Storthyngura yuzhmorgeo Malyutina, 2011, sp. nov.

Storthyngura yuzhmorgeo sp. nov.

(Figs 9–13)

Material examined. Holotype, male 1.8 mm long (MIMB 24420), the manganese nodule area of the Clarion-Clipperton Fracture zone, Pacific Ocean, St. 8535, 28.07.2007, 13°08.36´N, 134°29.43´W, 4809 m; Paratype, female, 2.3 mm long (MIMB 24421), St. 54, 28.08.2006, 13°14.69´N, 134°29.91´W, 4821 m.

Etymology. The species is named after the Scientific Center “Yuzhmorgeologia”, Gelendzhik, that carried out the expeditions responsible for collecting the species.

Diagnosis. Body devoid of dorsal spines, coxae anterior spine of pereopods 2–4 as long as corresponding pereonites length; natasome relatively narrow, tightly packed, anterolateral margins of pereonites 5–7 and pleotelson acute, pleotelson terminal apex rounded, length 0.3 pleotelson length.

Description. Male, holotype. Body (Fig. 9) length 2.7 width of pereonite 5, body height 0.25 of body length. Head length 0.7 width, equal to antennula article 1 length. Width between bases of antennulae subequal to antennula width; clypeus 1.6 as wide and 0.5 as long as labrum. Pereonites 1–4 subequal in medial length, length 0.4 head length; pereonite 4 longest laterally, pereonite 1 almost as wide as head, pereonites 2–4 slightly broader, anterolateral margins of pereonites 1–3 rounded, of pereonite 4 acute, length 0.5 coxae anterior spine length, coxae anterior spine of pereopods 2–4 as long as pereonites length. Natasome without dorsal projections, length 0.5 body length, width 1.5 width of head, lateral margins with sparse minute setae. Pereonite 5 longest, pereonite 7 shortest laterally; lateral sutures between pereonites 5–6 and 6–7 0.25 natasome width in mid-length. Pleotelson as long as wide, length 0.25 body length, anterolateral and posterolateral angles projected, each ended with spine-like seta, lateral margins slightly convex; terminal apex rounded, length 0.3 pleotelson length, preanal ridge low, rounded terminally, with a row of setae.

Antennula (Fig. 9 c) length 0.3 body length, 10 articles; article 1 length 1.75 width, medial spine length 0.2 article length, ending with spine-like seta, article 2 0.4 length and 0.5 width of article 1, with distal broom seta; article 3 length 0.6 article 2 length; article 4 length 0.5 article 3 length, with distal broom seta, article 5 broader than two previous and following articles, almost as wide and as long as article 3, article 6 and following articles subequal in length to article 4, two last articles with aesthetasc.

Antenna incomplete (Fig. 9 c): articles 1 and 2 subequal in lateral length, article 1 with small spine-like seta; article 3 length about 2 times article 2 length, medial projection as long as that on antennula article 1, with spinelike seta.

Pereopods (Figs 9 b, 12). Pereopod 1 length 0.4 body length, length ratios of ischium–dactylus to basis: 0.4, 0.25, 1.4, 0.8, 0.6; basis length 4.4 width, with 1 broom dorsal and simple distoventral setae; ischium length 1.8 width, with 1 dorsal and 1 ventral setae; merus length 1.1 width, with 2 distal setae; carpus length 8.7 width, with 1 dorsal seta; propodus length 7.2 width, with 3 distal setae; dactylus length 8.4 width. Pereopod 2 length 1.2 pereopod 1 length, length ratios of ischium– dactylus to basis: 0.45, 0.3, 1.3, 1.25, 1.1; basis length 4.3 width, with 1 broom dorsal and 1 simple distoventral setae, ischium length 2.0 width, with 2 small distal setae; merus length 1.25 width, with 1 dorsal seta; carpus length 5.5 width, with 5 ventral small setae and 2 long dorsal setae; propodus length 7.3 width, with 4 ventral sensory spines, 3 dorsal setae and 1 stout and 1 broom distodorsal setae; dactylus length 9.7 width. Pereopod 3 not complete, basis length 3.5 width, with 1 dorsal broom seta. Pereopod 4 length 1.5 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.9, 0.4, 2.1, 2.5, 1.5; basis length 2.3 width, with 1 broom dorsal seta; ischium length 2.0 width, with 1 broom dorsal seta and 2 small ventral setae, merus length 1.1 width, carpus length 4.1 width, with 2 dorsal setae, 1 broom and 1 whip distodorsal setae, ventral margin with 6 stout setae in two rows on distal half and 2 small setae on proximal half; propodus length 9.8 width, with 4 ventral, 5 dorsal setae and 1 broom and 1 whip distodorsal setae; dactylus length 10.5 width. Pereopod 5 length 1.3 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.7, 0.4, 1.1, 1.0, 0.5; basis length 3.7 width, with 1 small ventral seta; ischium length 3.0 width, with 1 small ventral and 2 plumose dorsal setae; merus length 1.4 width, with 1 dorsal seta; carpus length 1.8 width, with 20 dorsal and 7 ventral plumose setae and 2 whip and 1 broom distodorsal setae; propodus length 3.3 width, with 10 dorsal and 7 ventral plumose setae and 1 whip and 1 broom distodorsal setae; dactylus length 8.7 width. Pereopod 6 similar in shape and proportions to pereopod 5, slightly longer (1.03 of pereopod 5): basis and ischium slightly longer, merus and carpus slightly shorter than in pereopod 5, propodus and dactylus of the same length as in pereopod 5; carpus length 1.5 width, with 16 long and 1 stout simple dorsal setae and 6 ventral plumose setae; propodus length 1.5 width, with 5 ventral and 5 dorsal plumose setae and 2 spine-like distodorsal setae; dactylus length 4.1 width, claw tiny. Pereopod 7 not fully developed, length 0.5 pereopod 5 length.

