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Velvet catfish

Diplomystidae
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Siluriformes
Suborder: Diplomystoidei
Grande, 1987
Family: Diplomystidae
C. H. Eigenmann, 1890
Genera

Diplomystes
Olivaichthys


Diplomystes
Olivaichthys

The Diplomystidae, the velvet catfishes, are a family of primitive catfishes endemic to freshwater habitats in Argentina and Chile in southern South America. It currently contains six species in two genera.

In traditional schemes, the Diplomystidae family is the basal, primitive sister group to all other catfishes (Siluroidei). This is well supported by morphological evidence. However, a clade called Loricarioidei is hypothesized to be the most basal group of catfishes, which is sister to a clade including Diplomystidae and the rest of the catfishes; however, the traditional hypothesis could not be rejected.

Diplomystids retain more plesiomorphic characteristics than any other siluriforms, recent or fossil, including aspects of the maxillary bones, barbels, nares, otic capsule, anterior pterygoid bones, Weberian complex centra, caudal skeleton, and fin rays, and pectoral girdle. Monophyly for Diplomystidae is well supported by synapomorphies of the vomerine and palatine shapes, cranial articulation of the hyomandibula, and heavily skin.

Olivaichthys is a genus erected by Gloria Arratia in 1987. However, many recent authors synonymize this genus with Diplomystes. A molecular analysis has proposed that the trans-Andean Diplomystes and the cis-Andean Olivaichthys are so closely related (in addition to the close morphological similarity), that Olivaichthys should not be recognized. However, this is strange, as recent divergence is unlikely with the species on either side of the Andes.


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