Rectisura slavai, Malyutina, Marina V., 2011

Malyutina, Marina V., 2011, Description of two new species of munnopsid isopods (Crustacea: Isopoda Asellota) from manganese nodules area of the Clarion-Clipperton Fracture Zone Pacific Ocean, Zootaxa 2783, pp. 1-20 : 2-10

publication ID	https://doi.org/ 10.5281/zenodo.202831
DOI	https://doi.org/10.5281/zenodo.6185946
persistent identifier	https://treatment.plazi.org/id/6C304E62-FFDC-FFFD-B0F1-04A1FBE8F808
treatment provided by	Plazi
scientific name	Rectisura slavai
status	sp. nov.

Treatment

Rectisura slavai View in CoL sp. nov.

( Figs 1 – 8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Material examined. Holotype, female, 11.4 mm long (Museum of Institute of Marine Biology, Vladivostok, MIMB 24418), the manganese nodules area of the Clarion-Clipperton Fracture Zone, Pacific Ocean, St. 80, 20.08.2006, 13°15.35´N, 134°23.38´W, 4801 m; Paratypes, juvenile specimens ( MIMB 24419), St. 34, 0 2.09.2006, 13°18.84´N 134°19.16´W, 4742 m; St. 54, 28.08.2006, 13°14.69´N, 134°29.91´W, 4821 m.

Etymology. The species is named after V.F. Melnik, a Head of the Biological Department of the Scientific Center “Yuzhmorgeologia”, who collected the material. His short name is Slava.

Diagnosis. Caudal margin of the pleotelson rounded; dorsal and lateral spines of body weakly pronounced, less than half of pereonites length; pereonites 6 and 7 lacking dorsal spines.

Description. Body ( Figs 1 View FIGURE 1 , 2 View FIGURE 2 ) length 2.6 width of pereonite 5, body height 0.2 of body length. Head length 0.4 width, distance between antennulae insertion 0.5 of antennula width, clypeus 1.9 as wide and 0.3 as long as labrum. Pereonite 1 0.9 as wide and 0.5 as long as head, pereonites 2 and 3 as long medially as pereonite 1, slightly longer than pereonite 4, pereonite 1 shortest laterally, pereonites 2–4 subequal in lateral length, pereonites 1–3 anterolateral angle rounded without projections, pereonite 4 with anterolateral small spine-like projections shorter than coxal spine; anterior margin of pereonites 1–4 with small medial spine; coxae anterior lobe of pereonites 1–4 broad, acute. Natasome length 0.5 body length, width 1.4 head width; pereonites 5–7 subequal in lateral length, pereonite 5 shortest, pereonite 7 longest medially; pereonite 5 with pair of anteromedial small spines; pereonites 6 and 7 with pair of medial low tubercules. Pleotelson length 1.1 width, 0.25 body length, pleopodal cavity almost as wide as pleotelson width, preanal ridge rounded, weakly projected ventrally.

Antennula ( Fig. 3 View FIGURE 3 ) 0.25 of body length; article 1 length 1.8 width, with 1 distolateral and 7 dorsolateral broom setae, distomedial lobe shorter than article 2; article 2 length 0.3 article 1 length, with 3 distal broom setae; article 3 length 1.7 article 2 length, width 0.5 article 2 width, with 3 small medial setae; flagellum of 8–10 articles, article 4 length 0.2 article 3 length, with distal broom seta and 2 simple setae, article 5 length 3.8 article 4 length, following 19 articles slightly longer than article 4, last two articles with aesthetasc.

Antenna ( Fig. 3 View FIGURE 3 ) more than 2.3 as long as body (distal part of flagellum broken off); articles 1–3 subequal in lateral length, article 3 with stout distomedial seta; article 5 length 2.2 length of preceding articles together, with spars spine-like setae along; article 6 subequal to article 5, with spine-like setae on proximal half and 2 stout distal setae; flagellar articles 0.3 as wide as article 6, first article length about 3 times following articles length.

