Soon or later if you develop an interest in crayfish you have to learn at least the basic features of crayfish for keying specimens. Some are easy to key whilst others such as Engaeus need experts especially when more than one species share a homerange.One of the best and probably latest key is available from the Co-operative Research Centre for Freshwater Ecology, Murray Darling Freshwater Research Centre, PO Box 921 Albury NSW 2640.
The key is titled,
A PRELIMINARY KEY TO THE SPECIES OF DECAPODA ( CRUSTACEA: MALACOSTRACA ) FOUND IN AUSTRALIAN INLAND WATERS
by Pierre Horwitz.
1. Rostral carinae
3. Carpus, leads to the main claw ( chela ), the section between the carpus and the main body is the merus. There are five sets of legs on all decapod, simlply ten legs.
5. On these legs the female gonopore
6. On these legs if male, the male gonopores
8. Somites, there are five sections
9. Eggs, this particular female is in 'berry'.
10. Telsons, once again five sections.