Abstract:Outbreaks of the crown-of-thorns sea star (Acanthaster planci) are likely to be strongly associated with drastic changes in larval survival influenced by food availability. However, no quantitative or qualitative data are available on the distribution of A. planci larvae in the field nor on the environmental factors that influence their survivorship. Here we use a DNA barcoding approach to describe the distribution of A. planci larvae in Sekisei Lagoon, Ryukyu Archipelago, Japan after conducting three days of high-intensity sampling. High densities (53.3 individuals/m 3 ) of A. planci larvae were found outside of Yonara Channel, which is the largest reef channel in this lagoon. Surprisingly, most (94%) of the aggregated larvae were advanced-stage brachiolaria. Considering that it takes several days to develop to this stage, this result demonstrates that A. planci larvae were floating for some time and maintaining a high-density population. However, this dense larval cloud disappeared immediately after a typhoon. No spatial correlation was found between larval density and either nutrient or chlorophyll a concentrations, suggesting that A. planci larvae do not necessarily aggregate in nutrient-rich water. These data suggest that some high-density populations of late developmental stage A. planci larvae were produced under a low phytoplankton concentration and could potentially trigger an adult outbreak. Consequently, our data suggest that adult outbreaks may not necessarily be triggered by food availability alone.

A new species, Heteromysis komaii, is described from specimens obtained from the gastral cavity of sponges, Callyspongia confoederata, from the Uraga Channel, located at the entrance of Tokyo Bay, central Japan. Heteromysis komaii is distinguished from all known species of the genus by several features: the distal segment of the antennular peduncle has a flagellate spine at the inner distal angle, the antennal scale is longer than the antennal peduncle, the endopod of the third thoracopod has two flagellate spines at the inner distal angle of the carpus, the fourth to eighth thoracopodal endopods have the carpopropodus divided into two or three subsegments, the male pleopod is unmodified, the uropodal endopod is without spines, the telson has spines on the distal half of the lateral margin, and the apical cleft of the telson is with spinules throughout. The distribution and habitats of the species of Heteromysis are reviewed. RÉSUMÉUne nouvelle espèce, Heteromysis komaii, est décrite d'après des spécimens provenant de la cavité gastrique d'éponges Callyspongia confoederata de Uraga Channel, situé à l'entrée de la Baie de Tokyo, Japon central. Heteromysis komaii se distingue de toutes les espèces connues du genre par plusieurs caractères: le segment distal du pédoncule antennulaire a un flagelle à l'angle distal interne, l'écaille antennaire est plus longue que le pédoncule antennaire, l'endopodite du troisième thoracopode a deux flagelles à l'angle distal interne du carpe, les endopodites des quatrième à huitième thoracopodes ont le carpopropode divisé en deux ou trois sous-segments, le pléopode mâle n'est pas modifié, l'endopodite de l'uropode est dépourvu d'épines, le telson a des épines sur la moitié distale du bord latéral, et l'échancrure apicale du telson est entièrement ornée de spinules. La répartition et les habitats des espèces d'Heteromysis sont examinés.

Fifteen mysid species, including three new species, are reported from Iriomote Island, Ryukyu Islands, Japan. A new species, Iiella iriomotensis, is distinguished from related species by the shapes of the rostrum and the telson cleft, the number of spines arming the frontal margin of the labrum, and the endopod of the uropod being shorter than the exopod. Nipponomysis minuta, new species, closely resembles Nipponomysis imparis in respect to the fourth male pleopod, but is distinguished by the shorter telson and the smaller number of spines on the lateral margin of the telson and on the inner margin of the endopod of the uropod. Anisomysis hashizumei, new species, is distinguished from related species by a combination of characters found in the fourth male pleopod and the telson. Haplostylus pusillus, which has been known only from the Indian Ocean, is reported from the Pacific Ocean for the first time. Four species, Siriella inornata, S. anomala, Anchialina zimmeri, and Pseudanchialina pusilla are new records from Japanese waters.

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Twenty species of Acanthomysis s. l., distributed in Japanese, Korean and Chinese coastal waters, are revised. These species are distinguished from Acanthomysis s. str. by the following characters: the carpopropodus of the endopod of the third to eighth thoracic limbs divided into three to eight subsegments; the exopod of the fourth male pleopod with two long subequal terminal setae; the telson long linguiform or triangular without basal dilated portion and armed with spines throughout margins. On the basis of these characters, the genus Orientomysis, which was revived by Holmquist (1981b) and comprised O. japonica and O. mitsukurii, is redefined and recognized to contain the following 18 valid species: O.