Boreomysis (Petryashovia) urospina, Daneliya, 2023

Daneliya, Mikhail E., 2023, Mysid Subfamily Boreomysinae (Crustacea: Mysida: Mysidae) in the Southeast Australian Deep-sea, Records of the Australian Museum (Rec. Aust. Mus.) 75 (2), pp. 87-124 : 105-110

Boreomysis (Petryashovia) urospina sp. nov.

urn:lsid:zoobank.org:act:25C74221-0562-4508-BAF8-34BFD5CD5AEC

Figs 7–10

Etymology. Named for the excessive number of the spiniform setae on the uropods and the unique position of the spiniform setae of the uropodal exopod, shifted to the median part of the ramus. The name is an adjective after the New Latin (former Ancient Greek) prefix uro­, meaning tail, and as a part of uropods, and Latin spina, a spine.

Holotype. Male, 33 mm, Tasmania, Baseline 14, from 44°06'35"S 146°13'00"E to 44°06'09"S 146°11'49"E, 965– 941 m, 06 Dec 2018, coll. RV Investigator, BPT, IN2018 _ V06 _094, 4MBT ( AM P.106628) . Allotype. Female, 40 mm, same data as in holotype ( AM P.106629) . Paratypes. 6 females, 35–40 mm, male, 35 mm, same data as in holotype ( AM P.103318) ; 2 females, 37–40 mm, 2 subadult females, 35–36 mm, subadult male, 33 mm, male, 35 mm, male in two parts, female in two parts, juvenile, 28 mm, Tasmania, Punch’s Hill , from 44°11'14"S 147°11'12"E to 44°11'02"S 147°11'23"E, 919–1086 m, 13 Dec 2018, coll. same as previous, IN2018 _ V06 _ 157, 4MBT ( AM P.103331); male, same as previous ( AM P.106630; GenBank OQ699903, voucher B18) .

Additional material. 2 females (1 broken), subadult female, 4 males, 33–35 mm, subadult male, Tasmania, off southern Tasmania, Huon Commonwealth Marine Reserve , from 44°10'17"S 147°10'59"E to 44°10'33"S 147°10'33"E, 1046 m, 09 Apr 2015, coll. RV Investigator, BPT, S. J. Keable, M. A. McGrouther, IN2015 _E06_010, beam trawl ( AM P.98102); 5 females, (1 female 40 mm), 5 males, 5 cephalothoraxes, same locality, date, collector and gear, from 44°10'49"S 147°10'19"E to 44°11'12"S 147°09'52"E, 1070 m, IN2015 _ E06_011 ( AM P.98103); male, same as previous ( AM P.106631, GenBank OQ699904, voucher B20) ; 2 males, 36 mm, 1 female, Tasmania, Central north, from 44°09'07"S 147°11'02"E to 44°09'14"S 147°12'22"E, 1000–1038 m, 27 Nov 2018, coll. RV Investigator, BPT, IN2018 _E06_037, 4MBT ( AM P.103329).

Type locality. South of Tasmania, from 44°06'35"S 146°13'00"E to 44°06'09"S 146°11'49"E at depth 941–965 m.

Diagnosis. Anterodorsal margin of carapace ( Fig. 8A–C ) angular, apically rounded or blunt, reaching proximal part of antennular peduncle segment 1, with nearly strait lateral margins, bearing minute concavity on each side. Telson ( Fig. 8E,H,I ) 1.04–1.4 times as long as last abdominal segment, 2.9–3.5 times as long as wide anteriorly and 0.55–0.60 times as wide posteriorly as anteriorly. Telson lateral margins nearly straight, with 22–26 nearly equal in size spiniform setae, though somewhat arranged in about ten series, slightly increasing in length within series, and four terminal spiniform setae; longest terminal spiniform seta flanked by two medial and one lateral spiniform setae, 0.25–0.45 as long as longest terminal. Telson cleft 0.16–0.20 of telson length, with about 40 to 60 rather long spinules. Eyes ( Fig. 8A–D ) large, nearly globular, 0.40–0.43 of head width; cornea dominating over eyestalk; eye papilla absent. Antennular peduncle not extending beyond half of antennal scale ( Fig. 8D ). Antennal scale ( Fig. 8D, J ) five times as long as wide; apically with only slightly advanced distomedial angle, not exceeding beyond distolateral spine. Antennal peduncle with slight medial prominence between segments 2 and 4; segment 3 nearly indistinguishable ( Fig. 8J ). Pereopod ( Fig. 9M,N ) carpus with six or seven medial bunches. Uropodal exopod ( Fig. 8E ) with three lateral spiniform setae; its proximal segment 0.42–0.45 of ramus length. Endopod ( Fig. 8K ) with three to five medial spiniform setae.

Body length of females 35–40 mm, of males 33–36 mm.

