A NEW SPECIES OF THE SURF-INAHIBITING ATHERINIFORM ISO (PISCES ISONIDAE)

WA Museum Records and Supplements | Updated 1 decade ago

Abstract - Specimens of an atherinifonn fish collected in the American Samoa and Pitcairn Island are described as a new species of Iso. On external morphology, it is distinct from all other members of the genus except for Iso hawaiiensis, with which it shares gill Taker, midlateral and vertebral counts. Using a novel procedure to study small bones with a scanning electron microscope, Iso nesiotesis shown to be unique in having a short coracoid, long dorsal processes of the urohyal, and the third orbital possessing a lateral shelf. From its closest relative, Iso hawaiiensis, the new species can be distinguished by absence of the intercalar, structure of the pectoral girdle and the shapes of the opercle and haemal spines. Externally, the new species is recognised by the absence of an oval spoton the caudal peduncle. The two populations of Iso nesiotes show minor differences in the position of anus and in fin ray, gill raker and scale counts. A key to the species of Iso is also given.