118 U.S. NATIONAL MUSEUM BULLETIN 258 



abundant; holdfasts of Egregia and Laminaria, abundant; sponges, 

 abundant, pt. dume: Amaroucium sp., most abundant species; social 

 sandy tunicates, rare, corona del mar: Phragmatopoma masses, 

 abundant. 



Distribution. — Cayucos, California, to north Laguna Beach, 

 intertidal, especially in sponges, tunicates and beds of Phragmatopoma 

 sp. 



Elasmopus rapax Costa 



Elasmopus rapax Costa: J. L. Barnard, 1955a, pp. 10-12, fig. 5 (with literature); 

 1962b, pp. 94-96, figs. 16, 17. 



In the diagnostic key given below are described 6 forms of Elasmopus 

 rapax in the California-Mexico region plus two other species of similar 

 morphology, E. antennatus (Stout) and E. holgurus Barnard. The 

 three forms of couplet 1 are probably "true" E. rapax; they have the 

 normal inner ramus of uropod 3. The remainder, E. holgurus, E. 

 antennatus and E. rapax mutatus, are distinguished by the shortened 

 and narrowed inner ramus of uropod 3. Probably E. antennatus is a 

 good species because of its lack of palmar processes on male gnathopod 

 2 but E. holgurus has the aspect of E. rapax. If E. holgurus is to stand 

 as a good species, E. rapax mutatus may have to be elevated to full 

 specific status and the other form of E. rapax with a short inner ramus 

 may have to be described as a distinct species {rapax form II of Bahia 

 de Los Angeles). Even so, three distinct morphs of true rapax exist 

 in the region considered and others from extrinsic regions are known 

 from the literature (see later statement). The writer set a precedent 

 by describing E. holgurus at specific level, although it is no more 

 distinct from rapax than is E. rapax mutatus. Rather than confuse 

 the picture more, the writer maintains the status quo by continuing 

 to use E. rapax mutatus as a trinomial and erects a trinomial for another 

 subspecies which is so abundant and conspicuous that it requires 

 nomenclatural distinction. Without life history studies it is impossible 

 to determine whether these forms are distinct species, although their 

 predominance in one sample or another indicates they have ecological 

 exclusion. 



Key to Californian and Mexican Forms of Elasmopus rapax and Related 



Species of Elasmopus 



1. Inner ramus of uropod 3 equally as broad and long as outer ramus. In all 

 three forms pereopod 5 has article 2 closely serrate and bearing long setae; 

 palm of male gnathopod 2 with 3 processes, one near hinge, one in middle, 

 and one submarginally at defining corner of palm; palmar setae sparse 

 and evenly scattered; telsonic apices progressively developing into smooth 

 protrusions with spines attached only laterally and decreasing relatively 

 in size and number with age. 