Comparison. Boreomysis (P.) urospina sp. nov. has several unique features for the subgenus: the carapace anterior margin has a minute concavity on its lateral sides, which is not known even among other species of Boreomysis sensu lato; the uropodal exopod is rather wide (less than five against eight to ten times as long as wide in other species of the subgenus), bearing three spiniform setae (one or two in other species), set nearly by the half length of the ramus (in proximal part in other species of even Boreomysis sensu lato), and the uropodal endopod is with three or five medial spiniform setae (one or two in other species). It is most similar to B. (P.) megalops , differing from it, in addition to the above mentioned unique characters, by the longer antennal scales (less than twice as long as antennular peduncle in B. (P.) megalops ), modified male pleopods 3 (both pleopods 2 and 3 in B. (P.) megalops ), and the telson having larger number of the terminal spiniform setae (four against two in B. (P.) megalops ).

Description of holotype male. Anterodorsal margin of carapace angular, apically blunt; laterally with slight concavity at each side; anteroventral lobes small, triangular, pointed. Posterolateral lobes of abdominal segment 6 angular, apically blunt or rounded. Telson 1.04 times as long as last abdominal segment, 3.5 times as long as wide anteriorly, and 0.57 times as wide posteriorly as anteriorly. Cleft 0.16 of telson entire length, with about 42 spinules. Lateral margins nearly straight, with 24 spiniform setae (partly broken) (including four terminal), forming about ten groups of increasing length; longest terminal spiniform seta 0.08 of entire telson length, flanked by one lateral (broken) and two medial spiniform setae, 0.45 of longest one.

Eyes large, almost rounded, with cornea dominating over eyestalk; eye papilla absent. Antennular peduncle segments 1 dorsally flat, with slight distolateral elevation, apically with a bunch of setae; segment 2 with triangular dorsal elevation, apically with a bunch of setae; segment 3 large, nearly quadrangular from dorsal view. Antennal peduncle, sympod with lateral spine; segment 2 significantly longer than segment 1; segment 3 reduced to a slight prominence, bearing setae; segment 4, distal margin not broadened. Antennal scale more than twice as long as antennular and antennal peduncles.

Labrum apically nearly rounded. Mandible: left corpus, processus incisivus and lacinia mobilis both 4-cuspate, pars centralis with six serrated setae, pars praemolaris with fine setules, pars molaris with grinding plates and apical tuft of setules; right corpus, processus incisivus, lacinia mobilis 10-cuspate, pars centralis with 12 spiniform setae, among them proximal serrated and distal smooth, pars praemolaris with fine setules, pars molaris with serrated grinding plates and apical spiniform setae. Mandibular palp segment 2 with rather long plumose setae, set apart; segment 3 is 0.90–0.95 times as long as segment 2, with four or five lateral, one anterior distomedial, about 25–30 long proximomedial setae and 45 shorter distomedial setae, its margins nearly parallel. Maxilla 1. Outer ramus with about seven posterior serrated setae, three of them grouped medially and three shifted to medial margin, apical spiniform setae serrated. Inner ramus with five lateral, seven medial and six apical long setae, three apical setae distally serrated, similar to those of maxilla 2 and maxilliped 1 endites. Maxilla 2. Exopod oval, 2.5 times as long as wide, about as long as endopod, with plumose setae. Endopod segment 1 with about 12 anteromedial and three posteromedial setae; segment 2 is 1.6 times as long as wide, with lateral plumose setae and apical serrated setae; coxal endite notably prolonged; basal endites with strong serrated setae, similar to those of maxilliped 1 endites.

Maxilliped 1. Coxa with two short, plumose medial setae. Basis with posterolateral group of five plumose setae; endite rather long, barely reaching distal margin of ischium, with long setae of two types: thinner, longer and flexible, with setules, and thicker, shorter and stout, distally with rough serrations and spear-like apex. Preischium endite short, but well-established, compared to rather reduced ischium endite; both with long plumose setae. Merus the longest segment, 2.0 times as long as wide, with long, plumose medial setae. Ischium and merus with few weakly setulose lateral setae. Carpopropodus 0.78 times as long as merus, with long, plumose lateral and serrated medial setae. Dactylus 0.56 of carpopropodus, with numerous long, weakly setulose setae; its distomedial and posterior margins with serrated setae. Unguis strong, serrated, 0.53 of dactylus length.

Maxilliped 2. Exopod with about 25 segments; its basal part with blunt distolateral angle. Endopod general proportions and setation pattern typical for subfamily. Carpopropodus distomedial part without concavity, with setae only slightly more robust and stronger serrated than other setae, without special modifications.

