Gnathostenetroides solitaria, Malyutina & L.Bruce, 2019

Malyutina, Marina V. & L. Bruce, Niel, 2019, The first record of Gnathostenetroididea Kussakin, 1967 from Australian waters with description of four new species of Gnathostenetroides Amar, 1957 (Crustacea: Isopoda: Asellota) from the Great Barrier Reef, Zootaxa 4554 (2), pp. 301-350 : 327-333

Gnathostenetroides solitaria sp. nov.

( Figs 18–22 )

Material examined. Holotype: ♂ (1.42 mm), northern Great Barrier Reef , Yonge Reef, 14.60694°S, 145.62310°E, 20 April 2008, back reef, dead coral heads, 13 m, CReefs stn CGLI-047A, coll. M. Błażewicz-Paszkowycz (MTQ W31945).

Etymology. The epithet is the Latin word for solitary or alone, in reference to the single specimen of this species.

Description. Terminal male. Body ( Fig. 18 ) length 4.30 width, body height 0.10 of body length. Cephalon almost as long as wide, anterolateral margin of head with 4 setae, rostrum 0.15 cephalon length, 0.40 cephalon width. Eyes of 5 ommatidia located tightly to each other. Pereonite 4 length 0.60 pereonite 1 length; anterolateral projections acute, narrow, distinctly protruded, distal stout UB seta long, lateral margin of pereonites 1–3 with 4–5 setae, pereonite 4 with 2 setae laterally. Posterior body part length 0.40 body length; pereonite 7 length 1.65 pereonite 5 length, lateral margin of pereonites 5 – 7 with 3 – 4 setae. Pleotelson as long as wide, 0.20 body length; lateral margins to posterolateral indentation slightly tapering, with 3 long (1 anterior, 1 middle and 1 in front of denticle), 8 shorter setae and row of 14 small sublateral setae ventrally; posterion margin between indentations subtriangular, moderate projected, length 0.35 pleotelson length; posterolateral margin with 2 long setae directed laterally and 9 long sublateral setae ventrally directed posteriorly, 2 setae on posterior margin.

Antennula ( Fig. 19A ) length 0.35 body length; article 1 length 3 width, 2.50 as long as rostrum, 1 simple and 2 broom setae distolaterally, distomedially with 2 simple setae and 1 long broom seta; length ratios of articles 2–5 to article 1: 0.70, 0.35, 1.10; article 2 length 2.70 width, distomedially with 1 long broom and 1 simple setae, distolaterally with 1 simple and 2 broom setae; article 3 with 3 simple setae distally; article 4 with 1 simple short distomedial seta, article 5 with tuft of 4 long simple distal setae and 3 aesthetascs.

Antenna ( Fig. 19B, C ): left antenna shorter than right antenna, longer antenna length 0.65 body length, peduncle articles 1 – 4 reaching tip of antennula article 2. Article 3 scale with 3 lateral setae; article 4 with 2 small distal setae. Article 5 length 1.35 articles 1 – 4 total length; article 6 length 1.25 article 5 length, articles 5 and 6 with scattered long setae, article 6 with 2 broom setae distally, length together 0.30 body length. Flagellum of 15 articles, first article about 3 times longer than following ones, each article with few small distal setae.

Mandible ( Fig. 20A, B ) pars incisiva with 5 cusps; lacinia mobilis of left mandible broadening distally, almost reaching tip of pars incisiva, with 5 teeth; spine row with 7 and 8 spines on left and right mandibles respectively; pars molaris with 2 setae, length 0.65 pars incisiva length; palp length 0.90 mandibular body length, article 1 with 2 long distal setae, article 2 length 2 times article 1 length, with 3 short setae and 2 long distally serrated setae on distolateral half; article 3 with rows of cleaning setae gradually elongating from short proximal seta to long distal seta. Maxilla 1 ( Fig. 20C ) lateral endite width 2 mesial endite width, distally with 11 denticulate setae, setae length 0.70 endite width. Maxilla 2 ( Fig. 20D ) lateral and middle endite subequal in length, with 4 long distal setae each; mesial endite shortest, as wide as middle and lateral endites together, with numerous distal setae and distomedially few comb-like setae. Maxilliped ( Fig. 20E ) basis length 4.40 width, endite length 1.50 width, with 3 coupling hooks, distal margin slightly concave, with 5 broad fan-like setae and numerous simple slender setae; palp 0.50 as long and 0.70 as wide as basis and inserted after 0.5 basis length, article 2 as long as wide, medial margin length 1.25 lateral margin length, medial margin with 4 whip setae; articles 3 – 5 subequal in length as long as article 2 laterally, article 3 medial margin length 0.80 medial length of article 2, with 6 long setae; article 4 with 5 long distal setae; article 5 slender, with 4 long distal setae. Epipod length 4 width and 0.80 basis length.

