Vemathambema falciclava, Just, 2025

Just, Jean, 2025, Vemathambema falciclava sp. nov. from south-eastern Australia, first Indo- Pacific record of the genus, with a review of diagnoses in the family (Isopoda, Asellota, Echinothambematidae), Zootaxa 5725 (1), pp. 135-142 : 136-139

Vemathambema falciclava , sp. nov.

Figs 1 and 2

Type fixation. Holotype, male.—Here designated.

Etymology. The species name is a combination of the Latin falx meaning sickle and clavus meaning spike, alluding to the large sickle-shaped projection on article 1 of the antennulae.

Material examined. Holotype. Male , 1.7 mm, Bass Strait, south of Point Hicks, Victoria, Australia, 38°21.9’S 149°20.0’E, 1000 m, WHOI epibenthic sled, G.C.B. Poore et al., 23 Jul 1986, RV Franklin , stn SLOPE 32 , NMV J20273 .

Paratypes. Same data as holotype, NMV J74094 ( 1 female, 2.0 mm). Bass Strait, south of Point Hicks, Victoria, Australia, 38°19.60’S 149°24.30’E, 930 m, rock, rubble, clay, sand, WHOI epibenthic sled, M.F. Gomon et al., 23 Jul 1986, RV Franklin , stn SLOPE 33 , NMV J20274 , (1 manca, 1.1 mm) .

Description. Head, pereonites and pleotelson rugose. Entire length 4.7 width; all pereonites of subequal length. Head, front margin with broad concavity; dorsally with 2 broad, rounded bulges; length and width similar to pereonite 1, combined length of head and pereonite 1 as long as pereonite 2 and 3 combined. Pereonites broadly rounded laterally, posterior half of pereonites 1–4 tapering, pereonites 5–7 widening distally. Coxae small rings ventrally on pereonites. Pleon fully fused to pereonite 7, the combination as long as pereonites 4–6 combined, pleon widening at insertion of uropods to 1.5 width of proximal fusion, posterior projection broadly rounded at about 90° angle.

Mouthparts. Maxilliped palp with 5 articles, article 3 longest and broadest, about half width of endite; epipod broadly rounded distally, reaching to mid article 3 of palp; basis endite reaching to mid article 3 of palp, distal margin with 2 fan-shaped and a several simple setae.

Antennula article 1 swollen, as wide as long in ventral view, with long, sickle-shaped projection dorsally, curving overhead; article 2 shorter than 1, cylindrical, length twice width, article 3 about half length of 2, article 4 a tiny ring, article 5 as long as 3 and 4 combined, articles 6 and 7 subequal, combined as long as article 5, 7 with 3 terminal aestetascs ( ♂). Antenna article 1 as long as broad, slightly longer than subequal articles 2–4, article 5 as long as 3 and 4 combined, 6 about twice length of 5; flagellum broken (see female below).

Pereopod 1 basis length 6.0 distal width; ischium 0.4 length of basis, distal half expanded; merus nearly square, 0.5 ischium length; carpus as long as ischium and merus combined, anterior margin lightly convex, posterior margin straight with 3 to 4 robust setae and finely setulose margin; propodus slightly shorter than carpus, more slender, posterior margin distally finely setulose with several simple setae; dactylus length 0.7 length of propodus, broad, straight, with second claw straight, distally with dorsal and ventral spines, reaching about 0.8 along length of short, stout unguis. Pereopods 2 –7 ( ♀) slender, posterior legs slightly longer and thinner, and with fewer robust setae on carpus and propodus; basis slender straight, slightly widening distally; ischium length 0.3 basis length; merus length 0.6 ischium length, anterodistally expanded; carpus and propodus subequal, about 7 times longer than broad, with a few posterior robust setae; dactylus very slender, 0.6 length of propodus, second claw not observed, unguis needlethin, about half length of dactylus.

Pleopod 1 straight, slightly tapering to expanded distal 1/5, terminal margins evenly convex, with a few scattered short dorsal setae.

Uropods. Long, styliform, biarticulate inserted in large sockets on distolateral corners of pleon (tip broken off except in juvenile, see Discussion).

Female. Generally as described above, but body broader than in male relative to length; lateral margins of pereonites not as markedly projecting; pleon lateral margins nearly parallel. Antennula with single aesthetasc. Antenna flagellum with 7 articles. Operculum in lateral view with proximal bulge; in ventral view two bulges with lateral, distally joining, groves (forming heart-shaped area); otherwise broadly ovoid

Size. Largest ♂, 1.7 mm. Largest ♀, 2.0 mm.

Distribution. Australia, Eastern Bass Strait; 930–1000 m.

Remarks. Vemathambema falciclava sp. nov. differs from its two congeners V. elongata and V. argentinensis as follows: the antennula article 1 sickle-shaped projection is unique; the front margin of the head has an open Vshaped concavity; the pleon in male is much more expanded distally. The male opercular area in Vemathambema argentinensis covers a larger area of the ventral surface of the pleon than in the other two species.

Figures

FIGURE 1. Vemathambema falciclava sp. nov. H, holotype, ♂. F, paratype, ♀. dv, dorsal view, lv, lateral view, vv, ventral view. Scale = 0.5 mm, for all figures.

FIGURE 2. Vemathambema falciclava sp. nov. H, holotype, ♂. F, paratype, ♀. J, juvenile. mxp, maxilliped; op, operculum, ventral view; p1, 2, 7, pereopods 1, 2, 7; pl & per, lateral view of pleon, with pereonites 6 and 7; pl vv, ventral view of pleon with pleopods 1 and 2; r a, right antennula, up, uropod.