Onychatrium torosus, Bruce, Niel L. & Cumming, R. L., 2015

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 : 498-503

Onychatrium torosus sp. nov.

( Figures 6–8 , 10 )

Material examined. Holotype: ♂ (4.3 mm), Lizard Island lagoon, off Palfrey Island, 14.68687°S, 145.43764°E, 16 April 2008, hard, current swept bottom, 7 m, coll. M. Błażewicz-Paszkowycz (MTQ W34204).

Paratypes: 6 ♂ (3.9, 3.2, 3.0, 2.8, 2.8, 2.5 mm), 11 ♀ (ovig., 3.5, 3.2 mm, non-ovig., 4.0, 3.9, 3.8, 3.5, 3.0, 2.9, 2.7, 2.6, 2.2 mm), 2 juv. (2.1, 1.8 mm), same data as holotype (MTQ W14059). 9 ♂ (4.6 mm, 3.7–4.0 mm, 3.7 mm [dissected]), 8 ♀ (7 ovig., 3.4–4.0 mm, non-ovig., 4.1 mm), entrance to Lizard Island lagoon, near Seabird Islet, patch reef, 14.68900°S, 145.46710°E, 11 April 2008, small rubble on sand, 1–2 m, coll. N. Bruce & M. Błażewicz- Paszkowycz (MTQ W14076). 2 ♂ (3.1, 2.5 mm), 2 ♀ (3.8, 2.8 mm), same data as previous, dead coral heads, 1–2 m (MTQ W34209). 3 ♂ (4.3 mm [dissected], 4.2 mm, 4.0 mm [P7 dissected]), 3 ♀ (ovig., 3.8 mm [dissected], nonovig., 3.7 mm [P1 dissected], 3.7 mm), same data as previous (MTQ W34205). ♀ (4.3 mm), Lizard Island lagoon, “Big Vicky Reef”, north-west of Palfrey Island, patch reef, 13 April 2008, coarse coral rubble, 3 m, coll. K. Mills (MTQ W14081). 5 ♂ (3.0– 3.7 mm), 2 ♂ (2.6 mm [P1 dissected], 2.3 mm), ♀ (4.2 mm), juv. (1.7 mm), Lizard Island lagoon, patch reef off Palfrey Island, 14.68345°S, 145.44147°E, 16 April 2008, large dead Acropora head, 1.5 m, coll. N.L. Bruce (MTQ W34206). 4 ♂ (2.5-2.8 mm), 4 ♀ (ovig., 4.1, 2.8 mm, non-ovig., 3.1, 2.6 mm), North Point, 14.64553°S, 145.45335°E, 12 April 2008, compacted dead Acropora , 0.5 m, coll. N.L. Bruce (MTQ W34207). ♂ (3.2 mm), “Washing Machine”, North Point, reef edge, 14.65383°S, 145.4634°E, 27 August 2010, dead coral rubble, 5 m, coll. C. Buxton (MTQ W32624). 3 ♂ (2.9, 1.6 [P1 dissected], 1.5 mm), ♀ (2.5 mm), Lizard Island lagoon between Palfrey and South Islands, reef flat, 14.69893°S, 145.4487°E, 3 September 2010, coarse rubble, 3 m, coll. C. Buxton (MTQ W32760). 4 ♂ (4.0, 4.0, 3.8 [dissected], 3.3, 3.0 mm), 3 ♀ (ovig., 4.1 mm, nonovig., 3.9, 3.3 mm), Lizard Island, Casuarina Beach , patch reef, 14.68039°S, 145.44453°E, 15 April 2008, coral heads, 1 m, coll. N. Bruce (MTQ W34208).

Other material. Lizard Island. Patch reef off Casuarina Beach , 15 April 2008 (MTQ W14063); “Bommie Bay”, 2 September 2010 (MTQ W32741); North Point, 12 April 2008 (MTQ W34210, MTQ W34211, MTQ W14073); “Big Vicky Reef”, lagoon patch reef, 13 April 2008 (MTQ W34212); patch reef off Palfrey Island, 16 April 2008 (MTQ W34229); patch reef near Seabird Islet, 11 April 2008 (MTQ W34231).

Description. Body length 3.3 maximum width. Cephalon length 0.5 width, 0.9 pereonite 1 length; lateral spines subequal in length to antennal spines; space between lateral and antennal spines mesially oblique; lateral margins convex. Eyes with 17 ommatidia, pale brown. Pereonite 1 length 0.5 width, 1.6 pereonite 2 length, width 1.3 cephalon width; Pleotelson length 1.0 width.

