Onychatrium forceps, 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 : 491-498

Onychatrium forceps sp. nov.

( Figures 2–5 , 10 )

Material examined. Holotype: ♂ (3.8 mm), Broomfield Reef, back reef, 23.2623°S, 151.9256°E, 18 November 2010, reef flat, coral rubble on sand, 7 m, coll. M. Błażewicz-Paszkowycz (MTQ W34194).

Paratypes: ♂ (4.0 mm [dissected]), ♀ (ovig., 3.5 mm), same data as holotype (MTQ W33826). ♂ (4.1 mm), ♀ (ovig., 4.0 mm [P1 dissected]), Mast Head Reef, 23.53188°S, 151.71889°E, 19 November 2010, coll. M. Capa (MTQ W33835). ♂ (3.7 mm [pleopod 2 dissected]), northern Wistari Reef, reef flat, 23.45053°S, 151.8843°E, 21 November 2010, 17.1 m, coll. V. Ivanenko (MTQ W34195). 3 ♂ (3.9, 2.9 [P1 dissected], 3.0 mm), 6 ♀ (ovig., 4.2, 3.5, 3.0 mm, non-ovig., 4.1, 3.0, 2.2 mm), 10 juv. (1.0– 2.4 mm), northern Wistari Reef, 23°27.257’S, 151°52.840’1E, 23 November 2009, rubble on bommie, 3 m, coll. N. Bruce & K. Schnabel (MTQ 31601). ♂ (3.8 mm), Heron Island reef flat, 23.46053°S, 151.9293°E, 13 November 2010, “Harry’s Bommie”, dead coral on sandy bottom, 10 m, coll. C. Buxton (MTQ W33643). ♂ (3.3 mm), Broomfield Reef, back reef, 23.2623°S, 151.9256°E, 18 November 2010, coral rubble in bommie crevasse, 6.5 m, coll. C. Buxton (MTQ W33822). 2 ♂ (3.9, 2.9 [P1 dissected] mm), ♀ (ovig., 3.8 mm [P1, P2, P7 dissected]), 3 juv. (1.4–2.0 mm), northern Wistari Reef, reef flat, 23.45053°S, 151.8843°E, 21 November 2010, on hydrozoan, 16 m, coll. C. Buxton (MTQ W34196). ♂ (3.6 mm), southern Heron Island, 23.47437°S, 151.95047°E, 21 November 2009, Autonomous Reef Monitoring Structure ( ARMS), coarse rubble, 10–16 m, coll. S. Smith (MTQ W31671). 2 ♀(ovig., 3.9 mm, non-ovig. 2.7 mm), Heron Island lagoon, reef flat, 23.46671°S, 151.98102°E, 22 November 2010, coral rubble, 1–2 m, coll. C. Buxton (MTQ W34197). 4 ♀(ovig., 3.3, 3.3 mm, non-ovig., 2.2, 1.8 mm), Heron Island, 23.46053°S, 151.9293°E, 13 November 2010, “Harry’s Bommie”, coarse sand, 10 m, coll. C. Buxton (MTQ W33641). 3 ♂ (3.8, 3.5, 3.3 mm), 6 ♀(ovig. 4.0, 3.5 mm, non-ovig. 3.5, 3.1, 3.1, 2.8 mm), juv. (1.9 mm), Mast Head Reef, 23.53192°S, 151.7152°E, 19 November 2010, rubble on sand, 10 m, coll. C. Buxton (MTQ W33840). ♂ (3.1 mm [pleopod 2 dissected]), ♀ (3.1 mm), Sykes Reef, front reef slope, 23.4316°S, 152.0493°E, 14 November 2010, sand at base of wall, 27 m, coll. J. Reimer (MTQ W33684). ♂ (3.6 mm), Sykes Reef fore-reef, 23.43238°S, 152.03375°E, 14 November 2009, live coral, 30 m, coll. K. Schnabel (MTQ W31581). 2 ♂ (4.0 [pleopods 1, 2 dissected], 3.7 mm), Heron Island fore-reef, 23.47222°S, 151.95047°E, 13 November 2009, “Twin Peaks, Pinnacles”, coarse coral rubble, 12 m, coll. K. Schnabel (MTQ W31579). 2 ♂ (2.7, 1.4 [P1 dissected] mm), north Heron Island, reef edge, 23.43309°S, 151.92705°E, 20 November 2010, “Tenements 1”, coral rubble with Halimeda , 5 m, coll. C. Buxton (MTQ W34198). ♂ (4.2 mm [P1 and pleopod 2 dissected), ♀ (3.6 mm [pleopods and uropod dissected]), Heron Island, north-eastern side, 23.42996°S, 151.95050°E, 20 November 2009, dead coral heads, 4–5 m, coll. N. Bruce & K. Schnabel (MTQ W34199). 2 ♂ (3.6, 3.3 mm), ♀ (3.5 mm), Heron-Wistari channel, 23°27.248’S, 151°55.005’E, 25 November 2009, small rubble, 29–30 m, coll. K. Schnabel & S. Smith (MTQ W34200). ♂ (4.3 mm [pleopods dissected]), 4 ♀ (ovig. 4.3 mm, non-ovig. 3.7, 2.8, 2.2 mm), Heron Island, north eastern side, 23°25.990’S, 151°55.601’E, 22 November 2009, dead Acropora , 12 m, coll. N. Bruce & K. Schnabel (MTQ W31597). ♂ (3.8 mm), ♀ (ovig., 3.6 mm), juv. (2.5 mm), Lamont Reef, southern side, 23°36.125’S, 152°03.152’E, 19 November 2009, coral rubble, 10.5 m, coll. K. Schnabel & N. Bruce (MTQ W31589). 3 ♂ (3.6, 3.5, 3.4 mm), Heron Island, 23.44736°S, 151.91197°E, 26 November 2010, “Canyons”, rubble with sand, 15 m, coll. M. Błażewicz- Paszkowycz (MTQ W34201).

