Lasiognathus dinema, Theodore W. Pietsch & Tracey T. Sutton, 2015

Theodore W. Pietsch & Tracey T. Sutton, 2015, A New Species of the Ceratioid Anglerfish Genus Lasiognathus Regan (Lophiiformes: Oneirodidae) from the Northern Gulf of Mexico, Copeia 103 (2), pp. 429-432 : 429-432

Lasiognathus dinema , new specIes

Figures 1–3

Holotype.— UW 152603, female, 95 mm, NOAA FRV Pisces, Station B249, DD2, northern Gulf of Mexico, 27.5°N, 88.5°W, Irish Herring Trawl, depth of collection 0– 1271 m, bottom depth 2104 m, 26 June 2011 ( Fig. 2 A).

Paratypes.— UW 152604, female, 30 mm, R/V Meg Skansi, Station SW6D-net 2, northern Gulf of Mexico, 27.0°N, 90.1°W, 10 m 2 MOCNESS midwater trawl, depth of collection 999–1200 m, bottom depth 2559 m, 23 June 2011 ( Figs. 1 , 2 B); UW 154626, female, 36 mm, R/V Meg Skansi, Station SE3D-net 1, northern Gulf of Mexico, 26.6°N, 86.8°W, 10 m 2 MOCNESS midwater trawl, depth of collection 800–999 m, bottom depth 2967 m, 11 September 2011 ( Fig. 3 ).

Diagnosis.— Escal bulb with an elongate, cylindrical, internally pigmented anterior appendage; distal escal appendage a short cylindrical stalk, with an expanded distal end and a pair of tapering, filamentous prolongations emerging anteriorly from

bases of escal hooks; distal escal appendage bearing three, lightly pigmented, bony, hook-like denticles; posterior escal appendage membranous, antero-posteriorly compressed, with a scalloped or rounded distal margin ( Figs. 2 , 3 ).

Description.— Length of illicium 15–47 mm (49.5–50.0% SL); illicium of three known specimens fully extended anteriorly, cutaneous sheath surrounding posterior extension of illicial pterygiophore fully internalized ( Pietsch, 2009:84, fig. 85). A cylindrical, internally pigmented, anterior escal appendage (a light-guiding structure, without a homolog in any other known species of Lasiognathus ; Pietsch, 2009:237, figs. 245, 248), rounded distally in holotype, more elongate and tapering to a point in paratypes, length 1.3–2.8 mm (4.3– 2.9% SL). A thin, translucent, broad-based, antero-posteriorly compressed, posterior escal appendage, length 0.9–2.2 mm (3.0–2.3% SL), with a scalloped or rounded distal margin, emerging from below escal pore. Distal escal appendage cylindrical, with narrow base and distal swelling, length 1.9–4.8 mm (6.3–5.0% SL), bearing three lightly pigmented, strongly curved, bony hooks: one somewhat larger, length 2.0– 2.2 mm (6.7–2.2% SL), emerging from distal tip, directed posteriorly; and a pair of near equal size, length 1.4/1.6–1.4/ 1.9 mm (5.0/5.3–1.9/2.0% SL), situated somewhat below, directed anteriorly. A pair of elongate, filamentous, tapering prolongations of distal appendage emerging slightly above bases of anteriorly directed escal hooks, considerably smaller in paratypes, length 1.6/ 2.2 mm (6.7/7.3% SL); more highly developed in holotype, length 6.3/ 6.4 mm (6.6/6.7% SL).

The esca of all three type specimens is well preserved ( Figs. 2 , 3 ). The head and body of the holotype, however, is in extremely poor condition, so badly damaged upon capture that only a few of the standard ceratioid measurements can be made (the following are given in percent of standard length, values for the smaller paratype are followed by those of the holotype when available): tip of upper jaw to posteriormost margin of preopercle 41.7–?; tip of upper jaw to anteriormost margin of opercular opening 53.3–?; distance between tips of sphenotic spines 25.0–?; tip of sphenotic spine to posttemporal 13.7–?; tip of sphenotic spine to tip of quadrate spine 60.0–?; length of sphenotic spine 6.0–2.2; length of quadrate spine 5.8–2.3; length of premaxilla 36.7–35.8; length of lower jaw 34.7–28.4; longest tooth in upper jaw 11.7–6.3; longest tooth in lower jaw 4.7– 2.6. Total number of teeth on premaxillae 24–86, on dentaries 23–98; vomerine teeth absent; dorsal-fin rays 5– 6; anal-fin rays 5–5; pectoral-fin rays 18/19–19/19; pelvic fins absent; caudal-fin rays 9–9. Remaining description as for the genus ( Bertelsen and Pietsch, 1996; Pietsch, 2009).

