Latreille, 1803
Adult members of the decapod Infraorder Astacidea — freshwater crayfishes and marine lobsters— are crustaceans that have a usually subcylindrical or subovoid carapace. The abdomen is somewhat dorso-ventrally flattened and ends in a strong tailfan. The pereiopods are uniramous, the first three pairs are chelate and the first pereiopod is always greatly enlarged. The fifth pereiopod is often chelate. The pleopods are uni- or biramous; the uropods are biramous. The telson forms together with the broad uropods a tailfan.
The larval development is metamorphic or epimorphic.
Ecology
Astacidea are marine, brackish or freshwater animals, usually benthic. Adults are not included in the present keys, but their larvae are. Nephropidean Astacidea (see below) normally have three zoeal stages, occasionally four; the megalopa shows general resemblance with the adult (Williamson, 1983).
Distribution in the North Sea
Two astacidean species (belonging to the Family Nephropidae) occur in the area:
¥ Homarus gammarus, the marine lobster
¥ Nephrops norvegicus, the Norwegian lobster.
[Description after McLaughlin, 1980; Brusca and Brusca, 1990]