Owstonia rhamma, Smith-Vaniz, William F. & Johnson, David, 2016

Smith-Vaniz, William F. & Johnson, David, 2016, Hidden diversity in deep-water bandfishes: review of Owstonia with descriptions of twenty-one new species (Teleostei: Cepolidae: Owstoniinae), Zootaxa 4187 (1), pp. 1-103 : 77-79

Owstonia rhamma new species

( Figures 68 , 69 )

Holotype. MNHN 1995–0005, 102 mm SL, Vanuatu, 20°19'58.8"S, 169°49'1.2"E, MUSORSTOM 8, sta. 963, beam trawl in 400–440 m, 20 Sep. 1994.

Other material. MNHN 2013–0354 , (1, 50), Vanuatu, W. of Malo Island, 15°41'16.8"S, 167°2'34.8"E, 321– 336 m, Exped. Santo 6, sta. at18, 21 Sep. 2006 .

Diagnosis. A species of Owstonia with LL pattern type 3; Dorsal fin III, 21; anal fin I, 14; nape scaly and cheek scale rows 2-3; dentary with 4 or 5 mid-lateral teeth noticeably enlarged and hooked backwards ( Fig. 69 ).

Description. (Characters of the 50 mm SL specimen that are observable are given in parentheses when they differ from the holotype; also see below Remarks.) A species of Owstonia with LL pattern type 3, consisting of a lateral line that does not contact posttemporal sensory canal near anterodorsal margin of gill opening, but instead continues posteriorly just below dorsal-fin base to soft rays 19/20 (16) and anteriorly for about 5 scale rows beyond dorsal-fin origin (on left side) and on right side slightly beyond dorsal-fin origin but too many scales missing on nape to determine if the lateral line makes a complete loop across nape (nape loop definitely incomplete in the small specimen). Dorsal fin III, 21; anal fin I, 14; pectoral fin 19 (21/23); gill rakers 16 + 29 (15 + 30) (left gill arch of holotype missing). Vertebrae: precaudal 11, caudal 17, total 28; anal-fin pterygiophores anterior to 1st haemal spine 2. Oblique body scale rows in mid-lateral series about 50; nape scaly and cheek scale rows 2 or 3. Lower limb margin of preopercle with 5−6 very small blunt spines which could easily be overlooked ( Fig. 8 F). Papillae in slight depression behind tip of premaxillary ascending processes 4, arranged in 2 approximately equally spaced pairs. Teeth in outer row of each premaxilla 16/22 (14); 2 (0) inner teeth anteriorly. Teeth in lateral row of each dentary 11/12 (11), 4 or 5 mid-lateral teeth noticeably enlarged and hooked backwards ( Fig. 69 ); symphyseal teeth 4 (3) moderately large, conical, and with 2/1 (1) inner teeth anteriorly. Depressed pelvic fin extending to base of anal-fin soft ray 4 (2). Caudal fin lanceolate. Holotype with caudal fin 2.3 times in SL; head 3.0 times in SL; body depth at anal-fin origin 3.5 times in SL.

Color pattern in alcohol: Holotype with dorsal fin uniformly pale (small specimen with traces of melanophores distally in spinous dorsal fin); membrane connecting maxilla and premaxilla with prominent black stripe extending to near end premaxilla, but inner membrane covering posterior part of dentary pale with no trace of melanophores. Life coloration unknown.

Proportions of 102 mm SL holotype, with those of the 50 mm specimen (in parentheses), as percentages of SL: predorsal length 27.2 (27.9); preanal length 56.7 (55); dorsal-fin base 63.5 (63.6); anal-fin base 35.3 (32.9); pelvicfin length 27.9 (31.3); caudal-fin length 44.1 (27.6); body depth at anal-fin origin 28.7 (29.3); head length 33.0 (33.8); upper jaw length 16.3 (18.7); upper jaw depth 7.3 (8.6); orbit diameter 13.5 (16.4). As percentages of head length: upper jaw length 49.3 (55.4); orbit diameter 41.0 (48.5).

Comparisons. Owstonia maccullochi and O. doryptera are the only other species with most of the diagnostic characters of O. rhamma but differ (characters of O. rhamma given in parentheses) as follows: O. maccullochi typically has more dorsal- and anal-fin soft rays 22 and 15 respectively (vs. 21 and 14, see Table 4) more pectoral fin rays, typically 20 or 21 (vs. 19), and more cheek scale rows 5–6 (vs. 2–3). Owstonia doryptera has a lateral line with a complete nape loop (vs. lateral line apparently not united as a complete loop across nape), more cheek scale rows, 5–6 (vs. 2 or 3) and no enlarged lateral dentary canines (vs. several lateral canines noticeably enlarged, Fig. 69 ).

Etymology. From the Greek rhamma (seam or suture) in allusion to the lateral line ( Fig. 68 ), which is reminiscent of a surgeon’s suture. The name is treated as a noun in apposition.

Distribution. ( Fig. 22 ) Known only from the Vanuatu type locality and Malo Island vicinity, where trawled in 400–440 and 321– 336 m.

Remarks. The small individual from near Malo Island is tentatively identified as Owstonia rhamma based, in part, on the Vanuatu locality and similarity of its dentition to that of the holotype, but in the absence of body and cheek row scale counts we cannot make an unequivocal identification. The relatively larger orbit diameter 13.5% SL (vs. 16.4%) and traces of melanophores on the spinous dorsal fin of Malo Island specimen are presumably size related.

Figures

FIGURE 8. Margins of preopercle lower limb (not drawn to scale), showing relative spine development in selected species of Owstonia: A, O. contodon, USNM 438013, 162 mm SL; B, O. elongata, USNM 432454, 110 mm SL; C, O. geminata, ASIZP 68128, 79 mm SL; D, O. maccullochi, holotype (right side reversed), AMS IA. 5815, 156 mm SL; E, O. maccullochi, NTM S. 11765 − 001, 146 mm SL; F, O. rhamma, holotype, MNHN 1995 – 0005, 102 mm SL; G, O. sarmiento, ANSP 165126, 82 mm SL; H., O. scottensis, CSIRO H. 7136 − 04, 103 mm SL; I, O. sibogae, ANSP 152035, 113 mm SL; J, O. taeniosoma, CAS 133928, 126 mm SL; K, O. tosaensis, ANSP 153169, 100 mm SL; L, O. weberi, ZMUC P. 531552, 127 mm SL.

FIGURE 22. Distributions of selected species of Owstonia based on specimens examined.

FIGURE 68. Owstonia rhamma, holotype, MNHN 1995 – 0005, 102 mm SL, Vanuatu; insert below dorsal view showing suture-like appearance of lateral line. Photograph by Sandra J. Raredon.

FIGURE 69. Owstonia rhamma close-up of head of holotype to show large hooked dentary canines. Photograph by Sandra J. Raredon.