The pygmy ribbontail catshark (''Eridacnis radcliffei'') is a

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), ...

of finback catshark,

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Proscylliidae, distributed patchily in the western

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

from

Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

to the

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

. It occurs around the edges of continental and insular shelves at a depth of , typically on or near mud bottoms. One of the smallest living shark species, the pygmy ribbontail catshark grows to a maximum known length of . It has a slender body with a low, ribbon-like tail fin, and is dark brown in color with blackish dorsal fin markings and tail bands. This shark feeds mainly on

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

es, followed by

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s and then

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

. It is aplacental viviparous with females bearing litters of 1–2 relatively large pups. It is of minimal significance to

fisheries 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 grounds). Commercial fisheries include wild fisheries and fish farm ...

, being caught as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

in some areas.

Taxonomy

The first known specimens of the pygmy ribbontail catshark were collected during the 1907–1910 Philippine Expedition of the U.S. Fish Commission Steamer ''Albatross''. Hugh McCormick Smith, Deputy Fish Commissioner and director of the expedition, published a description of this shark in a 1913 issue of the ''Proceedings of the United States National Museum'', naming it for the expedition's General Assistant and Naturalist

Lewis Radcliffe Lewis Radcliffe (1880–1950) was a naturalist, malacologist, and ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha ...

, and creating for it the new

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 ...

''Eridacnis''. The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

is a long adult female caught off Jolo Island in the

Sulu Archipelago The Sulu Archipelago ( Tausug: Kapū'-pūan sin Sūg Sulat Sūg: , ) is a chain of islands in the Pacific Ocean, in the southwestern Philippines. The archipelago forms the northern limit of the Celebes Sea and southern limit of the Sulu Se ...

Distribution and habitat

By far the most widely (if sporadically) distributed member of its genus, the pygmy ribbontail catshark has been reported from

, the

Gulf of Aden The Gulf of Aden (; ) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Channel, the Socotra Archipelago, Puntland in Somalia and Somaliland to the south. ...

, the Gulf of Mannar, the

Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean. Geographically it is positioned between the Indian subcontinent and the Mainland Southeast Asia, Indochinese peninsula, located below the Bengal region. Many South Asian and Southe ...

, the

Andaman Islands The Andaman Islands () are an archipelago, made up of 200 islands, in the northeastern Indian Ocean about southwest off the coasts of Myanmar's Ayeyarwady Region. Together with the Nicobar Islands to their south, the Andamans serve as a mari ...

Vietnam Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...

, and the

. This bottom-dwelling shark occurs at depths of on outer continental and insular shelves or upper slopes, commonly over mud.

Description

The pygmy ribbontail catshark has a thin body with a short, rounded snout and elongated, oval eyes bearing rudimentary

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. Most ...

s. Each nostril is preceded by a short, triangular flap of skin. The mouth is wide and V-shaped, without furrows at the corners and containing numerous rows of small, multi-pointed teeth that become more comb-like towards the sides. There are papillae on the roof of the mouth and the edges of the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

arches. The two

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

s are of comparable size, the first positioned slightly closer to the pectoral than the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s and the second over 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 ...

. The

caudal 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 only ...

is low and long, comprising a quarter of the total length or more, and lacks a lower lobe. The coloration is a plain dark brown, with black markings on the dorsal fins and darker bands on the caudal fin. The maximum recorded lengths are for a male and for a female. One male shark long weighed , and a pregnant female long weighed .

Biology and ecology

The pygmy ribbontail catshark is reportedly very abundant in some places, such as off southern

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

and the Philippines. One study in Indian waters found that 55% of this shark's diet was composed of

es (mainly

lanternfish Lanternfish (or myctophids, from the Greek language, Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family (biology), family Myctophidae. One of two families in the order Myctophiformes, ...

es but also bristlemouths and small eels), 28% of

s (mainly

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

but also stomatopods and

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

), 14% of

, and the remainder of other items including a

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

. Reproduction is aplacental viviparous, with the developing young being sustained by a

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

until they are ready to be born. Female pygmy ribbontail catsharks are capable of becoming pregnant at long, though only females over long have been found with fully developed

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

es, suggesting that they grow substantially during the

gestation period In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once i ...

. One or two pups are born at a time; the newborns are extremely large relative to their mothers, measuring around in length. Males reach

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized ...

at a length of and females at perhaps . This is comparable to the sizes at maturity of the spined pygmy shark (''Squaliolus laticaudus'') and the dwarf lanternshark (''Etmopterus perryi''), ranking the pygmy ribbontail catshark among the world's smallest sharks. Due to the difficulties involved in assessing reproductive maturity in sharks, whether one of these species is truly smaller than the others cannot yet be definitively determined.Martin, R.A. (July 28, 1999
What is the Smallest Species of Shark?
ReefQuest Centre for Shark Research. Retrieved on September 27, 2009.

Human interactions

Pygmy ribbontail catsharks are captured incidentally in bottom trawls off the Philippines, but are not known to be utilized. Its conservation status has not been evaluated by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN).

References

{{Taxonbar, from=Q499477 Eridacnis Taxa named by Hugh McCormick Smith Fish described in 1913