Gnathostenetroides blazewiczae, 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 : 307-319

Gnathostenetroides blazewiczae sp. nov.

( Figs 3–12 )

Material examined: All material Great Barrier Reef.

Holotype: Terminal ♂ (1.5 mm), Lizard Island region, Hicks Reef, 14.44803°S, 145.4992E, 21 February 2009, outer reef front, coral rubble under bommie overhang, 15 m, CReefs stn LIZ09-16B, coll. N. Bruce & M. Błażewicz-Paszkowycz (MTQ W31233).

Paratypes: Lizard Island region : 2 ♀ (illustrated), 9 specimens juv. Day Reef 14.48283°S, 145.5564°E, 19 February 2009, outer reef front, small rubble in gully, 7.5 m, CReefs stn LIZ09-13A, coll. M. Błażewicz- Paszkowycz & N. Bruce (MTQ W31299) . 1 ♂, 1 ♀, Yonge Reef , 14.61575°S, 145.6196°E, 11 February 2009, back reef, dead fungiid coral, 14 m CReefs stn LIZ09-01D, coll. M. Błażewicz-Paszkowycz (MTQ W30444) . 15 specimens; North Direction Island , 14.75112°S, 145.52160°E, 4 September 2010, coarse clean rubble, 28 m, CReefs stn LI10-067A, coll. C. Buxton (MTQ W32773) . 3 specimens; 14.57735°S, 145.6105°E, Yonge Reef, 10 September 2010, ocean side of reef, coral rubble, 25 m, CReefs stn LI10-127F, coll. C. Buxton (MTQ W33024). 5 specimens; High Rock , 14.82428°S, 145.55270°E, 11 September 2010, coral rubble, 30 m, CReefs stn LI10-135, coll. S. Smith (MTQ W33052) .

Capricorn Group, southern Great Barrier Reef: 1 ♂, 2 ♀, juv, Broomfield Reef, Capricorn Group, 23.2623°S, 151.9256°E, 18 November 2010, Broomfield back reef; coral rubble in bommie crevasse; 6.5m, CReefs stn HI10-031B, coll. S. Smith (MTQ W33819).

Etymology: Named in recognition of tanaidacean taxonomist Magdalaina Błażewicz-Paszkowycz’s contribution to tanaidacean systematics and also for being an excellent dive buddy and collecting participant during the CReefs expeditions and who provided many of the samples reported here.

Description. Copulatory terminal male. Body ( Fig. 3 ) length 5.20 width, body height 0.10 body length. Cephalon almost as long as wide, rostrum length 0.15 cephalon length, width 0.30 head width; anterolateral angles of cephalon in dorsal view acute, with seta, lateral margin with 3 small setae. Eyes with 5 large ommatidia situated closely against each other. Anterior body part (cephalon and pereonites 1–4) of same length as posterior body part (pereonites 5–7 and pleotelson). Pereonite 4 length 0.50 pereonite 1 length; anterolateral projections acute, distinctly protruding, with distal stout UB seta. Pereonite 7 length 1.10 pereonite 5 length. Pleotelson length 0.80 width, 0.20 body length; lateral margins until posterolateral indentation almost straight, parallel, with 3 – 4 small setae and 4 long setae: 1 anterior, 1 middle and 2 in front of denticle; pleotelson posterior part behind indentations rounded, length 0.30 pleotelson length, posterolateral margin with 4 long subdorsal setae directed laterally and 5 – 6 subventral setae directed posteriorly; preanal bar flattened, almost as long as anal operculum.

Antennula ( Fig. 5A ) length 0.20 body length; length ratios of articles 2 – 5 to article 1: 0.75, 0.55, 0.60, 0.60. Article 1 nearly twice as long as rostrum, length 2.10 width, 1 broom seta distolaterally, 1 simple seta distomedially. Article 2 distomedially with 2 broom setae (1 long and 1 short) and 1 spine-like seta, distolaterally with 2 broom setae (1 long and 1 short), long broom seta reaching tip of article 4. Article 3 distolaterally with 1 long simple seta. Article 4 with simple short distomedial seta, article 5 with tuft of 5 long strong distal setae.

Antenna ( Fig. 9A ) length ± about 0.60 body length (tip of flagellum broken off), peduncle articles 1 – 4 not reaching tip of antennula article 3. Article 3 scale slender, as long as lateral margin of article 4, with 3 distoventral setae. Article 4 with 2 small distal setae. Article 5 length 1.10 articles 1 – 4 total length; article 6 length 1.2 article 5 length, articles 5 and 6 with scattered long setae, length together 0.35 body length. Flagellum of more than 8 articles (tip of flagellum broken off), first article about twice longer than following articles, each article with 2 small distal setae.

