Etmopterus molleri ( Whitley, 1939 )

Ng, Shing-Lai, Straube, Nicolas, Liu, Kwang-Ming & Joung, Shoou-Jeng, 2025, Confusions across the hemispheres: Taxonomic re-evaluation of two lanternshark species, Etmopterus lucifer and E. molleri (Squaliformes: Etmopteridae), Vertebrate Zoology 75, pp. 59-86 : 59-86

Etmopterus molleri ( Whitley, 1939)

( Figs 4 C , 5 C , 12 , 13 A, C , 14 A; File S 2: Table S 3 )

Acanthidium molleri Whitley, 1939: 265, fig. 1 (original description; holotype: AMS IA.5816, from off New South Wales, Australia, 33°50'S, 151°50'E; 1 paratype)

Etmopterus lucifer (not Jordan and Snyder 1902): Garrick (1960): plate 26: fig. D (specimen from Australia, reidentification from the figure)

Etmopterus molleri : Last and Stevens (1994): 83 (listed); Compagno and Niem (1998): 1226 (brief description); Compagno 1999: 473 (listed); Last et al. (2002): 223 (listed in key); Last and Stewart (2015): 144, fig. 25.4 (brief description, with taxonomic comment; figure based on NMNZ P.045558 ); Weigmann (2016): 896 (listed, southwest Pacific); Ebert et al. (2017): 380 (listed in key); Ebert and van Hees (2018): 207 (listed in key); Ebert et al. (2021): 14 (listed in key).

Materials examined.

36 specimens. Holotype: AMS IA.5816 , female 350 mm + TL, off New South Wales, Australia, 33°50'S, 151°50'E, 238 m, June 1933. Paratype: AMS IA.5817 , mature female 333 mm TL, collected with the holotype. Non-types: AMS I.15975 -001, female 275 mm TL; AMS I.15975 -002, juvenile male 266 mm TL; AMS I.15975 -003, female 291 mm TL; AMS I.15975 -004, female 303 mm TL; AMS I.15975 -005, 322 mm TL; AMS I.15975 -006, female 366 mm TL; AMS I.15975 -008, female 389 mm TL, off Macquarie Island, southeastern Australia, 33°11'S, 152°23'E, 29 April 1971; AMS I.19385 -004, mature male 335 mm TL, east of Broken Bay, southeastern Australia, 33°28'S, 152°05'E, 26 May 1976, coll. K. Graham; AMS I.19860 -008, pregnant female 415 mm TL, off Broken Bay, southeastern Australia, 33°35'S, 152°01'E, 20 December 1976, coll. K. Graham; AMS I.22642 -004, female 390 mm TL, east of Tuncurry, southeastern Australia, 32°07'S, 153°05'E, 27 July 1981, coll. K. Graham; AMS I.42758 -003, female 433 mm TL, Western Norfolk Ridge, Tasman Sea, 32°35'S, 167°38'E, 30 May 2003; AMS I.44904 -001, mature female 381 mm TL, Port Stephens, southeastern Australia, 32°30'S, 152°55'E, 9 September 2009, coll. K. Graham; AMS I.44907 -010, female 324 mm TL, off Coffs Habour, eastern Australia, 30°30'S, 153°25'E, 6 September 2009, coll. K. Graham; AMS I.44909 -007, female 359 mm TL, Browns Mountain, southeastern Australia, 34°00'S, 151°40'E, 16 September 2009, coll. K. Graham; AMS I.44992 -001 (4 specimens), females 346–380 mm TL, 31 Canyon, eastern Australia, 31°08'S, 153°20'E, 7 September 2009, coll. K. Graham; CSIRO H 7030-02 (3 specimens), juvenile males 219–267 mm TL; CSIRO H 7030-03 , mature male 351 mm TL; CSIRO H 7030-04 , female 376 mm TL, east of Port Stephens, southeastern Australia, 32°30'S, 152°55'E, 500 m, 9 September 2009; CSIRO H 7054-04 , mature male 349 mm TL; CSIRO H 7054-05 , female 356 mm TL, east of Sydney, southeastern Australia, 34°02'S, 151°39'E, 450 m, 16 September 2009; CSIRO H 7059-02 , female 389 mm TL, east of Sydney, southeastern Australia, 33°40'S, 151°55'E, 530 m, 15 September 2009; CSIRO H 7216-01 , adolescent male 323 mm TL, Britannia Seamount, eastern Australia, 28°39'S, 155°34'E, 366 m, 3 February 2011; NMNZ P.029400 (2 specimens), female 296–371 mm TL, southern New Caledonia, 24°55'S, 168°36'E, 502–610 m, 14 October 1992; NMNZ P.045558 , mature male 359 mm TL, Bay of Plenty, New Zealand, 37°42'S, 176°54'E, 367–450 m, January 2009; NMNZ P.045561 , mature female 409 mm TL, locality and date unknown; NMNZ P.047803 , mature male 366 mm TL, off Mayor Island, New Zealand, 37°29'S, 176°34'E, 220 m, 2010; NMNZ P.049671 , pregnant female 412 mm TL, southeastern Mayor Island, New Zealand, 37°41'S, 176°49'E, 360–373 m, 30 October 2010; NMNZ P.056140 , mature female 406 mm TL, off Tauranga, New Zealand, 37°40'S, 176°41'E, 21 July 2013.

