Boreomysis (Boreomysis) sibogae Hansen, 1910

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 : 98-101

Boreomysis (Boreomysis) sibogae Hansen, 1910

Fig. 4

Boreomysis sibogae Hansen, 1910: 25 , plate II, fig. 3a–e.—W. M. Tattersall, 1913: 870; 1951: 51.— Nierstrasz & Brender à Brandis, 1923: 109.— Illig, 1930: 414, 560.— Nouvel, 1943: 56, 58.—W. M. Tattersall & O. S. Tattersall, 1951: 63.—O. S. Tattersall, 1955: 5, 11, 15, 20, 22, 25, 66, 68, 74.—Holmquist, 1956: 428, 438, 442–445, 447.—Gordan, 1957: 343.—Birstein & Tchindonova, 1958: 281, 287, 290, 337, 338, 342.— Ii, 1964: 8, 13, 18, 19, 42, 47–49.— Pillai, 1965: 1682, 1686, 1687, fig. 6 (after Hansen, 1910, plate II, fig. 3e).— Mauchline & Murano, 1977: 50.—Fenton, 1986: 12, 55, 167–170, 185, 186, 194, 255, 331, fig. 2–3 (after Hansen, 1910, plate II, fig. 3d).— Lancraft et al., 1989: 227.— Müller, 1993: 29.— Petryashov, 1993a: 79, 81.— Ledoyer, 1995: 602, 603–605, fig. 1.—Hargreaves, 1997: 56.— Lowry & Stoddart, 2003: 430.— Sawamoto, 2014: 4.

Boreomysis spinifera Coifmann, 1937: 16 , plate 5, fig. 8a–e, plate 8, fig. 8f, g.—W. M. Tattersall, 1939 a: 206, 207, 232.

[Non Boreomysis spinifera .—Holmquist, 1956: 432, 434, 439, 445–447, fig. 4.—Birstein & Tchindonova, 1958: 289].

Type material. Syntypes, male and 2 females, Indonesia, 03°20'S 127°22.9'E, coll. Siboga , stn 185 ( NBC ZMA. CRUS.E.150021) .

Material. Female (illustrated), 31 mm, Tasmania, Flinders Commonwealth Marine Reserve , from 40°27'47"S 149°24'54"E to 40°27'40"S 149°21'50"E, 4129–4131 m, 21 May 2017, coll. BPT , L. E. Hughes, F. Köhler , E. K. Kupriyanova, IN2017 _ V03 _ 016, BES ( AM P.101174); juvenile (rostrum illustrated), 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. same as previous, IN2017 _ V03 _ 096, BES ( AM P.106640); juvenile, same as previous ( AM P.106641; GenBank OQ699905, voucher B6); subadult male (rostrum illustrated), 3 juveniles, New South Wales, off Bermagui , from 36°21'37"S 150°38'37"E to 36°19'24"S 150°39'01"E, 2835– 2739 m, 27 May 2017, coll. same as previous, IN2017 _ V03 _ 045, BES ( AM P.106643); subadult male (telson illustrated), 2 juveniles, 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.106642); juvenile, New South Wales, Hunter Commonwealth Marine Reserve , from 32°34'38"S 153°09'39"E to 32°36'47"S 153°08'56"E, 2434–2480 m, 03 Jun 2017, coll. same as previous, IN2017 _ V03 _ 076, BES ( AM P.106645); juvenile, Tasmania, Bass Strait , from 39°33'07"S 149°33'11"E to 39°29'46"S 149°35'53"E, 4197– 4133 m, 23 May 2017, coll. same as previous, IN2017 _ V03 _ 030, 4MBT ( AM P.106644); 2 juveniles, 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.101188); 26 damaged specimens, Tasmania, Bass Strait , from 39°27'43"S 149°16'37"E to 39°27'54"S 149°14'46"E, 2774– 2697 m, 22 May 2017, coll. same as previous, IN2017 _ V03 _ 023, BES ( AM P.101178); juvenile, same as previous ( AM P.106639; GenBank OQ699906, voucher B10) .

