Onychatrium thomasi ( Bolstad & Kensley, 1999 ) Bolstad & Kensley, 1999

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 : 503-506

Onychatrium thomasi ( Bolstad & Kensley, 1999) comb. nov.

( Figure 9 , 10 )

Hansenium thomasi Bolstad & Kensley, 1999: 169 , figs 3–5..— Bruce & Buxton, 2013: 450.

Material examined. Topotypes (Madang, Papua New Guinea): ♂ (3.6 mm), ♀ (2.3 mm), Masamoz Reef, 5.1350°S, 145.83833°E, 18 April 1989, rubble at base of reef slope, 18 m, coll. N.L. Bruce & M. Jebb (MTQ W19774). 2 ♂ (3.4, 2.7 mm), barrier reef south of Wongat Island, 5.14333°S, 145.850°E, 29 April 1989, coral rock from hard crest, 4 m, coll. N.L. Bruce & M. Jebb (MTQ W34213). 6 ♂ (3.9 [pereopod 1, pleopod 2 dissected], 3.2 [pereopod 1, pleopod 2 dissected], 3.1, 3.0, 2.8 [P1 dissected], 2.5 mm), 7 ♀ (ovig., 3.5, 2.8 mm, non-ovig. 3.3, 3.2 [pereopod 1, pleopod 2 dissected], 3.1, 2.9, 2.7 mm), Masamoz Reef, 5.1333°S, 145.8333°E, 24 April 1989, Halimeda and coarse sand, 5 m, coll. N.L. Bruce & M. Jebb (MTQ W19749). ♂ (3.0 mm), 2 ♀ (3.1, 2.1 mm), Masamoz Reef, 5.1350°S, 145.8333°E, 24 April 1989, coral rubble, reef top, 5 m, coll. N.L. Bruce & M. Jebb (MTQ W34214). 2 ♂ (3.6, 3.0 mm), 2 ♀ (3.8, 3.5 mm), Wongat Island, 5.1350°S, 145.8334°E, 25 April 1989, small rubble on sand, 10 m, coll. N.L. Bruce & M. Jebb (MTQ W34215). 4 ♂ (2.7, 2.5, 2.4, 2.2 mm), 10 ♀ (ovig., 2.6 mm, non-ovig., 3.5, 3.3, 3.2, 3.1, 3.1, 3.1, 2.8, 2.7, 2.1 mm), south of Wongat Island, outer reef, reef slope, 5.140°S, 145.85°E, 19 April 1989, dead coral, 16 m, coll. N.L. Bruce & M. Jebb (MTQ W34216). 2 ♂ (3.1, 2.0 [P1 dissected] mm), 8 ♀(ovig. 3.5, 3.4, 3.2, 3.0, 3.0 mm, non-ovig. 2.8, 2.7, 2.2 mm), barrier reef south of Wongat Island, reef crest and back reef, 5.1400°S, 145.84833°E, 25 April 1989, dead coral in gully, 6 m, coll. N.L. Bruce & J. Mizeu (MTQ W19762). 5 ♂ (2.9, 2.7, 2.6, 2.6, 1.4 mm), 8 ♀ (ovig. 3.8, 3.7, 2.8, 2.4 mm, non-ovig. 2.8, 2.8, 2.3, 2.1 mm), 3 juv. (1.5, 1.6, 2.0 mm), Wongat Island, north-west corner, 5.1350°S, 145.8433°E, 23 April 1989, semiexposed rubble among alcyonarians, 0.5 m, coll. N.L. Bruce (MTQ W34217). 3 ♂ (3.8, 3.6, 2.3 mm), 3 ♀ (2.9, 2.9, 2.5 mm), barrier reef south of Wongat Island, back reef, 5.1400°S, 145.84833°E, 28 April 1989, coarse rubble, Halimeda covered, 7 m, coll. N.L. Bruce & R. Ueba (MTQ W34218).

Supplementary description. Pereopod 1 basis length 2.1 width; superior margin with 2 short setae, 1 long seta proximally; submarginal row of short and long setae.

Ischium length 1.2 width; inferior margin with 1 short seta, inferodistal margin without setae, distal margin with 1 short seta, mesial distal margin with submarginal row of 5 long setae; superodistal margin not produced, with 3 long setae.

