2008 SOUTHEASTERN NATURAUST 7(2):207-218 Morphological and Developmental Differences in Three Species ofthe Snapping Shrimp Genus Alphetis (Crustacea, Decapoda) Heather R. Spence' and Robert E. Knowlton^' Abstract - Living, freshly collected individuals of three species of snapping shrimps were studied to determine any differing morpbological. developmental, and eco- logical features: Alphetis heterochaelis. collected from Beaufort, NC; A. angulosus, found mainly in Jacksonville, FL, but also at one site in Beaufort; and A. estuariensis, collected at another Jacksonville site. Structural characteristics of these superficially similar species are summarized, with particular attention to coloration. Adult A. ungulosiis individuals bave blue-green 2'"' antennal flagella (vs. tan in the other two species) that are significantly shorter than those of .^. heterochaelis. Alpheus angu- tosus and A, estuariensis bear smaller eggs (<1 mm, regardless of embryonic stage) than A. heterochaelis (>1 mm), and the former species displays the zoea larval form typical of alpheids (vs. abbreviated larval development in A. heterochaelis). Introduction Perhaps the most persistent and widespread noise in shallow-water tropi- cal and subtropical seas is that produced by "snapping shrimps." decapod crustaceans belonging to the family Alpheidae. In most alpheids. the chelate first pereiopods ("claws") are asymmetrical, one member of the pair (the major chela) being much larger and more heavily calcified than the other (Fig. 1). The noise is produced by vast numbers of individuals, each one rapidly closing the dactylus, or movable finger, of its major claw onto the pollex. or immovable finger, ofthe propodus. in the manner of a pistol ham- mer (hence the alternative name "pistol shrimp") (Knowlton and Moulton 1963, Versluis etal. 2000). Many alpheid species are morphologically very similar and consequently "difficult to recognize using traditional systematic methods" (Knowlton 1986). Preserved specimens have been relied upon in the process of defining species, but some distinguishing characteristics, such as color, cannot be considered as they are lost in the process of preservation (Knowlton 1986). Alternative methods are required to discern some species. A number of morphologically similar species from the so-called Al- pheus edwardsii group are found along coastlines of the southeastern United States. Alpheus heterochaelis Say (big-claw snapping shrimp) was first described in 1818. but since then new species have been delineated among specimens originally thought to be A. heterochaelis. One of these 'Department of Biology, University of Massachusetts. North Dartmouth, MA 02747-2300. ^Department of Biological Sciences, George Washington University. Washington, DC 20052. "Corresponding author - knowlton{%gwu.edu.