids light.
  • SEDENTARY. Fixed organism or of very limited mobility.
  • SENSU LATO. (Abbreviated S. L.), means “in broad sense” in Latin.
  • SENSU STRICTO. (Abbreviated S. S. or S. STR), meaning “in strict sense” in Latin.
  • SESSILE. Organism permanently attached to the substrate, with no ability to move.
  • SYMBIOSIS. Relationship established between two or more living beings that live in the same environment and use the same resources. If both benefit, we speak of “mutualism”, but if only one benefits, we speak of “commensalism”.
  • SYNONYM. A new name inadvertently assigned to an existing species.
  • SP. Abbreviation of the Latin term for “Species” (singular).
  • SP. IND. Abbreviation of the Latin term for “Indeterminate species”.
  • SP. NOV. or SPEC. NOV. Abbreviation of the Latin term for “new species”.
  • SPAWN or EGG SPAWN. Egg mass embedded in transparent jelly.
  • SPICLES. Calcareous spines incorporated into the mantle tissue that give it consistency and serve as a defense mechanism.
  • SPP. Abbreviation for the Latin term for “Species” (plural).
  • STELLATE. Star-shaped.
  • SUBAPICAL, SUBTERMINAL. Below the apex.
  • SUBSTRATE. Surface on which a nudibranch lives, is often its food.


  • TAXON. Organism classification unit, there are different categories.
  • TAXONOMY. Theory and practice of classifying organisms into hierarchically related groups.
  • TEGUMENT. Body wall or body tissues.
  • TONGUE. Muscle mass located in the mouth of molluscs, in most of them it is covered by a chitinous toothed lamina known as radula.
  • TRIPINNATE. Primary, secondary and tertiary branches of the branchial rachis.
  • TUBERCLE or TUBER. A more or less elevated protuberance formed on the outer surface of the mantle.
  • TYPE SPECIES. The species that served to describe a genus.


  • UNIPINNATE. Branches of the branchial rachis without further secondary ramifications.


  • VELIGER. Planktonic larval stage (often endowed with a shell protecting internal organs) of a marine mollusk.
  • VENTRAL. Relating to the bottom or foot of a nudibranch.
  • VERRUCOSE. Covered with papillae or tubercles.


  • ZOOPLANKTON. Complex of microscopic animal organisms that live in the water column and are the food of many aquatic animals.