GillA gill (ɡɪl) is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment. Branchia (pl. branchiae) is the zoologists' name for gills (from Ancient Greek ).
CephalopodA cephalopod ˈsɛfələpɒd is any member of the molluscan class Cephalopoda sɛfəˈlɒpədə (Greek plural κεφαλόποδες, kephalópodes; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink.
PolychaetePolychaeta (ˌpɒlɪˈkiːtə) is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (ˈpɒlɪˌkiːts). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Alitta.
Calcium carbonateCalcium carbonate is a chemical compound with the chemical formula . It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale.
OsphradiumThe osphradium is a pigmented chemosensory epithelium patch in the mantle cavity present in six of the eight extant classes of molluscs (it is absent in the scaphopoda and monoplacophora; among cephalopoda, only the nautilus has what appears to be a set of osphradia), on or adjacent to the ctenidia (gills). The main function of this organ is disputed but it is believed to be used to test incoming water for silt and possible food particles or, in some species, for sensing the presence of light.
ByssusA byssus ('bIs@s) is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilidae), and Dreissenidae. Byssus filaments are created by certain kinds of marine and freshwater bivalve mollusks, which use the byssus to attach themselves to rocks, substrates, or seabeds. In edible mussels, the inedible byssus is commonly known as the "beard", and is removed before cooking.
Ark clamArk clam is the common name for a family of small to large-sized saltwater clams or marine bivalve molluscs in the family Arcidae. Ark clams vary both in shape and size. They number about 200 species worldwide. The shells of ark clams are often white or cream, but in some species, the shell is striped with, tinted with, or completely colored, a rich brown. In life the shell of most species has a top shell layer that is thick brown periostracum affixed to the harder calcareous part of the shell.
AnaspideaThe clade Anaspidea, commonly known as sea hares (Aplysia species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the superfamilies Aplysioidea and Akeroidea. The common name "sea hare" is a direct translation from lepus marinus, as the animal's existence was known in Roman times. The name derives from their rounded shape and from the two long rhinophores that project upward from their heads and that somewhat resemble the ears of a hare.
CommissureA commissure (ˈkɒməʃər) is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. The most common usage of the term refers to the brain's commissures, of which there are five. Such a commissure is a bundle of commissural fibers as a tract that crosses the midline at its level of origin or entry (as opposed to a decussation of fibers that cross obliquely). The five are the anterior commissure, posterior commissure, corpus callosum, commissure of fornix (hippocampal commissure), and habenular commissure.
Sea slugSea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary time have either completely lost their shells, or have seemingly lost their shells due to having a greatly reduced or internal shell. The name "sea slug" is most often applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells.