Diagnosis. Anterodorsal margin of carapace ( Fig. 4A–D ) with rather short, acutely pointed and upwards to forwards directed rostrum, reaching proximal part of antennular peduncle segment 1, flanked by nearly smoothly rounded margins, not forming angles. Telson ( Fig. 4F–H ) 1.1–1.2 times as long as last abdominal segment, 3.0–3.4 times as long as wide anteriorly and 0.53–0.61 as wide posteriorly as anteriorly. Telson lateral margins slightly concave in central part, with 36–60 spiniform setae arranged in 8–15 series: setae increasing in length within series, and three terminal spiniform setae; longest terminal spiniform seta 1.0–3.0 times as long as shorter medial ones. Telson cleft 0.20–0.25 of telson length, without anterior dilatation and about 85 rather long spinules. Eyes ( Fig. 4A–D ) large to moderate in size, broad, slightly flattened dorsoventrally, 0.33–0.37 of head width; cornea shorter and wider than, but not dominating over eyestalk; eye papilla small to relatively long.Antennular peduncle extending beyond half of antennal scale ( Fig. 4A,D ).Antennal scale ( Fig. 4D,I ) 3.3–4.2 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. 4L ) carpus with seven medial bunches; propodus 2-segmented. Pereopod 1 propodus segment 2 is 1.6 times as long as segment 1. Uropodal exopod ( Fig. 4K ) with two lateral spiniform setae; its proximal segment 0.20–0.27 of ramus length. Endopod ( Fig. 4L ) with one or two medial spiniform seta or without them.

Body length 13–38 mm.

Comparison. Boreomysis (B.) sibogae is not known yet to have any unique characters in the genus, and its affinity cannot be clearly established as well. It seems to be most similar to B. (B.) brucei W. M. Tattersall, 1913 , B. (B.) californica Ortmann, 1894 , and B. (B.) intermedia Ii, 1964 . Boreomysis (B.) brucei and B. (B.) intermedia are similar to the immature specimens of B. (B.) sibogae , and their taxonomic status is unclear (see Remarks). From B. (B.) californica it is distinguishable by the somewhat deeper telson cleft, which is 0.20–0.25 of the telson length (0.15–0.18 in B. (B.) californica ), and the distal part of the antennal scale not produced beyond the outer spine (produced in B. (B.) californica ).

Description of Australian specimens (adults). Anterodorsal margin of carapace with relatively short, acutely pointed and upwards directed rostrum, reaching proximal part of antennular peduncle segment 1, flanked by nearly smoothly rounded margins; laterally without minute concavity; anteroventral lobes triangular, pointed. Posterolateral margins of the abdominal segment 6 with apically rounded or pointed scutella paracaudalia. Telson 1.08–1.15 times as long as last abdominal somite and nearly reaching tip of uropodal endopods; 3.3–3.4 times as long as wide anteriorly, and 0.58–0.60 times as wide posteriorly as anteriorly. Telson lateral margins slightly concave in central part, with about 36–58 spiniform setae arranged in about 15 series of short, alternated by one long spiniform seta; longest terminal spiniform seta 1.5–1.6 times as long as shorter medial ones. Cleft 0.22 of telson entire length, with about 85 spinules; dilatation absent.

Eyes of moderate size to relatively large from dorsal view, broader than long, slightly flattened dorsoventrally; cornea thinner and wider than, but not dominating over eyestalk. Eyestalk papilla present, short. Antennular peduncle 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 less than twice as long as antennular peduncle, 3.3–3.5 times as long as wide; apically with only slightly advanced distomedial angle, not produced beyond outer spine.

Mouthparts and maxillipeds similar to previous species.

