Palaeos		Decapoda
Arthropoda		Astacidea

Decapoda: Astacidea

MALACOSTRACA
|
`--DECAPODA
   |--Dendrobranchiata
   `--+--Caridea
      `--Reptantia
        |--Eryonoidea
        `--Eureptantia
           |--Astacidea
           |--Palinuroidea
           `--+--Anomura
              `--Brachyura

Taxa on This Page

1. Astacidea

Astacidea is a group of decapod crustaceans including lobsters, crayfish and their close relatives. It comprises five extant superfamilies, two of crayfish (Astacoidea and Parastacoidea), one of true lobsters (Nephropoidea), one of reef lobsters (the genus Enoplometopus), and a number of fossil taxa (De Grave et al 2009). As of 2009, the group contains 782 recognised species, over 400 of which are in the family Cambaridae. - Wikipedia

Taxonomy

Enoplometopoidea (reef lobsters) 
	Enoplometopidae
	Uncinidae †
Nephropoidea (true lobsters)
	Chilenophoberidae †
	Nephropidae
	Protastacidae †
	Stenochiridae †
Astacoidea (freshwater crayfish)
	Astacidae
	Cambaridae
	Cricoidoscelosidae †
Parastacoidea (freshwater crayfish)
	Parastacidae

Introduction

Freshwater crayfishes are taxonomically distributed among three families; two Northern Hemisphere families, Astacidae and Cambaridae and one Southern Hemisphere family, Parastacidae. There are two centers of species diversity for freshwater crayfishes. The first is located in the Southeastern United States where some 80% of the cambarid species can be found. The second center of diversity is in Victoria, Australia; housing a large proportion of the parastacid species. Freshwater crayfishes naturally occur on all of the continents except Africa (Figure 1). The Astacidae are distributed West of the Rocky Mountains in the Northwest United States into British Columbia, Canada and in Europe. The Cambaridae are found in the Eastern United States and south through Mexico. The Parastacidae are distributed in Australia, New Zealand, South America, and Madagascar.- KAC & JWF, ToL CC

Development

Hatching in Canadian crayfish occurs in two to twenty weeks. After they hatch, the larvae cling to the stalk still attached to their mother. In a few days they moult and lose the stalked connection with their mother, but they remain attached to her swimming legs with their chelae for up to two weeks. Third instar larvae begin to make excursions away from their mother and eventually leave permanently. Maturity is reached in six to ten moults. After their last juvenile moult, males enter their sexual form with larger chela, increased length, sharper spines and increased sclerotization. This form seeks out females and is ready to do battle with other males. At the end of the mating season, males moult back to a form that resembles the juvenile stage. - EoE - CC

Discussion of Phylogenetic Relationships

Figure 1. World distributions of the three crayfish families. - KAC & JWF, ToL CC

The phylogenetic relationships among the freshwater crayfish families and their relationships to lobster-like ancestors has been of considerable debate for at least 100 years. Two alternative hypotheses have been proposed for the origins of crayfishes. The first supposes a diphyletic origin of astacoids and parastacoids suggesting independent invasion of the freshwater habitat (Huxley, 1880). This idea is supported by the two centers of diversity in the northern and southern hemispheres and by a number of morphological features (Hobbs, 1974). However, Ortmann (1902) argued for a monophyletic origin of the crayfishes. This position has recently been supported by sperm ultrastructure characteristics (Jamieson, 1991) and by embryonic characters (Scholtz, 1993). Because of this ongoing debate, the positioning of Parastacidae is shown as unresolved.- KAC & JWF, ToL CC

Quoting Schram & Dixon 2004: "The monophyly of the freshwater crayfish, though previously doubted, is now universally accepted (Dixon et al 2003). If there was a single origin for the crayfish and they cannot survive in salt water, then they must have diverged before the continents they now inhabit had separated....The last time in which these continents were conjoined was in the Triassic, before Fenno-Scandia (Eurasia) separated from Greenland (North America) with the opening of the Atlantic Ocean (Scotese, 1997).". A Triassic origin also fits in witha post-Paleozoic evolutionary radiation, as evidenced in the fossil record. This means that the rare Paleozoic decapods are more likely to be either stem taxa or represent a simple Devonian bifurcation of a few early lineages such as Dendrobranchiata, Pleocyemata, and Reptantia MAK120527

References

Crandall, Keith A., D. James Harris, James W. Fetzner, Jr. 2000. The Monophyletic Origin of Freshwater Crayfish Estimated from Nuclear and Mitochondrial DNA sequences. Proc. R. Soc. Lond. B (2000) 267, 1679-1686.
Hobbs, H.H., Jr. 1974. Synopsis of the families and genera of crayfishes (Crustacea: Decapoda). Smithsonian Contributions to Zoology 164:1-32.
Hobbs, H.H., Jr. 1988. Crayfish distribution, adaptive radiation and evolution. Pp. 52-82 in D.M. Holdich and R.S. Lowery (eds), Freshwater crayfish: biology, management and exploitation. Timber Press, Portland.
Huxley, T.H. 1880. The crayfish: An introduction to the study of Zoology. D. Appleton, New York.
Jamieson, B.G.M. 1991. Ultrastructure and phylogeny of crustacean spermatozoa. Memoirs of the Queensland Museum 31:109-142.
Ortmann, A.E. 1902. The geographical distribution of freshwater decapods and its bearing upon ancient geography. Proceedings of the American Philosophical Society 41:267-400.
Scholtz, G. 1993. Teloblasts in decapod embryos: an embryonic character reveals the monophyletic origin of freshwater crayfishes (Crustacea, Decapoda). Zool. Anz. 230:s45-54.
Astacidea Scholtz, G. 1998. Von Zellen und Kontinenten-die Evolution der Flußkrebse (Decapoda, Astacidae). Neue Folge Nr. 137, 205-212.
Scholtz, G. & Richter S. 1995. Phylogenetic systematics of the reptantian Decapoda (Crustacea, Malacostraca). Zool. F. Linn. Soc. 113, 289-328.
Scholtz, V. G. 1995 Ursprung und Evolution der Flußkrebse (Crustacea, Astacida). Sitzungsberichte Gesellschaft Naturforschender Freunde Berlin 34, 93-115.

- KAC & JWF, ToL CC

Descriptions

Range: From the Jurassic

Phylogeny: Astacura : Glypheoidea + *

Under construction