Lizard Island and surrounds: 3 ♂ (3.7 [P1 dissected], 3.3, 3.0 mm), 3 ♀(ovig., 2.9, non-ovig., 3.7, 3.0), Day Reef, outer reef, 14.47045°S, 145.5284°E, 5 September 2010, dead coral heads, 17 m, coll. C. Buxton (MTQ W32851). ♂ (3.9 mm), Lizard Island, Bommie Bay, reef flat, 14.66157°S, 145.4716°E, 8 September 2010, dead coral heads, 10 m, coll. C. Buxton (MTQ W32558). 3 ♂ (4.1, 3.8, 3.2 mm), ♀ (ovig., 3.7 mm), Yonge Reef, northwest side, reef slope, 14.57735°S, 145.6105°E, 10 September 2010, coarse coral rubble, 10 m, coll. C. Buxton (MTQ W32988). ♂ (3.7 mm), Yonge Reef, outer fore-reef, 14.61575°S, 145.6196°E, 7 April 2008, bommie crest, Halimeda and rubble, 3 m, coll. M. Błażewicz-Paszkowycz (MTQ W14086). ♂ (2.8 mm), Yonge Reef, back reef, 14.58028°S, 145.60840°E, 21 April 2008, 9 m, coll. K. Mills (MTQ W34202). 10 juv. (2.1, 2.0, 1.5, 1.5, 1.5, 1.5, 1.4, 1.4, 1.3, 1.0 mm), Lizard Island, North Point, reef crest, 14.64553°S, 145.45335°E, 11 April 2008, compact dead Acropora , 0.5 m, coll. N. Bruce (MTQ W14070). 2 ♂ (2.6, 1.8 mm), Lizard Island, April 2008, 4– 8 m (MTQ W14077). ♂ (4.0 mm), Yonge Reef, outer reef slope, 14.57735°S, 145.6105°E, 10 September 2010, coarse coral rubble, 25 m, coll. C. Buxton (MTQ W34203). ♂ (2.6 mm), ♀ (ovig., 3.2, 2.9 mm, non-ovig., 3.0 mm), same data as previous (MTQ W33013).