Diagnosis.

A moderately small Etmopterus belonging to the E. lucifer group by having elongated anterior and posterior branches of lateral flank marking, and differing from other members by the following combination of characters: hook-like dermal denticles not overlapping each other, in well-defined rows; the origin of second dorsal fin well posterior to flank-marking base origin; infracaudal marking not connected with caudal-fin base marking through luminous lines; a long posterior caudal-fin marking, length 18.8–38.1 % caudal-fin length; caudal fin black; caudal-base marking bifurcated before caudal-fin origin; and ventral pectoral marking curved.

Redescription.

Morphometric information is provided in File S 2 (Table S 3). Proportional measurements and tooth counts are expressed as ranges for the paratype and the non-types, followed by the holotype in parentheses. A precise tooth count is not possible in the holotype as several teeth are missing.

Trunk sub-cylindrical, body width narrower than to slightly wider than height; abdomen usually longer than lower caudal peduncle, usually shorter in mature males; head subconical, moderately depressed. Snout fairly long (Fig. 12 ), preorbital length 25.5–43.3 (27.0) % head length; snout narrowly rounded in lateral and dorsal view. Eye oval. Spiracle bean-shaped. Gill openings short, slightly curved. Mouth broad, slightly arched. Preoral length relatively long, length 44.1–52.7 (44.1) % head length.

Teeth dissimilar in upper and lower jaw, having ontogenetic change and sexual dimorphism; multicuspid upper teeth in three functional series; unicuspid lower teeth in three series, with one functional; lower teeth blade-like, strongly oblique. No symphyseal and intermediate teeth. Upper teeth cusp thick; immature males and females with 1–2 cusplets on each side of the upper teeth (rarely 3 in mature females), while mature males having 3–4 cusplets (Fig. 3 C ); longest cusplet length about two-third of the cusp in mature individuals; cusp and cusplets of upper teeth narrowly triangular, lower teeth of mature individuals not erected. Tooth count of upper jaw 23–26, lower jaw 38–40, total count 61–66.

D 1 small, with a round apex, origin anterior to slightly posterior a vertical line through P 1 free rear tip. D 2 larger than D 1, apex angular, posterior margin especially concave, free rear tip moderately elongated; D 2 spine long and curved. P 1 moderate in size, with angular free rear tips, base narrow, posterior margin slightly concave. P 2 narrowly triangular. Clasper of mature males rather long. Caudal fin elongate, caudal folk not especially developed; terminal lobe broad.

Dermal denticles hook-like, fairly low, slightly reclined backwards, widely-spaced, not overlapped, giving a rough texture of the skin, in defined rows (Fig. 4 C ); denticles present on underside of snout, except for a broad area around mouth (small bare patch maybe present on underside of snout in juveniles); underside of gill slits fully covered with denticles (small bare patch maybe present between underside of gill slits in juveniles); Inner margin of fins with a broad naked area; denticles present on fin bases, but almost absent on fins (Fig. 5 C ).

Lateral body side with prominent short, dash-like markings which are usually still distinct after preservation; head dorsal surface scattered with dot-like markings; dorsal contour of the body with a single line of dot-like markings, extending mid-dorsally from about the level of anterior fontanelle to the D 2 origin; ventral pectoral marking elongated and arched, the tip not reaching P 1 insertion. Flank markings well defined, with elongated anterior and posterior branch; anterior flank marking slender, a little bit curved, extending above P 2 origin; posterior flank marking straight, not much thicker, longer than anterior flank marking; anterior flank marking length 53.8–91.8 (69.2) % posterior flank marking, usually with pointed tip; posterior flank marking usually not extending beyond D 2 free rear tip; flank marking base rather narrow, origin well anterior to D 2 origin. Infracaudal marking prominent, extending from flank marking base to about the same level of posterior flank marking tip, not connecting to the caudal-base marking by a pair of lines; caudal-base marking broad, with a moderately thick, slender extension, bifurcate before the lower caudal-fin origin (Fig. 13 A, C ), length 19.2–36.5 % caudal-fin length. Posterior caudal-fin marking long, its length 18.8–38.1 % caudal-fin length.

Coloration.

When fresh, body shiny to brownish grey; much darker ventrally; transition between lateral and ventral sides strongly demarcated. Dorsal midline with a pale stripe; Fins, except caudal fin, generally translucent, with darker anterior margins and bases. Caudal-fin dorsal and postventral margins black (Fig. 14 A ), with a very narrow translucent upper postventral margin; darker blotch present on mid-caudal fin. A black blotch present between infracaudal marking and caudal-base marking. Caudal fin with a distinct black tip on the terminal margin.

After preservation, body coloration becomes darker; black blotch on mid-caudal fin become difficult to be observed.

Size.

Up to 433 mm TL and 366 mm TL for females and males, respectively. Smallest mature female and male examined are 333 and 335 mm TL, respectively.

Distribution.

