Onychatrium entale ( Nordenstam, 1946 ) Nordenstam, 1946

Bruce, Niel L. & Cumming, R. L., 2015, A new genus of Stenetriidae Hansen, 1905 (Asellota: Isopoda: Crustacea) from the Great Barrier Reef, Australia and the southwestern Pacific, Zootaxa 3941 (4), pp. 485-508 : 489

Onychatrium entale ( Nordenstam, 1946) comb. nov.

( Figure 1 )

Stenetrium entale Nordenstam, 1946: 26 , figs 25–27.— Wolff 1962: 249. Hansenium entale .— Serov & Wilson, 1995: 81.

Material examined. Holotype: ♂ (3.8 mm), Tapateuen (=Tabiteue Island), Kiribati ( SMNH 798).

Description. Cephalon length 0.6 width; antennal spines acute; lateral spines subequal in length to antennal spines; lateral spines acute, short, not extending distally as far as antennal spines; space between lateral and antennal spines mesially oblique; lateral margins straight or weakly convex. Eyes pale brown (faded in specimen), arranged in two parallel rows. Pleotelson length 1.0 width.

Antennula article 1 length 1.7 width; article 2 length 1.2 width; article 3 length 2 width; article 4 length 0.5 width.

Maxilliped basis length 2.1 maximum width; endite distal margin with 5 fan setae, distomesial corner with 1 triangular RS; epipod length 3.1 width, width 1.1 basis width, distomesial margin with 5 regularly-spaced setae, lateral margin sinuate.

Pereopod 1 ischium length 1.3 width; inferodistal margin with 1 seta, mesial distal margin with submarginal row of long setae; superodistal margin produced, with 4 long setae, apex narrowly rounded.

Pereopod 1 merus length 0.7 width, 0.9 carpus length, 0.8 ischium length; inferior margin without setae; inferior submargin with a dense patch of long setae; superodistal margin not produced, densely setose with long setae; inferodistal meral process moderately long, extending distally approx. half way along carpal blade, length 1.6 merus length, inferior margin length 0.9 merus length, narrowly lanceolate, apex acute.

Pereopod 1 carpus sub-triangular; length 1.3 width, 0.9 ischium length; inferior margin not clearly defined, colinear with inferior process margin. Carpal process length 1.4 width, 1.1 carpal width; sub-triangular, extending distally more than half length of propodus; apex acute, not setose; inferior margin straight, densely setose along distal two-thirds, distal to meral process, with 1 row of straight setae, 1–2 rows of long distally angled setae; distal margin slightly concave, sparsely setose.

Pereopod 1 propodus robust superiorly; length 1.3 maximum width, 2.1 proximal width, 1.6 ischium length; inferior margin clearly defined, long, 0.5 propodus length, 0.3 superior margin length, with submarginal row of long setae; superior margin with mesial row of evenly-spaced setae, and submarginal lateral row of long setae. Propodal palm width 0.4 maximum propodus width; transverse; toothed lobe with 5 teeth, largest tooth 7.6 length of smallest tooth. Palm process length 3.1 width, RS at apex; inferior margin convex, setose, along distal half only; superior margin weakly convex. Dactylus weakly curved; length 6.8 basal width, 3.8 propodal palm width, 1.4 propodus length; superior margin distal third densely setose; inferior margin with 18 regularly-spaced robust setulated setae; mesial surface not setose.

Pleopod 3 endopod apex with 4 plumose setae. Pleopod 4 exopod apex with 8 plumose setae.

Remarks. The holotype of O. entale was examined and available appendages drawn. This species is similar to Onychatrium forceps sp. nov., but there are several points of distinction. These differences are (state in O. forceps sp. nov. in parentheses): lateral head spine short, not extending anteriorly to level of antennal spine (long, extending anteriorly to level of antennal spine); space between lateral and antennal spine mesially oblique (evenly rounded); lateral margin of head straight or very weakly convex (manifestly convex); maxilliped exopod with evenly convex lateral margin (lateral margin distally concave); pereopod 1 carpal blade acute, with a broad base (carpal blade more slender); meral lobe long, acute (meral lobe short, blunt).

The lateral and antennal head spines present a consistent appearance in O. forceps sp. nov., as well as for other congeneric species for which there are multiple specimens, and these differences are considered to be of specieslevel significance.

Distribution. Known only from the type locality, Tapateuen, Kiribati, central Pacific.

Figures

FIGURE 1. Onychatrium entale (Nordenstam, 1946) comb. nov. male holotype (SMNH 798), A, dorsal view of cephalon, B, pereopod 1, C, enlargement of pereopod 1 dactylus, D, pleopod 3, E, pleopod 4, F, pleotelson, G, enlargement of left maxilliped endite, H, left maxilliped.