| Taillight shark | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Squaliformes |
| Family: | Dalatiidae |
| Genus: | Euprotomicroides Hulley &M. J. Penrith, 1966 |
| Species: | E. zantedeschia |
| Binomial name | |
| Euprotomicroides zantedeschia Hulley &M. J. Penrith, 1966 | |
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| Occurrences of the taillight shark | |
Thetaillight shark (Euprotomicroides zantedeschia) is a little-knownspecies ofshark in thefamilyDalatiidae and theonly member of itsgenus.[2] It is known from only fourspecimens collected from deepoceanic waters in the southernAtlantic Ocean andPacific Ocean.[2] A small shark with a laterally compressed body and a bulboussnout, this species has unusualadaptations that indicate a specialized lifestyle: itspectoral fins are paddle-like and may be used for propulsion, unlike other sharks and it has a pouch-like gland on its abdomen that emits clouds ofluminescent blue fluid.[2] This shark is likelyaplacental viviparous and a formidablepredator for its size.
The first specimen of the taillight shark was collected by theCape TowntrawlerArum in 1963 and was initially identified as alongnose pygmy shark before being recognized as a hitherto unknown species. The genus nameEuprotomicroides comes from this shark's resemblance to thepygmy shark.
Phylogenetic analysis based ondentition indicates that the taillight shark is the most basal member of its family and is sister to theclade containing all other dalatiid species. Although no definitivefossil remains have been found, the taillight shark may have evolved in the earlyPaleoceneepoch (65.5–55.8 million years ago – Mya), as part of a largeradaptive radiation of dogfish sharks into midwater habitats. The teeth of the extinct sharkParaphorosoides ursulae, found in earlyCampanian (83.5–70.6 Mya) deposits inGermany, closely resemble those of the taillight shark.[3]
Thespecific epithetzantedeschia is derived fromZantedeschia aethiopica, a species ofarum lily for which the trawlerArum was named.[4]
The four specimens of the taillight shark were caught offSouth Africa in a trawl operating at a depth of 458–641 m (1,503–2,103 ft), offUruguay in a trawl operating at a depth of 195–205 m (640–673 ft) and offChile, nearJuan Fernández Islands.[2] These records suggest this shark is an inhabitant of the open ocean. However, whether the known specimens were captured near the sea bottom where the trawls operated or from midwater as the nets were being retrieved is unclear.[1]
The taillight shark is laterally compressed, with a long rounded snout and large oval eyes. The mouth is large, containing 29 tooth rows in theupper jaw and 34 tooth rows in thelower jaw. The upper teeth are small and needle-like, while the lower teeth are large and triangular, with their bases interlocking to form a continuous cutting surface. Thelips are thick and fringed, though not modified to besuctorial. The five pairs ofgill slits are large and increase in size from the first to the last.[4][5]
The twodorsal fins are rounded and lackspines; the first is smaller than the second and located about halfway between the pectoral andpelvic fins. Thepectoral fins are enlarged into rounded paddles. The pelvic fins are small and originate at the level of the second dorsal fin; theanal fin is absent. Thecaudal fin has a strong lower lobe and a long upper lobe with a prominent notch near the tip. The body is covered by small, non-overlappingdermal denticles; each denticle has radial ridges converging to a round central pit. The body is dark brown above and black below, with light margins on the fins.[4][5] Small, light-emittingphotophores are scattered over the body.[6] The first specimen was an immature female (originally reported incorrectly as a mature male) 17.6 cm (6.9 in) long, the second was a mature male 41.6 cm (16.4 in) long, the third was also a mature male 45.5 cm (17.9 in) long and the fourth specimen was a mature female 51.5 cm (20.3 in).[1][2]
The muscular, lobe-like pectoral fins of the taillight shark suggest they may be used for propulsion, in a manner more akin to that ofchimaeras than other sharks or at least for hovering in the water column.[5] Its strongly built jaws and teeth likely allow it to tackle relatively large prey.[7] On the belly in front of thecloaca is a pouch-like groove devoid of denticles and lined with a luminescent tissue formed into numerous, tightly packed papillae (nipple-like structures).[2] The entrance to the pouch is a slit lined with folds of skin. In life, the pouch emits a glowing blue fluid of unknown function.[6] Reproduction is presumablyaplacental viviparous as in the other members of its family.[5]
The taillight shark is not caught significantly by anyfishery, possibly due to its small size and habitat preferences. TheInternational Union for Conservation of Nature has assessed its conservation status asleast concern.[1]
