Owstonia ignota, 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 : 54-56

Owstonia ignota new species

( Figure 42 )

Owstonia n. sp. Myers & Donaldson, 2003:631 (listed, Saipan).

Holotype. USNM 344400, 118 mm SL, male, Mariana Islands, near Saipan, 15°36'N, 145°34'E, in vicinity of active submarine volcano (Ruby Volcano), found floating on surface over depth of 186 m, Division of Fish & Wildlife personnel, 25 Oct. 1995.

Diagnosis. A species of Owstonia with LL pattern type 1; lower limb margin of preopercle without spines; dorsal fin III, 19; no dark premaxillary stripe; adults with about 38–39 teeth in outer row premaxilla; papillae in slight depression behind tip of ascending process of premaxillae without a cluster of about 5 minute papillae present between the posterior pair of relatively large papillae.

Description. A species of Owstonia with LL pattern type 1, consisting of a simple lateral line that originates from posttemporal sensory canal near anterodorsal margin of gill opening, curves upward and backward then continues posteriorly just below dorsal-fin base to soft ray 19. Dorsal fin III, 20; anal fin I, 13; pectoral fin 20; gill rakers 14 + 27 = 43. Vertebrae: precaudal 11, caudal 17, total 28; anal-fin pterygiophores anterior to 1st haemal spine 3. Oblique body scale rows in mid-lateral series about 37 or 38; nape scaly and cheek scale rows about 3 or 4. Lower limb margin of preopercle without spines. Papillae in slight depression behind tip of premaxillary ascending processes 4, relatively large and arranged in 2 almost equally spaced pairs. Teeth in outer row of each premaxilla 38/39, anterior ones larger and more strongly hooked; 2‒3 inner teeth anteriorly. Teeth in lateral row of each dentary 15/16, with 6 or 7 of the anterior ones robust and strongly hooked ( Fig. 10 E); symphyseal teeth 3‒4, relatively large, conical, and with 2 similar-sized inner teeth anteriorly. Pelvic fin presumably sexually dimorphic, depressed pelvic fin extending beyond last anal-fin ray in male holotype. Other Owstonia species with individuals that have very long pelvic fins (e.g., O. contodon and O. whiteheadi ) for which a reasonable number of adults are available also include individuals with relatively short fins, strong evidence of sexual dimorphism. Caudal fin lanceolate. Holotype with caudal fin 2.5 times in SL; head 4.2 times in SL; body depth at anal-fin origin 3.7 times in SL.

Color pattern in alcohol: Adults with dorsal fin pale, membrane connecting maxilla and premaxilla, and inner membrane covering posterior part of dentary unpigmented. In fresh specimen, fins and body pink or red, paler below, and elongate pelvic-fin soft ray mostly white.

Proportions of 118 mm SL male as percentages of SL: predorsal length 28.6; preanal length 52.8; dorsal-fin base 60.8; anal-fin base 33.1; pelvic-fin length 64.2; caudal-fin length 40.1; body depth at anal-fin origin 27.2; head length 29.9; upper jaw length 16.1; upper jaw depth 7.4; orbit diameter 12.3. As percentages of head length: upper jaw length 54.0; orbit diameter 41.2.

Comparisons. Owstonia ignota is very similar to the allopatric O. hawaiiensis but differs in having larger and more strongly hooked mid-lateral dentary teeth (compare Figs. 10 D, 10E) and papillae in slight depression behind tip of ascending process of premaxillae without a cluster of about 5 minute papillae present between the posterior pair of relatively large papillae (vs. cluster of minute papillae present between the posterior pair of relatively large papillae in O. hawaiiensis ). The allopatric O. grammodon also shares many characters with O. ignota , including adults with relatively high numbers (33–39) of teeth in outer row of each premaxilla but differs in having a prominent black premaxillary stripe (vs. premaxillary stripe absent in O. ignota ). The only other congener from the central Pacific Ocean known from adults is the very distinctive O. mundyi , which differs in having nape and cheeks without scales (vs. nape and cheeks scaly), oblique body scale rows in mid-lateral series 97–108 (vs. 37‒38) and a black premaxillary stripe (vs. premaxillary stripe absent).

Etymology. The specific epithet, from the Latin ignotus (unknown), is in allusion to our initial uncertainty about how to taxonomically treat this specimen considering the minor characters that distinguish it from the holotype of Owstonia hawaiiensis . Furthermore, with only a single specimen of this species available, sexual dimorphism of the pelvic fin can be reasonably hypothesized but still remains unknown.

Distribution. ( Fig. 24 ) Known only from the Mariana Islands (Ruby Volcano vicinity) type locality. It is possible that O. ignota is a Pacific Plate endemic ( Springer, 1982), but because very few hard-bottom fishes that occur on the Pacific Plate in depths ≥ 200 m have been adequately sampled, their distributions are poorly known.

Remarks. Our decision to recognize Owstonia ignota and O. hawaiiensis as different species has the advantage of calling attention to both of them (despite their minor but presumably consistent distinguishing characters). With opposite sexes only and single specimens available for each of these species, we cannot dismiss the possibility that dentition differences ( Figs. 10 D, 10E) are due to sexual dimorphism. However, we have also been influenced by the fact that about 25% of the shore fishes of the Hawaiian Islands, including species to 200 m, are apparently endemic ( Randall, 2007). The Marianas Islands are located along the western margin of the Pacific Plate near the eastern edge of the Philippine Plate. Although the geological history of the region is very complex ( Springer, 1982), it is doubtful that a benthic deep water species whose ecology appears to be closely associated with sea-floor spreading would have a distribution that extends from near the western margin of the Pacific Plate to the Hawaiian Islands. Further discussion of the possible zoogeographic affinities of Owstonia ignota is unjustified in view of the limited sampling of seamounts in the central Pacific region at depths where species of Owstonia might possibly occur.

Figures

FIGURE 10. Premaxilla and dentary (mostly right side reversed) to show dentition in selected species of Owstonia. A, O. contodon, USNM 438013, 162 mm SL; B, O. fallax, CSIRO H. 763 ‒ 06, holotype, 110 mm SL; C, O. grammodon, USNM 149321, 127 mm SL; D, O. hawaiiensis, BPBM 29600, holotype, 124 mm SL; E, O. ignota, USNM 344400, holotype, 118 mm SL; F, O. japonica, ANSP 151948, 136 mm SL.

FIGURE 24. Distributions of selected species of Owstonia based on specimens examined, except records of O. mundyi from Kingman Reef based solely on submersible videos, and possibly could have been misidentifications of O. hawaiiensis.

FIGURE 42. Owstonia ignota, holotype, USNM 344400, 118 mm SL, male, Mariana Islands, near Saipan. Photograph by Robert F. Myers.