Eisothistos Haswell

Poore, Gary C. B., Lew, Helen M. & Ton, 2002, Expanathuridae (Crustacea: Isopoda) from the Australian region, Zootaxa 82, pp. 1-60 : 3-4

Eisothistos Haswell

Eisothistos Haswell, 1884: 677 –679.— Poore, 2001: 122 –123 (complete synonymy).

Remarks: Wägele (1979) described the differences between juveniles, adult females, postspawning females and adult males of species of Eisothistos and these were reviewed by Poore (2001). Juveniles and undifferentiated females have fused rami on pleopod 1 which is barely if at all operculiform, and reduced exopods on pleopods 2–5. The male is small and possesses pleonites 1–3 enlarged relative to the shorter pleonites 4 and 5 (fig. 1a). Its pleopods 1–3 are all biramous and have elongate peduncles and rami; the appendix masculina on pleopod 2 is simple; and pleopods 4 and 5 are as in the juvenile. The antenna 1 has dense rows of proximal aesthetascs on the first article of the flagellum. The eyes are grossly enlarged and the mouthparts are atrophied. The female probably passes through several instars. Mouthparts (except the maxilliped) are reduced to swollen lobes with reduced spines. Pereopod 1, and later pereopods 2–7, become covered with long setae. The presumed terminal vermiform phase is rarely seen (fig. 1b). No stage with oostegites has been reported and it is believed the eggs are brooded free in the serpulid tube. Knight­ Jones & Knight­Jones (2002) diagnosed all species briefly.

The material of Eisothistos from Australia, subantarctic Macquarie I., and the Coral Sea consists of few specimens from scattered localities. Most are very small and not in good condition. The material is in the collections of Museum Victoria and the Queensland Museum. Because each species is polymorphic and not all life stages are represented, the characters useful for specific separation are not clear. Specimens in the best condition have been described as five new species and these are separable from each other and previous species on the shape, ornamentation and setation of pereopods, and shape and setation of uropodal rami and telson. None is definitely referable to E. vermiformis Haswell, 1884 , the type species from New South Wales, of which the holotype is lost. Two other unnamed species are illustrated ( Fig. 1 ).

Figures

FIGURE 1. a. Eisothistos sp. Male from Britomart Reef, Qld, bommie near SE end (18 ° 17 ' S, 146 ° 38 ' E), 3 m, encrusted coral heads, 26 Nov 1982 (stn AIMS 23), NMV J 17213. Scale bar = 0.1 mm. b. Eisothistos sp. Post­spawning female from Port Kembla harbour, NSW (34 ° 28 ' S, 150 ° 54 ' E), epifauna, Feb 1977, NMV J 27673. Scale bar = 1 mm.