Boreomysis (Boreomysis) sphaerops Ii, 1964

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 : 101-104

Boreomysis (Boreomysis) sphaerops Ii, 1964

Figs 5 , 6

Boreomysis sphaerops Ii, 1964: 18 , 19, 30, 32, 39, 44,

50–56, figs 11–13.— Müller, 1993: 29.

Boreomysis spinifera .—Birstein & Tchindonova, 1958:

289, fig. 15.

Type specimens. Ii (1964) based his description on a large series of specimens, from which a 23 mm male was designated as “type”, and should probably be treated as the holotype, Japan, Shizuoka Prefecture, Sagami Bay, an islet near Ajiro, 4 miles [ca 6.4 km] east of Hashima , 1000–0 m, 02 Apr 1938, haul No. E-12, vertical net (Ii’s collection No. 67b); and a 25 mm female was designated as “ allotype ”, same locality, 32 Mar 1938, haul No. E-4 (Ii’s collection No. 65). Status unknown .

Type locality. Japan, Shizuoka Prefecture, Sagami Bay, an islet near Ajiro, about 6.4 km east of Hashima .

Material. Female (subadult), 27 mm, New South Wales, off Byron Bay, from 28°40'40"S 154°12'13"E to 28°42'57"S 154°11'20"E, 2591– 2566 m, 07 Jun 2017, coll. RV Investigator, BPT, L. E. Hughes, F. Köhler, E. K. Kupriyanova, IN2017 _ V03 _096, BES ( AM P.106636); male (subadult, rather damaged), 27 mm, juvenile, New South Wales, Central Eastern Commonwealth Marine Reserve , from 30°06'47"S 153°53'53"E to 30°06'58"S 153°52'01"E, 2634– 2324 m, 06 Jun 2017, coll. same as previous, IN2017 _ V03 _087, BES ( AM P.106637); male subadult, same as previous ( AM. P.106638; GenBank OQ 699909, voucher B3) .

Diagnosis. Anterodorsal margin of carapace ( Fig. 5A,B ) with rather short, acutely pointed and upwards directed rostrum, barely reaching proximal part of antennular peduncle segment 1, flanked by smoothly rounded angles. Telson ( Fig. 5C,E ) 1.2–1.3 times as long as last abdominal segment, 3.0–3.2 times as long as wide anteriorly and 0.47–0.52 as wide posteriorly as anteriorly. Telson lateral margins barely concave in central part, with 28–54 spiniform setae arranged in about 10 series: setae increasing in length within series, and three terminal spiniform setae; longest terminal spiniform seta flanked by one or two medial and one lateral spiniform setae, about half as long as central. Telson cleft 0.18–0.22 of telson length, with anterior dilatation and about 70–100 rather long spinules. Eyes ( Fig. 5A,B ) large from dorsal view, broad, slightly flattened dorsoventrally, about 0.4 of head width; cornea shorter and wider than, but not dominating over eyestalk; eye papilla small. Antennular peduncle extending beyond half of antennal scale ( Fig. 5A,B ). Antennal scale ( Fig. 5A,B,F,G ) 4.1–4.5 times as long as wide; its distolateral spine not armed with additional spinules; apically with only slightly advanced distomedial angle, not exceeding beyond distolateral spine. Pereopod ( Fig. 6C ) carpus with seven medial bunches; propodus 2-segmented. Pereopod 1 propodus segment 2 rather long and slender, about twice as long as segment 1. Uropodal exopod ( Fig. 5C,D ) with two lateral spiniform setae; its proximal segment 0.23–0.26 of ramus length. Endopod ( Fig. 5O ) with two or three medial spiniform setae.

Body length 27 mm (immature) in Australia (originally 21–25 mm, North-West Pacific).