Pleopods 1 and 2 (Fig. 9 d) not completely developed. Pleopod 1 length 3.4 mid-length width. Pleopod 2 semicircular, protopod cleft distally, length 2.3 width, distal margin with short plumose setae.

Uropod (Fig. 9 d) 0.4 pleotelson length. Protopod length 2.2 width in male 1.9 in female, broadening distally, with 2 distal setae; endopod length 1.2 protopod length, with 1 lateral stout, 2 broom 4 and 2 whip distal setae; exopod 0.6 endopod length and width, with 3 stout, 1 broom and 2 whip distal setae.

Female, paratype

Body (Fig.10) similar to that of male, length 2.6 width of pereonite 5, body height 0.2 of body length. Natasome length 0.6 body length, width 1.6 width of head.

Antennula (Fig. 11) more slender than in male, length 0.25 body length, 9 articles; article 1 length 1.7 width, medial spine length 0.2 article length, with spine-like seta, distal lobe with broom seta, 2-3 small broom setae dorsally, article 2 0.4 length and 0.3 width of article 1, with distal broom seta; following articles gradually getting slen- der, article 3 length 0.6 of article 2; article 4 length 0.5 article 3 length, with distal broom seta, article 5 almost as long as article 3, articles 6–8 longer that article 4, but shorter than article 3, two last articles with aesthetascs.

Antenna incomplete (Fig. 10 c), like in male.

Mandible (Fig. 11) pars incisiva with 3 cusps; lacinia mobilis of left mandible 0.6 of pars incisiva length, with 6 teeth; spine row with 7 and 9 spines on left and right mandibles respectively; molar process narrow with 2 distal setae; condyle as long as molar process; palp length 1.1 mandibular body length, article 1 with 1 seta, article 2 length 2.7 article 1 length, with 2 slender medial and 2 stout distal setae, article 3 broad, with row of lateral setae and dense combs on inner surface.

Maxilla 1 (Fig. 11) lateral endite width 1.6 mesial endite width, with 12 distal spine-like setae, longest setae slightly longer than endite distal width.

Maxilla 2 (Fig. 11) lateral and middle endites of same length and width, mesial endite longest, slightly narrower than lateral and middle endite together, with 8 strong and numerous slender distal setae; lateral and middle endites with 2 long and 2 near half shorter distal setae each.

Maxilliped (Fig. 11) basis length 3.7 width, endite width 0.6 basis width, with 3 coupling hooks, distal margin with 3 fan and numerous simple slender setae, lateral margin serrated, with simple slender setae; palp inserted after 0.6 length of basis, article 2 subequal to basis in width, lateral margin convex, medial margin slightly concave, lateral length 1.25 medial length; article 3 shortest laterally, medial margin slightly convex, with 8 setae, length 0.7 medial length of article 2; article 4 lateral length 2.4 article 3 lateral length, medial lobe of article 4 elongate, slightly shorter and subequal in width to article 5, with 4 distal setae; article 5 with 4 distal setae. Epipod length 3.1 width, length 0.9 basis length.

Pereopods (Fig. 13): Pereopod 1 length ratios of ischium–dactylus to basis: 0.4, 0.2, 1.3, 0.85, 0.6; basis length 4.7 width, with 1 small ventral seta; ischium length 2.0 width, merus length 1.25 width, with 2 distal setae; carpus length 8.1 width, with 2 ventral and 2 distodorsal setae; propodus length 7.2 width, with 4 distal setae; dactylus length 8.0 width.

