The taillight shark (''Euprotomicroides zantedeschia'') is a little-known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

in the family Dalatiidae and the only member of its

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

.Stehmann, M.F.W., Van Oijen, M. & Kamminga, P. (2016): Re-description of the rare taillight shark ''Euprotomicroides zantedeschia'' (Squaliformes, Dalatiidae), based on third and fourth record from off Chile. ''Cybium, 40 (3): 187–197.'' It is known from only four specimens collected from deep oceanic waters in the southern

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

and

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. A small shark with a laterally compressed body and a bulbous snout, this species has unusual adaptations that indicate a specialized lifestyle: its

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s 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 of luminescent blue fluid. This shark is likely aplacental viviparous and a formidable predator for its size.

Taxonomy and phylogeny

The first specimen of the taillight shark was collected by the

Cape Town Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...

trawler ''Arum'' in 1963 and was initially identified as a longnose pygmy shark before being recognized as a hitherto unknown species. The genus name ''Euprotomicroides'' comes from this shark's resemblance to the pygmy shark.

Phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis based on dentition indicates that the taillight shark is the most basal member of its family and is sister to the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

containing all other dalatiid species. Although no definitive

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

remains have been found, the taillight shark may have evolved in the early

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

epoch (65.5–55.8 million years ago – Mya), as part of a larger adaptive radiation of dogfish sharks into midwater habitats. The teeth of the extinct shark ''Paraphorosoides ursulae'', found in early Campanian (83.5–70.6 Mya) deposits in

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, closely resemble those of the taillight shark.Adnet, S. & Cappetta, H. (2001)
A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes: Squaliformes) based on dental characters.
''Lethaia, 34 (3): 234–248.''

Etymology

The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''zantedeschia'' is derived from '' Zantedeschia aethiopica'', a species of arum lily for which the trawler ''Arum'' was named.Hulley, P.A. & Penrith, M.J. (1966)
''Euprotomicroides zantedeschia'', a new genus and species of pigmy dalatiid shark from South Africa.
''Bulletin of Marine Science, 16 (2): 222–229.''

Distribution and habitat

The four specimens of the taillight shark were caught off

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

in a trawl operating at a depth of , off

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

in a trawl operating at a depth of and off

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, near

Juan Fernández Islands The Juan Fernández Islands () are a sparsely inhabited series of islands in the South Pacific Ocean, reliant on tourism and fishing. Situated off the coast of Chile, they are composed of three main volcanic islands: Robinson Crusoe Island, R ...

. 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.

Description

The taillight shark is laterally compressed, with a long rounded snout and large oval eyes. The mouth is large, containing 29 tooth rows in the upper jaw and 34 tooth rows in the lower 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. The lips are thick and fringed, though not modified to be suctorial. The five pairs of gill slits are large and increase in size from the first to the last. The two dorsal fins are rounded and lack spines; the first is smaller than the second and located about halfway between the pectoral and pelvic fins. The

s are enlarged into rounded paddles. The pelvic fins are small and originate at the level of the second dorsal fin; the

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

is absent. The caudal 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-overlapping dermal 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. Small, light-emitting photophores are scattered over the body. The first specimen was an immature female (originally reported incorrectly as a mature male) long, the second was a mature male long, the third was also a mature male long and the fourth specimen was a mature female .

Biology and ecology

The muscular, lobe-like pectoral fins of the taillight shark suggest they may be used for propulsion, in a manner more akin to that of chimaeras than other sharks or at least for hovering in the water column. Its strongly built jaws and teeth likely allow it to tackle relatively large prey. On the belly in front of the cloaca is a pouch-like groove devoid of denticles and lined with a luminescent tissue formed into numerous, tightly packed papillae (nipple-like structures). 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.Munk, O. & Jørgensen, J.M. (1988)
Putatively luminous tissue in the abdominal pouch of a male dalatiine shark, ''Euprotomicroides zantedeschia'' Hulley & Penrith, 1966.
''Acta Zoologica, 69 (4): 247–251.'' Reproduction is presumably aplacental viviparous as in the other members of its family.

Human interactions

The taillight shark is not caught significantly by any fishery, possibly due to its small size and habitat preferences. The International Union for Conservation of Nature has assessed its conservation status as least concern.

References

{{Taxonbar, from=Q728294 Dalatiidae Taxa named by P. Alexander Hulley Taxa named by Michael John Penrith Fish described in 1966 Marine fish genera