宮島近海産エビ類の幼生 : III.ヤマトモエビ  [in Japanese] Larvae of Decapoda Macrura in the vicinity of Miyazima Aquarium, Miyazima, the Seto Inland Sea : III. Eualus leptognathus (STIMPSON) (Caridea, Hippolytidae)  [in Japanese]

The present report is a description of the larval development of a hippolytid shrimp, Eualus leptognathus (STTMPSON) under laboratory conditions. It is one of the common species of Zostera beds in the vicinity of Miyazima Aquarium and the ovigerous females are observed from November to the next May there. This is the second Japanese species of this genus, in which the larval development is completely known. Like the other species, E. sinensis (Yu), the present species has nine zoeae and one megalopa stage and an exopod on the first three pereopods in ninth zoea stage. The species of this genus are divided into two groups by the number of pereopodal exopods in the last zoea stage. Except for two unidentified species from Kamchatka, only three, E. gaimardii and these two Japanese species, have an exopod on the first three pereopods in the last zoea stage. They, however, show rather apparent morphological differences, as well as discrepancies of the number of zoeal stages. E. gaimardii has only five zoeal stages and well developed rostrum in all larval stages. Moreover the larvae of these two Japanese species are readily distinguished from each other by the presence or absence of the rostrum, the pterygostomial spine, small spines on the ventral margin of carapace and outer spine on the antennal scale, by the shape of supraorbital and antennal spine, by the number of the lateral spines on the telson, etc. (Table 2). These considerable range of larval characters in the genus Eualus may reflect wide variations of the adult morphology.