The Crayfish, found in wetlands throughout the eastern half of the United States, is dissected here as a typical member of the arthropoda.
PHYLUM: Arthropoda [joint foot]
CLASS: Malacostraca, an extraordinarily varied group1, [soft shelled]
ORDER: Decapoda [ten feet]
GENUS: Cambarus sp.
EXTERNAL PARTS, illustrate ventral view: Before opening, identify the following,
Carapace back shell covering cephalothorax
Cephalothorax legs and chelipeds are attached to this body region
Abdomen segmented region behind cephalothorax (erroneously: "tail")
Chelipeds anterior-most pair, with big claws
four walking legs four pairs, posterior-most (last pair without pincers)
two pair antennae one set is split into two branches each
gonopore in female only (also termed seminal receptacle)
pleopods also called swimmerets. set #1 in male= gonopods
copulatory appendage in male only: swimmeret set #1 and #2
oviduct openings in female only, at base of second set of walking legs
MOUTH PARTS: Six pairs, pluck off one by one as listed, thoracic to cephalic:
maxillipeds, 3 pairs thoracic, posterior-most sets, with multiple branches
maxilla, two pair cephalic
mandible, one pair cephalic, hard with toothed mating surfaces
INTERNAL PARTS, illustrate a top view of the cephalothorax contents: (Carefully cut away carapace by making shallow cuts with scissors around its edge. As the shell is lifted, hold down underlying organs, especially the heart, so they are not torn off.)
heart towards rear between dig. glands, sack-like, with ostia (holes) & vessels
pericardial sinus space where heart is housed ("around the heart")
gills located laterally, fuzzy structures (Why are they so fuzzy?)
stomach, 2 parts tough membranous chamber just behind the mouthparts in anterior central thorax: the esophagus empties into the cardiac portion, pyloric portion empties into the intestine. The gastric mill is between these.
digestive gland lateral and posterior to stomach, yellow and soft
intestine emerges fr stomach, enters abdomen, exits anus (under telson)
ventral nerve cord twin fibers proceed to rear from ganglia into chitinous cavity
ganglia in head in front of stomach, ventral nerve cords emerge
green glands rounded, tucked into anterior carapace, sometimes called labyrinth (functions as a kidney), empty thru holes at base of antennae
ovaries between rear part of digestive glands, granular and more orange
1 See Elson's Zoology Coloring Book, plates 38-44.
2 See also Rust, A Guide to Biology Lab, p. 69-71 (1983)