Boreomysis (Boreomysis) inopinata, 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 : 93-98

Boreomysis (Boreomysis) inopinata sp. nov.

urn:lsid:zoobank.org:act:A9FAD035-4065-4881-90DF-A7682862CD78

Figs 1–3

Etymology. The species name inopinata (adjective) is Latin for unexpected, which is the reference to the unexpectedly excessive armature on the distomedial spine of its antennal scale.

Holotype. Male (partly dissected), 31 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. BPT, IN2018 _ V06 _157 (here and in further cases: the voyage and station code), 4MBT ( AM P.106632, GenBank OQ 699908, voucher B15) . Paratypes. 8 males, 28.5–32 mm, 1 subadult male, 12 subadult females, same as holotype ( AM P.106633) .

Additional material. Female (damaged), subadult female (damaged), 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, 1060 m, 09 Apr 2015, coll. BPT , S. J. Keable, M. A. McGrouther, IN2015 _ E02_010, beam trawl ( AM P.106634, GenBank OQ699907, voucher B8); juvenile (broken), 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. BPT , L. E. Hughes, F. Köhler, E. K. Kupriyanova, IN2017 _ V03 _087, BES ( AM P.106635).

Diagnosis. Anterodorsal margin of carapace ( Fig. 1A,B ) with acutely pointed and upwards directed short rostrum, reaching about half of antennular peduncle segment 1, flanked by smoothly rounded angles. Telson ( Fig. 1C,D ) 1.14–1.29 times as long as last abdominal segment, 2.6–2.9 times as long as wide anteriorly and 0.55–0.60 times as wide posteriorly as anteriorly. Telson lateral margins slightly concave in central part, with 54–60 spiniform setae arranged in series: numerous short alternated by about ten single long, and three or four terminal spiniform setae; longest terminal spiniform setae 0.06 of telson length and 1.1–2.0 of other terminal spiniform setae. Telson cleft 0.15–0.17 of telson length, without anterior dilatation, and with 51–60 rather long spinules. Eyes ( Fig. 1A,B,G ) moderate in size, pyriform, about 0.4 of head width; cornea oval, wider than, but not dominating over eyestalk; eye papilla small. Antennular peduncle ( Fig. 1A,B,H,I ) extending beyond half of antennal scale. Antennal scale ( Fig. 1A,B, J–L ) rather narrow, 4.7–5.5 times as long as wide; its distolateral spine secondarily armed with two to four spinules; apically with only slightly advanced distomedial angle, not exceeding beyond distolateral spine. Pereopod ( Figs 2I , 3D ) carpus with seven medial bunches; propodus 2-segmented. Pereopod 1 propodus segment 2 ( Fig. 2I ) rather long and slender, twice as long as segment 1. Only pleopod 3 exopod of male distally modified ( Fig. 3G ). Uropodal exopod ( Fig. 1C,N ) 4.5–5.8 times as long as wide, with two lateral spiniform setae nearly at one third of ramus length; its proximal segment 0.27–0.30 of ramus length. Endopod ( Fig. 1N ) with two or three medial spiniform setae.

Body length of males 28.5–32 mm.

Comparison. Boreomysis (B.) inopinata sp. nov. is uniquely distinguished from other species of the genus by the antennal scale distolateral spine secondarily armed with two to four spines. Otherwise, it is rather similar to B. (B.) tridens and differs from this species also by the smoothly rounded angles, flanking the rostrum (acutely pointed or occasionally brunt in B. (B.) tridens ); the pereopod 1 propodus segment 2 being twice as long as segment 1 (shorter than segment 1 in B. (B.) tridens ). Additionally, it may also differ by the telson lateral margins having 54–60 spiniform setae (34–40 spiniform setae in B. (B.) tridens ), and the telson cleft being 0.15–0.17 of the telson length (0.22–0.23 in B. (B.) tridens ), which needs to be confirmed on larger material. There is a similarity in the shape of the carapace anterior margin with B. (B.) sphaerops ; particularly in the presence of the lateral angles. However, B. (B.) inopinata sp. nov. has rather produced rostrum (short in B. (B.) sphaerops ), the telson cleft lacking anterior dilatation (present in B. (B.) sphaerops ), and the narrower antennal scale (4.7–5.5 times as long as wide against 4.1–4.5 in B. (B.) sphaerops ).

Description of holotype male. Anterodorsal margin of carapace with acutely pointed and upwards directed rostrum, flanked by distinct, apically smoothly rounded angles; laterally without minute concavities; anteroventral lobes large, triangular, pointed. Posterolateral margins of abdominal segment 6 with blunt or apically rounded scutella paracaudalia. Telson 1.29 times as long as last abdominal segment; 2.6 times as long as wide anteriorly, and 0.6 times as wide posteriorly as anteriorly. Cleft 0.15 of telson entire length, with about 60 rather long spinules; anterior dilatation absent. Lateral margins slightly concave, with 58 spiniform setae, including four terminal, forming groups of short, alternated by one long spiniform seta.

Eyes moderate in size, slightly flattened dorsoventrally, with oval cornea, slightly wider than and about as long as stalk. Eyestalk papilla present, rather small. Antennular peduncle, segment 1 with large distal dorsomedial tubercle; segment 2 with two dorsal tubercles; outer tubercle with apical process; segment 3 with lateral posterodistal bunch of long plumose setae; outer flagellum ventrally inflated near basis, with numerous long fine setae.Antennal peduncle with lateral spine; peduncle segment 2 about as long as segment 1 and segment 3, distomedially with slight prominence; segment 3, distal margin broadened like collar. Antennal scale rather narrow, 5.5 times as long as wide, and about twice as long as antennal peduncle.

