Crustaceans

• Crustacea are named for their hard exoskeleton.
• There are over 67,000 described living species of crustaceans
• Crustacea and Hexapoda share derived features and are united under Pancrustacea with crustacean subgroup Vericrustacea having members from Class Malacostraca
• Probably the most abundant animals in the world are members of the copepod genus Calanus such that they are called—insects of the sea
• Crustaceans show enormous variation in morphological characteristics such that insects and crustacea make up over 80% of all named animal species
• Crustaceans have two pairs of antennae
• Head of a Crustacean has a pair of mandibles and two pairs of maxillae
• All appendages of crustaceans, except perhaps first antennae, are biramous which means having two main branches
• There is one pair of appendages on each of the body segments of crustaceans but some segments may lack appendages
• Crustaceans are mostly marine with freshwater and terrestrial species
• Malacostracan body plan consists of a head with 5 fused segments, thorax has 8 and abdomen has 6 segments
• Anterior end of a crustacean is a nonsegmented rostrum
• Posteriorly, the telson, with the last abdominal segment and uropods, forms a tail fan in many forms of crustaceans
• Many crustaceans have dorsal cuticle of the head called the carapace.
• The carapace that may cover most of body including thoracic and abdominal segments or just the cephalothorax in some species
• Secreted cuticle is made of chitin, protein, and calcareous material.
• Heavy plates have more calcareous deposits - joints are soft and thin, allowing flexibility.
• Dorsal tergum and ventral sternum are plates on each somite lacking a carapace.
• Crustaceans are the only arthropods that have two pairs of antennae.
• Crustaceans have a pair of mandibles (jaw-like appendages) and two pairs of maxillae on the head.
• The ancestral condition in arthropods is to have many body segments.
• Muscular and nervous systems and segmentation exhibit metamerism of annelid-like ancestors.
• Hemocoel is persistent blastocoel that becomes filled with blood.
• Coelomic compartments remain as end sacs of excretory organs and gonads in crustaceans
• Striated muscles make up a major portion of crustacean body.
• Most muscles of crustaceans arranged as antagonistic groups.
• Flexors draw a limb toward the body and extensors straighten a limb out.
• Abdominal flexors of a crayfish allow it to swim backward.
• Strong muscles located on each side of stomach control the mandibles.
• Smaller crustaceans may exchange gases across thinner areas of cuticle.
• Larger crustaceans use featherlike gills for gas exchange.
• Crustaceans have an open circulatory system
• The dorsal heart of crustaceans is a single-chambered sac of striated muscle.
• Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange.
• Hemocyanin (blue) and/or hemoglobin (red) are respiratory pigments.
• Hemolymph may be colorless, reddish, or bluish.
• Hemolymphs contain ameboid cells that may help prevent clotting
• Antennal or maxillary glands are called green glands in decapods.
• End sac of antennal gland has a small vesicle and a spongy labyrinth.
• Labyrinth connects by an excretory tubule to dorsal bladder that opens to exterior pore.