Etmopterus burgessi, Jayna A. Schaaf-da Silva & David A. Ebert, 2006

Jayna A. Schaaf-da Silva & David A. Ebert, 2006, Etmopterus burgessi sp. nov., a new species of lanternshark (Squaliformes: Etmopteridae) from Taiwan., Zootaxa 1373, pp. 53-64 : 54-61

Etmopterus burgessi sp. nov.

Broad-snout Lanternshark

(Fig. 1, Table 1)

Holotype. CAS 223476, 355 mm TL, adult male, Ta-Chi, Taiwan, 24° 53' N, 122° 01' E, collected by David A. Ebert, 11 May 1988.

Paratypes. 3 specimens, all collected at Ta-Chi, Taiwan, 24° 53' N, 122° 01' E. CAS 223477 (Fig. 2), adult female, 406 mm TL, 22 May 2005 ; CAS 223478, juvenile female, 241 mm TL, 23 May 2005 ; CAS 223479, juvenile female, 239 mm TL, 21 May 2005 .

Diagnosis. A relatively large species of Etmopterus with the following combination of characters: snout broad, 8.0 (7.1-8.3)% TL; mouth broad and strongly arched; upper teeth in 2-3 series, each tooth with a median lanceolate cusp, flanked by three smaller lateral cusplets on each side; denticles short and robust, arranged in regular longitudinal rows over most of body; denticles conspicuous on ventral snout surface, and surface of second dorsal fin; second dorsal fin height short, 40.7 (34.6-36.2)% fin length; posterior branch of flank marking short, base of flank marking wide; caudal peduncle short, 11.4 (11.1-12.7)% TL; color in life charcoal grey above, darker grey to black below.

Description. Body fusiform, relatively stout; head long 22.1 (21.1-22.2)% TL, not depressed, height 0.93 (0.65-0.77) times width. Pre-orbital snout long, rounded in lateral view, width broad, 8.0 (7.1-8.3)% TL, horizontal length 2.10 (2.10-2.20) in length of eye. Eye large, oval-shaped, length 5.22 (4.57-5.03) in head, 1.65 (1.73-2.09) times height. Spiracle large, semicircular, greatest diameter 3.06 (3.62-4.11) in eye length. Nasals very large, oblique; nostril width about equal to internarial distance; nasal flaps poorly developed, anterior flap triangular. Gill openings very large, slightly oblique, subequal in size, becoming progressively smaller posteriorly, height of first gill slit 2.1 (1.6-1.9)% TL. Mouth broad, strongly arched, width 1.18 (1.22-1.45) in preoral length.

Teeth dissimilar in upper and lower jaws; upper teeth multicuspid in 2-3 series, each with a long median cusp flanked by lateral cusplets more than one half the length of median cusp; teeth in lower jaw in single series, unicuspid, interlocking, oblique, bladelike. Teeth in first row of upper jaw 26 (24-26), first row of lower jaw 40 (32-36). Vertebral count: 65.

Dermal denticles small, low, unicuspid with erect thorn-like conical crowns, recurved posteriorly; arranged in regular longitudinal rows on trunk, back, caudal fin, and second dorsal fin. Dermal denticles irregular on abdomen, flank markings above pelvic fins, and caudal markings.

Pelvic flank marking poorly defined, consisting of both an anterior and posterior branch; anterior branch long, slender, 8.1 (7.1-9.8)% TL, extending just forward of pelvicfin origin; posterior branch truncated distally, slightly shorter than anterior branch, 7.3 (8.4-9.2)% TL, terminating well past the second dorsal-fin insertion and in line with edge of free rear tip; base of flank marking wide. Caudal marking base broad, forming a saddle anteriorly, covering the entire ventral surface of posterior caudal peduncle; at about the lower caudal-lobe origin, marking extends dorsally to a level almost half of caudal peduncle height, tapering to a point forming the central caudal marking. Central caudal marking narrowly ovoid, slightly longer than eye length, 5.7 (4.7-6.4)% TL. Viewed laterally, central caudal marking is well apart from the flank marking, separated by at least one central caudal marking length. Upper caudal marking narrow, about equal to length of central caudal marking, 5.9 (6.4-7.4)% TL.

Distal margins of fins largely covered with skin, not fringed with naked ceratotrichia. Each dorsal fin with a grooved spine just anterior to the fin origin. First dorsal fin spine small, less than half the length of second dorsal spine. First dorsal fin low, slightly rounded, length 7.4 (6.5-7.0)% TL; fin-spine origin well behind pectoral-fin rear tip; insertion of base well forward of pelvic-fin origin; much smaller than second dorsal fin. Length of first dorsal fin 1.65 (1.38-1.48) in second dorsal fin; height of first dorsal fin 1.62 (1.75-2.13) in second dorsal fin. Second dorsal fin relatively small, upright, concave posterior margin, free rear tip long, spine length 0.74 (0.41-0.51) in height of second dorsal fin; fin-spine origin just behind insertion of pelvic fin; interdorsal space 0.96 (0.92-1.06) in length from snout tip to pectoral-fin origin. Dorsal -caudal space relatively short 11.4 (11.1-12.7)% TL.

Coloration. In life very darkly pigmented; charcoal gray to blackish. Dorsum, ventrum, and lateral surfaces have no obvious boundaries. Belly and flank markings may be weakly displayed; magnification shows an increased density of melanophores. Upper caudal lobe very dark; lower lobe and tips of fins sometimes lighter grey but not translucent.

Size. Maximum length at least 355 mm for adult male (holotype) and 406 mm for adult female (paratype CAS 223477).

Distribution. All four type specimens were collected on the continental slope off northeastern Taiwan at depths greater than 300 m.

Etymology. The species is named in recognition of George Burgess for his contributions to the systematics of this genus.