Labrum conical. Mandible: left corpus, processus incisivus and lacinia mobilis 5-cuspate, pars centralis with eight serrated setae, pars praemolaris with fine setules, pars molaris with grinding plates and apical tuft of setules; right corpus, processus incisivus 3- or 4-cuspate, lacinia mobilis with over 20 cusps, pars centralis with 14 spiniform setae, among them distal serrated, pars praemolaris with fine setules, pars molaris with serrated grinding plates. Mandibular palp segment 2 with rather long plumose setae set apart; segment 3 is 0.88 times as long as segment 2, with four lateral, fourteen anteromedial, about 25 long proximomedial and about 40 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 five lateral, five posterior, five 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, 3.0 times as long as wide, about as long as endopod, with plumose setae on lateral and distal margins. Endopod segment 1 with about 12 anteromedial and four posteromedial setae; segment 2 is 1.5 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. Exopod 24-segmented. Coxa with two plumose medial setae. Basis without posterolateral group of 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 longest segment, 2.2 times as long as wide, with long, plumose and serrated medial setae. Merus and carpopropodus with weakly setulose lateral setae. Carpopropodus 0.77 times as long as merus, with long, plumose anterolateral and serrated medial setae. Dactylus 0.65 of carpopropodus length, with numerous long, weakly setulose setae; its distomedial and posterior margins with serrated setae. Unguis strong, serrated, 0.67 of dactylus length.

Maxilliped 2. Exopod 26-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 segments. Endopod 1. Preischium with six anterior and five posterior setae. Ischium 0.79 times as long as merus, with numerous long sparsely plumose setae on medial and short smooth setae on lateral margins. Merus with numerous long sparsely plumose setae on medial and lateral margins, and 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, about as long as carpus; its muscle in both segments; segment 2 twice as long as segment 1, with smooth paradactylary setae. Unguis 0.77 times as long as dactylus. Other endopods. Preischium with four setae. Ischium 0.62 times as long as merus. Propodus segment 1 is 0.73–0.77 of segment 2; segment 1 and 2 together 0.81–0.87 times as long as carpus. Unguis 1.16–1.27 times as long as dactylus.

Penis with small posterodistal lobe; anterodistal margin with about 12 long setae. Pleopod 1 exopod with about 24 segments; endopod less than half as long as exopod, without separation on segments and with numerous long setae. Pleopod 2 exopod with about 26 segments; endopod slightly shorter than exopod, with about 23 segments. Pleopod 3 exopod with about 28 segments; its distal segments with shorter and stronger spiniform setae; endopod shorter than exopod, with about 21 segments, bearing unmodified setae. Pleopod 4 exopod with about 22 segments; endopod slightly shorter than exopod, with about 23 segments. Pleopod 5 exopod with about 23 segments; endopod slightly shorter than exopod, with about 21 segments. Uropodal exopod, proximal segment with two distolateral spiniform setae; endopod with three medial spiniform setae.

Variation. Eyestalk papilla from hardly visible, tubercle-like to quite large, prolonged. Pereopod exopod 23–29-segmented.

Distribution and habitat. Bathypelagic. Tasman Sea off the Australian coast at depth of 919–2634 m ( Fig. 16 ).

Molecular characters. I was able to obtain mtDNA COI gene sequences from two specimens of B. (B.) inopinata sp. nov., collected from neighbouring localities in Tasmania.

The sequences were nearly identical, with 0.17% of divergence between them. They also showed relatively low, 16% distance to the sequence of B. (B.) sphaerops , compared to a much deeper, 33–49% distance to other species of the subgenus. The two species indeed have certain morphological similarity (see Comparison above), however, a more extensive taxon and gene sampling should reveal actual phylogenetic relationships.

Figures

Figure 1. Boreomysis (Boreomysis) inopinata sp. nov., holotype, male, 31 mm, AM P.106632. (A) habitus, lateral; (B) head, dorsal; (C) posterior part of body, dorsal;(D) posterior part of telson, dorsal; (E) posterior margin of abdomen, lateral; (F) posteriormargin of abdomen and proximal part of uropod (left side), ventral; (G) eye cornea, frontal; (H) antennular peduncle, medial; (I) male process of antennula, posterior; (J) antennal peduncle and scale, posterior; (K) distal part of antennal scale; (L) distolateral spine of antennal scale; (M) antennal peduncle, lateral; (N) uropod, ventral. Scales (mm):A, B = 10.0; C, E, F, N = 1.0; D, H, I, K, L (same scale as for K) = 0.5; G, J, M = 0.25.

Figure 2. Boreomysis (Boreomysis) inopinata sp. nov., holotype, male, 31 mm, AM P.106632. (A) labrum, ventral; (B) right mandible, ventral; (C) left mandible, ventral; (D) right lacinia mobilis, ventral; (E) mandibular palp, posterior; (F) maxilla 1, posterior; (G) maxilla 2, posterior; (H) maxilliped 1 endopod, posterior; (I) pereopod 1 (with flexor muscle of dactylus in propodus), posterior; (J) serrated seta of pereopod 1 carpus; (K) penis, lateral. Scales (mm):A–C, E–I, K = 1.0; D = 0.1; J = 0.25.

Figure 3. Boreomysis (Boreomysis) inopinata sp. nov. (A–I) holotype, male, 31 mm, AM P.106632; (J) paratype, female, 32 mm, AM P.106633. (A) maxilliped 2 endopod, posterior; (B, C) serrated setae of maxilliped 2 carpopropodus; (D) pereopod 5 endopod (with flexor muscle of dactylus in propodus), posterior; (E) pleopod 1, posterior; (F) pleopod 2, posterior; (G) pleopod 3, posterior; (H) pleopod 4, posterior; (I) pleopod 5 (also showing endopod muscles), anterior; (J) pleopod 5, posterior. Scales (mm):A, D–J = 1.0; B, C = 0.25.

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