Molidae are a family of unique fish whose bodies end just behind their dorsal and anal fins, making the organism look like half of a complete fish. These fins are used to swim while the fish control steering by squirting jets of water out of their mouthes or gills. Molidae have the fewest vertebrae of any fish and lack a swim bladder. They have rough skin and poisonous meat.
- MASDEA (1997).
Molecular Biology and Genetics
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Molidae is the family of the molas or ocean sunfishes, unusual fishes whose bodies come to an end just behind the dorsal and anal fins, giving them a "half-fish" appearance. They are also the largest of the ray-finned bony fishes, with the ocean sunfish Mola mola recorded at up to 3.3 m (11 ft) in length and 2,000 kg (4,400 lb) in weight.
Molidae have the fewest vertebrae of any fish, with only 16 in Mola mola. Molidae also completely lack all caudal bones, and most of their skeletons are made of cartilage. No bony plates occur in the skin which is, however, thick and dense like cartilage and is fairly rough. They also lack swim bladders. Debate surrounds whether the meat contains the same toxin as in pufferfish and porcupine fish.
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, their teeth are fused into a beak-like structure, making it impossible for them to close their mouth. Despite this, they feed mainly on soft-bodied animals, such as jellyfish and salps, although they will also take small fish or crustaceans.
Molids have been filmed interacting with other species. Since molids are susceptible to skin parasites, they make use of cleaner fish. A molid in need of cleaning will locate a patch of floating algae or flotsam that is home to half moon perch. The molid then signals a readiness for cleaning by swimming almost vertically with its head near the surface of the water. It 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. The seabird will then dig worms and other stubborn parasites out of the molid's skin.
The known fossil history of this genus extends back to the Eocene with the genus Eomola containing the species E. bimaxillaria Tyler and Bannikov, 1992 known from the Upper Eocene of the North Caucasus. The fossil genus Austromola containing one species, A. angerhoferi Gregorova, Schultz, Harzhauser & Kroh, 2009, is known from the Lower Miocene Ebelsberg Formation near Pucking, Austria. This species was a resident of the Paratethys Sea and is estimated to have reached a length of around 320 cm (130 in). 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, USA. The genus Ranzania has five known fossil species: R. grahami Weems, 1985 and R. tenneyorum Weems, 1985, both from the Middle Miocene Calvert Formation 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 Algeria.
Only four species in three genera are described:
- Ocean sunfish (Mola mola)
- Southern ocean sunfish (Mola ramsayi)
- Slender sunfish (Ranzania laevis)
- Sharptail mola (Masturus lanceolatus)
- Matsura, Keiichi; Tyler, James C. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. p. 231. ISBN 0-12-547665-5.
- Alastair Fothergill (director), David Attenborough (narrator) (2001-09-12). Blue Planet, Seas Of Life Episode 3 (Television series). BBC Worldwide, Ltd. ISBN 0-563-38498-0.
- Ruzena, G., O. Schultz, M. Harzhauser, A. Kroh and S. Ćorić (2009): A Giant Early Miocene Sunfish from the North Alpine Foreland Basin (Austria) and its Implication for Molid Phylogeny. Journal of Vertebrate Paleontology 29(2):359–371
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