The comparative ecology of nemertean egg predators

Abstract

The nemertean family, Carcinonemertidae, is adapted to fill the specialized niche of ectocommensal and egg-predator on decapod crustacean hosts. The group has been known for over a century but its ecological role has only recently been elucidated. Information generated on the life history of nemertean egg predators has revealed that these worms are highly specialized as obligate symbionts on decapod crustaceans. Larvae are predominantly planktonic in the group with the exception of the new genus Pseudocarcinonemertes which has direct development into a crawling juvenile. Juvenile Carcinonemertes errans survive through direct uptake of dissolved amino acids leaked by the host at the sites of nemertean infestation. Worms are indiscriminate feeders able to feed on the eggs of several crab species other than their own host species. External fertilization is the normal case with the exception of C. epialti which has been seen to have internal fertilization. Female C. errans appear to be able to produce fertilized eggs without mating. The biological basis for this behavior is unknown. Up until 1978 the family consisted of four species in one genus. Recent descriptions of a new species and a new genus demonstrate the diversity of nemerteans living on crustaceans. Several distinctive new forms have now been found on the Pacific coast which probably represent several new species and at least one other new genus. Recent comparisons with Carcinonemertes suggest that the genus Pseudocardnonemertes might belong in the family Tetrastemmidae and represents an example of convergent evolution. © 1985 by the American Society of Zoologists.