Diastylis galtsevorum Mühlenhardt-Siegel & Lavrenteva, 2015, n.sp.

Diastylis galtsevorum n.sp.

(Figs 1–3)

Material. Holotype preparatory female, ZMH: K 44229; (coll. 23.08.12).

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: #2-10: 1 manca, 2 preparatory females (both with pleon broken off after Pl 4 or Pl1 respectively), 1 subadult male. ZMH K 44230; #5-9: 3 subadult females (one female with pereiopod 5 developed, but no (yet?) exopods on P3 and P4, damaged, dissected; ZMH: K 44231), 1 manca, 1 pleon. All more or less damaged. ZMH K 44232; #12-4: 2 preparatory females; ZMH: K 44252

Additional material: #6-12: 1 manca; ZMH: K 44253; #7-9: 1 manca; ZMH: K 44254; #7-10: 2 mancas; ZMH: K 44255; #1-10: 1 manca; MIMB 29173; #5-10: 1 damaged manca; MIMB 29174; #6-11: 1 manca; MIMB 29175; #7-9: 1 subadult female, 1 manca; MIMB 29176; #7-10: 1 damaged manca; MIMB 29177; #10-9: 1 manca; MIMB 29178

Etymology. The new species is dedicated to Lyubov Semenovna Galtseva and Gennadiy Sergeevich Galtsevone of the author’s (AVL) dear grandparents.

Diagnosis. Carapace almost egg shaped in dorsal view, with small and a few larger denticles, especially in the anterior part; carapace 3 times longer than free thoracic segments; short pseudorostrum; anteroventral margin of carapace with battlement-like crenulations; telson slightly shorter than uropod peduncle.

Description. Holotype, female (ZMH: K 44229), 13.5 mm (Fig. 1).

Carapace almost egg shaped in dorsal view, with dimples and small and a few larger denticles, especially in the anterior part; three times longer than free thoracic segments.

Pseudorostral lobes meeting in front of ocular lobe for a short distance, 0.1 of total carapace length, three times as long as ocular lobe length, with four denticles seen from lateral; siphonal tube very short; ocular lobe rounded; no eye lenses.

Antennal notch indistinct, no subrostral tooth; anteroventral margin of carapace with battlement-like crenulation.

Integument whitish, smooth except the armature on the carapace.

Five free thoracic segments visible dorsally, the first and second segments are hidden under the carapace in lateral view; 0.3 times as long as carapace.

Pereion 0.8 times shorter than pleon.

Telsonic segment not longer than pleonite 4; telson (Fig. 3, Uh) 0.8 times as long as peduncle, preanal part 1.8 times as long as postanal part. A pair of strong terminal setae and six to seven lateral cuspidate setae in holotype (two pairs in subadult female, Fig. 3, U).

Appendages: subadult female (ZMH K 44231).

Antenna 1 (Fig. 2, A1): relative length of peduncle articles 1 to 3: 50/26/24; a tooth on distal outer corner, distal margin with one long and a shorter simple seta, fringe of hair-like setae along inner margin of basal article; accessory flagellum three articulated, longer than basal article of main flagellum; main flagellum broken off after article 2 in dissected paratype.

Antenna 2 (Fig. 2, A2): rudimentary, of two articles.

Maxilliped 3 (Fig. 2, Mxp3): B/R ratio 1.2, relative length of articles I to D: 12/18/23 /29/18; basis with three teeth along distal inner margin, at outer distal corner one long and at inner distal corner one shorter pappose seta; merus with one tooth and a stout and a slender pappose seta; carpus with one long and three shorter pappose setae; propodus with two pappose and one broken setae; dactylus with one strong terminal, three long and three short simple setae subterminally; exopod present.

Pereiopod 1 (Fig. 2, P1): B/R ratio 0.9, relative length of articles I to D: 6/14/30 /32/18; basis with five strong teeth along outer margin (distal tooth on basis almost as long as merus), three pappose setae on distal part; merus with two teeth, carpus with one pappose and two simple setae; dactylus with two strong terminal and three simple setae subterminally (two of them broken off in dissected specimen); exopod present.

Pereiopod 2 (Fig. 3, P2): B/R ratio 0.6, relative length of articles I to D: 8/ 12/36/20 /24; basis with four teeth along upper margin, a (broken) tooth and a pappose seta on lower distal corner; ischium with a strong tooth on lower distal corner; merus with simple seta; setae on carpus and propodus broken off; dactylus with three setae on distal end, two of them broken off; exopod present.

Pereiopod 3 (Fig. 3, P3): B/R ratio 1.0, relative length of articles I to D: 14/21/ 43/17/5; basis with one pappose seta distally and four simple setae; merus with a simple seta subdistally; carpus with one terminally annulated and one simple setae on outer distal corner; propodus with one terminally annulated simple seta; short dactylus with one long terminal simple seta; exopod not present.

Pereiopod 4 (Fig. 3, P4): B/R ratio and relative length of articles I to D not given, endopod broken off after merus; basis with three teeth proximally, three simple seta, one strong pappose seta distally; ischium with a simple seta; merus with a strong seta (broken off); exopod not present.

Pereiopod 5 (Fig. 3, P5): B/R ratio 0.7, relative length of articles I to D: 16/22/ 45/13/4; basis with four simple setae; carpus with two strong setae broken off; propodus with one strong seta broken off; dactylus as figured, terminal seta (unguis) broken off.

Uropods (Fig. 3, U, Uh), peduncle with five cuspidate setae along uropod peduncle (two in young female); two-articulated exopod longer than endopod; uropod endopod three-articulated, first article with seven (two in young female), second article with three (one in young female) cuspidate setae, rest broken off in holotype (third article with one cuspidate seta in young female).

Subadult male similar to female.

Distribution. Kurile Kamchatka abyssal plains, 4859 to 5429 m depth.

Remarks. In mancas and preparatory females the dimples on the carapace are well developed but only one to two pairs of denticles are present on the pseudorostrum; the anteroventral margin of the carapace is beset with big teeth on the anterior third and battlement-like crenulations along the ventral margin.

The new species is similar to D. moskalevi Vassilenko & Tzareva, 2004 from the Sea of Japan (513 to 2720 m) in terms of denticules on the carapace and the length of the pseudorostrum to the total carapace (0.1 in the new species and in D. moskalevi); however, these two species differ in several other characters: The carapace is three times the length of the free thoracic segments in the new species (1.5 in D. moskalevi).

The telson is shorter than the uropod peduncle in the new species (equal in length in D. moskalevi).

The shape of the frontal lobe fissure seen from above is wide in the new species (narrow in D. moskalevi).

The new species has the carapace with small and a few larger denticles, especially in the anterior part, (D. moskalevi just with very fine denticles).

The proportion of the preanal part to the postanal part of the telson is 1.8 in the new species (equal in D. moskalevi).