Reproductive biology of a deep-sea brittle star Amphiura carchara (Echinodermata: Ophiuroidea) |
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Authors: | G Hendler L U Tran |
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Institution: | (1) Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007, USA Fax: +1-213-7462999 e-mail: hendler@nhm.org, US |
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Abstract: | New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional
among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although
most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in
a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single
bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential
and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for
an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were
positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients
from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal
plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences
in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples
indicated that there are seasonal trends in reproduction.
Received: 14 February 2000 / Accepted: 3 July 2000 |
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