Left mandible ( Fig. 4 View FIGURE 4 ) pars incisiva flattened dorsoventrally, with ventral pronounced tooth; lacinia mobilis stout, also flattened dorsoventrally, length about half of pars incisiva length, with 6 teeth; spine row with 14 spines; molar process smaller than pars incisiva, condyle about as long as molar process; palp length 1.1 mandibular body length, article 2 length 3.4 article 1 length, article 3 with dense row of short distal setae.

Maxilla 1 ( Fig. 4 View FIGURE 4 ) lateral endite width 2.4 mesial endite width, most of 12 distal spine-like setae denticulate, longest distolateral seta length 1.3 endite width.

Maxilla 2 ( Fig. 4 View FIGURE 4 ) middle endite shortest, lateral endites longest, with 2 long and 2 short distal comb-like setae each; mesial endite as wide as middle and lateral endites together, with 10 comb-like and numerous distal setae.

Maxilliped ( Fig. 3 View FIGURE 3 ) basis length 3.7 width, endite with 10 coupling hooks, distal margin serrated, with 6 fan setae and numerous simple slender setae; palp article 2 lateral margin convex, length 1.3 medial margin length, medial margin concave, with 4 distal setae; article 3 medial margin rounded, with small setae, medial length 0.8 article 2 medial length; articles 4–5 slender, article 4 lateral length 1.6 article 3 lateral length, medial lobe of article 4 length 0.4 article 5 length, with 8 distal setae; article 5 with 4 long distal setae. Epipod length 2.7 width and 0.9 basis length lateral hook in midlength.

Pereopods 1–4 ( Fig. 5 View FIGURE 5 ): pereopod 1 length 0.5 body length, length ratios of ischium–dactylus to basis: 0.45, 0.2, 1.0, 0.7, 0.2; basis length 6.6 width, with sparse setae; ischium length 3.4 width, with 4 dorsal setae and 1 ventral seta; merus length 1.25 width, with 3 distoventral setae; carpus length 13.2 width, with 8 small ventral setae; propodus length 9.5 width, with 4 distal setae; dactylus with tiny claw. Pereopod 2 length 1.4 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.7, 0.3, 1.5, 1.8, 0.6; basis length 4.3 width, with 4 proximal setae; ischium length 2.8 width, with 1 broom and 3 small dorsal setae; merus length 1.2 width, with 4 ventral setae; carpus length 6.9 width, ventral margin serrated, with 15 stout setae and 4 dorsal setae; propodus length 12.1 width, with 27 ventral setae stouter that ventral setae on carpus, dorsal margin serrated with small whip setae, 1 broom and 1 whip setae distodorsally; dactylus length 8.6 width, claw length 0.1 dactylus length. Pereopod 3 length 1.8 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.9, 0.3, 2.2, 3.1, 0.6; basis length 3.6 width, with 2 simple and 2 broom dorsal setae; ischium length 3.5 width; merus length 1.2 width, with 2 distoventral and 2 distodorsal setae; carpus length 9.5 width, with 7 setae on proximal half of ventral margin, 13 dorsal setae; propodus length 19 times width, with 9 setae on distal half of ventral margin, row of small dorsal setae, 1 broom and 4 long whip distodorsal setae; dactylus length 6.7 width, claw length 0.1 dactylus length. Pereopod 4 length 1.95 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.7, 0.4, 2.4, 3.3, 0.7; basis length 2.9 width, with 5 simple and 3 broom dorsal setae; ischium length 2.7 width; merus length 1.3 width, with 1 dorsal and 1 ventral setae; carpus length 10.5 width, ventral margin with 4 stout setae on proximal half and 3 small setae on distal half, 12 dorsal setae; propodus length 20.6 width, with 9 setae on distal half of ventral margin, 23 small dorsal setae, 1 stout and 1 tiny distoventral setae and 1 broom and 3 long whip distodorsal setae; dactylus length 7.5 width.