Mandible of holotype ( Fig. 5B ) was not dissected: projection on left mandible almost as long as mandible body length, projection on right mandible broken off with trace of it. Mandible of male paratype ( Fig. 6A, B ): pars incisiva with 5 cusps; lacinia mobilis of left mandible broadening distally, subequal in length to pars incisiva, with 5 teeth; spine row with 9 and 10 spines on left and right mandibles respectively; molar process subcylindrical, distally serrated, with 8 – 9 setae, length 0.55 pars incisiva length; palp as long as mandibular body, article 1 with 2 long distal setae, article 2 length 2.60 article 1 length, with 5 short lateral setae and 2 long distally serrated setae; article 3 with rows of short cleaning setae on distal half and long distal seta. Maxilla 1 ( Fig. 7A ) lateral endite width 1.40 mesial endite width, distally with 11 spine-like denticulate setae, distolateral seta length 0.75 endite width. Maxilla 2 ( Fig. 7B ) middle endite shortest, lateral endite longest, with 4 long distal setae each; mesial endite as wide as middle and lateral endites together, with numerous distal setae and few comb-like setae distomedially. Maxilliped ( Fig. 7C ) basis length 4.30 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 0.80 as wide as basis, inserted after 0.60 basis length, article 2 as long as wide, medial margin length 1.15 lateral margin length, medial margin with 4 whip setae, 1 small seta distolaterally; article 3 as long as article 2 laterally, medial margin length 0.80 medial length of article 2, with 9 long setae, 2 long setae distolaterally; article 4 length 0.85 article 3 length, with 6 long setae distally; article 5 slender, length 0.60 article 4 length with 5 long setae. Epipod as long as basis, length 4.10 width.

Pereopod 1 ( Fig. 8B, C , 9B ) length 0.6 body length, length ratios of ischium–dactylus to basis: 0.60, 0.65, 0.55, 1.20, 0.60. Basis length 1.90 width, with 4–5 slender dorsal setae and 2–4 ventral setae. Ischium length 1.70 width, with 3 stout dorsal setae and 3 simple ventral setae. Merus length 1.60 width, distodorsal projection slender, as long as proximal part of merus, terminating with spine-like UB seta, dorsal margin with swollen projection in midlength. Carpus length 1.65 width, with ventral row of thin long setae. Propodal palm subrectangular, length 2.60 width, ventral margin length 0.75 dorsal margin length, anteriorly and ventrally with dense long slender setae (proximoventral setae stronger); distoventral spine-like UB seta length 0.55 anterior margin width; propodus anterior margin straight, with 4 oblique pectinate small setae, setae length Ẽ 0.25 spine-like UB seta length. Dactylus including claw length 4.90 width, 1.5 propodus anterior margin width, claw length 0.20 dactylus length. Dactylus ventral (inner) margin with 6 stout short setae, 3 long whip setae proximally to claw, two long slender setae ventrally to claw ( Fig. 9B ).

Pereopods 2–7 ( Fig. 10 ) about half of pereopod 1 length, length ratios of pereopods 2–7 to pereopod 1: 0.55, 0.5, 0.5, 0.55, 0.6, 0.5. Dactylar claws of pereopods 2–7 subequal in size.

Pereopod 2 ( Fig. 10A ) length ratios of ischium–dactylus to basis: 1.00, 0.45, 1.10, 0.95, 0.30. Basis length 2.10 width, dorsal margin with 4 small setae and 1 broom seta proximally. Ischium length 3.65 width, with 1 strong distodorsal seta. Merus length 1.50 width, with 1 ventral and 2 distodorsal simple setae and 1 strong distodorsal seta. Carpus length 4.80 width, with 3 stout whip ventral setae and 3 small dorsal setae. Propodus length 5.40 width, with 5 stout ventral whip setae and 1 distoventral UB seta, 2 simple setae and 1 bifid seta dorsally. Dactylus length 3.60 width, claws length 0.30 total dactylus length, 3 setae midlength, 1 seta between claws.

Pereopod 3 ( Fig. 10B ) length ratios of ischium–dactylus to basis: 0.80, 0.40, 0.70, 0.90, 0.25. Basis length 2.70 width, dorsal margin with 3 small setae and 1 broom seta proximally. Ischium length 2.85 width, with 1 stout dorsal seta and 2 small setae. Merus length 1.50 width, with 1 distoventral and 1 distodorsal stout setae. Carpus length 3.10 width, with 4 whip ventral and 1 small distodorsal seta. Propodus length 6.60 width, with 3 ventral and 2 dorsal simple setae. Dactylus length 3.60 width, claw length 0.30 dactylus length.