Pereopod 1 ( Fig. 21A ) length 0.45 body length, length ratios of ischium–dactylus to basis: 0.50, 0.45, 0.30, 1.15, 0.75; basis length 3.60 width; ischium length 1.75 width, with 1 distoventral and 2 dorsal setae; merus length 1.20 width, ventral margin with 4 setae; carpus length 1.35 width, with 13 ventral long setae; propodal palm subtriangular, length 2.10 width, ventral margin length 0.70 dorsal margin length, with 4 long strong UB setae, distoventral spine-like UB seta length 0.45 anterior margin length, anterior margin with 7 setulated setae; dactylus with claw length 5.85 width, ventral (inner) margin with 7 slender short setae, claw length 0.30 dactylus length, small serrated seta ventrally, 2 long slender setae in between, 3 whip setae proximally to claw.

Length ratios of pereopods 2–7 to pereopod 1: 0.60, 0.50, 0.50, 0.45, 0.55, 0.55 ( Fig. 21 ). Pereopod 2 ( Fig. 21B ) length ratios of ischium–dactylus to basis: 0.65, 0.40, 0.70, 0.70, 0.30; basis length 2.85 width, dorsal margin with 2 small setae, ischium length 2.40 width, with 1 strong dorsal seta; merus length 1.70 width, with 1 distoventral simple seta and 1 strong distodorsal seta; carpus length 3.90 width, with 2 ventral setae and 1 small distodorsal seta; propodus length 4.65 width, with 3 stout ventral whip setae; dactylus claws length 0.30 total length, 3 setae proximally claws, 1 seta between claws.

Pereopod 3 ( Fig. 21C ) length ratios of ischium–dactylus to basis: 0.65, 0.40, 0.65, 0.65, 0.30; basis length 2.80 width, dorsal margin with 2 small setae; ischium length 2.65 width, with 2 small and i strong dorsal setae, 2 ventral small setae; merus length 1.85 width, with 1 distoventral and 1 distodorsal small setae; carpus length 3.50 width, with 1 distodorsal and 2 ventral small setae; propodus length 3.50 width, with 4 ventral setae, and 2 distodorsal simple setae; dactylus length 2.20 width, claw length 0.50 dactylus length.

Pereopod 4 ( Fig. 21D ) equal in length to pereopod 3, length ratios of ischium–propodus to basis: 0.65, 0.45, 0.75, 0.85; 0.35; basis length 2.15 width, with 2 dorsal simple setae; ischium length 2.50 width, 1 dorsal and 1 ventral setae; merus length 1.45 width, with 1 distoventral seta; carpus length 3.15 width, with 2 ventral setae and 1 dorsal simple setae; propodus length 4.30 width, with 1 distodorsal and 4 ventral simple setae; dactylus length 2.20 width with 1 seta between claws.

Pereopod 5 ( Fig. 21E ) length ratios of ischium–dactylus to basis: 0.65, 0.35, 0.55, 0.65, 0.30; basis length 2.50 width, with 3 dorsal setae; ischium length 3.10 width, with 1 dorsal and 1 ventral setae; merus length 1.35 width, with 1 distodorsal and 1 distoventral setae; carpus length 3.0 width, with 2 ventral setae; propodus length 3.20 width with 2 long whip ventral setae and 1 distoventral UB and 2 distodorsal small setae; dactylus length 2.50 width, claw length 0.50 dactylus total length, ventral claw slightly broader than dorsal claw.