Antennula length 1.6 cephalon length; article 1 length 1.6 width, mesial margin with 4 short penicillate setae, distolateral margin with 1 large penicillate seta, lateral margin with 1 long seta; article 2 length 1.6 width, distomesial margin with 1 cluster of setae, distolateral margin with 1 cluster of setae, including 1 penicillate seta, centre of inferior side with 1 cluster of setae; article 3 length 2.1 width, distomesial margin with 1 cluster of setae, mesial margin with 1 cluster of setae, including 2 penicillate setae, inferodistal margin with 1 cluster of setae; article 4 length 0.3 width, inferior distal margin without penicillate setae; flagellum with 11 articles, 1 aesthetasc per article on distal 9 articles.

Antenna length c 1.0 body length; peduncle article 1 length 0.9 width, distolateral margin with 1 cluster of setae; article 2 length 0.7 width, distolateral margin with 2 long setae; article 3 length 1.3 width, distomesial margin with 1 cluster of setae, mesial margin with 1 cluster of setae, lateral margin with 4 setae surrounding squama; article 4 length 0.6 width, distomesial margin with 1 seta; article 5 length 5.1 width, article 6 length 6.8 width, flagellum articles each with a cluster of 4 distally projecting setae, the cluster position serially repeating every 4 articles.

Mandible left spine row with 4 spines, right spine row with 10 spines; palp article 2 length 3.4 width, with row of 7 short serrate setae; article 3 length 2.5 width. Maxillula lateral lobe apex with 13 serrate RS; mesial lobe apex with 2 large plumose setae, distomesial margin with 1 setulate RS, 1 large seta. Maxilla mesial lobe mesial margin with 5 large plumose setae, 3 setulate RS, apex with 3 large setulate setae, 2 setae with spatulate tips; middle lobe apex with 4 large setulate setae, distal end with a row of 8 setae, decreasing in size proximally; lateral lobe apex with 4 large setulate setae, distal end with a row of 10 setae, decreasing in size proximally. Maxilliped basis length 2.2 maximum width; endite distal margin with 5 fan setae (4 only on right maxilliped of some individuals), distomesial margin with 4 serrate setae, distomesial corner with 1 triangular RS; epipod length 3 width, width 1.1 basis width, distomesial margin with 4 regularly-spaced setae, lateral margin sinuate.

Pereopod 1 basis length 2.8 width; superior margin with regularly-spaced short setae, 4 long proximally; submarginal row of short and long setae.

Pereopod 1 ischium length 1.4 width; inferior margin with 2 short setae, 1 long seta, inferodistal margin with 2 setae, distal margin with 7 short setae, mesial distal margin with submarginal row of 7 long setae; superodistal margin not produced, with 10 long seta.

Pereopod 1 merus length 1.0 width, 1.3 carpus length, 0.9 ischium length; inferior margin with 1 short seta, 3 long setae, inferior submargin with a dense patch of long setae, distal margin with 4 short setae; meral process long, extending distally past carpus–propodus border, length 1.2 merus inferior margin length, 0.8 merus length, lanceolate, apex rounded, mesial surface densely setose on proximal third only, lateral surface densely setose along full length of inferior margin.

Pereopod 1 carpus sub-quadrate; length 0.8 width, 0.7 ischium length; distal margin with 2 short setae; inferior margin clearly defined, length 0.8 carpus length. Carpal process short, a sub-triangular lobe, length 0.9 width, 0.2 carpal width; apex rounded, not setose; inferior margin convex, setose, with long setae.

Pereopod 1 propodus robust superiorly with pronounced narrowing medially and obliquely, proximal to the palm; length 1.4 maximum width, 1.6 proximal width, 1.2 ischium length; inferior margin not clearly defined, short, 0.07 propodus length, 0.07 superior margin length; superior margin with 2 short setae, a submarginal mesial patch of long setae. Propodal palm width 0.5 maximum propodus width; oblique; toothed lobe with 4 teeth, largest tooth length 5.0 smallest tooth length; distance from toothed lobe to propodal process 0.2 palm width, 0.2 propodal process width. Propodal process length 1.6 width, RS at apex; inferior margin weakly convex, setose along full length; superior margin straight. Dactylus curved; length 4.7 basal width, 2.5 propodal palm width, 1.5 propodus distal width (not including process), 1.0 propodus length; inferior margin with 15 regularly-spaced robust flagellated setae.

