Pseudoleptostyloides marinamalyutinae Mühlenhardt-Siegel & Lavrenteva, 2015, n. sp.

Pseudoleptostyloides marinamalyutinae n. sp.

(Figs 13–16)

Material. Holotype ovigerous female, ZMH: K 44243; (coll. 23 Aug. 2012).

Type locality. NW Pacific, Kurile Kamchatka abyssal plains, 40° 35,48' N 150° 59,92' E, 5399–5408 m depth, cruise 223 with RV “Sonne” (KuramBio), station #9-9, (EBS #15-S), gear: epibenthic sledge.

Paratypes: #12-4: 1 ovigerous female (pleon broken off), 3 preparatory females, 4 mancas; ZMH: K 44244; #8- 9: 1 carapace and thoracic segments; ZMH: K 44245; #8-9: 1 male, broken after Pl1, 2 preparatory small females; ZMH: K 44246; #9-9: 1 ovigerous female, 1 manca; ZMH: K 44247. #9-12: 1 preparatory female (7.8 mm), dissected; ZMH: K 44248. Telson (postanal part) not yet as long as in ovigerous female holotype.

Additional material. #2-9: 1 carapace and thoracic segments; MIMB 29189; #2-9: 1 preparatory female; MIMB 29190; #9-9: 1 preparatory female; MIMB 29191.

Etymology. The new species is dedicated to our very much esteemed colleague and dear friend Marina Malyutina Ph. D., a highly reputated taxonomist for Isopoda (Crustacea, Peracarida), especially for the family Munnopsidae.

Diagnosis. Battlement-like crenulated ridges start at the basis of the pseudorostrum, the upper part runs laterally from the frontal lobe directing to the dorsal middle behind the frontal lobe, the ridges from the left and right side do not meet dorsally but run almost parallel towards the posterior margin of the carapace, bending ventrally and running along the posterior, ventral and anteroventral margins of the carapace to meet the point of origin. A second, shorter ridge links the first ridge from antennal notch region to level of frontal lobe fissure end, which is the widest part of the first ridge seen from above. Uropods long and slender; peduncle as long as pleonites 4 to 6 combined, with 16 cuspidate setae along inner margin. Uropod exopod much longer than tri-articulated endopod. Telsonic subterminal setae not of same length as the terminal; between two strong terminal setae a short cuspidate seta is located dorsally, which is much shorter than the subterminal ones; telsonic postanal part almost as long as preanal part, postanal part laterally beset with 10 pairs of hair-like setae.

Description. Holotype, ovigerous female (ZMH: K 44243 ), 9.5 mm long (Fig. 13).

Carapace: In all investigated specimens the crenulated ridges run in the same pattern: starting at the basis of the pseudorostrum the upper part runs laterally from the frontal lobe directing to the dorsal middle behind the frontal lobe, both ridges do not meet dorsally but run almost parallel toward the posterior margin of the carapace, bending ventrally and running along the posterior, ventral and anteroventral margins of the carapace to meet the point of origin. A second, shorter ridge links the first ridge from antennal notch region to level of frontal lobe fissure end, which is the widest part of the first ridge seen from above. The frontal lobe fissure is submerged, therefore not visible from lateral view.

Pseudorostral lobes meet for a short distance (0.18 times of rest of carapace) in front of eye lobe; front margin little serrated; siphonal tube not protruding; ocular lobe roundish, no eye lenses.

Antennal notch not discernible; anterolateral tooth missing; anteroventral margin of carapace with battlementlike crenulation.

Integument whitish; smooth on carapace, but on pleon with small denticles.

Five free thoracic segments visible, pereionites 1–4 with small lobes extending laterally and horizontal ridges dorsally.

Pleon: measured without telson, little longer than free thoracic segments and carapace combined.

Telsonic segment 0.6 times as long as telson.

Telson (Fig. 16, U): 0.4 times of peduncle length; preanal part 1.1 times longer than postanal part; postanal part bearing laterally about 10 pairs of hair-like setae terminally and subterminally, a pair of strong cuspidate setae. The subterminal ones are not as long as the terminal ones. Between the two strong terminal setae a short cuspidate seta is located dorsally, which is shorter than the subterminal ones.

Appendages: preparatory female, 7.8 mm long (paratype ZMH: K 44248)

Antenna 1 (Fig. 14, A1): relative length of peduncle articles 1 to 3: 47/29/24; basal article with fringe of setae along inner margins, a long seta on inner distal corner, unfortunately the setae are mainly broken off; accessory flagellum tri-articulated, shorter than basal article of tri-articulated main flagellum; main flagellum bears one aesthetasc at the penultimate and one at the terminal article.

