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Crustaceans have a pair of mandibles that typically consist of an enlarged basal segment (coxa) and a palp (sensory feeler) consisting of all other segments. In some groups, such as the Branchiopoda, the palp is reduced or absent. Crustacean mandibles may be equipped with special teeth (molar and incisor processes).
Crustaceans comprise a number of classes, with various feeding modes supported by a range of adaptations to the mouthparts. In general, however, crustaceans possess paired mandibles with opposing biting and grinding surfaces. The mandibles are followed by paired first and second maxillae.
In all jawed fish (gnathostomes), the first arch pair (mandibular arches) develops into the jaw, the second gill arches (the hyoid arches) develop into the hyomandibular complex (which supports the back of the jaw and the front of the gill series), and the remaining posterior arches (simply called branchial arches) support the gills.
These structures show an incredible diversity throughout crustaceans but generally are very much flattened and leaf-like. The two pairs are normally positioned very close together and their apical parts generally are in direct contact with the mandible. [5] [page needed]
In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes. [1] It is generally a rigid structure, but can be connected by a hinged joint, as seen in Leptostraca. [2] Among insects, the rostrum is the name for the piercing mouthparts of the order Hemiptera as well as those of the snow scorpionflies, among many others.
Many crustaceans and a few chelicerates and tracheates use respiratory pigments to assist oxygen transport. The most common respiratory pigment in arthropods is copper-based hemocyanin; this is used by many crustaceans and a few centipedes. A few crustaceans and insects use iron-based hemoglobin, the respiratory pigment used by vertebrates.
The mandibular (lower) teeth and their associated periodontal ligament are innervated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off branches to all the lower teeth ( inferior dental plexus ).
Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are a part of the subphylum Crustacea (/ k r ə ˈ s t eɪ ʃ ə /), a large, diverse group of mainly aquatic arthropods including decapods (shrimps, prawns, crabs, lobsters and crayfish), seed shrimp, branchiopods, fish lice, krill, remipedes, isopods ...