Etmopterus lucifer Jordan & Snyder, 1902

Etmopterus lucifer Jordan & Snyder, 1902 View in CoL

( Figs 3 B View Figure 3 , 4 B View Figure 4 , 5 B View Figure 5 , 6 B, D View Figure 6 , 7 B, D View Figure 7 , 9 View Figure 9 , 10 View Figure 10 , 11; File S 2: Table S 2 View Figure 11 )

Etmopterus lucifer View in CoL Jordan & Snyder, 1902: 79, fig. 1 [original description; lectotype: CAS - SU 6863 (designated herein), off Misaki, Japan, 35°14'N, 139°37'E; paralectotypes in CAS, USNM; see Comments on type specimens]; Jordan and Fowler (1903): 634, fig. 5 (brief description); Böhlke (1953): 10; Nakaya in Okamura et al. (1982): 48, 49, 312, plate 12 (description in Japanese and English); Shirai in Amaoka et al. (1983): 46, 47, 164, plate 2 (description in Japanese and English); Compagno (1984): 70, 79, 80 (listed in key, description); Yamakawa et al. (1986): 197 –207, fig. 6 C (revision of the E. lucifer View in CoL group in Japan; brief description; listed in key); Bass et al. (1986): 55, 56, fig. 5.13 (listed in key, brief description); Howe and Springer (1993): 9 (type catalogue with remarks); Compagno and Niem (1998): 1220, 1226 (listed in key, brief description); Compagno (1999): 473 (listed); Nakabo (2000): 146 (listed in key), Compagno in Randall and Lim (2000): 580 (listed in key); Nakabo (2002): 146 (listed in key); Last et al. (2002): 223 (listed in key); Dyldin (2015): 55 (listed); Weigmann (2016): 896 (listed, northwest Pacific); Ebert et al. (2017): 380 (listed in key, erroneously listed in central north Pacific); Ebert and van Hees (2018): 207 (listed in key); Ebert et al. (2021): 15 (listed in key); Ng et al. (2024 b): 181, fig. 5 F.

Etmopterus burgessi View in CoL Schaaf-Da Silva & Ebert, 2006: 55, figs 1, 2 [original description; holotype: CAS 223476 , from Ta-Chi (= Daxi), northeastern Taiwan; 3 paratypes]; Ho and Shao (2011): 19 (listed); Ebert et al. (2013): 293 (listed), Weigmann (2016): 58 (listed); Ebert et al. (2017): 379 (listed in key); Ebert and van Hees 2018: 207 (listed in key); Ebert et al. 2021: 14 (listed in key).

Materials examined.

