చిమేర

వికీపీడియా నుండి
ఇక్కడికి గెంతు: మార్గసూచీ, వెతుకు
Chimaeras
Temporal range: Early Devonian-Recent[1]
Hydrolagus colliei
శాస్త్రీయ వర్గీకరణ
రాజ్యం: Animalia
విభాగం: Chordata
తరగతి: Chondrichthyes
ఉప తరగతి: Holocephali
క్రమం: Chimaeriformes
Obruchev, 1953
Families

Callorhinchidae
Chimaeridae
Rhinochimaeridae

Chimaeras[1] are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish (not to be confused with the rattails), spookfish (not to be confused with the true spookfish of the family Opisthoproctidae), or rabbitfishes (not to be confused with the true rabbitfishes of the family Siganidae).

They may be the "oldest and most enigmatic groups of fishes alive today".[2] At one time a "diverse and abundant" group (based on the fossil record), their closest living relatives are sharks, though in evolutionary terms they branched off from sharks nearly 400 million years ago and have remained isolated ever since.[2] Today they are largely confined to deep water.[2]

Description and habits[మార్చు]

Chimaera egg

Chimaeras live in temperate ocean floors down to 2,600 metres (8,500 ft) depth, with few occurring at depths shallower than 200 metres (660 ft). Exceptions include the members of the genus Callorhinchus, the rabbit fish and the spotted ratfish, which locally/periodically can be found at relatively shallow depths. Consequently, these are also among the few species from the Chimaera order that are kept in public aquaria.[3] They have elongated, soft bodies, with a bulky head and a single gill-opening. They grow up to 150 centimetres (4.9 ft) in length, although this includes the lengthy tail found in some species. In many species, the snout is modified into an elongated sensory organ.[4]

Like other members of the class Chondrichthyes, chimaeras have a skeleton constructed of cartilage. Their skin is smooth and largely covered by placoid scales, and their color can range from black to brownish gray. For defense, most chimaeras have a venomous spine located in front of the dorsal fin.

Chimaeras resemble sharks in some ways: they employ claspers for internal fertilization of females and they lay eggs with leathery cases. However, unlike sharks, male chimaeras also have retractable sexual appendages on the forehead (a type of tentaculum)[5] and in front of the pelvic fins.[4] The females lay eggs in spindle-shaped leathery egg cases.[1]

They also differ from sharks in that their upper jaws are fused with their skulls and they have separate anal and urogenital openings. They lack sharks' many sharp and replaceable teeth, having instead just three pairs of large permanent grinding tooth plates.They have gill cover or operculum like bony fishes.[4] Chimaera are the only vertebrates to retain traces of a third pair of limbs.[6]

Phylogenetics[మార్చు]

The evolution of these species has been problematic given the paucity of good fossils. DNA sequences have become the preferred approach to understanding speciation.[7]

The order appears to have originated about 420 million years ago during the Silurian. The 39 extant species fall into three families - the callorhinchids, rhinochimaerids and chimaerids with the callorhinchids being the most basal clade. The families appear to have diverged during the late Jurassic to early Cretaceous (170-120 MYA.)


మూలాలు[మార్చు]

Specific references:

  1. 1.0 1.1 1.2 మూస:FishBase order
  2. 2.0 2.1 2.2 "Ancient And Bizarre Fish Discovered: New Species Of Ghostshark From California And Baja California". ScienceDaily. September 23, 2009. సంగ్రహించిన తేదీ 2009-09-23. 
  3. Tozer, H., & D. D. Dagit (2004). Husbandry of Spotted Ratfish, Hydrolagus colliei., Chapter 33 in: Smith, M., D. Warmolts, D. Thoney, & R. Hueter (editors). Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays, and their Relatives. Ohio Biological Survey, Inc.
  4. 4.0 4.1 4.2 Stevens, J. & Last, P.R. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. పేజీ. 69. ISBN 0-12-547665-5. 
  5. Freaky New Ghostshark ID’d Off California Coast, a September 22, 2009 blog post from Wired Science
  6. American Wildlife, Wm. H, Wise & Co., Inc. New York, 1947. p. 279
  7. Inoue JG, Miya M, Lam K, Tay BH, Danks JA, Bell J, Walker TI, Venkatesh B.(2010). Evolutionary origin and phylogeny of the modern holocephalans (Chondrichthyes: Chimaeriformes): A mitogenomic perspective. Mol. Biol. Evol.

General references:

మూస:Chondrichthyes

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