The cephalic lateral-line system of Characiformes (Teleostei: Ostariophysi): anatomy and phylogenetic implications

Abstract

The lateral-line system has been traditionally recognized as an important source of phylogenetic information for different groups of fishes. Although extensively studied in Siluriformes and Cypriniformes, the lateral-line system of Characiformes remained underexplored. In the present study, the anatomy of the cephalic lateral-line canals of characiforms is described in detail and a unifying terminology that considers the ontogeny and homologies of the components of this system is offered. Aspects of the arrangement of lateral-line canals, as well as the number, location and size of canal tubules and pores, resulted in the identification of novel putative synapomorphies for Characiformes and several of its subgroups. The study also revised synapomorphies previously proposed for different characiform families and provided comments on their observed distribution across the order based on extensive taxon sampling. Information from the ontogenetic studies of the cephalic lateral-line canal system and a proposal for the proper use of these data to detect truncations in the development of the lateral-line canals across the order is also offered.

Ontogeny and homology of cranial bones associated with lateral‐line canals of the Senegal Bichir,Polypterus senegalus(Actinopterygii: Cladistii: Polypteriformes), with a discussion on the formation of lateral‐line canal bones in fishes

“…These tubular bones represent the ossification of the walls of the lateral‐line canal segment that starts in the vicinity of a neuromast and forms first a half‐pipe structure and then a fully enclosed tube with ossification of the canal roof over the CN. This developmental sequence generally agrees with the process of enclosure of CNs and formation of lateral‐line canals described by several authors (Allis, 1889; Pehrson, 1922; Tarby and Webb, 2003; Webb and Shirey, 2003; Bird and Webb, 2014; Pastana et al, 2019). However, during development these tubular ossifications may also interact with other adjacent ossifications not associated with neuromasts or, in some cases, may develop lamellar expansions or flanges, such that the development of each bone associated with lateral‐line canals in P. senegalus follows one of four distinct ontogenetic pathways.…”

“…In support of this view, there are examples of fishes that have antorbital bones consisting solely of plate‐like ossifications, without associated lateral‐line canals, e.g. many representatives of Characiformes and a few siluriforms (Bockmann, 1998; Pastana et al, 2019). In these fishes, the bone in question represents the antorbital s.s. , without associated tubular laterosensory‐derived ossifications.…”

“…the nasal s.s. ) is absent, so that there is only a tubular ossification at the dorsal nasal region that represents the tubular component of the ossifications associated with the supraorbital canal: e.g. Hiodontidae—Li and Wilson, 1994; 1996; 1999; Hilton, 2002a; Hilton and Grande, 2008; many characiforms and siluriforms: Ostariophysi—Arratia and Huaquin, 1995; Arratia, 2003, Pastana et al, 2019. There are also cases in which both the tubular and plate‐like components of the nasal are absent even though the nasal portion of the supraorbital canal is still present, so that the canal exists as an unossified tubular canal composed only of soft tissue.…”

“…Other ostariophysans (e.g. most siluriforms, Gymnotiformes) and a single, basal group of Characiformes (Erythrinidae), however, have antorbitals with associated lateral‐line canals (Pastana et al, 2019). This provides support for the view that the element associated with laterosensory canals identified as the ‘antorbital’ in many groups, including Amia , is actually a compound bone formed by the fusion between a tubular laterosensory component plus a membranodermal component, that is, the antorbital s.s.…”

“…As the name suggests, superficial neuromasts (SNs) are distributed on the surface of the head and body, and are the only type of neuromast present in jawless fishes and in larval and aquatic adult amphibians (Webb, 2014). Canal neuromasts (CNs), in turn, are located in the epithelium lying on the bottom of canals formed when neuromasts are enclosed in a stereotyped process (Tarby and Webb, 2003; Webb and Shirey, 2003; Bird and Webb, 2014; Wada et al, 2014; Webb, 2014; Pastana et al, 2019). Lateral‐line canals are distributed in a consistent fashion on the body and especially on the head of fishes, which allows comparisons across even distantly related taxa, including fossils (Garman, 1888; Allis, 1934; Stensiö, 1947; Webb, 1989; Webb and Northcutt, 1997; Rizzato and Bichuette, 2017; Pastana et al, 2019).…”