KriYrence: Bin!. Bull., 141: 162-166. (August, 1071) \KYAL DEVELOPMENT OF PAGURUS LONGICARPUS SAY REARED IN THE LABORATORY. IV. ASPECTS OF THE ECOLOGY OF THE MECALOPA 1 MORRIS H. ROBERTS, JR.-' Virginia Institute of Marine Science, Gloucester J'/>iut. I'iri/inia 23062 Many animals are able to delay metamorphosis to the juvenile or adult stage until some stimulus has been received from a suitable substrate (Wilson, 1952, 1958; Crisp and Barnes, 1954; Scheltema, 1961; and many others). In some cases the physiological basis for delayed metamorphosis has been carefully investi-gated (for example, Meadows, 1964a, 1964b, 1964c). During or immediately after the megalopal instar, the hermit crab must find a suitable shell in which to house its abdomen in order to protect itself from predation. For oceanic species, delayed metamorphosis might be an adaptation to permit larvae to reach the bottom while still capable of locomotion in the pelagic environment (Bouvier, 1905). Thompson (1903) suggested that lack of a shell could delay metamorphosis. Thompson (1903) and Bookhout (1964) have both reported that megalopae without shells have a higher per cent mortality than those with shells. If this is true, it implies physiological stress resulting from lack of a shell as does the observation that shell-less adults do not feed (Alice and Dough's, 1945). None of these hypotheses has been rigorously tested in controlled experiments. Thompson (1903) tested the effect of various shells on megalopae, but his con-clusions are questionable (see below). Reese (1962, 1968) and Hazlett and Provenzano ( 1965 ) have studied the behavior associated with selection and entry of shells by megalopae. Reese (1968) has made some observations on the role of shells in emigration of Birgits latro onto land and metamorphosis to the juvenile. The present study was made specifically to test the effect of shell presence on mortality and intermolt duration of the megalopa of Pa-gurus longicarpus. MATERIALS AND METHODS Megalopae used in these experiments were obtained from a number of dif-ferent cultures established for various experiments on zoeal instars. Culture con-ditions up to the megalopa differed between experiments, but were the same within each given experiment. In all experiments, the salinity was maintained as it was during zoeal development (23.7%c in Experiment 1. 30.0/c in Experiment 2, 25.5% in Experiment 3). Temperature was quite variable as culture dishes were kept on a sea table. The mean temperature was 24 C (21-26 C) in Experi-ment 1, 24.5 C (19-27 C) in Experiment 2, and 22 C (18-24 C) in Experi-ment 3. Megalopae were transferred to freshly prepared environments on a vari-able schedule. Mortality, molting, and shell entry were noted daily. The shells 1 Contribution Number 387 from the Virginia Institute of Marine Science, Gloucester Point, Virginia 23062. -Present address : Department of Biology, Providence College, Providence, Rhode Island 02918. This paper is part of a dissertation submitted to the School of Marine Science of the College of William and Mary in partial fulfillment of the requirements for the Doctor of Philosophy Degree. 162
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