Introduction and Acknowledgments

Iais is a genus of small asellote isopods found associated with certain sphaeromid isopods, usually on the ventral surface of the larger animal, between the peraeopods and on the pleopods. The exact relationship of Iais to its host and its dependence on the Sphaeromid is still uncertain Chilton (1892, 1909) claims to have found specimens of Iais living freely on seaweed and under stones on beaches and at the mouths of freshwater streams. Menzies and Barnard (1951), in their recent revision of the genus, suggest that these reports may be in error.

The specimens discussed below came from sphaeromid isopods collected by Mr. E. M. Sladden, Engineer for the Hutt Valley River Board, and received through the courtesy of Professor L. R. Richardson, of Victoria University College, Wellington.

I am extremely grateful to Captain Allan Hancock for the use of facilities at the Hancock Foundation, to Dr. John S. Garth of the Foundation; and to Dr. J. Laurens Barnard, from whom I have had much assistance during the preparation of this paper. This work has been carried out during the tenure of a Fulbright Research Scholarship.

Genus Iais Bovallius, 1887.

Menzies and Barnard, 1951: 137.

“Eyes present, each consisting of two facets. First antenna with six articles. Second antenna without a scale. Epimeral plates visible in dorsal view on all peraeonal somites. Lateral margins of peraeonal somites not deeply incised, borders setiferous. Apex of male first pleopod not widely expanded laterally. Third pleopod without pluniose setae on endopod. Dactyls of first peraeopods with two claws; those of others with three claws. First two articles of maxillipedal palp as wide as endite; apical three articles much narrower than endite. Mandible with a triarticulate palp and with an evident, elongate, apically blunt molar process.'

Iais californica (Richardson). Figs. 1-13.

Iais californica (Richardson). Menzies and Barnard, 1951: 141-143, Pls. 44-45.

Iais pubescens (Dana) var. longistylis Chilton. Chilton, 1912: 132, 134.

Iais singaporensis Menzies and Barnard, 1951: 144, Pls. 46-50.

“First antenna about one-sixth the length of the body and nearly three-tenths as long as the second antenna Second antenna about six-tenths the length of the body; flagellum with twenty-four articles. Maxilliped with three coupling

hooks. Peraeonal somite 4 overlapping the border of somite 3 but overlapped by the border of the fifth somite; peraeonal setae moderately developed. Inferior claw of dactyl of peraeopods one to seven simple, not bifid. Lateral subapical processes of sympod of male first pleopod not diverging laterally, lateral margins smooth; medial processes subtriangulate, provided with 5 marginal setae, Pleotelson wider than long, posterior border medially produced into a lobe. Uropod slightly more than one-half as long as pleotelson; rami subequal in length, twice as long as peduncle. Operculum of female wide, with a small rounded medial process on distal margin.”

Material Examined. Numerous specimens from Sphaeroma quoyana Milne Edwards (cf. Chilton, 1912: 134) found eroding a large trunk of matai (Podocarpus spicatus). The wood was jammed against the upstream side of the railroad bridge about a mile from the Hutt River mouth. The Sphaeroma were numerous, each packed into a shallow open pit or short groove. There were no concealed tunnels in the wood. Associated with the isopods were a species of Elminius and a marine polyzoan. Most of the Sphaeroma carried from three to twelve or more Iais. Collected by E. M. Sladden, 14/9/54.

Remarks. The above description is that given by Menzies and Barnard for I. californica and must be modified in view of the proposed synonymy. The New Zealand specimens were identical with the Californian ones except for possessing only two coupling hooks on the maxilliped. This distinction was the decisive one accepted by Menzies and Barnard in separating Iais singaporensis from I. californica. The remarkable coincidence of morphological details, apart from this one character, casts doubt on its validity as a specific criterion, and this doubt is further strengthened by the discovery that the New Zealand host attributed to Sphaeroma quoyana, is identical with the Californian host, S. pentodon Richardson. It is not appropriate to pursue the identity of the hosts further in this paper, but it should be remarked that there are two possibilities. The New Zealand specimens may be wrongly attributed to Milne Edwards' S. quoyana, which is the older species, or S. pentodon may be a synonym of S. quoyana.

Granted that the New Zealand and Californian specimens are conspecific, it becomes much more difficult to accept Iais singaporensis as a valid species. There are few qualitative differences of great import between the New Zealand specimens and the specimens from Singapore and the Philippines which Menzies and Barnard described. The one possible exception to this is the uropod of the Philippine material.

Menzies and Barnard suggest the possible existence of a “rassenkreis” involving two or possibly more subspecies to explain the slight differences between their Singapore and Philippine material. The above information tends to support this, but on the present material I do not feel it appropriate to establish subspecies on either morphological or geographical grounds. It is worth noting, however, that the hosts concerned in the Singapore and Philippine localities appear to belong to a distinct and different species in each country.

The specific diagnosis may be easily emended by the following changes: “First antenna from one-fifth to one-sixth the length of the body, about one-third the length of the second antenna. Second antenna about six-tenths the length of the body. flagellum of up to 24 articles. Maxilliped has two or three coupling hooks…. Lateral subapical processes of sympod of male first pleopod not diverging laterally, medial processes have rounded, slightly acute apices; each has 5 to 8 marginal setae. … Uropod one-half to one-third the length of pleotelson; rami subequal in length, longer than peduncle. Female operclum wide, with small to pronounced rounded apical lobe.”