Abstract
A new and previously cryptic fish species, Polymixia hollisterae, new species, proposed common name “Bermuda Beardfish,” is described from two voucher specimens collected in 1997 at a depth of about 280 fm or 512 m on the NW slope of the Bermuda Platform, and a third voucher collected by a midwater trawl in the north-central Gulf of Mexico. The species belongs to the paracanthopterygian acanthomorph genus Polymixia, family Polymixiidae, order Polymixiiformes, and is named after pioneering ichthyologist, ocean explorer, and conservationist Gloria E. Hollister (Anable). It is distinguished from all other species in the genus by its greater dorsal and anal fin heights (19% and 14% of SL, respectively), its extremely long pectoral and pelvic fins (22% and 14% of SL, respectively), its relatively large eye diameter (34% of total head length), and its morphologically distinctive first anal-fin radial. It has a unique pigmentation pattern on the dorsal, anal, and caudal fins consisting of narrow, dark black patches near the tips of the longest few soft dorsal- and anal-fin rays, and a caudal-fin margin with a dark black fringe covering the distal fourth of the fin. Based on an earlier molecular study that revealed it to be a cryptic species, P. hollisterae, new species, is closely related to P. japonica, but it differs by 20–33 nucleotides in a total alignment of 4,983 nuclear and mitochondrial sites. The new species shares a distinctive scale morphology with P. japonica and P. nobilis (the type species); an intermediate number of dorsal-fin rays (V,31–32), like P. japonica (V,31–34); a distinctive preopercle shape with P. japonica, P. lowei, and P. berndti; and a low number of pyloric caeca with P. lowei and P. berndti. Pored lateral-line scales number 35, an intermediate number compared to reported counts of other species (31–39). The three supraneurals are sigmoid-shaped like those of P. nobilis, while dorsal-fin proximal radials interfinger with neural spines in a unique pattern. Body shape, as studied with measurement proportions and multivariate morphometrics, is distinguished by a relatively large head, large eyes, long jaws, and a more streamlined pre-dorsal body profile than its congeners. Further research and additional collecting will be needed to ascertain the geographic distribution and conservation status of the new species.
Highlights
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Measurements specific to this study.—BD, maximum body depth measured vertically from the origin of the dorsal fin; Height/depth of head (HDH), head height measured vertically from ventral body margin at the anteroventral tip of the preopercle to the dorsal body margin at the tip of the supraoccipital; Preopercular head length (POHL), preopercular head length measured from the tip of the snout horizontally to the posterior margin of the preopercle; Standard length (SL), Grande and Wilson—New Bermuda species of Polymixia standard length measured from the tip of the snout to the end of the hypural plate; Total head length (THL), total head length measured from the tip of the snout to the posterior margin of the opercle
In the other examined species, there is a single radial between spines 5 and 6. In both specimens of P. hollisterae, there is one radial between each of spines 4 and 5 and 5 and 6, followed by two each between spines 6 and 7, 7 and 8, and 8 and 9, and one between spines 9 and 10 (Figs. 4, 7). These sequences (Fig. 8) can be summarized as P. japonica 1-2-2-2-1-2, P. hollisterae 11-2-2-2-1, P. nobilis 1-1-2-2-2-2, and P. lowei 1-1-2-2-1-2
Summary
Measurements specific to this study.—BD, maximum body depth measured vertically from the origin of the dorsal fin; HDH, head height measured vertically from ventral body margin at the anteroventral tip of the preopercle to the dorsal body margin at the tip of the supraoccipital; POHL, preopercular head length measured from the tip of the snout horizontally to the posterior margin of the preopercle; SL, Grande and Wilson—New Bermuda species of Polymixia standard length measured from the tip of the snout to the end of the hypural plate; THL, total head length measured from the tip of the snout to the posterior margin of the opercle. The vertical distances from the origin of the anal fin to the lateral line (AO–LL) represent 59% and 57% of BD, respectively and 48.5% for the juvenile paratype This species, like other species of Polymixia (e.g., Kotlyar, 1993; Borden et al, 2019), has 29 total vertebrae, 10 of which are abdominal (defined as lacking a complete haemal arch) and 19 of which are caudal vertebrae (Fig. 4). A trait that differs among individuals and among species is that six neural spines are counted in radiographs between the last dorsal-fin radial and the epurals in the holotype of P. hollisterae, but seven in the Bermuda paratype, while seven haemal spines occur between the last anal radial and the parhypural in both specimens (Fig. 4). P. hollisterae differs in the pattern of interdigitation of the anterior dorsal-fin proximal radials from P. japonica, P. nobilis, and P. lowei, and from about half of examined specimens of P. berndti. P. hollisterae appears to be the most streamlined of all species of Polymixia, suggesting that it is among the fastestswimming species of the genus
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