Southwestern Pacific, off southeastern Australia to northern New Zealand, and New Caledonia, at 366–530 m depth.

Remarks.

Bigelow and Schroeder (1957) concluded that E. molleri does not differ from E. brachyurus based on the description and illustration of the former. In contrast, Garrick (1960) considered E. molleri a junior synonym of E. lucifer based on the similar relative lengths of upper caudal margin to the pelvic – caudal space (80 % vs. 83 % in the E. lucifer specimen Garrick examined). He also considered E. brachyurus to be distinct from E. molleri as the former has a shorter relative length of the upper caudal margin to the pelvic – caudal space (70 % vs. 80 % in E. molleri ). However, the relative length of the upper caudal margin to the pelvic – caudal space, as well as the two measurements relative to total length, show prominent intraspecific variation and perhaps sexual dimorphism, which results in substantial overlap. As a result, the characters proposed by Garrick (1960) arguing for synonymy of the two species cannot be supported in the present study. In addition, at least one of the E. lucifer specimens examined by Garrick (1960) represents E. molleri , based on the characters defined here for E. molleri , i. e., the position of the characteristic anterior origin of the flank-marking base relative to that of the second dorsal-fin origin (plate 26: Figure D).

Comparisons.

Etmopterus molleri can be assigned to the E. lucifer group and is most similar to E. schmidti , which explains why the two species have been confused for nearly 40 years. Morphometrics of the two species almost entirely overlap, except for snout length, in which E. molleri has a significantly longer preorbital length relative to the head length (25.5–43.3 % vs. 19.7–29.6 % in E. schmidti ; Mann-Whitney U test, p <0.05); and a significantly longer preoral length relative to the head length (44.1–52.7 % vs. 32.7–45.4 % in E. schmidti ; Mann-Whitney U test, p <0.05). Further, E. molleri possesses slightly more total vertebrae (89–93 vs. 78–88 in E. schmidti ). In addition, E. molleri can be distinguished from E. schmidti by having the caudal-base marking bifurcate before the caudal-fin origin (bifurcate after caudal-fin origin, especially prominent when viewed laterally in E. schmidti ; Fig. 13 ), and having a black caudal-fin upper lobe (vs. translucent upper lobe in E. schmidti ; Fig. 14 ). Geographically, E. molleri is restricted to the southwestern Pacific, being found from Eastern and Southeastern Australia to New Caledonia, and northern New Zealand.

Etmopterus molleri is also quite similar to E. brachyurus , yet can be separated by the underside of snout and gill slits being mostly fully covered with denticles (vs. underside of snout with a reversed ‘ W’ shaped naked area, underside of gill slits with a ‘ V’ shaped naked area connecting the first gill slits in E. brachyurus ); the second dorsal fin lacking denticles in all developmental stages (vs. covered with denticles in subadults and adults); caudal-fin base marking with a narrowly rounded tip (vs. strongly pointed tip).

Figures

Figure 3. Boxplot showing difference in the cusplet pairs of sexes and ontogenetic stages between Etmopterus spp. A Etmopterus abernethyi B E. lucifer C E. molleri D E. schmidti. The ontogenetic stages of female are not shown as they were not determined in most cases.

Figure 4. Dermal denticles below second dorsal fin of Etmopterus spp. A Etmopterus abernethyi, holotype, NMMZ P. 01951, immature male 330 mm TL B Etmopterus lucifer, EBFS-NG 00105, mature male 371 mm TL C E. molleri, NMMZ P. 045558, mature male 359 mm TL D E. schmidti, EBFS-NG 00095, mature female 307 mm TL.

Figure 5. Details of the dermal coverage on the second dorsal fin of Etmopterus spp. A Etmopterus abernethyi, holotype, NMMZ P. 01951, immature male 330 mm TL B E. lucifer, EBFS-NG 00105, mature male 371 mm TL C E. molleri, AMS I. 44904-001, mature female 381 mm TL D E. schmidti, EBFS-NG 00095, mature female 307 mm TL.

Figure 12. Etmopterus molleri. A holotype, AMS IA. 5816, female 350 mm + TL, off New South Wales, Australia B Paratype, AMS IA. 5817, mature female 333 mm TL, off New South Wales, Australia C fresh specimen, CSIRO H 7059-02, female 389 mm TL, east of Sydney, southeastern Australia (photo provided by CSIRO Australian National Fish Collection, used with permission). Scale bars = 20 mm. All images are horizontally flipped.

Figure 13. Lateral (A, B) and ventral view (C, D) of the caudal-base marking of Etmopterus molleri (A, C) and E. schmidti (B, D). A, C holotype, AMS IA. 5816, female 350 mm + TL B, D EBFS-NG 00095, mature female 307 mm TL. Blue arrows in (B) and (D) indicates the small black portion covering the lower caudal-fin origin. Grey dotted lines depict the lower caudal-fin origin.

Figure 14. Details of the coloration of the caudal fin. A Etmopterus molleri, NMMZ P. 045558, mature male 359 mm TL B E. schmidti, EBFS-NG 00095, mature female 307 mm TL. Black arrow in (B) indicates the translucent portion of the caudal fin.