Merus length 0.7 width, 1.0 carpus length, 0.7 ischium length; inferior margin with 1 short seta, inferior submargin with a dense patch of long setulate setae, distal margin without setae. Inferodistal meral process short, oblong, length 0.7 merus inferior margin length, 0.5 merus length, mesial surface with numerous long setulate setae, lateral surface with 1 seta.

Carpus sub-triangular; length 0.7 width, 0.6 ischium length; distal margin with 3 short setae; inferior margin not clearly defined. Carpal process long, tapering, straight; length 1.9 width, 1.4 carpal width; extending distally adjacent to propodal palm, oriented c 63 degrees to propodal longitudinal axis, parallel with propodal process; apex rounded, densely setose; inferior margin straight, densely setose, setae becoming submarginal on proximal third, 1 row of straight setae, 1–2 rows of long setae angled distally; superior margin straight, setose along full length.

Propodus robust superiorly with pronounced narrowing medially; length 1.5 maximum width, 1.7 proximal width, 1.7 ischium length; inferior margin clearly defined, short, 0.07 propodus length, 0.07 superior margin length, submarginal setae setulate; superior margin with a marginal row of evenly-spaced setae, a submarginal lateral row of long setae. Palm width 0.6 maximum propodus width, oblique; toothed lobe with 4 teeth, largest tooth length 15.5 smallest tooth length; distance from toothed lobe to propodal process 0.7 palm width, 0.9 propodal process width. Propodal process length 4.7 width, including RS at apex; inferior margin convex, setose along distal quarter only; superior margin straight. Dactylus straight in mid-section, slightly curved at ends; length 7.3 proximal width, 3.5 propodal palm width, 2.2 propodus distal width (not including process), 1.5 propodus length; inferior margin with 15 regularly-spaced robust flagellated setae.

Pleopod 2 protopod length 3.3 maximum width, basal lobe width 1.6 medial width, distal lobe sub-triangular, lateral margin with 1 seta; endopod length 0.4 protopod length. Appendix masculina length 1.9 endopod length, 0.8 protopod length; without lateral spine.

Female. Pereopod 1 basis length 2.3 width, superior margin with 5 short setae, inferior margin with 7 short setae, inferodistal margin with 3 setae. Carpus inferodistal margin slightly produced, process triangular. Propodus length 1.0 distal (maximum) width, 2.1 proximal width, 3.0 ischium length; inferior margin length 0.6 propodus length, setae restricted to distal two-thirds of margin; palm width 1.1 inferior margin length, with 5 teeth, articulation with 1 long seta. Dactylus length 5.6 width, 1.7 palm width, inferior margin with 12 regularly-spaced robust flagellated setae.

Pleopod 2 length 1.4 maximum width; lateral margins not parallel, narrowing posteriorly; posterolateral margins straight to slightly concave; apex rounded.

Remarks. Onychatrium thomasi may be identified and distinguished from its congeners by the male pereopod 1 having an elongate and distinctly curved propodal process (approximately 4.7x basal width; as long as propodus), the propodal inferior margin with a very short free margin proximal to the propodal process, a robust, large and straight-sided (“triangular”) carpal process and a short and blunt carpal process.

Distribution. Known only from the Madang region, Papua New Guinea; at depths of 0.5 to 18 m.

Figures

FIGURE 9. Onychatrium thomasi (Bolstad and Kensley, 1999) comb. nov. A, B, male 3.2 mm (MTQ W 19749), A, pereopod 1, B, enlargement of pereopod 1 dactylus; C – E, female (MTQ W 19749), C, pereopod 1, D, enlargement of pereopod 1 dactylus, E, pleopod 2; F, male 3.9 mm (MTQ W 19749) pleopod 2, with enlargement of appendix masculina; G, male 3.2 mm (MTQ W 19749) apex of appendix masculina.

FIGURE 10. Onychatrium male pereopod 1 variation—comparison between species, developmental stages and locations. Onychatrium entale (Nordenstam, 1946) comb. nov. holotype (SMNH 798). Onychatrium forceps sp. nov., A, paratype (MTQ W 31594), B, paratype (MTQ W 32851), C, holotype (MTQ W 34194), D, paratype (MTQ W 34196), E, paratype (MTQ W 34198). Onychatrium torosus sp. nov., A, holotype (MTQ W 34204), B, paratype (MTQ W 14076), C, paratype (MTQ W 34206), D, paratype (MTQ W 32760). Onychatrium thomasi (Bolstad and Kensley, 1999) comb. nov., A – C, topotypes (MTQ W 19749), D, topotype (MTQ W 19762).