SEXUAL DIMORPHISM AND REPRODUCTIVE BEHAVIOR IN ALMYRACUMA PROXIMOCULI (CRUSTACEA: CUMACEA): THE EFFECT OF HABITAT

¹ Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543

Individuals of Almyracuma proximoculi are the least sexually dimorphic cumaceans known, because the males are progenetic, i.e., they are precociously sexually mature at a morphologically immature state. This species lives in dense aggregations in the upper intertidal zone and has eliminated the morphologically complex, apparently pheromone-sensitive, and highly motile terminal male stage found in other cumacean species. The sexually dimorphic characters that are present are predominantly ones that facilitate the rapid removal of the female's exuviae by the male during her fertilization molt. The removal rate is critical, because the partially detached exuviae blocks access to the female's ventrum. With the exception of the rudimentary penes found in two genera, male cumaceans do not possess an intromittent organ and apparently must deposit one or more spermatophores on the female's ventrum before the developing oostegites completely enclose this area.