Pereopod 5 length 1.3 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.7, 0.4, 1.15, 1.05, 0.5; basis length 3.8 width, with 2 broom dorsal setae; ischium length 2.4 width, with 1 plumose dorsal seta; merus length 1.3 width; carpus length 1.95 width, with 15 dorsal and 9 ventral plumose setae and 3 distodorsal setae; propodus length 5.2 width, with 8 dorsal and 5 ventral plumose setae and 1 whip and 1 broom distodorsal setae; dactylus length 4.6 width.

Pereopod 6 similar in shape and proportions to pereopod 5, length 1.1 pereopod 5 length: basis and ischium slightly longer, merus–propodus slightly shorter than in pereopod 5, and dactylus 1.4 times longer than pereopod 5; length ratios of ischium–dactylus to basis: 0.6, 0.2, 0.8, 0.7, 0.5; carpus length 1.7 width, with 13 dorsal and 10 ventral plumose setae; propodus length 4.5 width, with 7 ventral and 5 dorsal plumose setae and 2 spine-like distodorsal setae; dactylus length 8.2 width. Pereopod 7 more slender and shorter that pereopods 5 and 6, length 0.9 pereopod 5 length; length ratios of ischium–dactylus to basis: 0.6, 0.2, 0.7, 0.6, 0.4; carpus length 2.1 width, with 10 dorsal and 6 ventral plumose setae; propodus length 4.1 width, with 5 ventral and 8 dorsal plumose setae and 2 spine-like distodorsal setae; dactylus length 8.2 width.

Pleopods (Figs 10 d, 13): Pleopod 2 (Fig. 10 d) length 1.1 width, with dense row of distal setae. Pleopod 3 endopod length 1.5 width, distal plumose setae length 0.4 endopod width; exopod of single article, 1.3 length and 0.3 width of endopod, 4 distal plumose setae of same length as on endopod. Pleopod 4 endopod length 1.7 width, exopod length 1.1 endopod length, distal plumose seta as long as distal plumose setae on pleopod 3. Pleopod 5 length 1.7 width.

Uropod (Fig. 10 d) like in male, 0.4 pleotelson length.

Distribution. The species is only known from the type locality.

Remarks. The study S. yuzhmorgeo sp. nov. attracted attention to a similar looking species, Ilyarachna defecta Menzies & George, 1972 from the Peru-Chile Trench, Eastern Pacific, collected at depths between 6073– 6281 m. The tubular biramous uropods, fused natasomal pereonites and the characteristic “chevron”-like shape of the pleotelson – features diagnostic for Storthyngura, indicate the species should have been placed in Storthyngura instead of Ilyarachna Sars, 1864. Indeed the authors noted in the remarks to the description, that it was an unusual Storthyngura- like species. Based on I. defecta’s similarities to S. yuzhmorgeo sp. nov., it is here moved to the genus Storthyngura. The new species and S. defecta (Menzies & George, 1972) comb. nov. differ from other known species of Storthyngura by nearly absence of mediodorsal spines on pereonites 2–4, tightly packed narrow natasome, especially narrow pleotelson. S. yuzhmorgeo sp. nov. differs from S. defecta by having longer coxa of pereopods 1– 4, more acute anterolateral margins of pereonites 4–7 and pleotelson; rounded, not angular caudal projection of the pleotelson and shorter uropods.

To date 12 species are known for the genus Storthyngura (Malyutina & Brandt 2004b). Here a new species combination is proposed. S.? intermedia was excluded from the genus and the new species S. yuzhmorgeo sp. nov. and morphologically similar species S. defecta moved from Ilyarachna. Thus now four species of Storthyngura are known from the Pacific: S. octospinosalis Menzies & George, 1972 and S. defecta from the Peru-Chile Trench, S. parka Malyutina & Wägele, 2001 from the Peru Basin and S. yuzhmorgeo sp. nov. from the Clarion-Clipperton Fracture zone. All these species are from the eastern side of the Pacific; no species are known from the western side. Five species are known from the Southern Ocean: S. elegans Vanhöffen, 1914, S. phyllosoma (Just, 2001), S. kussakini Brandt & Malyutina, 2002, S. longispina Malyutina & Brandt, 2004, and S. antarctica Malyutina & Brandt, 2004. Three species were described from the north-western Atlantic: S. magnispinis (Richardson, 1908a), S. truncata (Richardson, 1908b), and S. vemae Menzies, 1962. One species, S. snanoi Menzies, 1962 is recorded from the Caribbean Sea. Thus, the species of the genus occur mainly around the Americas.