Other material. Broomfield Reef and surrounds: Broomfield Reef, reef flat, 17–18 November 2010 (MTQ W33779, MTQ W33780, MTQ W33799, MTQ W33827, MTQ W33830). Wistari Reef, outer fore-reef, 11 November 2009 (MTQ W31578). Heron Island, outer fore-reef, 13 November 2009 (MTQ W31580). Sykes Reef, outer fore-reef, 14–18 November 2009 (MTQ W31582, MTQ W31588). Sykes Reef, back reef, 14 November 2009 (MTQ W31583). Lamont Reef, back reef, 16 November 2009 (MTQ W31584). Lamont Reef, southern side, 19 November 2009 (MTQ W31590, MTQ W31592, MTQ W34219). Heron Island, Harry’s Canyon, 18 November 2009 (MTQ W31585, MTQ W31586, W31587). Heron Island reef, north-eastern side, 20–22 November 2009 (MTQ W31594, MTQ W31596, MTQ W31598, MTQ W31599). Wistari Reef, northern side, 23 November 2009 (MTQ W31600). Heron Island –Wistari Reef channel, 25 November 2009 (MTQ W31602, MTQ W31603). Heron Island, The Patches (Mystery Bommie), 28 November 2009 (MTQ W31605). Heron Island reef, southern side (Twin Peaks), 28 November 2009 (MTQ W31607). Heron Island reef, Autonomous Reef Monitoring Structure ( ARMS) #9, 28 November 2009 (MTQ W31608 ). Heron Island outer fore-reef, ARMS #41, 12 November 2009 (MTQ W31609). Lamont Reef, south-east, reef wall, 16 November 2010 (MTQ W33755). Mast Head Reef, reef flat, 19 November 2010 (MTQ W33849). Heron Island, northern reef edge, Tenement 1, 20 November 2010 (MTQ W34223). Wistari Reef, edge, Heron Island –Wistari Reef channel, 30 November 1979 (MTQ W34224).

Lizard Island and surrounds: Patch reef near Seabird Islet, 8–11 April 2008 (MTQ W14071, MTQ W14072). Lagoon patch reef off Casuarina Beach , 17 April 2008 (MTQ W14078). Day Reef, outer reef, 5 September 2010 (MTQ W32827, MTQ W32828, MTQ W32839). Yonge Reef, reef flat, 10 September 2010 (MTQ W32997). Lizard Island, Big Vicky Reef, lagoon patch reef, 13 April 2008 (MTQ W34220). Lizard Island, North Point, reef crest, 12 April 2008 (MTQ W34221). Lizard Island, 14 April 2008 (MTQ W34222). Hicks Reef, outer reef front, 21 February 2009 (MTQ W34225). Day Reef, outer reef slope, 13 February 2009 (MTQ W34226).

Description. Body length 2.9 maximum width. Cephalon length 0.5 width, 1.4 pereonite 1 length; lateral margins convex, sparsely setose; lateral spines equal in length to antennal spines; space between lateral and antennal spines evenly rounded; lateral margins convex. Eyes with 20 ommatidia, pale brown. Pereonite 1 length 0.4 width, 1.2 pereonite 2 length, width 1.1 cephalon width. Pleotelson length 0.9 width.

Antennula length 1.6 cephalon length; article 1 length 1.4 width, mesial margin with 7 short penicillate setae, distolateral margin with 1 large penicillate seta, lateral margin with 1 long seta; article 2 length 1.7 width, distomesial margin with 1 cluster of setae, including 1 penicillate seta, distolateral margin with 1 cluster of setae, including 1 penicillate seta, proximolateral margin with 1 penicillate seta, centre of inferior side with 1 cluster of setae, including 1 penicillate seta; article 3 length 1.9 width, distomesial margin with 1 cluster of setae, distolateral margin with 1 cluster of setae, mesial margin with 1 seta, inferodistal margin with 1 cluster of setae; article 4 length 0.4 width, inferior distal margin with 2 penicillate setae; flagellum with 9 articles, flagellar article 1 length 2.5 article 2 length, 1 aesthetasc per article on distal 7 articles.

