Diastylis moskalevi, Vassilenko, Stella & Tzareva, Ludmila, 2004

Vassilenko, Stella & Tzareva, Ludmila, 2004, New Cumacea species (Malacostraca, Peracarida) from the deepwater area of the Sea of Japan (Collections of the 52 Cruise by the R / V « Vityaz », 1972), Zootaxa 702, pp. 1-16 : 2-6

Diastylis moskalevi sp. nov.

( Figs. 1–2 )

Material examined: holotype, female of 16 mm length (with telson) with eggs, eggs diameter is 0.6 mm, kept in the collection of Zoological Institute, ( ZIN ­ 1/88366), R/V “Vityaz”, 52 cruise, sta. 6671; 23.06.1972, Pacific Ocean, 40º19´N, 143º35´4´´E, depth 2400–2720 m; “SIGSBI ” trawl, washed, only large ground fractions were left.

Paratypes: ( ZIN ­ 2/88367) 1 female, 20 mm length, with an empty marsupium; 1 female 19 mm length with, 2 females 15 mm and 15.5.mm length with oostegite rudiments; 2 females with eggs and abdomen torn away, same locality; ( ZIN ­ 3/88368) 1 female 14 mm length with eggs; 1 male 9 mm long with 2 pairs of pleopods; R/V “Vityaz”, 52nd cruise, sta. 6666, 20.06.1972, Sea of Japan, 37º52´3´´N, 136º20´E, depth 513– 365 m; substrate: large silted aleurite, “SIGSBY” trawl; ( ZIN ­ 4/88369) 1 male 8.5 mm long with developed pleopods and long antenna II; R/V “Vityaz”, 52nd cruise, sta. 6659, 16.06.1972, Sea of Japan, 40º14´5´´N, 134º42´8´´E, depth 1340–1610 m; substrate: washed trawl, many large foraminiferans were collected, “SIGSBY” trawl.

Diagnosis: Carapace swollen, covered with very fine denticles, lower lateral borders of carapace with groove. Pseudorostrum short, not pointed. Postero­lateral angles of last thoracic segment slightly elongated and round­shaped. Pre­anal part of telson almost equal to that post­anal part; post­anal part of telson gradually narrowing, bearing eight­nine lateral and two apical spines. Peduncle length of uropods equal to telson length; endopodite slightly longer exopodite.

Description of the holotype: Female ( Figs. 1 , A, D, E). Carapace swollen, widely oval without folds. Carapace surface sculpture very typical for the species: entire carapace densely and almost evenly covered with very fine denticles and sparse thin setae. In dorsal view, carapace length slightly exceeds width, lateral sides parallel and slightly rounded, beginning from middle smoothly narrowing to end of pseudorostrum. Pseudorostrum relatively short, not pointed. Two rounded cavities in anterior part of carapace, triangular impression with sharp elongated forward peak, in posterior part of carapace, which passes into lengthwise crevice. Lower lateral borders of carapace finely serrate. Antero­lateral angles not pronounced.

First and second thoracic segments finely serrate along anterior edge, almost fringed. Postero­lateral angles of last thoracic segment slightly elongated backwards, roundshaped, with small denticle.

Abdomen section (without telson) shorter than thoracic one. Postero­lateral angles of abdominal segments I­V produced; every abdominal segment with oblique edge on lateral side.

Pereopod I ( Fig. 1 , C) long, thin, considerably longer than other pereopods, basis thin and slightly shorter than total length of ischium­propodus, plumose setae along entire lower edge; ischium and merus short and approximately equal in length; three distal articles, very thin and elongated; carpus and propodus equal in length; dactyl slightly thinner and shorter than propodus one.

Pereopod II ( Fig. 2 , D) considerably shorter than pereopod I, basis slightly reinforced, covered with rounded plates; carpus long, almost twice longer than two final articles combined.

Pereopods III­V ( Fig. 2 , A, B, C) shorter than pereopod II and have a similar structure, gradually diminishing from III to V pair, basis very long and thin; propodus of pereopod III and pereopod IV with long stout terminal setae.

Telson ( Fig. 2 , E) three times longer than last abdominal segment, length of post­anal part of telson almost equal to that of pre­anal part, pre­anal part of telson with parallel lateral sides, post­anal part of telson gradually narrowing, bearing eight­nine lateral spines and two apical spines.

Uropods ( Fig. 2 , E) thin and long, peduncle length equal to telson length, inner and outer sides of peduncle bearing nine­ten setae; endopod slightly longer than its exopod, it consisting of three articles, inner side of articles bearing spine­like setae with terminal hair; exopod double­articled. Proximal articles of exopodite and endopodite almost equal in length; terminal article of exopodite bearing two long terminal setae, terminal article of endopod bearing one long and one short setae.

Male. ( Fig. 1 , B). Carapace narrower in comparison with female; pseudorostrum longer and more pointed, carapace surface sculpture covered with small denticles, posterolateral angles of abdominal segments ending with small spines. Post­anal part of telson shorter than pre­anal.

Remarks: When comparing paratypes of the new species with holotype some distinctions can be observed: postero­lateral angles of abdominal segments of smaller individuals (females with oostegite rudiments) are pointed or bear spines. Post­anal part of telson is shorter than pre­anal one. D. moskalevi resembles in appearance D. hirsuta (Lomakina, 1955) . When describing D. moskalevi , n. sp. we reviewed collection materials of ZIN RAS on D. hirsuta . Since these species are similar in appearance, it is necessary to pay attention to the following distinctive features of the new species:

1. The most characteristic distinctive feature is carapace surface structure: carapace of D. moskalevi is covered with multiple small ripples, whereas carapace surface of D. hirsuta is fine­grained.

2. Females and males of the new species are considerably bigger (females have 15–20 mm length, males – 9 mm) than that of D. hirsuta (females 9–13 mm, males are unknown).

3. D. moskalevi pseudorostrum is shorter than that of D. hirsuta . 4. D. moskalevi has a groove along the lower edge of carapace, whereas D. hirsuta has not it.

Figures

FIGURE 1. Diastylis moskalevi sp. nov. A — adult female, holotype, lateral view; B — adult male, lateral view; C — pereopod I; D — carapace (female), dorsal view; E — carapace (female), lateral view

FIGURE 2. Diastylis moskalevi sp. nov. A — pereopod IV; B — pereopod III; C — pereopod V; D — pereopod II; E — telson with uropods, dorsal view.