Gnathostenetroides altapetra sp. nov.

(Figs 23–29)

Material examined. Holotype: ♂ (1.9 mm), Lizard Island region, High Rock, 14.82553°S, 145.5517°E, 6 September 2010, fine coral rubble, 6 m, CReefs stn LI10-091D, coll. C. Buxton (MTQ W32896).

Paratypes: 1 ♂ (1.6 mm), 3 ♀ (1.6, 1.8, 1.9 mm), same sample as holotype (MTQ W34960).

Etymology. The epithet alludes to the type locality, formed by combining and adapting the Latin altus (high) with petra (rock or rock ledge).

Description. Terminal male. Body (Fig. 23, 24C) length 5.50 width, body height 0.10 of body length. Cephalon length 0.85 width, lateral margin with 4 setae; rostrum 0.30 cephalon length, 0.40 cephalon width. Pereonite 1 almost as long as cephalon, pereonite 4 length 0.40 pereonite 1 length; anterolateral projections slightly protruded, distal stout UB seta as long as projection. Posterior body part length 0.45 body length; pereonite 5 subequal in length to pereonite 4, pereonite 7 length 1.35 pereonite 5 length. Lateral margins of all pereonites with 3 long and few short setae. Pleotelson length 1.15 width, 0.20 body length; lateral margins to posterolateral indentation almost parallel, posterior margin between indentations subtriangular, moderate projected, length 0.30 pleotelson length; lateral margin with 6 long and few small setae, scattered small submarginal setae dorsally and ventrally; posterolateral margin with 6 – 7 long sublateral setae ventrally directed posteriorly and 3 long dorsolateral setae directed laterally, 6 setae posteriorly. Pleopodal chamber length 0.60 pleotelson length, pleopods 1 length 0.75 width.

Antennula (Fig. 25A) length 0.20 body length; article 1 length 1.70 width, 1.40 as long as rostrum, with 1 broom and 3 simple setae distolaterally, distomedially with 2 simple setae; length ratios of articles 2 – 5 to article 1: 0.70, 0.50, 0.50, 0.30; article 2 length 1.60 width, distomedially with 1 broom, 2 spine-like and 1 simple setae, laterally with 3 simple and 1 distolateral broom setae; article 3 with 4 simple setae distally; article 4 with 2 long distomedial setae and 2 simple medial setae; article 5 with tuft of 4 short, 1 long simple setae and 1 broom distal seta and 2 aesthetascs.

Left antenna (Fig. 25B) length 0.60 body length, peduncle articles 1 – 4 not reaching tip of antennula article 3. Article 3 scale longer than article 4, with 3 distoventral setae. Article 5 length 0.90 articles 1 – 4 total length; article 6 length 1.4 article 5 length, with scattered long setae, length of articles 5 and 6 together 0.55 body length. Flagellum of 20 articles, first article about 3 times longer than following ones, each article with few small distal setae. Right antenna (Fig. 23C) length 0.70 left antenna length, peduncle articles 1 – 4 length 0.85 articles 1 – 4 of antenna left length. Article 5 length 0.70 article 5 of antenna left length; article 6 length 0.65 article 6 of antenna left length. Flagellum of 14 articles.