Pereopod 4 ( Fig. 10C ) length ratios of ischium–propodus to basis: 0.65, 0.40, 0.90, 0.90; 0.30. Basis length 2.50 width, with 3 dorsal simple setae. Ischium length 2.50 width, 2 simple distal setae. Merus length 1.45 width, with 1 distoventral and 1 distodorsal setae. Carpus length 4.45 width, with 3 ventral whip setae and 3 dorsal simple setae. Propodus length 5.25 width, with 4 ventral and 3 dorsal simple setae. Dactylus length 3.70 width.

Pereopod 5 ( Fig. 10D ): length ratios of ischium–dactylus to basis: 0.80, 0.40, 0.70, 0.80, 0.30. Basis length 2.90 width, with 3 ventral and 2 dorsal setae. Ischium length 3.40 width, with 2 ventral and 2 dorsal setae. Merus length 1.55 width, with 1 distodorsal seta. Carpus length 2.90 width, with 1 distodorsal and 2 ventral setae. Propodus length 4.80 width with 3 long whip ventral setae and 2 distoventral and 2 distodorsal small setae. Dactylus length 3.60 width.

Pereopod 6 ( Fig. 10E ) length ratios of ischium–dactylus to basis: 0.75, 0.30, 0.75, 0.70, 0.30. Basis length 2.50 width, with 3 dorsal and 3 ventral setae. Ischium length 3.30 width, with 2 distoventral setae. Merus length 1.35 width, with 1 distoventral and 1 distodorsal setae. Carpus length 3.20 width, with 2 ventral and 2 dorsal simple setae. Propodus length 4.40 width, with 3 long whip ventral setae and 2 distodorsal small setae. Dactylus of same size as pereopod 5 dactylus.

Pereopod 7 ( Fig. 10F ) length ratios of ischium–dactylus to basis: 0.75, 0.35, 0.75, 0.75, 0.30. Basis length 2.45 width, with 2 ventral and 2 dorsal simple setae. Ischium length 3.40 width, with 1 whip dorsal seta and 2 small ventral setae. Merus length 1.30 width, with 1 distoventral and 1 distodorsal setae. Carpus length 3.15 width, with 2 ventral and 2 distodorsal setae. Propodus length 5.0 width, with 6 long whip ventral setae and 2 distodorsal small setae. Dactylus of same size as pereopods 5 and 6 dactylus.

Pleopod 1 ( Fig. 11A, D ) length 1.50 pleopod chamber length, tip reaching anus; pleopod rami length 2.80 width, distal margins rounded, with 8–9 setae each. Pleopod 2 ( Fig. 9C, D ) protopod length 1.65 width, 0.45 pleopod 1 length, lateral margin without setae; endopod article 1 length 0.45 protopod length, article 2 length 0.75 protopod length; exopod length 1.90 width, 0.30 protopod length.

Pleopod 3 ( Fig. 11E ) protopod length 0.35 width, endopod length 1.95 width, distal plumose setae 0.35 endopod length, position: 1 distomedial seta situated in distance from 2 distolateral setae closely located to each other; exopod length 5.20 width, 1.35 endopod length and 0.50 endopod width, laterally with 3 slender setae, distal article separated, length 0.30 basal article length, with two distal setae. Pleopod 4 ( Fig. 11F ) endopod length 1.75 width, exopod length 0.60 endopod length, width 0.30 endopod width, 2 simple fine setae laterally. Pleopod 5 ( Fig. 11G ) length 2.05 width.

Uropod ( Fig. 11A, H ) 0.65 pleotelson length. Protopod length 2.10 width, lateral margin slightly concave, with 3 setae, medial margin slightly convex, with 2–3 long setae; 5 setae distally; endopod length 5.80 width and 1.50 protopod length, with 3 medial setae, distally 6–8 long and 2–3 broom setae; exopod length 5.0 width, 0.60 endopod length, with 6 long distal setae.

Adult female ( Fig. 4A, B ) similar in general body proportions to male, brooding female having longer pereonites 3 and 4 and antenna shorter than in male. Pereopod 1 ( Fig. 8A ) length 0.3 body length, length ratios of ischium–dactylus to basis: 0.45, 0.35, 0.40, 0.90, 0.50. Basis length 2.75 width, with 3 small dorsal setae. Ischium length 1.60 width, with 1 small and 1 stout dorsal setae. Merus length 1.20 width, with 4 subdorsal setae, distodorsal projection terminating with small spine-like seta. Carpus length 1.35 width, with row of ventral thin long setae. Propodal palm subrectangular, length 2.25 width, ventral margin length 0.60 dorsal margin length, anterior and ventral margin with dense row of long slender setae, distoventral spine-like UB seta length 0.40 anterior margin width, anterior margin with 7 comb-like stout distal setae length about half of spine-like seta length. Dactylus together with claw length 5.20 width, claw length 0.40 total length. Dactylus ventral (inner) margin with 4 stout short setae, 3 long whip setae proximally to claw, two long slender setae ventrally to claw.

