| Blurred lanternshark | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Squaliformes |
| Family: | Etmopteridae |
| Genus: | Etmopterus |
| Species: | E. bigelowi |
| Binomial name | |
| Etmopterus bigelowi | |
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| Occurrences of the blurred lanternshark | |
Theblurred lanternshark (Etmopterus bigelowi) is a little-knownspecies ofdogfish shark in thefamilyEtmopteridae, found around the world inbenthic andpelagichabitats from a depth of 110 m (360 ft) to over 1 km (0.62 mi) down. This shark forms theE. pusillusspecies group with thesmooth lanternshark, which are distinguished from other members of its family by having irregularly arranged, flat-toppeddermal denticles that give them a "smooth" appearance. Both species are slender-bodied with long heads, twodorsal fins bearing spines, noanal fins, and light-emittingphotophores. The blurred lanternshark is larger, reaching 67 cm (26 in) or more in length. This species feeds on smallsquid,fishes, andfish eggs, and isovoviviparous. It has been assessed as ofLeast Concern by theInternational Union for Conservation of Nature, because of its wide distribution and lack of threat from fishing pressure.
Japaneseichthyologists Shigeru Shirai and Hiroyuki Tachikawa described the blurred lanternshark in a 1993 article in thescientific journalCopeia, as part of ataxonomic revision of theEtmopterus pusillusspecies group. Shirai and Tachikawa found that the species group comprises thesmooth lanternshark (E. pusillus) and a hitherto unrecognized second species, which they namedE. bigelowi in honor of Henry B. Bigelow (who, along withWilliam C. Schroeder andStewart Springer, first described the blurred lanternshark in 1955, but did not see it as being separate fromE. pusillus).[2] TheE. pusillus species group is distinguished from other lanternsharks in having truncate (ending in a flat crown as though the tip were cut off), irregularly arrangeddermal denticles.[2] This species may also be referred to as the smooth lanternshark or the blurred smooth lanternshark.[3]
Blurred lanternsharks have been caught around the world overcontinental and insular shelves andslopes, submarine ridges, andseamounts.[1] In theAtlantic Ocean, it is known from theGulf of Mexico toArgentina, and offwestern andsouthern Africa. In theIndo-Pacific, it has been reported from offOkinawa andAustralia, as well as on the Emperor and HancockSeamounts in the centralNorth Pacific and over theNazca Plate offPeru.[2] It is partiallypelagic and occurs at depths of 110–700 m (360–2,300 ft) in open water, and from 163 m (535 ft) to over 1 km (0.62 mi) near the bottom.[4] Like many other lantern sharks, adults are found deeper than juveniles.[2]
Growing to a length of at least 67 cm (26 in), the blurred lanternshark has a slender body, large head, and short tail. The snout is wedge-shaped and slightly flattened, tapering to a point. Thenostrils are large, with short flaps of skin in front. The eyes are oval in shape with a deep anterior notch in theorbit. The mouth has long furrows at the corners that extend halfway to the first of fivegill slits. There are 19–24 tooth rows in the upper jaw, each with a narrow central cusp flanked by 2–4 pairs of smaller cusplets, increasing in number with age in males over 45 cm (18 in) long. There are 25–39 tooth rows in the lower jaw, each tooth with a smooth-edged, knife-like cusp and their bases interlocked to form a single cutting surface; the teeth of males over 43 cm (17 in) long and females over 35 cm (14 in) long become more erect with age.[2][4]
The firstdorsal fin is close to thepectoral than the pelvic fins, and bear a straight, grooved spine in front. The second dorsal fin is half again as tall as the first and bears a longer, curved spine. The pectoral fins are rounded at the tips, with the distance between them and the medium-sized, angular pelvic fins about equal to the distance between the dorsal fins. Theanal fin is absent. Thecaudal peduncle is narrow, leading to acaudal fin with a well-developed lower lobe and a broad upper lobe with a ventral notch near the tip. The small, blocky dermal denticles are densely but irregularly arranged, each with a flat, truncate crown. The coloration is brown or gray above, with a pale spot over thepineal gland, and black below extending in faint markings over the sides of the head, under the pectoral fins, over the pelvic fins, and below the caudal peduncle.[2][4] Like other lanternsharks, the blurred lanternshark possesses a species-specific light-emittingphotophores, which are not placed in prominent bands.[5] The blurred lanternshark is very similar to the smooth lanternshark, but is larger and can be reliably differentiated by the number of turns in thespiral valveintestine (16–19 versus 10–13).[2]
The diet of the blurred lanternshark consists ofsquid, smallerdogfish sharks,lanternfishes, andfish eggs.[4] Reproduction isovoviviparous, with developingembryos being sustained by ayolk sac and being born live at a length of 16 cm (6.3 in).[1] Males attainsexual maturity at around 31–39 cm (12–15 in) long, and females at 38–47 cm (15–19 in) long.[4]
Blurred lanternsharks are harmless and of nocommercial significance, but may be caught and discarded by deepwaterfisheries. Because of its wide distribution and the lack of evidence for heavy fishing mortality, theIUCN has assessed this species as ofLeast Concern.[1]