Pereopods 5–7 ( Fig. 6 View FIGURE 6 ): Pereopod 5 length 1.3 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.7, 0.3, 1.2, 1.15, 0.5; basis length 3.2 width; ischium length 2.9 width, with 5 plumose dorsal setae; merus length 1.2 width; carpus length 1.95 width, with 41 dorsal and 22 ventral plumose setae subequal in length to carpus width; propodus length 3.2 width with 10 ventral and 13 dorsal setae; dactylus length 10.3 width, claw length 0.1 dactylus length. Pereopod 6 subequal in length to pereopod 5 (1.02), length ratios of ischium–dactylus to basis: 0.6, 0.2, 1.15, 1.5, 2.0, 0.4; basis length 3.4 width, with 3 broom dorsal setae; ischium length 2.5 width, with 10 plumose setae; merus length 1.2 width; carpus length 2.0 width, with 38 dorsal and 25 ventral plumose setae; propodus length 3.9 width, with 31 dorsal and 26 ventral plumose setae; dactylus similar in shape to those of pereopod 5, but slightly longer. Pereopod 7 length 0.8 pereopod 5 length, length ratios of ischium–dactylus to basis: 0.6, 0.2, 0.8, 0.85, 0.4; basis length 4.2 width, with 4 dorsal setae; ischium length 3.3 width, with 6 plumose dorsal setae; merus length 1.3 width; carpus length 2.0 width, with 28 dorsal and 14 ventral plumose setae; propodus length 4.1 width, dactylus as in pereopods 5 and 6. Carpus/propodus length ratios: 1.0, 1.0, 0.9 for pereopods 5–7 respectively; carpus/propodus width ratios: 1.9, 2.0, 1.9 for pereopods 5–7 respectively.

Pleopods: Pleopod 2 ( Fig. 2 View FIGURE 2 a, d, e) tightly closed respiratory chamber, length 0.8 width, keel weakly pronounced with small spine at proximal third, lateral and distal margins with row of plumose setae. Pleopod 3 ( Fig. 6 View FIGURE 6 ) endopod length 1.4 width, distal plumose setae length 0.3 endopod width; exopod width 0.3 endopod width, as long as endopod and protopod together, basal article length 1.5 distal article length, distal article with 15 lateral plumose setae, separated distal seta and thin setulae proximally. Pleopod 4 ( Fig. 6 View FIGURE 6 ) endopod length 1.25 width, exopod length 0.8 endopod length, width 0.5 endopod width, distal plumose seta as long as that of pleopod 3 exopod. Pleopod 5 ( Fig. 6 View FIGURE 6 ) length 1.3 width.

Uropod ( Fig. 2 View FIGURE 2 ) length 0.4 pleotelson length. Protopod length 2.7 width; endopod length 1.4 protopod length, with 3 medial simple setae, 1 stout lateral and 4 stout, 2 broom and 3 simple distal setae; exopod subequal in width to endopod, length 0.6 endopod length, with 1 simple and 3 stout distal setae.

Juvenile specimen ( Fig. 7 View FIGURE 7 ) without developed pereonite 7 and without pereopods 7. Configuration of the pleotelson is the same as for the holotype, but lateral margins between anterior and posterior projections more straight, not rounded as in the holotype.

Distribution. The species is only known from the type location at 4742–4821 m depth.

Remarks. From a picture the holotype of the new species was preliminarily identified as Vanhoeffenura sp. ( Melnik & Melnik 2009), because of its large size and the rounded caudal margin of the pleotelson similar to species such as Vanhoeffenura birsteini ( Menzies, 1962) , V. eltanae (George & Menzies, 1968) and V. g e o rg e i ( Malyutina, 2003). However the following detailed investigation of the specimen revealed that the key characters, namely the antennular article 1 without a subrectangular distolateral lobe, a relatively short and broadened distomedially article 2, absence of a lateral projection on antenna article 2, shape of the dorsal head and rounded anterolateral margins of pereonite 3 indicate that the species belongs to the genus Rectisura Malyutina, 2003 and do not fit the generic diagnosis of Vanhoeffenura Malyutina, 2004 (= Vanhoeffenella Malyutina, 2003 nom. preoc.). Moreover, the new species differs from above mentioned species of Vanhoeffenura by presence of a dorsomedial spine on pereonite 1, a feature typical for all species of Rectisura .

