NO. 3586 CYCLOPOID COPEPODS — HUMES AND HO 19 



Color in life in transmitted light similar to that of small male. 



Etymology. — 'The specific name corallophilus , from the Greek 

 words KopQ:XXov= coral and 0tXos=loving, alludes to the association 

 of this species with a coral. 



Specific identity of females, small males, and large males. — 

 The differences in external anatomy between males and females of 

 Rhynchomolgus corallophilus are so striking that the question arises 

 whether or not they represent opposite sexes of the same species. 

 One can not fail to be impressed by the great difference between the 

 males and females in body form, the nature of the first and second 

 antennae, the labrum, the mouthparts (with mandibles, paragnaths, 

 and first maxillae absent in males), and the form of legs 1-5 (with 

 legs 4 and 5 absent in males) . The differences in the second maxillae 

 and maxillipeds in the two kinds of males (with the maxillipeds 

 absent in large males) also contribute to the impression that they 

 represent separate forms. 



Since no specimens in our collections were in amplexus, judgment in 

 respect to their specific identity must be made on other grounds 

 than sexual behavior. 



We believe that the three groups of specimens represent one species, 

 R. corallophilus, for several reasons based on their external anatomy. 

 Both kinds of males and the females have a similar snoutlike rostrum 

 and all possess a prominent lobe external to the base of the second 

 antenna. The small males and large males, differing in their second 

 maxillae (reduced to a spinous process in large males) and maxillipeds 

 (absent in large males), are otherwise similar in their appendages. 

 It is our opinion that the small males are immature, and represent 

 the last pre-adult instar. This interpretation is based on the facts 

 that in small males there seem to be, at most, three postgenital seg- 

 ments and the body does not contain formed spermatophores, while 

 in large males there are four postgenital segments and there are often 

 partly formed spermatophores within. A molt from the small imma- 

 ture male to the large mature male would have to be presumed in 

 order to account for the reduction in the second maxilla and the loss 

 of the maxilliped. 



Further justification for considering all three groups as one species 

 may be found in the circumstantial evidence of the numbers of speci- 

 mens collected. It would seem unlikely, if the males and females 

 represent separate species, that large numbers of females of one 

 species and large numbers of males of the other species would occur 

 together in the same host without there being at least a few of the 

 opposite sex in each case. For this to happen it would be necessary 

 to suppose a very unequal and improbable sex ratio. We therefore 