Comparison. Boreomysis (B.) sphaerops is rather similar to B. (B.) obtusata G. O. Sars, 1883 , from which it is distinguished by the presence of the anterior dilatation in the telson cleft (absent in B. (B.) obtusata ), one of the lateral terminal spiniform setae of the telson being twice as long as the flanking ones (about equal in length in B. (B.) obtusata ), the rather big eyes, which, when both directed forward, touching each other by lateral margins, extending in adult specimens beyond the head sides (not extending in B. (B.) obtusata ), and by the shape of the eye cornea, which is rather distinctly narrow from the dorsal view, shorter than the eye stalk (about as wide as the stalk in B. (B.) obtusata ). There is a similarity in the shape of the carapace anterior margin with B. (B.) inopinata sp. nov., particularly in the presence of the lateral angles. However, B. (B.) sphaerops has rather short rostrum (produced in B. (B.) inopinata sp. nov.), the telson cleft having the anterior dilatation (absent in B. (B.) inopinata sp. nov.), and the slightly wider antennal scale (4.1–4.5 times as long as wide against 4.7–5.5 in B. (B.) inopinata sp. nov.).

Description of Australian specimens. Anterodorsal margin of carapace with rather short, acutely pointed and upwards directed rostrum, not reaching proximal part of antennular peduncle segment 1, flanked by smoothly rounded angles; laterally without minute concavity; anteroventral lobes large, triangular, pointed. Posterolateral margins of the abdominal segment 6 with apically pointed scutella paracaudalia. Telson 1.2–1.3 times as long as last abdominal segment and nearly reaching tip of uropodal endopods; 3.2 times as long as wide anteriorly, and 0.52 times as wide posteriorly as anteriorly. Telson lateral margins barely concave in central part, with 53–54 spiniform setae arranged in about ten series: setae increasing in length within series, and three terminal spiniform setae; longest terminal spiniform seta 0.05 of entire telson length, flanked by one lateral and one medial spiniform setae, half as long as central. Cleft 0.20–0.22 of telson entire length, with 70–100 spinules; dilatation present.

Eyes large from dorsal view, broader than long, slightly flattened dorsoventrally; cornea narrower than eyestalk. Eyestalk papilla present, rather small. Antennular peduncle longer than half of antennal scale; segment 1 with distal dorsomedial tubercle; segment 2 with two dorsal tubercles, outer tubercle with apical process; segment 3 medially with seven setae and one posterodistal bunch of long plumose setae; outer flagellum ventrally inflated near basis, with numerous long fine setae. Antennal scale 4.1–4.2 times as long as wide; apically with only slightly advanced distomedial angle.

Labrum conical. Mandible: left corpus, processus incisivus and lacinia mobilis both 3-cuspate, pars centralis with eleven serrated setae, pars praemolaris with fine setules, pars molaris with grinding plates and apical tuft of setules; right corpus, processus incisivus 4-cuspate, lacinia mobilis with over 20 cusps, pars centralis with 14 spiniform setae, among them distal serrated, pars praemolaris with fine scales, pars molaris with serrated grinding plates. Mandibular palp segment 2 with rather long plumose setae, set apart proximally and dense distally; segment 3 is 0.81 times as long as segment 2, with five or six lateral, six anteromedial, about fifteen long proximomedial and about 30 shorter distomedial setae. Maxilla 1. Outer ramus with nine posterior plumose setae, three of them grouped medially and two shifted to medial margin, apical spiniform setae serrated. Inner ramus with seven lateral, four posterior, five medial and seven apical long setae, five 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, reaching its second segment, with plumose setae. Endopod segment 1 with about 14 anteromedial and four posteromedial setae; segment 2 is 1.6 times as long as wide, with lateral plumose setae and apical serrated setae. Coxal endite notably prolonged, with dense marginal and sparse posteromedial setae. Basal endites with strong serrated setae, similar to those of maxilliped 1 endites.

Maxilliped 1. Coxa with two plumose medial setae. Basis with posterolateral 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, 2.2 times as long as wide, with long, plumose and serrated medial setae. Ischium and merus with weakly setulose lateral setae. Carpopropodus 0.75 times as long as merus, with long, plumose anterolateral and serrated medial setae. Dactylus 0.67 of carpopropodus, with numerous long, weakly setulose setae; its distomedial and posterior margins with serrated setae. Unguis strong, serrated, 0.63 of dactylus length.