Mandible (Fig. 26A, B) pars incisiva with 5 cusps; lacinia mobilis of left mandible broadening distally, not reaching tip of pars incisiva, with 5 teeth; spine row with 11 spines on right mandible; molar process subcylindrical, distally serrated, with 1 seta, length 0.60 pars incisive length; palp length 0.85 mandibular body length, article 1 with 2 long distolateral setae, article 2 length 2.10 article 1 length, with 5 short setae and 2 long distally serrated setae on distolateral half; article 3 length 0.70 article 2 length, with rows of short cleaning setae on distal half and one long and one shorter distal setae. Maxilla 1 (Fig. 26C) lateral endite width 1.80 mesial endite width, distally with 11 denticulate setae, setae length 0.70 endite width. Maxilla 2 (Fig. 26D) lateral endite longest, lateral and middle endites with 3 long and 1 shorter distal setae each; mesial endite shortest, distally with numerous setae and few comb-like setae. Maxilliped (Fig. 26E) basis length 4.50 width, endite length 2 width, with 3 coupling hooks, distal margin slightly concave, with 4 broad fan-like setae and numerous simple slender setae; palp 0.65 as long and 0.70 as wide as basis and inserted after 0.55 basis length, articles 1 with distolateral acute projection 0.25 of lateral length ending with long whip seta; article 2 length 0.40 width, distomedial acute projection subequal to this of article 1, medial margin with 3 whip setae. Articles 3 length 0.90 article 2, with 5 long medial setae and 1 distolateral seta; article 4 with 5 long distal setae; article 5 slender, with 4 long distal setae. Epipod length 4.20 width and 0.90 basis length.

Male pereopod 1 stout, about twice longer than following pereopods. Length ratios of pereopods 2–7 to pereopod 1: 0.85, 0.75, 0.70, 0.75, 0.85, 0.80.

Pereopod 1 (Fig. 27A, B) length 0.55 body length, length ratios of ischium–dactylus to basis: 0.50, 0.30, 0.33, 0.90, 0.35; basis length 3.40 width, with distodorsal rounded lobe on outer side; ischium length 0.90 width, with 2 dorsal setae; merus length 0.50width, distodorsal projection with 6 marginal setae, ventral margin with 2 strong and 2 small setae; carpus as long as wide, with 11 ventral long setae; propodal palm subrectangular, length 2.45 width, ventral margin length 0.70 dorsal margin length, with dense row of about 20 long strong setae, distoventral spinelike UB seta length 0.40 anterior margin width, anterior margin with 4 teeth, 5 whip setae, 3–4 slender setulated setae, length Ẽ 0.60 spine-like seta length; dactylus length with claw 6.0 width, ventral (inner) margin with 5 spinelike short setae, claw length 0.20 dactylus length, 1 short and 1 long whip setae ventrally to claw, 3–5 setae proximally to claw.

Pereopod 2 (Fig. 27C) length 0.55 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.75, 0.60, 0.75, 0.65, 0.25; basis length 1.9 width, dorsal margin with 2 small setae and 2 small setae distoventrally, ischium length 2.40 width, with 1 strong dorsal seta; merus length 1.70 width, with 1 distoventral simple seta, 1 strong distodorsal seta and 3 small setae; carpus length 4.60 width, with 3 ventral setae; propodus length 5 width, with 5 stout small ventral UB setae, 3 simple setae dorsally; dactylus claws length 0.3 total length, 3 setae midlength, 1 seta between claws.

Pleopod 1 (Figs 23C, 29A) length 1.25 pleopod chamber length; pleopod length 2.65 width, distal margins rounded, with 9–10 setae. Pleopod 2 (Fig. 29B) protopod length 1.40 width, 0.50 pleopod 1 length, without setae, endopod article 1 length 0.55 protopod length, article 2 length 0.90 protopod length, exopod length 1.35 width, 0.35 protopod length. Pleopod 3 (Fig. 29C) protopod as long as wide, endopod length 1.40 width, distal plumose setae 0.60 endopod length; exopod length 5.20 width, 1.80 endopod length and 0.5 endopod width, article 1 with 7 slender setae laterally, distal article length 0.35 basal article length, with 2 distal setae. Pleopod 4 (Fig. 29D) endopod length 2.10 width, exopod length 0.65 endopod length, width 0.30 endopod width, two simple fine setae laterally. Pleopod 5 (Fig. 29D) length 2.50 width.

Uropod (Fig. 23C) 0.60 pleotelson length. Protopod length 1.30 width, lateral margin with 2 distal setae, medial margin slightly convex with 2–3 setae; 2 setae distoventrally; endopod length 5.20 width and 2 protopod length, with 3 medial, 3 lateral setae and 6 simple long setae distally; exopod length 3.75 width, 0.55 endopod length, with 2 medial, 1 lateral and 4 long distal setae.