Pereopods. Exopod with 23–27 segments; its basal part with rounded outer corner. Endopod 1. Preischium with six posterior setae. Ischium 0.64 times as long as merus, with numerous long sparsely plumose setae on medial and anteromedial margins, and shorter setae on lateral margin. 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 two to four shorter bent plumose setae, becoming stronger and more strongly serrated in distal bunches. Propodus 2-segmented; its muscle in both segments; segment 1 is 0.62 times as long as segment 2; segment 1 and 2 together 0.73 as long as carpus; segment 2 with smooth paradactylary setae. Unguis 0.54 times as long as dactylus. Other endopods. Propodus segment 1 is 0.60 times as long as segment 2; segment 1 and 2 together 0.86 times as long as carpus. Unguis 0.76 times as long as dactylus.

Uropodal exopod about 6 times as long as wide, 1.4 times as long as endopod and 1.22 times as long as telson; its proximal segment 0.20–0.22 of ramus length, with two distolateral spiniform setae. Endopod with 0–1 medial spiniform setae.

Variation. The rostrum is rather variable in length and direction, depending on the age the specimens ( Fig. 4A–D ). It is relatively short and directed upwards in mature individuals. In the juveniles the rostrum is extended forward till the middle of the antennular peduncle segment 1. The eyes are wider in adults, with smaller papilla, compared to juveniles. In the antennal scale, the distal projection is occasionally slightly advanced beyond the outer spine in immature individuals. The adult specimens from the Gulf of Aden (Arabian Sea) are distinguished by the smaller size (13–14 mm against 28–38 mm in other parts of the range), the longer eye papilla and longer outer terminal spiniform setae of the telson (3.0 against 1.0–1.6 times as long as the shorter medial ones in other parts of the range). Possible taxonomic significance of this difference has to be studied on a larger material.

Distribution. The species was first described from the Banda Sea near Manipa Island in Indonesian waters (Hansen, 1910). Later it was collected from the Indian Ocean off Somali ( Illig, 1930), the Gulf of Aden (Coifmann, 1937; W. M. Tattersall, 1939), the South and Mid-Atlantic Ocean (O. S. Tattersall, 1955; assigned with doubt), the Okhotsk Sea (W. M. Tattersall, 1951; Birstein & Tchindonova, 1958) and in the North-West Pacific (Birstein & Tchindonova, 1958), Southern Indian Ocean ( Ledoyer, 1989, 1995), in the Weddell Sea of the Southern Ocean ( Lancraft et al., 1989), and possibly also in the North-eastern Atlantic (Hargreaves, 1997). Birstein & Tchindonova (1958) considered B. (B.) sibogae the Pacific species, sporadically recorded in the Atlantic and Indian Oceans. If the records from the Atlantic, Indian and Southern Ocean are correct, the species definitely has a wider range. First collected in the Australian waters from a fish stomach in the Tasman Sea east of Tasmania (Fenton, 1986). In the current study its presence in Australia is confirmed by eight records all along the Tasman Sea coast ( Fig. 16 ).

Habitat. Epi-bathypelagic. Found above the depths of 50–5000 m; in the Australian waters at depth of 200–4197 m. Parasitized by the dajid isopods Streptodajus equilibrans Nierstrasz et Brender à Brandis, 1923, which was sampled from the type specimens at the depth of 1536 m (Nierstrasz & Brender à Brandis, 1923).

Molecular characters. The two mtDNA COI gene sequences, one from the Tasmanian coast and another from the New South Wales, were 7.5% distant from each other, which is rather deep intraspecific differentiation within the Tasman Sea. Boreomysis (B.) sibogae was 43–54% distant from other species of the subgenus.