Pereopod 6 ( Fig. 21F ) length ratios of ischium–dactylus to basis: 0.65, 0.30, 0.55, 0.60, 0.25; basis length 2.50 width, with 2 dorsal setae; ischium length 3.25 width, with 1 dorsal seta; merus length 1.35 width with 2 distoventral and 1 distodorsal setae; carpus length 3.15 width, with 2 ventral and 1 distodorsal simple setae; propodus length 4.0 width, with 2 long whip ventral setae, one UB distoventral seta and 2 distodorsal small setae.

Pereopod 7 ( Fig. 21G ) length ratios of ischium–dactylus to basis: 0.70, 0.35, 0.60, 0.65, 0.25; basis length 3.1 width, with 2 dorsal and 1 ventral simple setae; ischium length 3.25 width, with 1 whip dorsal seta and 3 small ventral setae; merus length 1.35 width, with 1 distoventral and 1 distodorsal setae; carpus length 3.40 width, with 2 ventral and 1 distodorsal setae; propodus length 4.80 width, with 3 long whip ventral setae, 1 distoventral UB seta and 1 distodorsal small seta; dactylus length 2.60 width.

Pleopod 1 ( Fig. 22A ) length 1.30 pleopod chamber length; pleopod length 1.50 width, distal margins rounded, with 9–11 setae each. Pleopod 2 ( Fig. 22C ) protopod length 1.65 width, 0.35 pleopod 1 length, lateral margin without setae, endopod article 1 length 0.50 protopod length, article 2 length 0.70 protopod length, exopod length 1.35 width, 0.20 protopod length. Pleopod 3 ( Fig. 22D ) protopod length 0.90 width, endopod length 1.85 width, distal plumose setae 0.50 endopod length, position: 1 distomedial seta separated from 2 distolateral setae closely located to each other; exopod length 6.90 width, 1.60 endopod length and 0.45 endopod width, article 1 with 3 slender setae laterally, distal article separated, length 0.40 basal article length, with 2 distal setae. Pleopod 4 ( Fig. 22E ) endopod length 1.80 width, exopod length 0.65 endopod length, width 0.30 endopod width, 2 simple fine setae laterally. Pleopod 5 ( Fig. 22E ) length 2.05 width.

Uropod ( Fig. 22F ) 0.40 pleotelson length. Protopod length 1.55 width, lateral margin with 3 distal setae, medial margin slightly convex with 2–3 setae; 5 setae distally; endopod length 6 width and 1.90 protopod length, with 3 medial setae and 6 simple long and 2 broom setae distally; exopod length 6.0 width, 0.60 endopod length, with 5–6 long distal setae.

Female. Not known.

Remarks. The species differs from most species of Gnathostenetroides in having a relatively stout body (L/W 4.30), with only G. pugia being more stout (L/W 3.90); most species are slender L/W (4.60 – 5.50). The pleotelson is wider than the cephalon and uropods are relatively short, 0.40 pleotelson length (0.50–0.60 in other three described new species). The male pereopod 1 propodus broadens distally, with a convex anterior margin. The spine-like UB seta is situated more proximally from a distoventral corner.

Distribution. Known only from the type locality, Yonge Reef; at a depth of 13 metres.

Figures

FIGURE 18. Gnathostenetroides solitaria sp. nov. 3: male (1.42 mm), holotype MTQ W31945: A, dorsal view; B, ventral view; C, lateral view.

FIGURE 19. Gnathostenetroides solitaria sp. nov. 3: male (1.42 mm), holotype MTQ W31945: A, head and pereonite 1, dorsal view; B, right antenna; C, propodus and dactylus of pereopod 1.

FIGURE 20. Gnathostenetroides solitaria sp. nov. 3: male (1.42 mm), holotype MTQ W31945: A, left mandible; B, right mandible; C, maxilla 1; D, maxilla 2; E, maxilliped.

FIGURE 21. Gnathostenetroides solitaria sp. nov. 3: male (1.42 mm), holotype MTQ W31945: A–G, pereopods 1–7.

FIGURE 22. Gnathostenetroides solitaria sp. nov. 3: male (1.42 mm), holotype MTQ W31945: A, pleotelson, ventral view; B, penis; C, pleopod 2; D, pleopod 3; E, pleopods 4 and 5; F, uropod.