Maxilliped 2. Exopod 23-segmented; 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.

Pereopods. Exopod with 23–26 segments; its basal part with rounded outer corner. Endopod 1. Preischium with seven posterior setae. Ischium 0.67 times as long as merus, with numerous long sparsely plumose setae on medial and anteromedial margins, and shorter setae in proximal part of lateral margin. Merus with numerous long sparsely plumose setae on medial and lateral margins, and a distolateral bunch of long plumose setae. Carpus with seven medial bunches of setae, each bunch containing one long straight and four to six shorter bent plumose setae, becoming stronger and more strongly serrated in distal bunches. Propodus 2-segmented; its muscle in both segments; segment 1 is 0.51 of segment 2; together 0.88 length of carpus; segment 2 with smooth paradactylary setae. Unguis 0.58 times as long as dactylus.

Other endopods. Preischium with four to seven setae. Ischium 0.51–0.62 times as long as merus. Propodus segment 1 is 0.56–0.73 of segment 2; together 0.83–0.95 times as long as carpus. Unguis 0.41–0.69 times as long as dactylus.

Uropodal exopod 6.3 times as long as wide, 1.26 times as long as endopod and 1.26 times as long as telson; its proximal segment 0.23 of ramus length, with two distolateral spiniform setae. Endopod with three medial spiniform setae.

Variation. The Australian specimens were distinguished by the larger number of the telson lateral spiniform setae (53–54) than in the Japan material (28–42). However, the Australian specimens were somewhat larger than the Japanese (see above the Body length section). Additionally, the Tasman Sea specimens differ from the North-West Pacific ones by the slightly more produced anterior margin of the antennal scale, reaching the tip of the outer spine (not reaching in the North-West Pacific) and the three against two medial spiniform setae of the uropodal endopod. I had only three immature and damaged specimens at my disposal, and a more extensive collection is necessary to confirm any special status of the Australian population.

Distribution and habitat. West Indo-Pacific species. Meso-bathypelagic. Originally described from the North-West Pacific off Japan at depth 600–1200 m (possibly also shallower due to vertical sampling) ( Ii, 1964). An immature specimen, reported in the North-West Pacific by Birstein & Tchindonova (1958) at depth 0–4400 m, probably also belongs to this species. In this study, B. (B.) sphaerops is found in the Tasman Sea off New South Wales at depth 2324–2634 m ( Fig. 16 ).

Molecular characters. The only COI sequence that I was able to obtain was 16% distant from B. (B.) inopinata sp. nov., to which it also shows some, albeit weak, morphological affinity (see Comparison above). Divergence from other species of the subgenus was 32–51%.

Remarks. Ii (1964) provided a rather detailed description and illustrations of B. (B.) sphaerops and compared it with B. (B.) obtusata as the most closely related species. An immature specimen, identified by Birstein & Chindonova (1958) as B. (B.) spinifera , most probably belongs to B. (B.) sphaerops .

Figures

Figure 5. Boreomysis (Boreomysis) sphaerops. (A–F, H–N) subadult female, New South Wales, AM P.106636; (G) subadult male, New South Wales,AM P.106637. (A) head, dorsal (antennal scale spine missing); (B) head, lateral; (C) posterior part of abdomen with telson and uropods (setae not shown), dorsal;(D) posterior margin of abdomen,lateral;(E) posterior part of telson;(F) antennal scale (distolateral spine missing); (G) distal part of antennal scale; (H) labrum,ventral;(I) mandibular palp, posterior;(J) left mandible, ventral; (K) right mandible, dorsal; (L) pars centralis of right mandible; (M) maxilla 1, posterior; (N) maxilla 2, posterior. Scales (mm):A–K, M, N = 1.0; L = 0.25.

Figure 6. Boreomysis (Boreomysis) sphaerops, subadult female, New South Wales, AM P.106636. (A) maxilliped 1 endopod, posterior; (B) maxilliped 2, anterior; (C) pereopod 1 endopod, anterior. Scales (mm): 1.0.

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