C. H. Eigenmann, 1890
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 papillose 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.
Diplomystids are the only extant catfish family with teeth on a well-developed maxilla (although this is also true of the extinct genus Hypsidoris). Diplomystids possess maxillary barbels. The dorsal and pectoral fins have spines. The largest species reaches 32 cm (13 in).
Relatively little is known of the habits and life history of diplomystids. In Chile, diplomystids are mostly found to be benthic in fast-moving streams, and D. camposensis also occurs in lakes. O. viedmensis has been taken from rivers near sea level to about 1,900 m.
Diplomystids are generalized carnivores that consume annelids, mollusks, and arthropods. Specimens of D. nahuelbutaensis from fast-flowing, moderate-elevation (370–520 m) tributaries of the Río Bío Bío had eaten aquatic insect larvae, especially chironomids, and the relatively large decapod crustacean Aegla.
Reproduction occurs at least during the austral summer based on captures of females with maturing eggs, and the juveniles reported here were collected in December.
All diplomystids are considered to be potentially or actually threatened or endangered due to habitat deterioration and predation or competition by introduced trout, Oncorhynchus mykiss and Salmo trutta. D. chilensis may be extinct.
- Nelson, Joseph S. (2006). Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7.
- Sullivan, JP; Lundberg JG; Hardman M (2006). "A phylogenetic analysis of the major groups of catfishes (Teleostei: Siluriformes) using rag1 and rag2 nuclear gene sequences". Molecular Phylogenetics and Evolution. 41 (3): 636–62. doi:10.1016/j.ympev.2006.05.044. PMID 16876440.
- Lundberg, John G.; Berra, Tim M.; Friel, John P. (March 2004). "First description of small juveniles of the primitive catfish Diplomystes (Siluriformes: Diplomystidae)" (PDF). Ichthyological Exploration of Freshwaters. 15 (1): 71–82.