Discussion

Etmopterus burgessi can be separated from other western North Pacific Etmopterus species based on a combination of the following characters: snout width, first gill slit length, caudal peduncle length, second dorsal fin height, flank and caudal markings, tooth morphology, and dermal denticle placement. The snout width of E. burgessi increases in proportion to head length (Fig. 3) compared to the other four regional examples. Etmopterus brachyurus and E. splendidus have snout widths that decrease slightly with increased head length. The sample size for E. lucifer and E. molleri are not robust, but both cluster closely with E. brachyurus .

The gill slit length of E. burgessi is relatively long (Fig. 4) in proportion to head length. In the new species, as head length increases, so does the length of the first gill slit in proportion to the head length. For E. brachyurus , the relationship is negatively allometric, with head length increasing as the length of the first gill slit decreases proportionately.

The length of the caudal peduncle is shorter in E. burgessi than in the other species examined. The measurement of this length is 11.4 (11.1-12.7)% TL in E. burgessi , but 13.7-15.5% TL in E. brachyurus and 12.8% TL in E. lucifer . Etmopterus molleri has a dorsal -caudal fin space of 14.1-14.9% TL, and E. splendidus has a measurement of 12.5-14.8% TL.

The height of the second dorsal fin in E. burgessi is relatively low; its height ranges from to 34.6-40.7% of its overall length (Fig 5), and overlaps with that of E. lucifer which ranges from 34.5-44.7%. This measurement in E. brachyurus is slightly higher, with a range of 42.1-48.4% fin length. The height of the second dorsal fin in E. molleri is much higher than for its congeners, ranging from 50-60%. Yamakawa et al. (1986) reports similar range values for the three aforementioned species. Etmopterus splendidus has a second dorsal fin height to length of 31.4-47.6%. Although percentages of the height in overall length overlap between species, the second dorsal fin is generally lower in E. burgessi than in either E. molleri or E. brachyurus .

Etmopterus burgessi has a flank marking that is distinct from three of the four species examined; E. splendidus , E. molleri , and E. brachyurus (Fig. 5). Comparatively, the anterior extension of E. burgessi has a broad base, 21.9 (21.7-29.3)% of anterior extension and short anterior branch, 78.1 (70.1-78.3)% of anterior extension. Etmopterus splendidus also has a broad flank marking base (34.3-46.3% of anterior extension) and a relatively short anterior branch (53.7-65.7% of anterior extension), but lacks a posterior branch entirely. The flank marking base is relatively narrow in both E. molleri (12.3-16.7% anterior extension) and E. brachyurus (12.1-16.8% anterior extension). The new species has a relatively short and blunt posterior branch, 41.4 (42.3-45.3)% of total flank marking length, that is similar to E. lucifer (29.1-37.3%). In comparison, the flank marking length is much shorter, its base broader, and the branches shorter in E. burgessi than either E. brachyurus or E. molleri .

The upper tooth morphology of E. burgessi consists of a single medial cusp, flanked on each side by three lateral cusplets, a condition similar to E. splendidus (Yano, 1988). However, the upper tooth morphology of E. brachyurus (Smith and Radcliffe, 1912; Compagno et al., 2005; direct observation), E. lucifer (Compagno et al., 2005; direct observation), and E. molleri (Whitley, 1939; Compagno et al., 2005) consists of a medial cusp flanked by two cusplets on each side.

The dermal denticles of E. burgessi are present over most of the body surface, and are useful for identification. Indeed, dermal denticles are present on the second dorsal fin surface of the new species. All of the other species examined have denticles on this surface except E. molleri , for which this area is relatively smooth (Yamakawa et al., 1986; direct observation). The ventral surface of the snout of E. burgessi has a thick grouping of dermal denticles, but in contrast, E. brachyurus displays a pattern where denticles are lacking around the nasals and along the medial section of the snout. The ventral snout of E. lucifer and E. molleri is sparsely covered with denticles.

The known distribution of Etmopterus species in the western North Pacific is problematic given the apparent high degree of endemism within this group. At the present, E. burgessi is known only from off the east coast of Taiwan. The other four “ E. lucifer group ” etmopterids, E. brachyurus , E. lucifer , E. molleri , and E. splendidus have variously been reported from Taiwanese waters. However, despite extensive field sampling and examination of museum specimens, we can only confirm the presence of E. brachyurus and E. splendidus , both of which were quite commonly observed at Taiwanese fish markets. Etmopterus brachyurus , originally described from the Philippines (Smith & Radcliffe, 1912), has been reported throughout the western Pacific from Japan to Australia (Compagno et al., 2005). Etmopterus splendidus was originally described from southern Japan (Yano, 1988) and has since been found in Taiwan and possibly Java, Indonesia (Compagno et al., 2005). Although we did not collect E. lucifer or E. molleri both have variously been reported by several authors (Teng, 1959; Chen, 1963; Joung & Chen, 1992; Compagno et al. 2005) as occurring in Taiwanese waters. Shen and Ting (1972) documented two forms of E. lucifer from the waters around Taiwan. However, based on the illustrations of Shen and Ting (1972: Fig 2-A & 2-B) the two E. lucifer forms are actually examples of E. molleri and E. splendidus , respectively. Furthermore, according to Joung and Chen (1992), the description of E. lucifer by Chen (1963) is actually that of E. molleri ; an observation with which we concur. Compagno et al. (2005) commented that the presence of E. lucifer , originally described from Japan, needed confirmation from some western Pacific localities. Etmopterus molleri , originally described from Australian waters, has been reported to occur throughout the western Pacific, including New Zealand, Taiwan, and Japan (Compagno et al., 2005). Although this species has been illustrated (Shen & Ting 1972) and reported (Joung & Chen, 1992) as occurring in Taiwanese waters, we could not confirm its occurrence.