Caecilian

This article is about an order of amphibians. For the bishop of Carthage, see Caecilianus.

Caecilian
Temporal range:
Late Triassic (Norian) – Present, 223–0 Ma
Oscaecilia ochrocephala (Caeciliidae)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Subclass: Lissamphibia
Order: Gymnophiona
Müller, 1832[1]
Subgroups
Synonyms[1]

Caecilians (/sɪˈsɪliən/; New Latin for 'blind ones') are a group of limbless, vermiform (worm-shaped) or serpentine (snake-shaped) amphibians with small or sometimes nonexistent eyes. They mostly live hidden in soil or in streambeds, and this cryptic lifestyle renders caecilians among the least familiar amphibians. Modern caecilians live in the tropics of South and Central America, Africa, and southern Asia. Caecilians feed on small subterranean creatures such as earthworms. The body is cylindrical and often darkly coloured, and the skull is bullet-shaped and strongly built. Caecilian heads have several unique adaptations, including fused cranial and jaw bones, a two-part system of jaw muscles, and a chemosensory tentacle in front of the eye. The skin is slimy and bears ringlike markings or grooves and may contain scales.[2]

Modern caecilians are a clade, the order Gymnophiona /ˌdʒɪmnəˈfaɪənə/ (or Apoda /ˈæpədə/), one of the three living amphibian groups alongside Anura (frogs) and Urodela (salamanders). Gymnophiona is a crown group, encompassing all modern caecilians and all descendants of their last common ancestor. There are more than 220 living species of caecilian classified in 10 families. Gymnophionomorpha is a recently coined name for the corresponding total group which includes Gymnophiona as well as a few extinct stem-group caecilians (extinct amphibians whose closest living relatives are caecilians but are not descended from any caecilian).[3][4] Some palaeontologists have used the name Gymnophiona for the total group and the old name Apoda for the crown group[5]. However, Apoda has other even older uses, including as the name of a genus of Butterfly making its use potentially confusing and best avoided. 'Gymnophiona' derives from the Greek words γυμνος / gymnos (Ancient Greek for 'naked') and οφις / ophis (Ancient Greek for 'snake'), as the caecilians were originally thought to be related to snakes and to lack scales.[6]

The study of caecilian evolution is complicated by their poor fossil record and specialized anatomy. Genetic evidence and some anatomical details (such as pedicellate teeth) support the idea that frogs, salamanders, and caecilians (collectively known as lissamphibians) are each other's closest relatives. Frogs and salamanders show many similarities to dissorophoids, a group of extinct amphibians in the order Temnospondyli. Caecilians are more controversial; many studies extend dissorophoid ancestry to caecilians. Some studies have instead argued that caecilians descend from extinct lepospondyl or stereospondyl amphibians, contradicting evidence for lissamphibian monophyly (common ancestry). Rare fossils of early gymnophionans such as Eocaecilia and Funcusvermis have helped to test the various conflicting hypotheses for the relationships between caecilians and other living and extinct amphibians.

  1. ^ a b Frost, Darrel R. (2019). "Gymnophiona Müller, 1832". Amphibian Species of the World: an Online Reference. Version 6.0. American Museum of Natural History. Retrieved 11 September 2019.
  2. ^ Wilkinson M (2012). "Caecilians" (PDF). Current Biology. 22 (17): R668–R669. Bibcode:2012CBio...22.R668W. doi:10.1016/j.cub.2012.06.019. PMID 22974987.
  3. ^ Cite error: The named reference Santosetal20 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference :1 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Evans&SigogneauRussell2001 was invoked but never defined (see the help page).
  6. ^ Wilkinson, M. (2012). Caecilians. Current Biology, 22(17), R668-R669.