Eisothistos bellonae, Poore, Gary C. B., Lew, Helen M. & Ton, 2002

Poore, Gary C. B., Lew, Helen M. & Ton, 2002, Expanathuridae (Crustacea: Isopoda) from the Australian region, Zootaxa 82, pp. 1-60 : 4-9

Eisothistos bellonae n. sp. ( Figs 2–4 )

Material examined.– Holotype. Coral Sea, N end of lagoon, Bennett I., Chesterfield Reefs (19°S, 158°E), 1 m, N.L. Bruce, 8 May 1979, QM W11545 (juvenile, 5.0 mm, with 1 slide).

Description: Juvenile. Body progressively broader posteriorly; head and pereonites 1– 3 about equal length, pereonites 4–7 progressively shorter, 7 about half as long as 6; pleonites 1–5 very short, together about as long as pereonite 7, each with plumose setae laterally; pleon and pleotelson about one­third body length.

Head without ommatidia, produced well beyond bases of antennae that attach at midpoint on side of head. Antenna 1 with short broad article 1; article 2 little longer but narrower; article 3 1.5 times as long as 2; flagellum with short article 1 bearing pappose seta, 6 additional articles, progressively shorter, terminal 2 each with 1 aesthetasc. Antenna 2 peduncle longer than that of antenna 1, article 5 longer than all others together; flagellum of 6 articles.

Mandible produced anteriorly to front margin of head, styliform; molar process absent, laminar dentata with 3 teeth. Maxilla 1 outer lobe reaching to front margin of head, with 5 distal teeth, penultimate finer than others; inner lobe obsolete. Maxilliped small, with subcircular epipod; short basis and palp of 1 elongate article with 5 distal and lateral setae.

Pereopodal coxal plates 1–7 progressively produced laterally. Pereopod 1 not subchelate; propodus 3 times as long as broad, with row of 4 mesial setae, spiniform seta (half length of dactylus) distally on palm against which dactylus closes. Pereopods 2 and 3 more elongate than pereopod 1, pereopod 3 with ischium having semicircular ridges on posterolateral margin, both otherwise similar to pereopod 1. Pereopod 4 ischium with long plumose seta on anterior margin; ischium­carpus with semicircular ridges along posterior margin; carpus with posterodistal spiniform seta; propodus with pectinate scales posteriorly and strong distal spiniform seta as in pereopods 1–3. Pereopods 5–7 more elongate than more anterior limbs; ischium–propodus with scales along posterior margins; ischium with long plumose seta(e) on anterior margin; carpus with strong distal spiniform seta on posterior margin; propodus with distal spiniform seta as in pereopods 1–4.

Pleopod 1 with rami fused, distally with 7+6 plumose setae and anteriorly with short simple setae. Pleopod 2 endopod smaller than pleopod 1, with 7 plumose setae on rounded apex; exopod two­thirds length of endopod, narrow, with 7 lateral plumose setae. Pleopods 3–5 similar to pleopod 2 but shorter.

Uropodal peduncle broadening distally, dorsolateral margin ending in erect triangular spine; endopod attached obliquely, lateral margin with proximal erect dentate lobe, remainder of margin irregularly dentate­lobate; exopod with central spike reaching as far as inner margin of peduncle, outer lobe with serrate margin, curving ventrolaterally outside peduncle, inner lobe also with serrate margin and acute apex overlapping its opposite in midline. Telson broadest distally, margin dentate beyond widest point and with few setae; minute denticles in middorsal row.

Adult male and female. Unknown.

Distribution: Coral Sea, Chesterfield Reefs; lagoon.

Etymology: For the Bellona Plateau on which the Chesterfield Reefs sit.

Remarks: Eisothistos bellonae n. sp. is notable for the long spiniform seta on the distal palm of all pereopods, acting with the dactylus as an asymmetrical chela. This seta is similar to that on the carpus in other species and is seen also in E. tayronae Müller, 1990 a and E. societensis Müller, 1990 b, two other tropical species. The latter is also from the South Pacific but differs in shorter head, narrower pleon and telson, and less pronounced spike on the uropodal exopod. There are no sutures visible on the maxillipedal palp of E. bellonae as are sometimes seen in other species.

Figures

FIGURE 2. Eisothistos bellonae n. sp. Holotype, QM W 11545. a, lateral view of pleotelson and uropod. Scale bar = 0.5 mm.

FIGURE 3. Eisothistos bellonae n. sp. Holotype, QM W 11545. a, ventral view of head with left antenna 2, maxilla 1 and hypopharynx removed.

FIGURE 4. Eisothistos bellonae n. sp. Holotype, QM W 11545.