(Žgure 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, Žve ocelli per eye (Žgure 8A), each antennule basal article with anterior projection, antepenultimate and penultimate articles each with an aesthetasc (Žgure 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. Žgure 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 (Žgure 8G) like Žgure 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 (Žgure 9A). Male characters are (1) absence of leaf-like forward extensions from antennule 1 basal articles (also absent in Žgure 7A and in male Eisothistos teri) and (2) pleonites 1–3 each as long as pereonite 7 (Žgure 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 Žgure 9A), (4) ca seven ischial studs on each pereopods 2 and 3, arranged as in Žgure 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 (Žgure 8J).
Other material. Manca from Miller’s Point, 1.8 mm long (Žgure 8C), telson with three small keel spines, hind margin (Žgure 8F) as in holotype; antennule 1 basis with small anterior protrusion, antennule 2 (Žgure 8E) as in many of this genus; pereopod 2 (Žgure 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 (Žgure 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 (Žgure 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 Žgure 8H). This Žgure also shows a large seta protruding posteriorly from distal corner of each uropod basis, as in most Eisothistos species.
Etymology. Latin biŽdus 5biŽd, applied here because the two plumose setae of hind telson are separated by a single tooth with a biŽd tip.
Remarks. A male E. antarcticus is the only Eisothistos previously Žgured as having plumose setae of hind telson separated by only one biŽd tooth (Wägele, 1984, Žgure 5). Eisothistos teri has that pair separated by two teeth, and is very like E. biŽdus, but with 11 studs forming transverse ridges on pereopod 2 ischium, and a single recurved tooth on uro-exopod main fang. Since a biŽd tooth looks like two teeth E. biŽdus 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.