Geographic distribution.— Lasiognathus dinema is known from three female specimens collected in the northern Gulf of Mexico, over the Mississippi Fan bathyal accumulation (27–28°N, 87–90°W; bottom depths 2000–3000 m). Specimens were collected in closing trawls fished between 800– 1000 and 1000–1200 m, and in a non-closing trawl fished between 0–1271 m.

Etymology.— The name dinema , is derived from the Greek, di, a prefix meaning ‘‘two,’’ and nema, ‘‘thread,’’ in allusion to the two elongate, thread-like prolongations emerging anteriorly from the bases of the escal hooks of this species ( Figs. 1–3 ).

DISCUSSION

The specimens for this study were collected as part of an ongoing Natural Resource Damage Assessment Process conducted by the National Oceanic and Atmospheric Administration (for more information, see http://www.darrp.noaa.gov/about/nrda.html) pursuant to the Deepwater Horizon Oil Spill (DWHOS). The stations at which the type specimens were collected were within a 250 km radius of the Macondo wellhead, at depths between 800– 1300 m. The depths coincided with the depths of massive horizontal intrusions of hydrocarbons during and after DWHOS (~ 800–1200 m; Camilli et al., 2010; Valentine et al., 2010; Kessler et al., 2011), though the specimens described herein were not necessarily exposed. The finding of a new species in this region adds to our knowledge of the deep-pelagic Gulf in particular, and to the bathypelagic zone in general, which post-Census of Marine Life surveys have identified as the most chronically under-sampled environment on earth ( Webb et al., 2010). In addition to describing a new species, this report is the first record of the genus Lasiognathus in the Gulf.

Like the majority of ceratioid anglerfishes, examination of all available material of Lasiognathus has revealed no characters that allow separation of the species other than those of the esca and its appendages ( Bertelsen and Pietsch, 1996; Pietsch, 2005, 2009). The differences in escal morphology, however, now strongly indicate the existence of six species. Lasiognathus dinema differs from all previously recognized species of the genus in having an anterior escal appendage and a pair of elongate, filamentous prolongations of the distal escal appendage, the former having no apparent homolog in any of its congeners; the latter represented by a single prolongation in L. saccostoma , L. intermedius , and L. amphirhamphus , but absent altogether in L. beebei and L. waltoni . The new species differs further from L. beebei in having the escal hooks emerging from a cylindrical distal appendage, rather than from a transverse, fanshaped distal appendage ( Bertelsen and Pietsch, 1996:404, fig. 2); from L. intermedius in having a broad-based, anteroposteriorly compressed posterior escal appendage instead of a cylindrical appendage ( Bertelsen and Pietsch, 1996:406, fig. 4); from L. saccostoma in having simple distal prolongations of the distal escal appendage instead of bearing numerous lateral serrations or filaments ( Bertelsen and Pietsch, 1996:407, fig. 5); and from L. amphirhamphus in having three escal hooks instead of only two ( Pietsch, 2005:78, fig. 2).

Figures

Fig. 1. Lasiognathus dinema Pietsch and Sutton, new species, paratype, UW 152604, female, 30 mm SL.

Fig. 2. Escae of Lasiognathus dinema Pietsch and Sutton, new species, in preservation: (A) Holotype, UW 152603, female, 95 mm SL, left lateral view; (B) Paratype, UW 152604, female, 30 mm SL, right lateral view (prolongation of distal escal appendage rotated to show anterior face).

Fig. 3. Esca of Lasiognathus dinema Pietsch and Sutton, new species, paratype, UW 154626, female, 36 mm SL, left lateral view, in preservation. Image courtesy of L. Malarky (NSUOC).