Maxilliped 2 (Fig. 14, Mxp2): B/R ratio 0.7, relative length of articles I to D: 8/27/ 33/22/10; basis with three plumose setae on distal margin; merus with one plumose seta on inner margin; carpus with fringe of hair-like setae along inner margin and seven strong plumose setae along inner margin and two long plumose setae on outer distal corner; propodus with five plumose setae on distal margin and a long plumose setae from middle part of the article; dactylus with strong simple terminal seta (unguis) and four simple setae subterminally.

Maxilliped 3 (Fig. 14, Mxp3): B/R ratio 1.7, relative length of articles I to D: 10/17/22 /29/22; basis with five short proximal and distally four strong teeth along inner margin, three long and one shorter plumose setae on outer distal corner, 11 thin plumose setae along inner margin; inner and outer margin with fringe of hair-like setae; ischium with one simple and one plumose setae; merus with a strong tooth, two plumose setae, one on each inner and outer corner; carpus with two strong teeth, two simple setae and five plumose setae; propodus with three plumose setae along inner margin; dactylus with one terminal and four subterminal simple setae; slender exopod present.

Pereiopod 1 (Fig. 15, P1): B/R ratio and relative length of articles I to D not given, broken after basis; basis with ten plumose fine setae along outer margin, two long and strong plumose setae on inner distal corner, a fringe of hair-like setae and four fine plumose setae along distal part of upper margin¸ two short and hair-like simple setae proximally at upper and lower margin; exopod present.

Pereiopod 2 (Fig. 15, P2): B/R ratio 0.3, relative length of articles I to D: 5/ 10/23/37 /25; eight simple setae along basis; ischium with a tooth and a hair-like simple seta; merus with three simple setae; carpus with five simple setae along upper margin and three robust simple seta at distal margin; propodus with nine simple setae along margins; dactylus with six simple setae along margin, terminal seta broken off; exopod present.

Pereiopod 3 (Fig. 16, P3): B/R ratio and relative length of articles I to D not given, broken after carpus; eleven simple setae along margins of basis; ischium with one simple seta; merus with one simple seta; carpus with two long and four thin simple setae; rudimentary exopod present.

Pereiopod 4 (Fig. 16, P4): B/R ratio 0.7, relative length of articles I to D: 13/ 26/32/11 /18; eight thin simple setae along margins of basis, most of them broken off; merus with one thin simple seta, carpus with three thin simple setae along margins, two terminally annulated setae on distal corner; propodus with one strong terminally annulated seta on distal corner; dactylus with terminal seta broken off; exopod not visible in dissected paratype; however, exopod was present in holotype.

Pereiopod 5 (Fig. 16, P5): B/R ratio not given, basis broken during dissection, relative length of articles I to D: 12/19/40 /15/14; basis with two simple setae; ischium with one simple seta; merus with two simple setae; carpus with a short and a longer simple seta and a blunt tooth distally; propodus with a long terminally annulated seta distally; dactylus with a strong simple seta terminally and a shorter one subterminally.

Uropods (Fig. 16, U), long and slender; peduncle as long as pleonites 4 to 6 combined, with 16 cuspidate setae along inner margin; uropod exopod two-articulated, distal article ten times longer than basal, total length1.7 times longer than tri-articulated endopod; endopod with a short seta on distal inner corner of each article; basal article longest, but shorter than article 2 and 3 combined.

Distribution. NW Pacific, 4830–5408 m depth.

Male similar to female.

Remarks. The new Pseudoleptostyloides species is the first record of this genus for the Pacific.

The known species are P. mediosetosus Mühlenhardt-Siegel, 2014 from the western and eastern South Atlantic up to the Weddell Sea (3055 to 5055 m) and P. longiappendiculata (Ledoyer, 1997) from the tropical Atlantic. In both species the ornamentation of the carapace, a crenulated battlement-like carina, is similar; however, it is different in the new species.

The main difference between P. longiappendiculata and P. mediosetosus is the proportion of the uropods and the entire pleon, the uropods being longer than the pleon in P. longiappendiculata and shorter in P. mediosetosus and the new species.

The proportion of the telson to pleonite 6 is 1.8 in P. marinamalyutinae n. sp., and equal in P. longiappendiculata and P. mediosetosus. Besides the pair of subterminal lateral setae, the telson in the new species has numerous hair-like setae along the lateral margins of the postanal part, which are missing in P. longiappendiculata as well as in P. mediosetosus. The proportion of the preanal part to the postanal part is 1.1 in the new species and 1.6 in P. mediosetosus.

The median seta between the two strong terminal telsonic setae is very short in the new species and in P. mediosetosus from the Cape Basin (Mühlenhardt-Siegel, 2014) but only little shorter than the lateral setae in the female from the Weddell Sea, while equal in length to the lateral setae in males from the Weddell Sea and Brazil Basin.