Worm pearlfish

{{Short description|Species of fish}} {{Speciesbox | status = LC | status_system = IUCN3.1 | status_ref= <ref>{{cite iucn |author=Ho, H. |date=2020 |title=''Encheliophis vermicularis'' |volume=2020 |article-number=e.T135444957A137454756 |doi=10.2305/IUCN.UK.2020-1.RLTS.T135444957A137454756.en |access-date=29 December 2021}}</ref> | taxon = Encheliophis vermicularis<ref name=AnimalDiversity>{{cite web|title=Encheliophis vermicularis Finless pearlfish|url=http://animaldiversity.ummz.umich.edu/accounts/Encheliophis_vermicularis/classification/|publisher=Animal Diversity|access-date=3 February 2013}}</ref> | authority = [[Johannes Peter Müller|J. P. Müller]], 1842 | synonyms = *''Encheliophis jordani'' [[Edmund Heller|Heller]] & [[Robert Evans Snodgrass|Snodgrass]], 1903 *''Encheliophiops hancocki'' [[Earl D. Reid|Reid]], 1940 *''Encheliophis hancocki'' (Reid, 1940) | synonyms_ref = <ref name = FishBase/> }}

The '''worm pearlfish''' (''Encheliophis vermicularis'') is an eel-like fish in the family Carapidae.

== Description == The worm pearlfish is typically 15 cm long and is characterized by its long, slender body and lack of scales.<ref name=":2"/><ref name=":03">{{Cite journal|last=Trott|first=Lamarr|date=1981|title=A general review of the pearlfishes (Pisces, Carapidae).|journal=Bulletin of Marine Science|volume=31|page=625}}</ref>

== Morphology == Worm pearlfish lack the pectoral or pelvic fins that are common characters of the family ''Carapidae''.<ref name=":03"/> The upper half of its body is blackish-pinkish in color and its underside is silver. Its tail is black and tapered.

Compared to other members of the family ''Carapidae'', the worm pearlfish has a relatively weak jaw. The maxillaries and premaxillaries in worm pearlfishes are joined by short connective fibers in the small mouth opening. Both the maxillaries and premaxillaries are connected to the fish's skin, which creates a small mouth opening.<ref name=":3">{{Cite journal|last=Parmentier|first=Eric|date=2004|title=Encheliophis chardewalli: a new species of Carapidae (Ophidiiformes) from French Polynesia, with a redescription of Encheliophis vermicularis.|url=https://orbi.uliege.be/handle/2268/12700|journal=Copeia|volume=1|pages=62–67|doi=10.1643/CI-03-085R2|hdl=2268/12700 |s2cid=84158874}}</ref> Worm pearlfishes' mouths are smaller and weaker than mouths of pearlfishes in other genera because they feed on soft, unresisting food in a confined space, as opposed to swift-moving, unconstrained prey.<ref name=":4">{{Cite book|title=Fish Adaptations|last=Parmentier|first=Eric|publisher=Oxford & IBH|year=2003|location=India|pages=261–276|chapter=11 - Morphological adaptations of pearlfish (Carapidae) to their various habitats.}}</ref> Their upper jaw is lined with an outside row of strong, curved teeth, and an inner row of conical teeth.<ref name=":3" /> Worm pearlfishes' lower jaws contain one row of 20 conical teeth or more.<ref name=":4" /> Teeth are arranged in a cardiform (comb-like) design – Parmentier suggests they are used in a saw-like fashion to cut into internal tissues of their hosts.<ref name=":4" />

==Habitat and range== ''E. vermicularis'' lives in a marine, reef-based environment in a tropical climate.<ref name="FishBase">{{cite web|url=http://www.fishbase.se/summary/Encheliophis-vermicularis.html|title=Encheliophis vermicularis|publisher=FishBase|access-date=3 February 2013}}</ref> They are an epibenthic species – they live near to the bottom of the seafloor. They seek out shallow-water sea cucumbers around in inshore waters and coral reefs which range in depth from 0-30 meters.<ref name=":03"/><ref name=EOL>{{cite web|title=Encheliophis vermicularis|url=http://eol.org/pages/218336/overview|publisher=Encyclopedia of Life|access-date=3 February 2013}}</ref>

