The star pearlfish, ''Carapus mourlani'', is a species of slender,

ray-finned Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin ...

fish in the

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 ...

Carapidae Pearlfish are marine fish in the ray-finned fish family Carapidae. Pearlfishes inhabit the tropical waters of the Atlantic, Indian, and Pacific Oceans at depths to , along oceanic shelves and slopes. They are slender, elongated fish with no s ...

. It normally lives inside a

starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...

or a

sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

Description

The star pearlfish is a long, slim, silvery fish growing to a maximum length of . It has dark-pigmented spots, known as melanophores, scattered irregularly across its translucent, scaleless body. The dorsal and anal fins run the length of the body, with the dorsal fin rays being shorter than those of the anal fin. No pelvic fins are present. The posterior part of the upper jaw has numerous pointed, cardiform teeth arranged in rows, but no large fangs or gaps occur between groups of teeth. The eyes are well developed, although these fish mainly live in darkness. The swim bladder lies below the 9th and 10th vertebrae and has two chambers. The precaudal vertebrae are 15 to 17 in number.''Carapus mourlani'' (Petit, 1934)
FishBase. Retrieved 2012-01-18.

Distribution

''C. mourlani'' is found on reefs in the

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 ...

Ocean down to about . Its range includes the coastlines of South and East Africa, the Seychelles, India, Indonesia, the Philippines, Japan, Micronesia, northern Australia, and Hawaii.

Biology

The star pearlfish is a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

of starfishes such as ''

Culcita novaeguineae ''Culcita novaeguineae'' (common name, cushion star) is a species of starfish. It has short arms and an inflated appearance and resembles a pentagonal pincushion. It is variable in colour and can be found in tropical warm waters in the Indo-Pacif ...

'' and holothurians such as ''

Bohadschia argus ''Bohadschia argus'', the leopard sea cucumber, leopardfish, or tigerfish, is a species of sea cucumber in the family Holothuriidae. It is native to the tropical Western Indo-Pacific region. Description ''Bohadschia argus'' has the same roughly ...

'' and ''Stichopus'' spp. It spends most of its time in the

coelom The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, i ...

ic cavity of its host, emerging, usually at night, to feed. Some species of ''Carapus'' feed on small

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, other carapid fish, and possibly,

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

worms. This species is usually found singly in its host, or sometimes as a male and female pair. The fish works its way in through the anus of the sea cucumber. When it is living in a starfish, it enters its host's body cavity through the grooves associated with the tube feet. A pair of fish may release their gametes within the body cavity of the host, and the fertilised eggs may later emerge into the water column.When Fish Live in your Cloaca & How Anal Teeth are Important! The Pearlfish-Sea Cucumber Relationship
Echinoblog. Retrieved 2012-01-18. A study designed to discover whether there were genetic differences between the pearlfish living in holothurians and those living in starfish was inconclusive. During the experimental work, a large sea cucumber, ''

'', was put in a bucket of relatively cold water, which caused 14 pearlfish to emerge, with a further one remaining inside. This is believed to be the record number of carapid fish ever found in a single holothurian.

References

{{Taxonbar, from=Q5037725 Carapidae Fish described in 1934