Pearlfish is a general name for a variety of marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 fish species in the Carapidae family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

. Pearlfish have been found in tropical waters of the Atlantic

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, Indian

Indian Ocean

The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

, and Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

s at depths up to 2000 metres (6,561.7 ft) along oceanic shelves and slopes.

Pearlfish are slender fish, distinguished by having dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 rays that are shorter than their anal fin rays. They have translucent, scaleless bodies reminiscent of eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

s. The largest pearlfish are about 50 centimetres (19.7 in) in length. They reproduce by laying oval-shaped eggs, about 1 millimeter in length.

Pearlfish are unusual in that the adults of most species live inside various types of invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

. Typically, they live inside clam

Clam

The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...

s, starfish or sea squirts, and are simply commensal, not harming their hosts. However, some species are known to be parasitic on sea cucumbers, eating their gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

s, and they live in their anal pore. Regardless of the habits of the adults, the larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e of pearlfish are free-living among the plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

. Pearlfish larvae can be distinguished by the presence of a long filament in front of their dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

, sometimes with various appendages attached.

Classification

The genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 are divided into three major groupings based on their level of symbiosis

Symbiosis

Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

:

• Echiodon and Snyderidia - Free-living
• Carapus and Onuxodon - Commensal
• Encheliophis
  Encheliophis
  Encheliophis is a pearlfish genus in the family Carapidae.-Species:* Encheliophis chardewalli* Encheliophis gracilis* Encheliophis homei* Encheliophis sagamianus* Encheliophis vermicularis* Encheliophis vermiops...
  
  - Parasitic: Fish in this group live in invertebrate hosts found in shallow-water coral
  Coral
  Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
  
   communities such as bivalves, sea cucumbers, and starfish.

Pearlfish are currently divided into 7 genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 and 31 species:

Genus Carapus

• Carapus acus
• Carapus bermudensis
• Carapus boraborensis
• Carapus dubius
• Carapus mourlani
• Carapus sluiteri

Genus Echiodon Thompson, 1837

• Echiodon anchipterus
• Echiodon atopus
• Echiodon coheni
• Echiodon cryomargarites Markle, Williams & Olney, 1983
• Echiodon dawsoni
• Echiodon dentatus
• Echiodon drummondii
• Echiodon exsilium
• Echiodon neotes
• Echiodon pegasus
• Echiodon pukaki
• Echiodon rendahli
  Echiodon rendahli
  Echiodon rendahli is a pearlfish of the family Carapidae, found in the south west Pacific oceans around Australia and New Zealand at depths down to 60 m. Its length is between 10 and 12 cm....
  
  

Genus Encheliophis

Encheliophis

Encheliophis is a pearlfish genus in the family Carapidae.-Species:* Encheliophis chardewalli* Encheliophis gracilis* Encheliophis homei* Encheliophis sagamianus* Encheliophis vermicularis* Encheliophis vermiops...

• Encheliophis chardewalli
• Encheliophis gracilis
• Encheliophis homei
• Encheliophis sagamianus
• Encheliophis vermicularis
  Encheliophis vermicularis
  Encheliophis vermicularis is a pearlfish species in the genus Encheliophis.-External links:*...
  
  
• Encheliophis vermiops

Genus Eurypleuron

• Eurypleuron cinereum
• Eurypleuron owasianum

Genus Onuxodon

• Onuxodon fowleri
• Onuxodon margaritiferae
• Onuxodon parvibrachium

Genus Pyramodon

• Pyramodon lindas
• Pyramodon parini
• Pyramodon punctatus
• Pyramodon ventralis
  Pyramodon ventralis
  Pyramodon ventralis is a pearlfish of the family Carapidae, found in the Indo-western Pacific oceans at depths of between 100 and 400 m. Its length is between 25 and 30 cm.-References:...
  
  

Genus Snyderidia Gilbert, 1905

• Snyderidia canina Gilbert, 1905