Adult female. Pereopod 1 (Fig. 28A) length 0.45 body length, about 1.20 pereopod 2 length; length ratios of ischium–dactylus to basis: 0.50, 0.35, 0.35, 1.0, 0.50; basis length 3.10 width, with distodorsal rounded lobe on outer side; ischium length 1.90 width, with 1 dorsal and 2 ventral setae; merus as long as wide, distodorsal projection with 2 setae, distoventral margin with 3 strong setae; carpus as long as wide, with 5 ventral long setae; propodal palm length 2.30 width, ventral margin length 0.70 dorsal margin length, with dense row of 15–16 long strong setae, distoventral spine-like UB setulated seta length 0.55 anterior margin width, anterior margin with 3 low teeth, 9 whip setae; dactylus length with claw 3.75 width, ventral (inner) margin distal third with 4 spine-like short setae, claw length 0.20 dactylus length, 1 long whip seta ventrally to claw, 3 setae proximally to claw.

Pereopods 2–7 similar in proportions, shape and setation of articles, but slightly shorter. Pereopod 2 (Fig. 28B) length 0.85 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.65, 0.40, 0.70, 0. 70, 0.35. Basis length 2.50 width, ventral margin with 1 small seta, 2 small setae dorsally, ischium length 1.75 width, with 1 strong dorsal seta and 1 distoventral seta; merus length 1.70 width, with 1 distoventral simple seta, 1 strong distodorsal seta and 1 distoventral long seta; carpus length 4 width, with 2 ventral setae; propodus length 4 width, with 4 small ventral US setae, 1 simple dorsal seta and 1 simple and 1 broom setae distodorsally; dactylus claws length 0.25 total length, 2 setae midlength, 1 seta between claws.

Pereopod 3 (Fig. 28C) length ratios of ischium–dactylus to basis: 0.60, 0.45, 0.70, 0.70, 0.35. Pereopod 4 (Fig. 28D) shortest, 0.85 of pereopod 1 length, length ratios of ischium–propodus to basis: 0.70, 0.50, 0.70, 0.80; 0.35. Pereopod 5 (Fig. 28E) as long as pereopod 3, length ratios of ischium–dactylus to basis: 0.65, 0.45, 0.65, 0.80, 0.35. Pereopod 6 (Fig. 28F) as long as pereopod 2, length ratios of ischium–dactylus to basis: 0.70, 0.45, 0.70, 0.70, 0.35. Pereopod 7 (Fig. 28G) slightly shorter than pereopod 6; length ratios of ischium–dactylus to basis: 0.70, 0.45, 0.70, 0.65, 0.35.

Pleopods (Fig. 29E, F): pleopod 2 length 1.25 width, slit length 0.13 pleopod midlength, distal margins fringed with 7–8 long setae each half. Pleopod 3 (Fig. 29F) protopod length 1.45 width, endopod length 1.8 width, distal margin exopod length 4.60 width, 1.80 endopod length and 0.70 endopod width, laterally with 5 thin setae, distal article length 0.35 basal article length. Pleopod 4 (Fig. 29F) endopod length 2.80 width, exopod length 0.60 endopod length, width 0.60 endopod width with 1 small distal seta.

Uropod (Fig. 29E) similar to this of male.

Remarks. The head of the species is relatively short (L/W 0.85) with a relatively long rostrum in comparison to the other three Great Barrier Reef species (0.3 cephalon length, 0.15–0.20 in the other new species); pereonite 1 is relatively long and the pleotelson is relatively small (short and narrow, L/W 1.15, 0.20 body length); the anterolateral projections of the pereonites are short and the antennule is more stout than in the other new species. The pereopod 1 basis in both sexes has a distodorsal rounded projection, (similar to that of G. indica and G. laodicense). The merus has a distodorsal lobe and the palm has denticles on the anterior margin.

Distribution. Known only from the type locality, norther Great Barrier Reef, Lizard Island region at High Rock; at a depth of 6 metres.