Phylogenetic interrelationships of the eel families Derichthyidae and Colocongridae (Elopomorpha: Anguilliformes) based on the pectoral skeleton

Abstract

A cladistic analysis of the eel families Derichthyidae and Colocongridae is herein proposed for the first time on the basis of morphological data. We discovered dozens of new phylogenetic characters derived from a detailed analysis of the pectoral skeleton, an anatomical system neglected by most previous studies. Our maximum parsimony analysis indicates that Colocongridae sensu lato is paraphyletic, with its two constituent genera Coloconger and Congriscus appearing as successive sister groups of derichthyids. Monophyly of the family Derichthyidae, which has been questioned by some studies, is herein strongly supported by 10 unambiguous synapomorphies. We also stress the importance of the appendicular skeleton as a useful source of phylogenetic information for the resolution of systematic problems within Anguilliformes.

The lateral line system and its innervation in the Japanese eel Anguilla japonica (Teleostei: Elopomorpha: Anguillidae)

“…Because the tTRC is usually associated with the extrascapula and posttemporal (Webb, 1989), the two elements of A. japonica are likely to be two extrascapulae, one extrascapula (anterior) and one posttemporal (posterior), or two posttemporals. Such tube-like elements have not before been reported in extant anguilliforms (e.g., da Silva João Paulo et al, 2019;Forey et al, 1996;Johnson et al, 2012;Robins, 1989), although a fossil anguilliform, Luenchelys minimus Belouze et al, 2003, had an extrascapula and posttemporal in the putative position of the tTRC (Forey, Yi, Patterson, & Davies, 2003), a pattern consistent with the second suggestion (above). Therefore, the presence or absence of tube-like elements (putative extrascapula and posttemporal) should be reassessed throughout the order and their identity confirmed.…”

“…Because the STC (and tTRC) passes through the extrascapula in almost of elopomorphs (except for anguilliforms ;Forey, 1973;Forey et al, 1996), the two tube-like elements of A. japonica might be homologous with the extrascapula(e) of non-auguillifom elopomorphs. However, extrascapula(e) has not before been reported in extant anguilliforms (e.g., da Silva João Paulo, Datovo, & Johnson, 2019;Forey et al, 1996;Johnson et al, 2012;Robins, 1989), their homology should be confirmed in further studies.…”

Morphological evolution and diversity of pectoral fin skeletons in teleosts

“…We showed that some species in teleosts have different numbers of proximal radials (Fig. 2), and we also found some examples in Anguilliformes (da Silva and Johnson, 2018;da Silva, Datovo and Johnson, 2019), Osteoglossiformes (Cavin and Forey, 2001), Alepocephaliformes (Johnson and Patterson, 1996), Siluriformes (Starks, 1930;Brousseau, 1976b), Stomiatiformes (Fink, 1985), Gadiformes and Lophiiformes (Starks, 1930). These species seem to have secondarily deviated from the four-basal rule (Fig 6, 7, black and white circles).…”

“…In Anguilliformes, the connections of distal radials and fin rays look similar (one-to-one) (Fig. 2B) (da Silva, Datovo and Johnson, 2019), suggesting that the fishes have acquired the one-to-one connections independently.…”

“…In previous studies (Starks, 1930;da Silva and Johnson, 2018;da Silva, Datovo and Johnson, 2019), pectoral fin skeletons in the other 11 species of Anguilliformes, 3 species of Elopiformes and 1 species of each Albuliformes and Notacanthiformes in Elopomorpha have been reported. Regarding Anguilliformes, while some species such as blackbelly spoonbill eel (Nessorhamphus danae) and narrownecked oceanic ell (Derichthys serpentinus) have retained four proximal radials, others show an increase or decrease in the number of proximal radials (da Silva and Johnson, 2018;da Silva, Datovo and Johnson, 2019).…”