The postembryonic development of fish copepod (Caligoida, Lernaeoceriformes) in pelagic snails (Janthina spp.)
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In all, 7587 copepods were recovered from 115 pelagic snails of two species, Janthina janthina (Linnaeus) and J. globosa Swainson, which had been collected from the West Indies,and Madagascar. They were found either free inside the mantle cavities or fixed on to the gill lamellae of the snails, and represent a complete series of the postembryonic developmental stages of a lernaeoceriform copepod. Five stages were recognized. They are: 1. Free-swimming copepodid: 0.42-0.48 mm. The body has an oblong cephalothorax and four free segments. There are two pairs of well-developed biramous legs. The third pair is represented merely by a pair of spines on the second free segment. The third free segment represents the fourth thoracic segment and carries no legs. The last free segment carries a pair of caudal rami which bear 4 plumose setae and one short setule. The first antenna is indistinctly 4-segmented, with the formula 1, 1, 1, and 11 plus one aesthete; the two long setae on the terminal segment are bifurcate. The second antenna is 3-segmented, chelate and powerful. The mouth tube is of the usual form found in lernaeoceriform copepods, There is, however, a pair of spatulate labial palps which have not been described before in any known lernaeoceriform copepodids. The mandible is lanceolate, without teeth. The first maxilla is bipartite: a small exopod armed with a single seta and a large endopod tipped with two stout setae. The second maxilla is 3-segmented, with a falciform terminal segment bearing striations. Each ramus of the first two pairs of legs is 1-segmented; the first exopod: III,I,3; the first endopod: 7; the second exopod: II,I,3; and the second endopod: 6 [TRUNCATED].
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