Pereopod 2 basis superior margin with 2–3 penicillate setae; ischium superior margin with 1 large seta; merus superodistal margin with 1 RS, 1 large seta; carpus superodistal margin with 5 setae (including 1 penicillate seta), inferior margin with 6 flagellated RS (most distal paired with 1 RS); propodus superior margin sparsely setose; superodistal margin with 5 setae (including 1 penicillate seta); inferior margin with 5 flagellated RS (and 1 flagellated serrate RS at inferodistal corner).

Pereopod 7 basis superior margin with 2 penicillate setae; carpus inferior margin with 5 flagellated RS (most distal paired with 1 RS); propodus inferior margin with 4 flagellated RS (and 1 flagellated serrate RS at inferodistal corner).

Pleopod 1 protopod length 0.4 width; lateral margins with 1 seta; distal margin without pair of RSe; surface setae absent; rami lateral margins with regularly-spaced setae along distal half (becoming closer together distally); inferior surface with a few setae. Pleopod 2 protopod length 2.9 medial width; basal lobe width 1.6 medial width; distal lobe slightly shorter than exopod, triangular; lateral margin with 2 setae; endopod without setae, medial ength 0.4 protopod length. Appendix masculina length 1.8 endopod medial length, 0.8 protopod length; with lateral, proximally-directed robust spine; lateral margin with distal groove; mesial margin with small, evenly spaced setae; apex with narrowly rounded, laterally concave lobe, without interior pocket of scale setae; 1 proximally projecting distolateral spine. Pleopod 3 endopod apex with 5 plumose setae. Pleopod 4 exopod apex with 11 plumose setae. Pleopod 5 apex with 6 plumose setae.

Uropod length 0.2 body length, 0.6 pleotelson length; protopod length 2 width; endopod length 1.1 protopod length, distal and sub-distal margins with 9 penicillate setae, distal tip with cluster of elongate setae, maximum length 2.2 endopod length; exopod length 0.8 protopod length, 0.7 endopod length, distal tip with cluster of elongate setae, maximum length 2.9 exopod length.

Female. Pereopod 1 basis length 2.4 width, inferior margin with 5 short setae, inferodistal margin with 3 setae. Carpus inferodistal margin slightly produced, process rounded. Propodus length 1.1 distal (maximum) width, 1.9 proximal width, 2.4 ischium length; inferior margin length 0.5 propodus length, setae restricted to distal threequarters of margin; palm width 1.0 inferior margin length, with 6 teeth, articulation with 4 long setae. 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 parallel; posterolateral margins concave; apex slightly notched, asymmetric.

Remarks. Male Onychatrium torosus sp. nov. can be identified by the large pereonite 1 (1.6 pereonite 2 length) and the characters of pereopod 1: elongate meral process, carpal process a small blunt lobe, propodus inferior margin with no clear margin proximal to the propodal process, and a relatively short and stout propodal process. Pereopod 1 dactylus is relatively shorter than in the other congeneric species. Onychatrium thomasi differs in having a very short meral process, a robust, broad-based meral process and long curved propodal process.

Distribution. Lizard Island and adjacent reefs, northern Great Barrier Reef; generally shallow from depths of 0.5 to 7 m.

Etymology. The epithet is the Latin word torosus (brawny, muscular), referring to the large pereonite 1 and pereopod 1; noun in apposition.

Figures

FIGURE 6. Onychatrium torosus sp. nov. A – C, male paratype (MTQ W 14076), A, antennula, B, antenna, C, enlargement of antennal flagellum articles 24 – 34; D, male holotype (MTQ W 34194) dorsal view of cephalon; E, F, male paratype (MTQ W 14076), E, uropod, F, enlargement of setae on disto-lateral border of endopod; G, male holotype (MTQ W 34194) dorsal view.

FIGURE 7. Onychatrium torosus sp. nov. A, B, male holotype (MTQ W 34202), A, pereopod 1, B, enlargement of pereopod 1 dactylus; C, D, male paratype (MTQ W 14076), C, pereopod 7, D, pereopod 2; E – G, female paratype (MTQ W 34205), E, pereopod 1, F, enlargement of pereopod 1 dactylus, G, pereopod 7.

FIGURE 8. Onychatrium torosus sp. nov. A – E, male paratype (MTQ W 14076), A, pleopod 1, B, pleopod 2, with enlargement of appendix masculina apex, C, pleopod 3, D, pleopod 4, E, pleopod 5; F, female paratype (MTQ W 34205) pleopod 2; G, H, male paratype (MTQ W 14076), G, left maxilliped, with enlargement of endite, H, right maxilliped endite setae.

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).