Unformatted text preview: Arthropoda (Crustacea)-aquatic mandibulates, Ch. 19 Subphylum Crustacea—Crustaceans, (crusta = shell); crabs, lobsters, shrimp, copepods, ostracods, others ·30,000+ species described, many more out there; huge numbers of individuals · Most numerous genus may be a copepod (Calanus) · Typically aquatic, though some are terrestrial, many are planktonic · Monoecious or dioecious (usually), sometimes parthenogenic ·First larval stage typically a nauplius (three appendages, medial eye) ·Three tagmata: head, thorax, abdomen (head and thorax may be fused into a cephalothorax) · Heavily calcified exoskeleton for protection in larger crustaceans · Exoskeleton over the cephalothorax is called the carapace · Two pairs of antennae (first-antennule (uniramous), secondantenna); only arthropods like this · Ancestrally biramous appendages, one pair per somite (some have no abdominal appendages) · Basal protopod with lateral exopod and medial endopod branches (fig. 19.4, p. 380) · Large crustaceans have gills for gas exchange, smaller ones respire through thin cuticle · Predatory, filter feeders or detritivores (scavengers) Classification—5 classes (at least currently recognized) Class Remipedia—remipedes, (fig. 19-14, p. 387) Many ancestral features—uniformly-shaped biramous limbs, reduced tagmatization Small cave dwelling crustaceans Class Cephalocarida—cephalocarids, (fig. 19-14, p. 387) Also very primitive —limbs very similar and biramous Tiny coastal crustaceans, monoecious with one genital opening for eggs and sperm Class Branchiopoda— branchiopods, including Daphnia and shrimp (e.g. Artemia) Flattened leaf-like limbs used for respiration, swimming, feeding Mostly freshwater forms (19-15) Some (Order Cladocera) have reproductive cycle like rotifers (parthenogenic/sexual) Class Maxillopoda— maxillopods, diverse group formerly recognized as several classes Includes Ostracods (should be in own class?), Copepods, and Cirripeds (barnacles) Pelagic and benthic species (19-16, 19 -19) Very abundant (esp. Copepods) Some barnacles are economic/biological pests and some are endoparsites Barnacles have no chitinous exoskeleton; replaced with calcareous plates Filter feed with setae on extended limbs Class Malacostraca—largest, most diverse crustacean class (fig. 19-26, p. 394) 14 or more orders including Isopoda, Amphipoda, Decapoda Crabs, lobsters, crayfish, shrimp, pillbugs, others Pillbugs are only truly terrestrial crustaceans not all isopods are terrestrial Ancestrally 19 segments with limbs on each (table 19.1, fig. 19-4) 8-head(feeding/sensory), 5-thorax(walking), 6abdomen(swim/respire/reprod.) First pair of thoracic limbs often chelate Respire with gills at base of limbs protected by branchiostegite “shield” of carapace ...
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- Spring '08