The discovery of this new species allowed more precise taxonomic evaluation of the similar species, Storthyngura ? intermedia ( Beddard, 1885) from the Northeastern Basin of the Pacific (37°52’N, 160°17’W, 5011 m). Storthyngura ? intermedia was moved by Wolff (1962) from genus Eurycope Sars, 1864 to the genus Storthyngura Vanhöffen, 1914 and Malyutina (2003) left the species in the genus Storthyngura tentatively when she revised members of the subfamily Storthyngurinae . In a subsequent paper ( Malyutina & Brandt 2004a) S.? intermedia was tentatively put into the magnispinis -group of the genus Storthyngura . However, the shape of the pleotelson of this species with a rounded caudal margin devoid of notches for uropod insertions was noted as peculiar for the genus Storthyngura . Since the new species described here, which undoubtedly belongs to Rectisura , is similar to S.? intermedia , the latter is considered to also belonging to Rectisura . These morphologically similar species were found a great distance from each other at similar depths in the Northeastern Basin of the Pacific. Another similar species (a damaged female lacking the head and first two pereonites), which I identified some years ago as Storthyngura sp. was collected by the Russian expedition aboard the RV “Akademik Kurchatov” (1973) in the deep Argentine Basin (5218 m) of the southwestern Atlantic ( Fig. 8 View FIGURE 8 ).

Rectisura slavai sp. nov. together with the most similar species R. intermedia comb. nov. and Rectisura sp. from the Argentina Basin differ from other known species of the genus by the rounded caudal margin of the pleotelson while the others species have the pleotelson with a projecting truncated caudal margin. By this character the three species resemble species of the magnispinis -group of Storthyngura but distinct from them by absence of notches for uropod insertions. Moreover, R. slavai sp. nov., like all species of Rectisura , has an acute projection at mid-length on the lateral margin of the maxilliped epipod, whereas Storthyngura species have smooth lateral margins on their epipods.

Rectisura slavai sp. nov. differs from R. intermedia by the weakly pronounced sculpture: all dorsal and lateral projections in the new species are about half as long as those in S. intermedia and pereonites 6 and 7 are lacking the dorsal spines. The damaged specimen of Rectisura sp. has similar pleotelson shape, but differs from the new species by possessing longer anterolateral spines on pereonite 4 and pereonites 5–7, dorsomedial projections on pereonite 5 are short and situated close to each other, so look like a notch on the pereonite frontal margin; dorsomedial projections on pereonite 3 and 4 are absent.

Only 11 species of Rectisura were known prior to the present description ( Malyutina & Brandt 2004a). Most Rectisura species are known from the western part of the Pacific: six species, R. brachycephala , R. herculea , R. kurilica , R. tenuispinis (Birstein, 1957) , and R. distincta (Birstein, 1970) are known from the north-western trenches: Aleutian, Kurile-Kamchatka and Japan Trenches, R. furcata (Wolff, 1956) was described from the е rmаdеc Trench, south Pacific, and R. serrata (Wolff, 1962) was recorded from the eastern Pacific, the Gulf of Panama. As a result of the present investigation two species from the Northeastern Basin of the Pacific were added. Three species were known from the Atlantic sector of Antarctic: R. sepigia (George & Menzies, 1968) from the South Sandwich Trench, R. richardsonae Malyutina, 2003 from the Scotia Sea and R. menziesi Malyutina & Brandt, 2004a from the Weddell Sea. Rectisura sp. from the Argentina Basin is the fourth recorded south Atlantic species of the genus. No Rectisura species are reported from the North Atlantic.