Crustaceans {crustacean}| (Crustacea) are aquatic and live mostly in ocean. They have one mandible pair, have two maxillae pairs, respire by gills, and molt. They have compound eyes. They have two antenna pairs. Shrimp, crayfish, lobster, and crab have ten legs and can have carapace. Barnacles, water fleas, and krill have six or eight legs. Copilia has two eye lenses, for close vision. Vargula firefleas make intense light.
Crustaceans have eyes {compound eye}| with similar parts.
Crustaceans respire by membranes {gill, crustacean}| in contact with flowing water in association with blood vessels.
Crustaceans have upper and lower jaws {mandible, crustacean}|.
Crustaceans have two cheek-part pairs {maxillae}|.
Small tidal filter feeders {barnacle} have free-swimming larvae. Cirripedia adults have hard shells and attach to rocks.
Trilobites {trilobite} (Trilobita) are extinct, lived at ocean bottom, had three larval periods, had three longitudinal lobes, and were 60% of all animals during Ordovician. They began in Pre-Cambrian and lasted until Permian, 300,000,000 years. They most closely relate to horseshoe crab. Trilobites swam, crawled, and burrowed.
parts
They had head {cephalon}, thorax, and tail {pygidium}, each with side lobes {pleura, trilobite} and central lobe {axis, trilobite}. Cephalon has top central plate {glabella} with side shells {fixed cheek}, making structure {cranidium}. Segments had two arthropod jointed legs, which branched to have gill surface and walking leg. Two antennae were on head.
The most important crustaceans have ten legs {decapoda} {decapod} and can have carapace. They include shrimp, crayfish, lobster, and crab.
Decapoda can have chitin {carapace}| with calcium salts.
Warm fresh-water decapods {crayfish} {crawfish} (Astacus) have claws.
Small long-tail decapods {shrimp, crustacean} (Natantia) have fused head and thorax and segmented abdomen.
Decapods {prawn, crustacean} can be large shrimp.
Baleen whales eat euphausiacea crustaceans {krill}.
Large decapods {lobster, crustacean} have claws. Homaridae have eye stalks {eyestalk}. Homaridae have astaxanthin pigment, which binds to beta-crusta-cyanin protein and is insoluble.
Decapods {spiny lobster} (Palinuridaecan) can have no claws and spiny carapace.
Simple crabs (Merostomata) {crab} have ten legs, have pinching claws, and are chelicerates. Crabs include king crab. Horseshoe-crab eyes can see contrasts and use reflection. Blue-crab males have blue claws. Callinectes sapidus are soft-shell swimming crabs.
Burrowing crabs {fiddler crab} can have males with one large claw and one small claw.
Large crustaceans {horseshoe crab} have hard tails.
Alaska king crab or Japanese king crab {king crab} has claw width up to 3 meters, weighs up to 5 kilograms, and is white inside.
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Date Modified: 2022.0225