Antenna length approximately 1.1 body length; peduncle article 1 length 0.6 width, distolateral margin with 1 cluster of setae; article 2 length 0.8 width, distolateral margin with 1 long seta; article 3 length 1.2 width, distomesial margin with 1 cluster of setae, mesial margin with 1 cluster of setae, lateral margin with 3 setae surrounding squama; article 4 length 0.7 width, distomesial margin with 2 setae; article 5 length 5.0 width, article 6 length 6.0 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 3.3 width, with row of 8 short serrate setae; article 3 length 2.6 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, 2 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 7 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 3.2 width, width 1.1 basis width, distomesial margin with 4 regularly-spaced setae, lateral margin sinuate.

Pereopod 1 basis length 3.2 width; superior margin with regularly-spaced short setae, 2 long proximally; submarginal row of short setae.

Pereopod 1 ischium length 1.3 width; inferior margin with 1 short seta, inferodistal margin without setae, distal margin without short setae, mesial distal margin with submarginal row of 4 long setae, 1 short seta; superodistal margin not produced, with 4 long setae.

Pereopod 1 merus sub-quadrate; length 0.8 width, 1.1 carpus length, 0.8 ischium length; inferior margin without setae; inferior submargin with a row of 4 long setulate setae; distal margin without setae; superodistal margin not produced; densely setose with 6 long setae; inferodistal meral process short, not extending distally to carpal blade, length 0.5 merus inferior margin length, 0.3 merus length, oblong, apex rounded, mesial surface setose, with long setulate setae and shorter simple setae.

Pereopod 1 carpus sub-triangular; length 1.1 width, 0.7 ischium length; distal margin with 5 short setae; inferior margin clearly defined, length 0.25 carpus length. Carpal process length 2.0 width, 1.6 carpal width; long, curved and tapering, extending distally more than half length of propodus; apex densely setose, rounded; inferior margin slightly convex, densely setose, along full length, 1 row of straight setae, 1–2 rows of long setae angled distally; superior margin concave, setose along full length.

Pereopod 1 propodus robust superiorly with pronounced narrowing obliquely, proximal to the palm; length 1.6 maximum width, 2.6 proximal width, 1.6 ischium length; inferior margin clearly defined, long, length 0.5 propodus length, 0.5 superior margin length, with submarginal row of long setulate setae; superior margin with 2 long setae, a submarginal mesial row of long setulate setae, a submarginal lateral row of long setae. Propodal palm width 0.4 maximum propodus width; slightly oblique; toothed lobe with 5 teeth. Palm process length 3.4 width, RS at apex; inferior margin weakly convex, densely setose, at apex and distal quarter only; superior margin straight to weakly concave. Dactylus curved; length 6.6 basal width, 4.2 propodal palm width, 1.3 propodus length; superior margin distal third setose, with regularly - spaced setae; inferior margin with 16 regularly-spaced robust flagellated setae; mesial surface densely setose on distal half.

Pereopod 2 basis superior margin with 3 penicillate setae; ischium superior margin with 1 large seta; merus superodistal margin with 1 RS, 1 large seta; carpus superodistal margin with 4 setae (including 1 penicillate seta), inferior margin with 5 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 2–3 penicillate setae; carpus inferior margin with 4 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 0.5 width; lateral margin with 2 simple setae; distal margin with pair of acute RS; surface setae absent; rami lateral margins with regularly-spaced simple setae along distal half (becoming closer together distally); inferior surface with few setae. Pleopod 2 protopod length 3.1 medial width; basal lobe width 1.7 medial width; distal lobe sub-triangular; lateral margin with 2 setae; endopod without setae, medial length 0.5 protopod length. Appendix masculina length 1.8 endopod medial length, 0.9 protopod length; with lateral, proximally-directed robust spine; lateral margin with distal groove. Pleopod 3 endopod apex with 6 plumose setae. Pleopod 4 exopod apex with 8 plumose setae. Pleopod 5 apex with 7 plumose setae.

Uropod length 0.2 body length, 0.7 pleotelson length; protopod length 2.3 width; endopod length 1.1 protopod length, distal and sub-distal margins with 10 penicillate setae, distal tip with cluster of elongate setae, maximum length 1.9 endopod length; exopod length 0.8 protopod length, 0.7 endopod length, distal tip with cluster of elongate setae, maximum length 2.1 exopod length.

