The Molidae comprise the family of the molas or ocean sunfishes, unusual fish whose bodies come to an end just behind the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

and

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 s ...

s, giving them a "half-fish" appearance. They are also the largest of the ray-finned bony fish, with the

southern sunfish The giant sunfish or bumphead sunfish (''Mola alexandrini''), also known as the Ramsay's sunfish, southern sunfish, southern ocean sunfish, short sunfish or bump-head sunfish in many parts of the world,Diane J. Bray, 2011, Short Sunfish, or even ...

, ''Mola alexandrini'', recorded at in length and in weight.

Description

Molidae have the fewest

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e of any fish, with only 16 in ''Mola mola''. They also completely lack all

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

bones, and most of their

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

is made of

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

. No bony plates occur in the skin, which is, however, thick and dense like cartilage and is fairly rough. They also lack swim bladders. Molids mostly swim by using their anal and dorsal fins; the pectoral fins are probably just stabilizers. To steer, they squirt a strong jet of water out of their mouths or gills. They can also make minor adjustments in the orientation of the anal fin or the dorsal fin so as to control the amount of force it produces and the angle at which the force is produced. In this respect, they use their fins much like a bird uses its wings. Molids are said to be able to produce sound by grinding their pharyngeal teeth, which are long and claw-like. Typical of a member of

Tetraodontiformes The Tetraodontiformes are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the order Perciformes. The Tetraodontiformes are represented by 10 extant families and at least ...

, their teeth are fused into a beak-like structure, making it impossible for them to close their mouths. Despite this, they feed mainly on soft-bodied animals, such as jellyfish and salps, although they also take small fish or crustaceans.

Behavior

Molids have been filmed interacting with other species. Since molids are susceptible to skin parasites, they make use of

cleaner fish Cleaner fish are fish that show a specialist feeding strategy by providing a service to other species, referred to as clients, by removing dead skin, ectoparasites, and infected tissue from the surface or gill chambers. This example of cleaning ...

. A molid in need of cleaning will locate a patch of floating

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from u ...

flotsam In maritime law, flotsam'','' jetsam'','' lagan'','' and derelict are specific kinds of shipwreck. The words have specific nautical meanings, with legal consequences in the law of admiralty and marine salvage. A shipwreck is defined as the rema ...

that is home to

halfmoon The halfmoon (''Medialuna californiensis''), also known as the blue perch, is a species of marine ray-finned fish, a sea chub from the subfamily Scorpidinae, part of the family Kyphosidae. It is native to the coasts of the eastern Pacific Ocean ...

s. The molid signals a readiness for cleaning by swimming almost vertically with its head near the surface of the water, and waits for the smaller cleaner fish to feed on the parasite worms. Similarly, the molid may break the surface of the water with its dorsal fin and beak to attract the attention of a gull or similar

seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envir ...

. The seabird will then dig worms and other stubborn parasites out of the molid's skin.

Fossil record

The known fossil history of Molidae extends back to the Eocene with the genus ''

Eomola ''Eomola'' is an extinct genus of sunfish from the middle Eocene. Its fossils have been found in Russia. ''Eomola'' was described in 1992 by James Tyler and Alexandre Bannikov, and the type species In zoological nomenclature, a type species ...

'' containing the species '' E. bimaxillaria'' Tyler and Bannikov, 1992 known from the Upper Eocene of the

North Caucasus The North Caucasus, ( ady, Темыр Къафкъас, Temır Qafqas; kbd, Ишхъэрэ Къаукъаз, İṩxhərə Qauqaz; ce, Къилбаседа Кавказ, Q̇ilbaseda Kavkaz; , os, Цӕгат Кавказ, Cægat Kavkaz, inh, ...

. The fossil genus ''

Austromola ''Austromola angerhoferi'' is an extinct species of ocean sunfish. It is known from the Lower Miocene Ebelsberg Formation near Pucking Pucking is a small town in the Linz-Land district in the Austrian state of Upper Austria Upper Austri ...

'' containing one species, '' A. angerhoferi'' Gregorova, Schultz, Harzhauser & Kroh, 2009, is known from the Lower Miocene

Ebelsberg Formation The Ebelsberg Formation is a geologic formation in Austria. It preserves fossils dated to the Chattian to Aquitanian ages of the Oligocene to Miocene epochs.Pucking, Austria. This species was a resident of the Paratethys Sea and is estimated to have reached a length around . At least one fossil species of ''Mola'', '' M. pileata'' (van Beneden, 1881), is known from the Upper and Middle Miocene of Europe with a possible second species known from the Lower Miocene of North Carolina, United States. The genus ''Ranzania'' has five known fossil species: '' R. grahami'' Weems, 1985 and '' R. tenneyorum'' Weems, 1985, both from the Middle Miocene

Calvert Formation The Calvert Formation is a geologic formation in Maryland, Virginia, and Delaware. It preserves fossils dating back to the early to middle Miocene epoch of the Neogene period. The formation is a destination for amateur fossil hunters as well as p ...

of Virginia, USA; '' R. zappai'' Carnevale, 2007 from the Middle Miocene of Italy; '' R. ogaii'' Uyeno & Sakamoto, 1994 from the Middle Miocene of Japan; and an as yet unnamed species from the Upper Miocene of

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Species

Only five extant species in three extant genera are described: * Ocean sunfish (''

Mola mola The ocean sunfish or common mola (''Mola mola'') is one of the largest bony fish in the world. It was misidentified as the heaviest bony fish, which was actually a different species, ''Mola alexandrini''. Adults typically weigh between . The spe ...

'') * Southern ocean sunfish (''

Mola alexandrini The giant sunfish or bumphead sunfish (''Mola alexandrini''), also known as the Ramsay's sunfish, southern sunfish, southern ocean sunfish, short sunfish or bump-head sunfish in many parts of the world,Diane J. Bray, 2011, Short Sunfish, or even ...

''), has been recognized as a senior synonym of ''Mola ramsayi'' (Gaglioli 1889), the "bump-head sunfish" * Hoodwinker sunfish (''

Mola tecta ''Mola tecta'', the hoodwinker sunfish, belongs to the family Molidae and genus '' Mola''. It is closely related to the more widely known ocean sunfish (''Mola mola''). The Latin word "tecta" means hidden. The word "hidden" was adopted for the n ...

'') * Slender sunfish (''

Ranzania laevis The slender sunfish (''Ranzania laevis'') is a mola of the family Molidae, the only extant member of the genus ''Ranzania'',Matsuura, K. (2014): Taxonomy and systematics of tetraodontiform fishes: a review focusing primarily on progress in the ...

'') * Sharptail mola (''

Masturus lanceolatus The sharptail mola (''Masturus lanceolatus'') is a species of mola found circumglobally in tropical and temperate waters. It is similar in appearance to the ocean sunfish (''Mola mola''), but can be distinguished by the projection on its clavus ...

'')

References

{{Taxonbar, from=Q726231 Ray-finned fish families Extant Eocene first appearances Eocene vertebrates of Europe Neogene vertebrates of Europe Paleogene vertebrates of Europe Taxa named by Charles Lucien Bonaparte