A new ectoparasitic distichodontid of the genus Eugnathichthys (Characiformes: Citharinoidei) from the Congo basin of central Africa, with a molecular phylogeny for the genus

Abstract

A new species of ectoparasitic distichodontid, Eugnathichthys virgatus, is described from localities in the central and western Congo basin. The new species is a fin-eater even at small sizes and, in common with congeners, is capable of biting off sections of heavily ossified fin-rays of large prey species. Prior to the present study, two species were included in this distinctive distichodontid genus: the type species, Eugnathichthys eetveldii, and a second species, E. macroterolepis, both of which are widely distributed throughout much of the Congo basin. Morphologically, E. virgatus is readily distinguished from its two congeners based on a combination of meristic and morphometric attributes. The new species possesses a unique pigmentation pattern, a reduced number of pectoral-fin rays, and a markedly reduced dentition on the fifth ceratobranchial elements of the pharynx, all of which are derived features considered diagnostic for the new species. With molecular data the species is further diagnosed by four apomorphic, non-synonomous nucleotide transitions in two sampled genes (NADH dehydrogenase subunit 2 and glycosyltransferase). Phylogenetic analysis of those mtDNA and ncDNA markers supports a sister-group relationship between E. virgatus and E. eetveldii rather than with E. macroterolepis, the species with which it bears closest phenetic similarity.Key words: Eugnathichthys virgatus, new species, ectoparasite, generic intrarelationships ResuméUne nouvelle espèce de distichodontid ectoparasite, Eugnathichthys virgatus, est décrite à partir des localités du centre et de l'ouest du bassin du Congo. La nouvelle espèce se nourrit de nageoire, et cela même à petites tailles. Elle a en commun avec les autres espèces congénères la capacité de manger, par morsure, de morceaux de nageoire fortement ossifiés d'espèces proies de grande taille. Avant la présente étude, deux espèces avaient été incluses dans ce genre distinctif de distichodontid: il s'agit des espèces type, Eugnathichthys eetveldii, et E. macroterolepis qui, tous deux, sont largement distribuées dans une grande partie du bassin du Congo. Morphologiquement, E. virgatus se distingue facilement de ses deux congénères sur base d'une combinaison de caractères méristiques et morphométriques. Cette espèce possède un motif de pigmentation unique, un nombre réduit de rayons des nageoires pectorales et une dentition nettement réduite sur les éléments du cinquième cératobranchial du pharynx, qui sont tous des traits dérivés, considérés comme diagnostic pour la nouvelle espèce. De surcroît, l'espèce est encore diagnostiquée par la présence de quatre nucléotides apomorphes de transition, non-synonymes, dans les deux gènes testés (NADH déshydrogénase sous-unité 2 et glycosyltransférase). L'analyse phylogénétique de ces marqueurs mtADN et ncADN soutient que E. virgatus et E. eetveldii sont issus d'un même groupe et ont un lien de parenté étroit plutôt qu'avec l'espèce E. macroterolepis qui porte la plus proche similitude phénotypique. STIASSNY ET AL.480 · Zoot...

Morphometry and DNA barcoding reveal cryptic diversity in the genus Enteromius (Cypriniformes: Cyprinidae) from the Congo basin, Africa

“…However, the uncritical use of molecular tools to identify species, especially using only a single molecular locus (mt genome), is unwarranted (DeSalle et al 2011), and traditional morphology has proven its value as a suitable technique to assess the diversity in many taxa. Therefore, we combined both methodologies in the present study, an approach that has already proven to be successful in several taxonomic studies (e.g., Olayemi et al 2012;Stiassny et al 2013;Lavoué & Sullivan 2014).…”

Are characiform Fishes Gondwanan in Origin? Insights from a Time-Scaled Molecular Phylogeny of the Citharinoidei (Ostariophysi: Characiformes)

“…Likewise, levels of species endemism in distichodontids are centered in the Congo Basin, where, in addition to representation of all but one genus (the West-African and Nilo-Sudanic Paradistichodus ), five genera are endemic (Figure 1). While not as speciose as some other characiform families (such as the African Alestidae or the hyperdiverse Neotropical Characidae), distichodontids exhibit noteworthy morphological variation—particularly in jaw anatomy and dentition—that is reflected in diversified trophic ecologies, ranging from herbivory to carnivory, and including highly specialized ectoparasitic fin-eating behaviors [41,42]. Body size variation is equally noteworthy, with records of total length spanning from less than 2 cm (in certain Neolebias species) to over 80 cm (in large Distichodus species), and anecdotal reports suggesting that D. nefasch can reach over a meter in length.…”

DNA barcoding reveals novel insights into pterygophagy and prey selection in distichodontid fishes (Characiformes: Distichodontidae)

“…Based on an observed similarity in caudalfin coloration and patterningas revealed by traditional stomach content analysisbetween the ectoparasitic distichodontids Eugnathichthys eetveldii and E. macroterolepis and their putative prey Synodontis decorus and Mesoborus crocodilus, respectively, Roberts (1990) hypothesized that the barred caudal-fin pattern in pterygophagous distichodontids reflects a form of aggressive mimicry, allowing them to avoid detection by their monospecific prey. Four distichodontid genera -Eugnathichthys, Belonophago, Ichthyborus, and Phagoare reportedly ectoparasitic (i.e., feeding primarily on fish fins as adults) (Roberts 1990;Stiassny et al 2013), but until the present study, there was virtually no information regarding the actual prey preferences of any of them.…”

“…Four distichodontid genera – Eugnathichthys , Belonophago , Ichthyborus , and Phago – are reportedly ectoparasitic (i.e., feeding primarily on fish fins as adults) (Roberts ; Stiassny et al. ), but until the present study, there was virtually no information regarding the actual prey preferences of any of them.…”