Female. Female pereopod 1 basis length 2.5 width, superior margin with 2 short setae, submarginal ridge with irregularly-spaced short setae. Ischium superodistal margin strongly produced, apex with large, long seta. Merus superodistal margin produced, triangular, apex blunt. Carpus inferodistal margin produced, process bluntly triangular, apex rounded. Propodus length 1.1 distal (maximum) width, 2.5 proximal width, length 2.9 ischium length; distal width 2.4 proximal width; inferior margin length 0.6 propodus length, densely setose, with a row of setulate setae and a row of simple setae, setae restricted to distal half of margin. Propodal palm width 0.6 distal propodus width, 1.1 inferior margin length; straight, slightly oblique, with 8 teeth, setose, without a cluster of setae at articulation; terminal end with single robust flagellated seta, and single robust serrate seta adjacent to first tooth. Dactylus length 7.2 width, 1.6 palm width; inferior margin with 14 regularly-spaced robust flagellated setae.

Female pleopod 2 length 1.3 width; lateral margins with 3 setae; distal margins slightly concave; apex acute, with 2 setae; inferior surface with 3 setae.

Remarks. Onychatrium forceps sp. nov. may be identified by the adult male pereopod 1 having a long acute carpal process, a short, blunt meral process, and the propodus with a long free inferior margin proximal to the propodal process. The most similar species is O. entale , and the differences between the two species are discussed under the remarks for O. entale . The principal pereopodal differences are: O. forceps has a short and blunt meral lobe and a basally narrow carpal lobe while O. entale has a long and acute meral lobe and a basally broad carpal lobe.

On the Great Barrier Reef the sympatric Onychatrium torosus sp. nov. can be distinguished from O. forceps by several characters of the male pereopod 1, including a more elongate merus with a large process, a small blunt carpal process and a relatively short pereopod 1 dactylus. In adult male O. forceps pereonite 1 is slightly longer than pereonite 2 (as for many stenetriids), but in O. torosus pereonite 1 appears massive, being 1.6 as long as pereonite 2.

Distribution. Great Barrier Reef, from Capricorn Group in the south and Lizard Island and adjacent reefs in the north; intertidal to 30 m.

Etymology. The epithet is the Latin word forceps , alluding to the forcep-like opposition of the elongate dactylus to the propodal process.

Figures

FIGURE 2. Onychatrium forceps sp. nov. A, B, male holotype (MTQ W 34194), A, dorsal view, B, dorsal view of cephalon; C – G, male paratype (MTQ W 33826), C, antennula, D, antenna, E, enlargement of antennal flagellum articles 23 – 29, F, uropod, G, cluster of penicillate setae on distolateral border of endopod (marked by asterisk).

FIGURE 3. Onychatrium forceps sp. nov. male paratype (MTQ W 33826), A, left mandible with palp; B, right mandible; C, maxillula, with details of mesial and lateral lobes; D, left maxilla, with enlargements of setal types; E, right maxilliped, with enlargement of endite; F, left maxilliped endite setae.

FIGURE 4. Onychatrium forceps sp. nov. A, B, male holotype (MTQ W 34194), A, pereopod 1, B, enlargement of pereopod 1 dactylus; C, D, male paratype (MTQ W 33826), C, pereopod 2, D, pereopod 7; E – H, female paratype (MTQ W 34196), E, pereopod 1, F, enlargement of pereopod 1 dactylus, G, pereopod 2 carpus and dactylus, H, pereopod 7 merus, carpus and dactylus.

FIGURE 5. Onychatrium forceps sp. nov. A, male paratype (MTQ W 33826) pleopod 1; B – C, male paratype (MTQ W 31579), B, pleopod 2, C, enlargement of appendix masculina apex; D – F, male paratype (MTQ W 33826), D, pleopod 3, E, pleopod 4, F, pleopod 5; G, female paratype (MTQ W 34199) pleopod 2; H, male paratype (MTQ W 33826) pleotelson.

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).