Allodiplophryxus unilateralis n. sp.

Fig. 1

Material examined. Holotype female, ovigerous, 1.53 mm (maximum length, from anterior end of head to uropods), paratype male, 0.94 mm, WAM C75202 & C75203 (ex UF Arthropoda 23161), Australia, Western Australia, Ningaloo Reef, S shallow bommies, back reef, patchy corals on sand, in rubble 2–3 meters snorkel, by hand, 22.7415°S, 113.6836°E, coll., Robert Lasley, 15 May 2009. Infesting Jocaste lucina (Nobili, 1901) WAM C 75204 (ex UF Arthropoda 21490).

Description. Holotype female (WAM C75202) length 1.53 mm, pleonal length 0.67 mm. Body outline oval, sinistrally distorted (Fig. 1A, B).

Head subovate, embedded in pereon, not visible in dorsal view, covered by oostegite 2. Eyes not discernible (Fig. 1A). Antennulae with two articles; antennae absent (Fig. 1C). Right maxilliped articulated, anterior article triangular, much large than posterior one, without palp, plectron short and blunt, (Fig. 1D). Anterior apex of left maxilliped rolled inward (Fig. 1E). Barbula (Fig. 1F) with 12 irregular marginal projections, as well as two pairs of short, blunt projections on raised layer.

Pereon with segments distinct on concave side only (Fig. 1A). Pereomere 2 ventrally produced into several irregular fleshy projections (Fig. 1B). First oostegite of two sides different, left (Fig. 1G) much wider than right (Fig. 1H, I); right with long, slender posterior part and internal ridge with two tubercles (Fig. 1H, I); left with broad posterior part and internal ridge nearly entire (Fig. 1H). Five pereopods discernible on short side, anterior two well developed, while posterior three small and clustered together. Three pereopods present on long side, first two well developed (Fig. 1J), third represented only by scar-like basis.

Pleon of six pleomeres, first four bearing biramous lateral plates (Fig. 1A), fifth with uniramous lateral plates, pleotelson small and globose, embedded into fifth pleomere (Fig. 1K). Biramous pleopods present on first four pleomeres only, restricted to short side (Fig. 1B).

Paratype male (UF 23161) length 0.94 mm, maximum width (across pereomere 4) 0.39 mm, head length 0.18 mm, head width 0.25 mm, pleonal length 0.18 mm. Black pigmentation on dorsal surface of first pereomere and head.

Head oblong; black eyes near lateral margin (Fig. 1L). Antennulae and antennae each with 3 articles (Fig. 1M, N).

Pereon segments distinct (Fig. 1L), with truncate margins and lacking midventral projections (Fig. 1M). First three pereopods with large dactyli, decreasing in size posteriorly, last four pereopods with smaller dactyli; all dactyli sharp and pointed (Fig. 1O, P). Carpi and meri of first pereopods larger than those of others (Fig. 1M, O, P).

Pleon fused into single piece, but with obscure indentation demarcating first pleomere; narrower than the last pereomere (Fig. 1M); with scattered black pigmentation on ventral surface. Pleopods and uropods absent.

Etymology. The specific name, unilateralis, refers to the restriction of pleopods to the short side of the body in the female.

Remarks. Species in four genera within the Hemiarthrinae have biramous lateral plates on the pleon: Allodiplophryxus, Diplophryxus, Micropodiphryxus, and Cataphryxus. The present specimens are placed in Allodiplophryxus because the female has biramous lateral plates and two prominent pereopods on the long side but five on the short side, and because the male has a fused pleon. The new species differs from the only congener, A. floridanus Markham, 1985, in the following characters of the female (character states in A. floridanus given in parentheses): 1) pleon with six segments (five segments); 2) first oostegite asymmetrical (symmetrical); 3) pleopods restricted to short side (pleopods on both sides). The new species extends the range of Allodiplophryxus from the West Atlantic to the Indo-West Pacific.