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Chimaera

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Title: Chimaera  
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Subject: Chondrichthyes, Evolution of fish, Diversity of fish, Placodermi, Holocephali
Collection: Chimaeriformes, Early Devonian First Appearances
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Chimaera

Chimaeras
Temporal range: Early Devonian-Recent[1]
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Hydrolagus colliei
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order: Chimaeriformes
Obruchev, 1953
Families

Callorhinchidae
Chimaeridae
Rhinochimaeridae

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

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.[3]

Contents

  • Description and habits 1
  • Classification 2
  • Phylogenetics 3
  • See also 4
  • References 5

Description and habits

Chimaera egg

Chimaeras live in temperate ocean floors down to 2,600 m (8,500 ft) deep, with few occurring at depths shallower than 200 m (660 ft). Exceptions include the members of the

  1. ^ a b c Froese, Rainer, and Daniel Pauly, eds. (2014). "Chimaeriformes" in FishBase. November 2014 version.
  2. ^ a b "Ancient And Bizarre Fish Discovered: New Species Of Ghostshark From California And Baja California".  
  3. ^  
  4. ^ Tozer, H. & Dagit, D.D. (2004): .Hydrolagus collieiHusbandry of Spotted Ratfish, , 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.
  5. ^ a b c Stevens, J. & Last, P.R. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. p. 69.  
  6. ^ T.H. Bullock; R.H. Hartline; A.J. Kalmijn; P. Laurent; R.W. Murray; H. Scheich; E. Schwartz; T. Szabo (6 December 2012). Electroreceptors and Other Specialized Receptors in Lower Vertrebrates. Springer Science & Business Media. p. 125.  
  7. ^ Freaky New Ghostshark ID’d Off California Coast, a September 22, 2009 blog post from Wired Science
  8. ^ Inoue, J.G., Miya, M., Lam, K., Tay, B.H., Danks, J.A., Bell, J., Walker, T.I. Venkatesh, B. (2010): Evolutionary origin and phylogeny of the modern holocephalans (Chondrichthyes: Chimaeriformes): A mitogenomic perspective. Molecular Biology and Evolution, 27 (11): 2576-2586.

References

See also

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.)

The evolution of these species has been problematic given the paucity of good fossils. DNA sequences have become the preferred approach to understanding speciation.[8]

Phylogenetics

A renewed effort to explore deep water and to undertake taxonomic analysis of specimens in museum collections led to a boom during the first decade of the 21st century in the number of new species identified.[2] They are 50 extant species in six genera and three families are described; an additional three genera and two families are only known from fossils):

In some classifications, the chimaeras are included (as subclass Holocephali) in the class Chondrichthyes of cartilaginous fishes; in other systems, this distinction may be raised to the level of class. Chimaeras also have some characteristics of bony fishes.

Classification

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 also have gill covers or opercula like bony fishes.[5]

Chimaeras resemble sharks in some ways: they employ claspers for internal fertilization of females and they lay eggs with leathery cases. They also use electroreception to locate their prey.[6] However, unlike sharks, male chimaeras also have retractable sexual appendages on the forehead (a type of tentaculum)[7] and in front of the pelvic fins.[5] The females lay eggs in spindle-shaped, leathery egg cases.[1]

Like other members of the class Chondrichthyes, chimaera skeletons are 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.

[5]

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