Animal Biology Spring 2010

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C) Development and Life Styles

Crustacean Life Cycle:

1)     Nauplius Stage – perceived as being a defining link among all crustaceans. First larval stage and consists only of the head and telson (no abdomen nor the thorax has developed). The nauplius has only a single eye located atop the head and three pairs of cephalic appendages that allow them to swim.

2)    Zoea Larval Stage -  when the zoea name was given to the crustacean, naturalists believed that it was an entirely separate species. During this stage, the larvae will swim with thoracic appendages rather than cephalic appendages.

3)    Mysis or Megalopa Stages – stage of growth. The megalopa stage is the final stage of growth for most decapod crustaceans including lobster and crabs. The mysis or megalopa stages of development are the final stages of development before reaching the post-larval stage.

4)    Post-Larval Stage - the maturing crustacean will begin to look more like its adult form. The crustacean will depend more on foraging and grazing to feed. This is the period of growth where the crustacean will begin to develop its legs for swimming and walking. By the end of its post-larval growth stage, it will be at its full size and its adult appearance.

5)    Adult Growth Stage - reached by one year of age for most crustaceans. After a year has passed, most crustacean varieties will be capable of mating and reproducing. By the adult stage of life, has finished growing and is grazing and feeding on its own rather than relying on nutrients from its egg.
Fossil Record
(canapasis)

·         The fossil record of the Crustacea is exceptionally good, stretching back to the Cambrian.

  •                 don't appear in any abundance until the Carboniferous.

·         The first undisputed crustaceans are Canadaspis and Perspicaris which belong to the Subclass Phyllocarida and were found in the Middle Cambrian Burgess Shale.

·         By the Carboniferous, all the other major groups of crustaceans are present except for the Eucarida. Most of these fossils are found within shallow marine sediments because these offered good potential for preservation.

o   The Eucarida appeared in the Mesozoic, but they had their origins in the Devonian/Carboniferous. The Eucarida, especially the Decapoda, underwent an adaptive radiation during the Jurassic, with the appearence of crabs and modern shrimps.