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

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Dalatiidae The Dalatiidae are the family of kitefin sharks of the order Squaliformes (the term "kitefin shark" also refers specifically to the species ''Dalatias licha''). Members of this family are small, under long, and are found worldwide. They have cig ...

and the only member of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

.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 oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and

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

. A small shark with a laterally compressed body and a bulbous

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

, this species has unusual

adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

s that indicate a specialized lifestyle: its

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

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 Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...

blue fluid. This shark is likely

aplacental viviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

and a formidable

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

for its size.

Taxonomy and phylogeny

The first specimen of the taillight shark was collected by the

Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the 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 (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis based on

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

indicates that the taillight shark is the most basal member of its family and is sister to the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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 preserved ...

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), E ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

(65.5–55.8 million years ago - Mya), as part of a larger

adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...

of dogfish sharks into midwater habitats. The teeth of the extinct shark ''Paraphorosoides ursulae'', found in early

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

(83.5–70.6 Mya) deposits in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, 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, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''zantedeschia'' is derived from ''

Zantedeschia aethiopica ''Zantedeschia aethiopica'', commonly known as calla lily and arum lily, is a species of flowering plant in the family Araceae, native to southern Africa in Lesotho, South Africa, and Eswatini. Description ''Zantedeschia aethiopica'' is a rhizo ...

'', a species of

arum lily ''Zantedeschia'' is a genus of eight species of herbaceous, perennial, flowering plants in the family Araceae, native to southern Africa from South Africa north to Malawi. The genus has been introduced on all continents except Antarctica. Com ...

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 southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

in a trawl operating at a depth of , off

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del 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 ...

in a trawl operating at a depth of and off

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, near

Juan Fernandez Islands ''Juan'' is a given name, the Spanish and Manx versions of ''John''. It is very common in Spain and in other Spanish-speaking communities around the world and in the Philippines, and also (pronounced differently) in the Isle of Man. In Spanish, t ...

. 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 The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

and 34 tooth rows in the

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. 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 The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

are thick and fringed, though not modified to be

suctorial Suctorial pertains to the adaptation for sucking or suction, as possessed by marine parasites such as the Cookiecutter shark, specifically in a specialised lip organ enabling attachment to the host. Suctorial organs of a different form are possesse ...

. The five pairs of

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s are large and increase in size from the first to the last. The two

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

s are rounded and lack spines; the first is smaller than the second and located about halfway between the pectoral and

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

s. 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 distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

is absent. The

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

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 denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...

s; 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

photophore A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

s 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

chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At ...

s 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 In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...

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

as in the other members of its family.

Human interactions

The taillight shark is not caught significantly by any

fishery Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...

, possibly due to its small size and habitat preferences. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

has assessed its conservation status as

least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

References

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