51 specimens. Lectotype (designated herein): CAS - SU 6863 , mature male 264 mm TL, off Misaki, Japan, 35°14'N, 139°37'E, depth and date unknown. Paralectotype: CAS - SU 7832 (1 of 4 specimens), mature male 284 mm TL, collected with the lectotype. Holotype of Etmopterus burgessi : CAS 223476 , mature male 355 mm TL, Daxi, Taiwan, 24°53'N, 122°01'E, 300 m, 11 May 1988. Paratypes of Etmopterus burgessi : CAS 223477 , female 405 mm TL, CAS 223478 , female 241 mm TL, CAS 223479 , female 235 mm TL, Daxi, Taiwan, 24°53'N, 122°01'E, 300 m, 21 May 2005. Non-types: ASIZP 0060498 (2 specimens), females 345–357 mm TL, 24°56'N, 121°54'E, off Daxi, northeastern Taiwan, 10 February 1997; CAS - SU 26782 , female 305 mm TL, Japan, depth and date unknown; EBFS-NG 00020 , juvenile female 150 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 15 April 2022; EBFS-NG 00047 , mature male 317 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 19 November 2021; EBFS-NG 00048 , mature male 342 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 25 November 2022; EBFS-NG 00049 , female 298 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 1 March 2022; EBFS-NG 00074 , mature male 313 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 9 July 2021; EBFS-NG 00105 , mature male 371 mm TL, off Donggang, southwestern Taiwan, ca. 22°N, 120°E, ca. 400 m, 25 March 2022; EBFS-NG 00124 , mature male 324 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 18 May 2022; EBFS-NG 00142 , mature male 328 mm TL, EBFS-NG 00143 , juvenile female 204 mm TL, EBFS-NG 00144 , female 314 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 8 July 2022; EBFS-NG 00145 , juvenile female 189 mm TL; EBFS-NG 00146 , juvenile female 247 mm TL, EBFS-NG 00147 , juvenile female 284 mm TL, EBFS-NG 00148 , juvenile female 274 mm TL, EBFS-NG 00149 , juvenile male 287 mm TL, EBFS-NG 00150 , juvenile male 296 mm TL, EBFS-NG 00151 , juvenile male 261 mm TL, EBFS-NG 00152 , juvenile male 284 mm TL, EBFS-NG 00153 , juvenile male 315 mm TL, EBFS-NG 00154 , juvenile male 300 mm TL, EBFS-NG 00155 , mature male 333 mm TL, EBFS-NG 00156 , mature male 334 mm TL, EBFS-NG 00157 , mature male 365 mm TL, off Daxi, northeastern Taiwan, ca. 24°53'N, 122°00'E, ca. 400 m, 30 May 2022; EBFS-NG 00267 , off Donggang, southwestern Taiwan, ca. 22°N, 120°E, ca. 400 m, 24 August 2022; EBFS-NG 00270 , female 259 mm TL, EBFS-NG 00271 , mature male 313 mm TL, EBFS-NG 00272 , female 213 mm TL, EBFS-NG 00273 , EBFS-NG 00274 , EBFS-NG 00275 , off Donggang, southwestern Taiwan, ca. 22°N, 120°E, ca. 400 m, 7 October 2022; EBFS-NG 00286 , juvenile female 165 mm TL, EBFS-NG 00287 , juvenile male 173 mm TL, EBFS-NG 00288 , juvenile male 175 mm TL, EBFS-NG 00289 , juvenile male 161 mm TL, off Donggang, southwestern Taiwan, ca. 22°N, 120°E, ca. 400 m, 9 November 2022; EBFS-NG 00323 , juvenile male 290 mm TL, EBFS-NG 00324 , juvenile male 321 mm TL, off Donggang, southwestern Taiwan, ca. 22°N, 120°E, ca. 400 m, 10 January 2023; EBFS-NG 00354 , juvenile male 287 mm TL, South China Sea, ca. 19°N, 114°E, ca. 500 m, 12 March 2023; HUMZ 214505 , off Tohoku, Japan, 40°17'N, 142°16'E, 441–459 m, 10 October 2011; HUMZ 232154 , neonate female 131 mm TL; HUMZ 232155 , mature male 268 mm TL, off Miyagi, Japan, 38°36'N, 142°02'E, 378 m, 22 October 2021; HUMZ 232462 , female 358 mm TL, off Tomakomai, Japan, 42°13'N, 141°41'E, 656–684 m, 24 November 2021; NTUM 16305 , mature male 283 mm TL, CP 4175, northeastern Taiwan, ca. 25°25'N, 122°08'E, ca. 434–535 m, 28 June 2018; USNM 51282 , mature male 285 mm TL, off Sagami Bay, Japan, depth unknown, 1900.

Diagnosis.

A moderately small Etmopterus of the E. lucifer group by showing elongated anterior and posterior branches of lateral flank marking, and differing from other members of the E. lucifer group by the following combination of characters: hook-like dermal denticles not overlapping each other, in well-defined rows; origin of second dorsal fin anterior to flank-marking base origin; infracaudal marking not connected with caudal-fin base marking through luminous lines; posterior caudal-fin marking long, its length 23.1–39.8 % caudal-fin length; and ventral pectoral marking knife-shaped, straight.

Redescription.

Morphometric information is provided in File S 2 (Table S 2). Proportional measurements and tooth counts are provided as ranges for the paralectotype and the non-types, followed by the lectotype (designated herein) in parentheses (if available). A precise tooth count of the lower jaw teeth is not possible in the lectotype as several teeth are missing.

Trunk sub-cylindrical, body width narrower than to slightly wider than height; abdomen longer than lower caudal peduncle; head subconical, slightly depressed. Snout moderately short (Fig. 10 View Figure 10 ), snout narrowly rounded in lateral and dorsal view. Eye oval. Spiracle bean-shaped. Gill openings moderate, slightly curved. Mouth broad, nearly straight.

Teeth dissimilar in upper and lower jaw, exhibiting ontogenetic change and sexual dimorphism; upper teeth multicuspid in three functional series; lower teeth unicuspid, in three series, one functional; lower teeth blade-like, with strongly oblique cusp. No distinctive symphyseal and intermediate teeth. Upper teeth cusp thick; immature males and females with 1–2, rarely 3 cusplets on each side of the upper teeth, while mature males having 3, rarely 2 or 4 cusplets (Fig. 3 B View Figure 3 ); 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 22–28 (25), lower jaw 25–35, total count 47–62.

