ARTHROPODA (IV): Crustacea (Crustacea study images;
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b) terminal moveable spine(s) on telson, and
c) a nauplius larval stage (median eye has 3 - 7 units, but not ommatidia like true compound eye)
b) head covered by a shield: a carapace (a structure) may extend over some or all thoracic segments, yielding a cephalothorax(body region)
c) some thoracic segments may fuse with the head and their limbs modified as maxillipeds for feeding; walking legs= periopods
d) abdominal segments may or may not have limbs (pleopods)
e) primitively had an elongate body and many similar biramous legs
b) habitats: most classes are marine, but one class (Branchiopoda) is primarily freshwater and three others have freshwater members
c) lifestyles: most are free living; but 3 classes have a number of parasitic species, and one subclass (Cirripidea) is entirely sessile as adults
d) classes are distinguished by: number of tagmata, number of segments per tagmatum, number of thoracic segments covered by a carapace, number of segments fused with the carapace, and presence/absence of movable spines (rami) on the telson (bears anus)
e) Remipedia & Cephalocarida: marine, both exhibit primitive traits
f) Branchiopoda: mainly freshwater particle feeders; includes water fleas, tadpole shrimp, clam shrimp & brine shrimp (=sea monkeys)
g) Maxillopoda: a heterogeneous, mainly marine group that includes barnacles, copepods (some in freshwater) & 3 odd parasitic groups
h) Malacostraca is the most diverse class
ii) 3 general body forms: shrimp-like, lobster-like, crab-like (multiple origins).
iii) includes representatives from many familiar groups:
Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)