They can be found in the Indo-Pacific, the Gulf of Aden, around the Philippines and Society Islands, and north to the Ryukyus to the eastern Pacific.<ref name="FishBase" />

==Diet== The worm pearlfish is a parasite of [[holothurians]], each host is normally home to a pair of these fishes. Species recorded as hosting the worm pearlfish include ''[[Holothuria leucospilota]]'', ''[[Holothuria scabra|H. scabra]]'', ''[[Holothuria lubrica|H. lubrica]]'' and ''[[Thelenota ananas]]''.<ref name = FishBase/> The worm pearlfish is an uncommon species.<ref name = FAO>{{cite book | author1 = Jørgen G. Nielsen | author2 = Daniel M. Cohen | author3 = Douglas F. Markle | author4 = C. Richard Robins | name-list-style = amp | year = 1999 | title = OPHIDIIFORM FISHES OF THE WORLD (Order Ophidiiformes) An annotated and illustrated catalogue of pearlfishes, cusk-eels, brotulas and other ophidiiform fishes known to date | series = FAO Species Catalogues | volume = 17 | publisher = [[Food and Agriculture Organization]] of the United Nations | place = Rome | isbn = 92-5-104375-2 | page = 16}}</ref>

While other members of the family ''Carpidae'' can be [[commensal]], the genus ''Encheliophis'' is obligately parasitic. Worm pearlfish, specifically, prefer the coelomic cavity of the genus ''Holothuria'' (sea cucumbers). In particular, worm pearlfish have been found to prefer the sea cucumber species ''H. leucospilota,'' though they have been found in the sea cucumber species ''Holothuria atra'' as well.<ref name=":1">{{Cite journal|last=Miyazaki|first=Sachiko|date=2014|title=Chemoattraction of the pearlfish Encheliophis vermicularis to the sea cucumber Holothuria leucospilota|journal=Chemoecology|volume=24|issue=3|pages=121–126|doi=10.1007/s00049-014-0152-7|bibcode=2014Chmec..24..121M |s2cid=14272837}}</ref><ref name=":2">{{Cite journal|last=Smith|first=Laveti|date=1964|title=Some pearlfishes from Guam, with notes on their ecology.|journal=Pacific Science|volume=18|page=34}}</ref>

Worm pearlfish feed exclusively on the internal tissue of the host, entering through the anal region of the sea cucumber without causing the sea cucumber to release its [[Cuvierian tubules]] – a defense mechanism which entangles possible predators.<ref name=":2" /> The pearlfish appears to be chemotaxic (responsive to chemical gradients in water) and is attracted to chemicals the coelomic fluid and Cuvierian tubules, which leads it to the sea cucumber's anus.<ref name=":1" /> Because the other species worm pearlfish prey on, ''H. atra'', lack Cuvierian tubules, worm pearlfish are most likely not only attracted by the Cuvierian tubules.<ref name=":2" /> The anus of the sea cucumber contracts upon tactile stimulation by the worm pearlfish, but once it needs to respire and relax the anus again, pearlfish is able to penetrate the anus headfirst.<ref name=":03"/> Once inside, the worm pearlfish eats the sea cucumber's internal tissues – mostly the gonads.

== Reproduction and life cycle == Not much is known about the sexual behavior of worm pearlfish. Sexually mature male-female pairs of worm pearlfish been found cohabiting in sea cucumbers, so worm pearlfish are thought to mate and spawn inside their hosts.<ref name=":5">{{Cite book|title=Symbiosis in Fishes: The Biology of Interspecific Partnerships|last=Karplus|first=Ilana|publisher=Wiley-Blackwell|year=2014|isbn=978-1-405-18589-9|location=West Sussex, UK|page=410}}</ref> Larvae may then be expelled by the normal expiration of the sea cucumber. Like all members of the family ''Carapidae'', worm pearlfish are hatched as holoplanktonic – i.e. temporarily planktonic – larvae from planktonic elliptical eggs, but it is unclear if spawning is seasonal or sporadic.<ref name=":5" />

== References == {{Reflist}}

==External links== * [http://animaldiversity.ummz.umich.edu/site/accounts/classification/Encheliophis_vermicularis.html#Encheliophis_vermicularis ''Encheliophis vermicularis'' on animaldiversity.ummz.umich.edu]

[[Category:Carapidae]] [[Category:Fish described in 1842]]