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

Dermal denticles hook-like, rather high, reclined backwards, widely-spaced, not overlapping, giving a rough texture of the skin, in defined rows (Fig. 4 B View Figure 4 ); denticles present on underside of snout, except for a broad area around mouth; underside of gill slits fully covered with denticles (small bare patch maybe present between underside of gill slits in juveniles); P 1 inner margin with a broad naked area, D 1, D 2 and P 2 inner margins with narrow naked areas; denticles present on fin bases; denticles scarcely present on fins in neonates, increasing the coverage to most of the areas of ceratotrichia, particularly on D 2 (Fig. 5 B View Figure 5 ).

Body lateral side with very short, dash-like markings which are usually difficult to observe after preservation; head dorsal surface scattered 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 knife-like, straight, the tip not reaching P 1 insertion (Fig. 6 B, D View Figure 6 ). Flank markings well defined, with elongated anterior and posterior branch; anterior flank marking slender, very slightly curved, extending above P 2 origin; posterior flank marking straight, usually thicker, shorter than anterior flank marking; anterior flank marking length 101.7–180.4 (167.4) % posterior flank marking; posterior flank marking not extending beyond D 2 free rear tip; flank marking base rather narrow, origin well posterior 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 (Fig. 7 B, D View Figure 7 ); caudal-base marking broad, with a moderately thick, slender extension, bifurcate before the lower caudal-fin origin, 15.7–38.5 (29.6) % caudal-fin length. Posterior caudal-fin marking long, its length 23.1–39.8 (35.2) % caudal-fin length.

Coloration.

When fresh, body usually dark grey to brown, rarely pale grey, turning almost black after frozen or when the specimen is no longer fresh; darker ventrally; transition between lateral and ventral sides strongly demarcated in life (moderately demarcated when not fresh). Dorsal midline with a pale stripe; P 1 and P 2 generally translucent, with darker bases; dorsal fins mostly pale grey in the proximal two-thirds of ceratotrichia. Caudal-fin dorsal and postventral margins black, with a dark blotch on mid-caudal fin (faded when not fresh). 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 usually much darker, black blotches between infracaudal marking and caudal-base marking, and on mid-caudal fin, become less distinct. Transition between lateral and ventral sides becomes less demarcated.

Size.

Largest examined mature male is 371 mm TL. One female reported to attain about 450 mm TL ( Dolganov 2006). Schaaf-Da Silva and Ebert (2006) considered the largest female paratype of E. burgessi ( CAS 223477, 405 mm TL) to be mature, however, the gonads of this specimen were not available for observation as it was not dissected, thus, the maturity cannot be determined by us. No mature female was examined in the present study. The lectotype (designated herein) represents the smallest mature male examined (264 mm TL). The size at birth is about 131 mm TL.

Distribution.

Northwestern Pacific, from sub-boreal northern Japan to the tropical South China Sea, at depths of 300– 500 m. Common in Japanese waters and around Taiwan, but seems rare in the northern South China Sea.

Comments on the type specimens.

Etmopterus lucifer was originally described by Jordan and Snyder (1902) from off Misaki (Sagami Bay, Japan) based on a number of specimens. We examined all available syntypes in the present study and we found that they belong to two different species. To solve this confusion and to unambiguously fix the name E. lucifer , we select one of the syntypes, CAS - SU 6863 , as the lectotype of this species (Fig. 10 A View Figure 10 ). The remaining syntypes, CAS - SU 7832 (four specimens), USNM 50728 , are paralectotypes, which we have re-identified as Etmopterus schmidti Dolganov, 1986 , except the sole male specimen of CAS - SU 7832 , which we have identified as E. lucifer .

Previously, the single specimen in CAS - SU 6863 , which we have designated as lectotype here, was incorrectly considered as holotype of E. lucifer (e. g., Böhlke 1953; Yamakawa et al. 1986; Schaaf-Da Silva and Ebert 2006; Ebert et al. 2016; White et al. 2017) mainly based on Böhlke’s (1953) assessment, which does not conform to ICZN Art. 74.5.

Comments on the status of E. burgessi .

Schaaf-Da Silva and Ebert (2006) described E. burgessi from Taiwan, and stated that this species differed from E. lucifer by having more lateral cusplets (3 on each side vs. 2 on each side in E. lucifer ) and shorter caudal peduncle (11.1–12.7 vs. 12.8 % TL). Schaaf-Da Silva and Ebert (2006) also stated in their key that E. burgessi possessed {Gill openings very long, snout broad. Ventral surface of snout covered with thick dermal denticles. Color in life dark gray above, black below}, which differed from the characters of E. lucifer {Gill openings moderately long, snout narrow. Ventral surface of snout lacking dermal denticles. Color in life brown above, black below}. Later, Ebert and van Hees (2018) assigned E. burgessi and E. lucifer into two subgroups of the E. lucifer group, the E. burgessi subgroup and the E. lucifer subgroup, by the relative length of the anterior and posterior flank-marking branches: members of the E. burgessi subgroup have similar length of anterior and posterior flank-marking branches, while members of the E. lucifer subgroup shows notably longer anterior flank-marking branch.

