Eisothistos, Haswell, 1884

Knight-Jones, E. W. & Knight-Jones, Phyllis, 2002, Four new species of Eisothistos (Anthuridea: Isopoda) from tubes of Spirorbidae (Serpuloidea: Polychaeta), Journal of Natural History 36 (12), pp. 1397-1419 : 1413-1414

Eisothistos bi dus sp. nov.

(gure 8)

Material. Holotype female and senescent individual from Kalk Bay, manca from Miller’s Point, all south of Cape Town in False Bay, ca 34ss18¾S, 18ss28¾E; manca from Hermanus, in Walker Bay, ca 34ss30¾S, 19ss14¾E. All from spirorbid tubes ( Paralaeospira , Pileolaria or Protolaeospira ) collected in shallow water, August 1971 ( Knight-Jones and Knight-Jones, 1974).

Description. HOLOTYPE. Mature female 2.1 mm long, ca 0.2 wide, ve ocelli per eye (gure 8A), each antennule basal article with anterior projection, antepenultimate and penultimate articles each with an aesthetasc (gure 8D), each pereopod with subdistal wheel-joint, pereopods 2 and 3 each with two or three studs on merus and ca seven on ischium, distributed as in related species (e.g. gure 6F, i.e. with two ‘elbow’ studs separated by a small gap from main distal group on ischium). Telson with six long keel spines, hind telson (gure 8G) like gure 4B, C but without central seta; small dorsal seta adlateral on each side.

PARATYPE. Senescent female?, body length 2.1, extended further 0.65 mm by antennules 1 and 2, which are very swollen basally (gure 9A). Male characters are (1) absence of leaf-like forward extensions from antennule 1 basal articles (also absent in gure 7A and in male Eisothistos teri ) and (2) pleonites 1–3 each as long as pereonite 7 (gure 8J). Preponderance of female characters in paratype include (1) lack of aesthetascs and large setae from antennules 1 and 2, (2) lack of subdistal wheel-joints from pereopods, (3) lack of ‘scales’ on pereopod 1 propodus (as in gure 9A), (4) ca seven ischial studs on each pereopods 2 and 3, arranged as in gure 6F, (5) wide tail-fan (ca 0.35 mm). Telson with ca nine keel spines, hind margin as in holotype; each uropodal exopod with row of three pointed studs on dorsal side along axis of main fang (gure 8J) .

Other material. Manca from Miller’s Point, 1.8 mm long (gure 8C), telson with three small keel spines, hind margin (gure 8F) as in holotype; antennule 1 basis with small anterior protrusion, antennule 2 (gure 8E) as in many of this genus; pereopod 2 (gure 8B) with only seven ‘scales’ on propodus (cf. 12 scales there in holotype) and six ischial studs spaced regularly; pereopod 3 like pereopod 2; uroexopods lack dorsal studs on very slender main fang. Ripe female from Hermanus 1.7 mm long with plump pereonites 0.2 mm wide, perhaps a manca (damaged between pereon and pleon), telson (gure 8H) lacking keel spines, with two small dorsal setae in adlateral positions and another pair closer together on mid-telson, hind margin as in New Zealand material (gure 4B, C) but without a central seta, the two central teeth being linked by a tall base. Transparency of this tail-fan reveals the cross-striated oval body within each uropod basis (shown on one side in gure 8H). This gure also shows a large seta protruding posteriorly from distal corner of each uropod basis, as in most Eisothistos species .

Etymology. Latin bi dus 5bi d, applied here because the two plumose setae of hind telson are separated by a single tooth with a bi d tip.

Remarks. A male E. antarcticus is the only Eisothistos previously gured as having plumose setae of hind telson separated by only one bi d tooth ( Wägele, 1984, gure 5). Eisothistos teri has that pair separated by two teeth, and is very like E. bi dus, but with 11 studs forming transverse ridges on pereopod 2 ischium, and a single recurved tooth on uro-exopod main fang. Since a bi d tooth looks like two teeth E. bi dus is best separated from E. adlateralis by the more prominent studs or spines which it has on the ischia of pereopods 2 and 3 and (usually) on the telson keel and uropodal exopod main fang.