Pleopod 2 ( Fig. 12A, B ) length 1.40 width, distal margin rounded, lateral and distal margins fringed with 7 long setae each, 1 small simple seta laterally, slit length 0.35 pleopod medial length. Pleopod 3 ( Fig. 12C ) protopod length 0.3 width, endopod length 1.6 width, exopod length 6.25 width, 1.15 endopod length and 0.2 endopod width, laterally with 5 thin setae, distal article separated, length 0.35 basal article length. Pleopod 4 ( Fig. 12D ) endopod length 1.80 width, exopod length 0.50 endopod length, width 0.3 endopod width with 2 simple lateral setae. Pleopod 5 ( Fig. 12E ) length 2.10 width.

Uropod ( Fig. 12A ) 0.50 pleotelson length. Protopod length 2.20 width, with 3 long distomedial and 2 lateral whip setae; endopod length 6.0 width and 1.40 protopod length, with 5 long whip distal setae; exopod length 0.65 endopod length, with 3 long whip distal setae.

Remarks. Gnathostenetroides blazewiczae sp. nov. can be identified by the following characters: dactylus of the male pereopod 1 is markedly longer than the anterior margin of the propodus; the distinct sexual dimorphism is seen not only in the different size of pereopod 1 in the male and in female, but also in the armament of the anterior margin of the palm: in females the pectinate setae are longer than the small setulated setae in males ( Fig. 9C, B ). The proximal part of pars incisiva of the mandible including the spine row is broader than in other species.

Only one male with mandibular projections (“horns”) and a huge pereopod 1 was found among about 100 collected specimens. The horn on one mandible is broken off and there is a trace of that missing process. Another terminal male with the large pereopods 1 has no mandibular projection. The other characters besides the enormous pereopod 1 and the horn of mandible are similar to those of other specimens.

Distribution. Known from the northern Great Barrier Reef, Lizard Island region, including the outer barrier reefs of Day, Hicks and Yonge Reefs, and the shelf reefs at North Direction Island and High Rock; also, southern Great Barrier Reef at Broomfield Reef in the Capricorn–Bunker Group; at depths from 6.5 to 30.0 metres.

Figures

FIGURE 3. Gnathostenetroides blazewiczae sp. nov., terminal male (1.5 mm), holotype MTQ W31233: A, dorsal view; B, lateral view; C, pleotelson, ventrolateral view.

FIGURE 4. Gnathostenetroides blazewiczae sp. nov., female with eggs, (1.9 mm), paratype MTQ W31299: A, dorsal view; B, lateral view; C, male (1.6 mm), paratype MTQ W31299, dorsal view.

FIGURE 5. Gnathostenetroides blazewiczae sp. nov., A, male, paratype MTQ W31299: anterior part of head with appendages, dorsal view; B, terminal male, holotype MTQ W31233: mandibles.

FIGURE 6. Gnathostenetroides blazewiczae sp. nov., male, paratype MTQ W31299: A, right mandible with enlarged incisor and molar processes; B, left mandible; C, hypopharynx.

FIGURE 7. Gnathostenetroides blazewiczae sp. nov., male, paratype MTQ W31299: A, maxilla 1 with enlarged distal margins; B, maxilla 2 with enlarged distolateral margin; C, maxilliped with enlarged distal margin of endite.

FIGURE 8. Gnathostenetroides blazewiczae sp. nov.: A, pereopod 1 of female, paratype MTQ W31299. Terminal male, holotype MTQ W31233: B, left pereopod 1; C, right pereopod 1.

FIGURE 9. Gnathostenetroides blazewiczae sp. nov., paratypes MTQ W31299: A, antenna of male; B, distal margin of propodus and dactylus of male pereopod 1; C, distal margin of propodus and dactylus of female pereopod 1.

FIGURE 10. Gnathostenetroides blazewiczae sp. nov., A, terminal male, holotype MTQ W31233 (1.5 mm): A, pereopod 2 with enlarged propodus and dactylus; B, pereopod 3; C, pereopod 4 with enlarged dactylus; D, pereopod 5; E, pereopod 6; F, pereopod 7.

FIGURE 11. Gnathostenetroides blazewiczae sp. nov., A, terminal male, holotype MTQ W31233 (1.5 mm), pleotelson, ventral view; male MTQ W 31299, paratype; B, right penis attached from coxa 7; C, pleopods 1 and 2; D, stylet of pleopod 2; E, pleopod 3; F, pleopod 4; G, pleopod 5; H, uropod.

FIGURE 12. Gnathostenetroides blazewiczae sp. nov., female, paratype MTQ W34282: A, pleotelson, ventral view; B, pleopods 2; C, pleopod 3; D, pleopod 4; E, pleopod 5.