The above characters are not diagnostic when comparing numerous specimens from near the type localities: the lateral cusplet number of upper teeth is depending on the sex, with males having more cusplets ( Straube et al. 2008; Straube and Pollerspöck 2020; Ng et al. 2024 a; present study); all of the specimens have their underside of the snout fully covered with denticles, except the lectotype of E. lucifer (designated above), which has a rather smooth underside of snout. Visual inspection using a microscope reveals numerous holes corresponding in size and density to former denticle positions suggesting that abrasion of dermal denticles on the underside of the snout is the most likely explanation for their lack in the lectotype; morphometric characters substantially overlap between E. burgessi and E. lucifer when examining further specimens; coloration in life varies greatly depending on the environment and the condition of the specimen, and is very rarely used for distinguishing lanternshark species. Particularly noteworthy is the relative length of the anterior and posterior flank-marking branches. After analyzing DNA sequence information of numerous specimens collected from around Taiwan, and some in Japan and the South China Sea, we found very little genetic differences between specimens with longer anterior flank-marking branches and specimens with both branches similar in length (K 2 P distance = 0–0.007), which strongly suggests intraspecific morphological variation and therefore conspecificity of these specimens, which otherwise would have been identified as E. burgessi and E. lucifer . Further, the length of the anterior flank marking of the holotype of E. burgessi is 155.2 % of that of the posterior flank marking (Fig. 11 View Figure 11 ), which is in conflict with the establishment of sub-groups as defined in Ebert and van Hees (2018).

Straube et al. (2013) stated that E. burgessi formed a distinct cluster in their molecular analysis which is the sister group to a group comprising E. lucifer . However, the analyzed E. lucifer samples were collected off New Zealand, which is not only far away from the type locality (= Japan), but these samples represent E. abernethyi based on results of our present study. Straube et al. (2013) simply lacked samples of true E. lucifer in their study. Here, we included E. lucifer from Japan in the molecular analyses for the first time, which showed that E. lucifer and E. burgessi together form a group with small intra-group genetic distances. The genetic divergence between E. burgessi from Taiwan and E. lucifer from Japan is only 0.1–0.7 % (x ̄ = 0.3 %) and well within the range of intraspecific variation. As we were not able to detect significant morphological and molecular differences between E. burgessi and E. lucifer , we herein synonymize the former species name with the latter.

Remarks.

Compagno et al. (2005) reported the occurrence of E. lucifer around the Philippines based on specimens mentioned in Smith and Radcliffe (1912). These specimens, currently housed at USNM and examined in the course of the present study, are all reidentified as E. marshae Ebert & van Hees, 2018 . Ebert and van Hees (2018) further confirmed the presence of E. lucifer in the Philippines based on two specimens ( CAS 233994 ). However, the specimens could not be located during SLN’s visit to CAS, and might have been lost and the occurrence of E. lucifer from around Philippines needs to be confirmed. The southernmost distribution of E. lucifer according to the present study ( EBFS-NG 00354 ) is the northern South China Sea.

Despite great sampling effort, no mature females were collected and these are also poorly represented in museum collections, with the largest being the 405 mm TL paratype of E. burgessi ( CAS 223477 ). It is possible that mature females escape sampling efforts because they inhabit much greater depths, than males and immature females, which are both sampled more frequently. Sexual segregation in habitats has also been reported in two congeners (Porcu et al. 2014; Karampetsis et al. 2022; Ng et al. 2024 a).

Preliminary data suggest males to mature at larger sizes around Taiwan (smallest mature male = 313 mm TL) than Japan (smallest mature male: 264 mm). This would be unusual as usually in sharks the size at maturity is smaller at lower latitudes (e. g., Baje et al. 2018). While little is known on the biology of lanternsharks in general, this phenomenon needs further investigation.

Comparisons.

Etmopterus lucifer is most similar to E. abernethyi (see comparisons of the latter species). It differs from E. molleri and E. schmidti by flank marking base originating behind a vertical line through the D 2 origin (vs. origin of flank marking base well before vertical line through D 2 origin in E. molleri and E. schmidti ), dorsal fins densely covered with denticles in adults (vs. almost naked in E. molleri and E. schmidti ; Fig. 5 View Figure 5 ), and knife-shaped, straight ventral pectoral marking (vs. elongated and arched marking in E. molleri and E. schmidti ; Fig. 6 View Figure 6 ).