MARINE FLORA AND FAUNA OF THE 



NORTHEASTERN UNITED STATES. 



Crustacea: Decapoda 



AUSTIN B. WILLIAMS' 



ABSTRACT 



The manual includes an introduction to general classiHcation, an illustrated key, an annotated system- 

 atic list, a selected bibliography and a systematic index to the marine decapod crustaceans of the in- 

 shore and continental shelf waters of the northeastern United States. 



INTRODUCTION 



The Order Decapoda contains the largest and 

 probably most familiar crustaceans occurring along 

 seacoasts of the United States. Generally speaking 

 there are two main body types exhibited by this 

 group. The first group is long tailed with a conspicu- 

 ously extended abdomen and the whole body usually 

 compressed (narrow and deep). These are the 

 shrimps (Suborder Natantia) with abdominal swim- 

 merets (pleopods) well developed and adapted for 

 swimming (Fig. 1). The second group (Suborder Rep- 

 tantia) is diverse in shape, lobsterlike or crablike, 

 with the body more or less depressed (dorsoven- 

 traliy flattened). Three subsets within this assem- 

 blage are fairly distinct: 1) lobsters and mud shrimps 

 (Section Macrura) with abdomen extended and al- 

 ways equipped with a tail fan, adapted for feeble 

 swimming, crawling, or burrowing; 2) an anom- 

 alous group (Section Anomura) that either have the 

 body asymmetrical and adapted for housing in hol- 

 low objects (hermit crabs), or symmetrical with the 

 abdomen fairly well developed but more or less 

 fiexed under the thorax (porcellanid crabs and rela- 

 tives); and 3) short tailed true crabs (Section Brach- 

 yura) with greatly reduced abdomen more or less 

 permanently flexed beneath the thorax, adapted 

 primarily for locomotion on a substrate (Fig. 2). 

 These body types have been variously treated in 



' Systematics Laboratory, National Marine Fisheries Service, 

 NOAA, National Museum of Natural Historv. Washington, 

 n.C. 20560. 



forming classifications of the higher categories of 

 decapod crustaceans for nearly 200 yr and the one 

 that is adopted here has become the conservative 

 (and practical) arrangement used for the last few 

 decades. It is a classification that considers the long 

 tailed forms to be most primitive, the anomalous 

 group to be composed of radiating side branches of 

 the main stem, and the short tailed forms to be the 

 most specialized in the order. Such a broad state- 

 ment does not do justice to fine points of supposed 

 relationships based on many lines of evidence but 

 will serve as a working outline. 



The decapod crustaceans treated here are re- 

 stricted to species living within the 200-m limits of 

 the neritic province, on beaches, or nearby marshes 

 along the northeastern United States. Species living 

 primarily outside these limits off the northeastern 

 United States have distributions which extend far 

 beyond the region, hence are seldom part of the local 

 fauna. A few species bridge the neritic and oceanic 

 provinces and these have been selectively included. 

 Within the continental shelf area, only species with 

 recorded occurrence between southern New Jersey 

 and the northern border of Maine are considered. 



The shrimps and crabs of this area belong essen- 

 tially to two temperature regimes, a boreal compo- 

 nent in the north which includes some arctic species 

 and a temperate component in the south which em- 

 braces a few invaders from both the boreal as well as 

 the warmer Carolinian Province south of Cape Hat- 

 teras. Cape Cod forms a landward boundary be- 

 tween these regimes of temperature, though offshore 