Remarks. The subadult specimens, originally shortly described by Hansen (1910), were not fully developed and had somewhat smaller eyes than the adult female from the Tasman Sea, which was at my disposal. Similarly, the subadults and juveniles in the Australian collection also had smaller eyes. Boreomysis (B.) brucei was originally considered to be closely related to B. (B.) sibogae (W. M. Tattersall, 1913) , differing only by the longer rostrum and slightly advanced distal part of the antennal scale. It was described from two immature specimens. Birstein & Tchindonova (1958) also considered a possibility of B. (B.) brucei to be a variety of B. (B.) sibogae . Plausible unity of the two taxa was later expressed by Ii (1964). He also described B. (B.) intermedia , entirely based on small immature specimens, which looked like immature B. (B.) sibogae from the Australian waters, with prolonged rostrum and thinner antennal scales with somewhat produced distal part. Ii also considered B. (B.) arctica to be closely related to B. (B.) sibogae , with slightest possibility of them even being conspecific. However, B. (B.) arctica is more distant than B. (B.) brucei , B. (B.) intermedia and B. (B.) sibogae by the rostrum being always rather long with smoothly rounded lateral margins, having rather long telson and deep cleft, long and narrow antennal scale. The mtDNA lineages of B. (B.) arctica and B. (B.) sibogae were 50–54% distant from each other. Finally, Ii (1964) suggested that also B. (B.) californica may be close to B. (B.) sibogae . The difference is indeed rather small (see Comparison), but I will leave this question open for future. Ledoyer (1995) noticed that his previous record of B. (B.) brucei from the Southern Indian Ocean ( Ledoyer, 1989) belonged to B. (B.) sibogae .

W. M. Tattersall (1939) mentioned that B. (B.) sibogae is also distinguished from other species by the great length of the first segment of the uropodal exopod. As I measured it in the Australian species and from illustrations of other species of the genus, I found it to be similar to the majority of them.

O. S. Tattersall (1955) synonymized B. (B.) spinifera Coifmann, 1937 with B. (B.) sibogae , which was not supported by Holmquist (1956) and Birstein & Tchindonova (1958), but supported by Ii (1964), Pillai (1965) and Fenton (Fenton, 1986; Fenton in Lowry & Stoddart, 2003). According to the original figures of Coifmann (1937), the small, 14 mm long, male had a rather short rostrum, small eyes with long papilla, the antennal scale 3.7 times as long as wide, the uropodal endopod with two spiniform setae, the telson cleft without dilatation, and the longest terminal spiniform setae of the telson about 3.0 times as long as the shorter medial ones. From the adults of B. (B.) sibogae they were only distinguished by the smaller size, longer eye papilla, and longer terminal spiniform setae. At the current stage of our knowledge this is indeed a rather small difference, and I tend to support the synonymization. According to the illustrations of Holmquist (1956), the specimens from the collection of Illig (1930), which she assigned to B. (B.) spinifera , had clear dilatation at the anterior part of the telson cleft. This is not characteristic either to B. (B.) sibogae or to B. (B.) spinifera in its original sense. Due to poor preservation of specimens it is not possible to assign them to any species. In my opinion, an immature specimen under the name B. (B.) spinifera in Birstein & Chindonova (1958) probably belongs to B. (B.) sphaerops (see details in the remarks section about B. (B.) sphaerops ).

The overall identity of B. (B.) sibogae and its various related taxa still remain rather confusing due to poor preservation of the specimens and wide morphological variation concerning the rostrum, eyes, antennal scales and uropods.

Figures

Figure 4. Boreomysis (Boreomysis) sibogae. (A, D–G, I–K) female,31 mm, Tasmania,AMP.101174;(B) subadult male, New South Wales, AM P.106643; (C) juvenile, New South Wales,AM P.106640; (H) subadult male, New South Wales,AM P.106642. (A) head, lateral; (B) rostrum and eyes, lateral; (C) rostrum and eyes, lateral; (D) head, dorsal; (E) posterior margin of abdomen, lateral; (F) posterior margin of abdomen and telson (lateral spiniform setae not shown), dorsal; (G) posterior part of telson; (H) telson; (I) antennal scale; (J) uropodal endopod, ventral; (K) uropodal exopod (most of setae not shown); (L) pereopod 1 endopod, posterior. Scales (mm): 1.0.

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