| Molidae | |
|---|---|
 | |
| Mola mola | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Tetraodontiformes |
| Suborder: | Tetraodontoidei |
| Family: | Molidae Bonaparte, 1832 |
| Genera[2] | |
TheMolidae comprise the family of themolas orocean sunfishes, unusual fish whose bodies come to an end just behind thedorsal andanal fins, giving them a "half-fish" appearance. They are also the largest of the ray-finned bony fish, with thesouthern sunfish,Mola alexandrini, recorded at 4.6 m (15 ft) in length[3] and 2,744 kg (6,049 lb) in weight.
The family name comes from theocean sunfish's scientific nameMola mola, both its genus name and epithet come from the Latin wordmola for "millstone" because of its circular shape.[4]
Molidae have the fewestvertebrae of any fish, with only 16 inMola mola. The axial musculature,caudal and pelvic fins are completely lost during development, and most of theirskeleton is made ofcartilage. They also lackswim bladders. No bony plates occur in the skin, which is, however, thick and dense like cartilage and is fairly rough. Under the skin there is a stiff and gelatinous layer consisting of 89.8% water with a collagen and elastin meshwork, acting like an exoskeleton. Due to its greasy texture, it may also contain lipids. This layer, which is horizontally separated by a septum, provides the fish with buoyancy, and makes up a larger part of the animal's total mass the bigger the individual is.[5]
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.[6] 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.[7]
Molids are said to be able to produce sound by grinding theirpharyngeal teeth, which are long and claw-like. Typical of a member ofTetraodontiformes, 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 andsalps, although they also take small fish or crustaceans.[6]
Molids have been filmed interacting with other species. Since molids are susceptible to skinparasites, they make use ofcleaner fish. A molid in need of cleaning will locate a patch of floatingalgae orflotsam that is home tohalfmoons. 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 agull or similarseabird. The seabird will then dig worms and other stubborn parasites out of the molid's skin.[7]
The known fossil history of Molidae extends back to theEocene, with the genusEomola containing the speciesE. bimaxillaria, known from the mid/lateEocene (Bartonian) of theNorth Caucasus.[1] The fossil genusAustromola containing one species,A. angerhoferiGregorova, Schultz, Harzhauser & Kroh, 2009, is known from the LowerMioceneEbelsberg Formation nearPucking, Austria. This species was a resident of theParatethys Sea and is estimated to have reached a length around 320 cm (130 in), making it the largest Cenozoic fossilteleost known.[8]
At least one fossil species ofMola,M. pileata(van Beneden, 1881), is known from the Upper and Middle Miocene ofEurope with a possible second species known from the Lower Miocene ofNorth Carolina, United States. The genusRanzania has five known fossil species:R. grahamiWeems, 1985 andR. tenneyorumWeems, 1985, both from the Middle MioceneCalvert Formation ofVirginia, USA;R. zappaiCarnevale, 2007 from the Middle Miocene of Italy;R. ogaiiUyeno & Sakamoto, 1994 from the Middle Miocene of Japan; and an as yet unnamed species from the Upper Miocene ofAlgeria.[8]
AnEarly Miocene-aged fossil molid beak (potentially ofRanzania) from theGaiman Formation ofChubut, Argentina represents one of the southernmost known fossil records oftetraodontiform fish. Although it may have been a stray to the region, it is also possible that the warmer climate of the Miocene allowed molids to inhabit the seas that then coveredPatagonia. In modern times, molids are only occasional strays to the region due to its cold climate.[9]
Only five extant species in three extant genera are described:
| Rank | Molid species | Common name | Year | Mass (kg) | Total length (m) | Clavus (pseudo-tail) appearance | Shape of head and chin | Image |
|---|---|---|---|---|---|---|---|---|
| 1 | Mola mola | Ocean sunfish | 1758 | 2300 | 3.33 | Scalloped | Less bumpy and less protruding | .jpg) |
| 2 | Mola alexandrini | Southern sunfish | 2021 | 2744 | 3.0 | Rounded | Bumps on head and chin | .jpg) |
| 3 | Mola tecta | Hoodwinker sunfish | 2017 | 1870 | 2.42 | Rounded with medial indentation | No lumps and bumps on head and chin |  |
| 4 | Masturus lanceolatus | Sharptail mola | 1840 | 2000 | 3.37 | Pointed projection | Convex forehead |  |
| 5 | Ranzania laevis | Slender sunfish | 1776 | NA | 1.0 | Slant and flat | Pointed and bump-less |  |
Authority control databases: National |
|---|