Re-definition of the genus Javanisomysis Băcescu, 1992 as a subgenus in the genus Anisomysis Hansen, 1910 (Mysida, Mysidae) and a new species of the subgenus from coastal waters in Phuket, Thailand

Abstract

Anisomysis (Javanisomysis) gutzui Băcescu, 1992 was reported as a characteristic species, of which the fourth male pleopod possesses an un-segmented exopod and no endopod. The species is placed in the valid genus Javanisomysis on the basis of the characteristics of the fourth male pleopod; however, the definition of the genus was insufficient. In the present paper, re-examination of the genus Javanisomysis is carried out on the basis of paratypes loaned from the depository in Romania. We found that major morphological characteristics of the types are common to those of the species of the genus Anisomysis, particularly in the forms of the antennal scale, labrum, thoracopodal endopods, and fourth male pleopod. On the basis of the present results, the genus Javanisomysis is reinstated as a subgenus in the genus Anisomysis. The subgenus Javanisomysis is allied to the subgenus Anisomysis in the forms of the body, eye, antennular peduncle, and mandibular palp, but is separable in the following characteristics: carapace armed with spinules on the antero-lateral margin; in the fourth male pleopodal exopod the first segment as long as or slightly shorter than the third segment, excluding the terminal setae; and the telson with un-articulated denticles on the lateral margin. In addition, A. (J.) similis n. sp. is described on the basis of specimens collected from Phuket, Thailand. The new species can be separated from A. (J.) gutzui as follows: the fourth male pleopod without a projection at the expanded corner on the first segment, the telson distally triangular in shape, and an undivided carpopropodus of the sixth thoracopodal endopod in females. Anisomysis (A.) thurneysseni Nouvel, 1973 also shares with the new species such remarkable features as those in the spinules on the carapace, denticles on the telson, and the length of the first segment relative to the third one in the fourth male pleopodal exopod; and accordingly this species is also considered to be a member of the subgenus Javanisomysis. This subgenus thus currently contains three species, A. (J.) gutzui Băcescu, 1992, A. (J.) similis n. sp. and A. (J.) thurneysseni Nouvel, 1973.