Pereopod exopod with 23–30 segments. Endopod. Preischium with or without setae. Ischium and merus with numerous long sparsely plumose setae on medial margin. Ischium 0.52–0.65 times as long as merus; its medial setae lather long, set along entire margin; anteromedial setae shorter, in distal half; posterolateral setae rather short, along proximal 2/3. Merus setae along entire margins; medial, anteromedial and posterolateral setae rather long; anterolateral setae short; anteromedial margin also with group of serrated setae. Carpus with seven medial bunches of setae, each bunch containing one long straight and two (proximally) to eight (distally) shorter bent plumose setae, becoming stronger and more strongly serrated in distal bunches. Propodus 0.46–0.56 times as long as carpus with smooth paradactylary setae. Unguis 0.73–1.00 times as long as dactylus. Musculus flexor dactyli attached at about distal 1/3 of carpus.

Pleopods. Pleopod 1 exopod with about 25 segments; endopod less than half as long as exopod, without separation on segments and with numerous long setae. Pleopod 2 exopod with about 25 segments; endopod slightly shorter than exopod, with about 20 segments. Pleopod 3 exopod with about 27 segments; its distal segments with shorter and stronger spiniform setae; endopod shorter than exopod, with about 20 segments, bearing unmodified setae. Pleopod 4 exopod with about 25 segments; endopod shorter than exopod, with about 20 segments. Pleopod 5 exopod with about 25 segments; endopod shorter than exopod, with about 20 segments.

Uropodal exopod with three distolateral spiniform setae. Endopod with four medial spiniform setae.

Description of female. Antennular peduncle, segment 3 smaller than in male, almost rounded. Marsupium with seven pairs of oostegites. All pleopods reduced to short setose plates, set on basal segment and coxa, increasing in length posteriorly. Uropodal exopod 4.7–4.8 times as long as wide, 1.17–1.3 times as long as endopod and 1.5 times as long as telson; its proximal segment 0.42–0.45 of ramus length.

Colour. Red ( Fig. 7 ).

Distribution and habitat. Recorded only from the southern part of the Tasman Sea, south of Tasmania at depth of 919–1086 m ( Fig. 16 ). This is the most deep-water species in the subgenus, found at the border between the meso- and bathypelagic zones.

Molecular characters. Two nearly identical sequences of B. (P.) urospina sp. nov. from Tasmanian coast were 0.5% distant from each other and 57–84% diverged from other species Boreomysis .

Figures

Figure 7. Boreomysis (Petryashovia) urospina sp. nov., allotype, female, 40 mm, AM P.106629. Scale (mm): 10.0. Photographed by K. G. Holmes, with permission.

Figure 8. Boreomysis (Petryashovia) urospina sp. nov. (A, C, E–H, J, K) holotype, male, 33 mm,AM P.106628; (B, D, I) allotype, female, 40 mm, AM P.106629. (A, B) head, dorsal; (C) head, lateral; (D) head (carapace not shown), lateral; (E) posterior part of abdomen with telson and uropods (setae and spiniform setae mostly not shown), dorsal; (F) posterior margin of abdomen and proximal part of uropod (left side), ventral; (G) posterior margin of abdomen, lateral; (H) telson; (I) posterior part of telson; (J) antenna 2, ventral; (K) uropodal endopod, ventral. Scales (mm): 1.0.

Figure 9. Boreomysis (Petryashovia) urospina sp. nov., holotype, male, 33 mm, AM P.106628. (A) labrum, ventral; (B) mandibular palp, posterior; (C) right mandible, ventral; (D) left mandible, ventral; (E) maxilla 1, posterior; (F) maxilla 2, anterior; (G) maxilliped 1, anterior; (H) dactylar claw of maxilliped 1; (I) medial seta of maxilliped 1 basal endite; (J) maxilliped 2, anterior; (K) medial serrated seta of maxilliped 2 dactylus; (L) medial seta of maxilliped 2 carpopropodus; (M) pereopod 1 endopod, posterior; (N) pereopod 1 carpus, anterior; (O) medial setae of pereopod 1 merus; (P) medial seta of pereopod 1 carpus; (Q) paradactylary seta of pereopod 1; (R) penis, lateral. Scales (mm): A–G, J, M, N, R = 1.0; H, I, K, L, Q = 0.25; O, P = 0.5.

Figure 10. Boreomysis (Petryashovia) urospina sp. nov. (A–F) holotype, male, 33 mm,AM P.106628; (G) allotype, female, 40 mm, AM P.106629. (A) pleopod 1, posterior; (B) pleopod 2, anterior; (C) pleopod 3, posterior; (D) pleopod 3 distal part, posterior; (E) pleopod 4, anterior; (F) pleopod 5, anterior; (G) pleopod 5, anterior. Scales (mm): A–C, E–G = 1.0; D = 0.5.

Figure 16. Records ofthe species ofthe subfamily Boreomysinae inAustralia and adjacent waters(the whitesymbols indicate formerrecords).