The lateral line system and its innervation in Lateolabrax japonicus (Percoidei incertae sedis) and two apogonids (Apogonidae), with special reference to superficial neuromasts (Teleostei: Percomorpha)

Abstract

The lateral line system and its innervation were examined in a generalized perch-like species, Lateolabrax japonicus (Percoidei incertae sedis), and compared with those in two species of Apogonidae (Fowleria variegata in Apogonichthyini and Ostorhinchus doederleini in Ostorhinchini) characterized by proliferated superficial neuromasts (SNs) on the head, trunk lateral line scales and caudal fin. The total number of SNs differed greatly between the two groups, being 271 in the former, and 2,403 and 4,088 in the latter. The mandibular ramus (MDR) was extensively ramified in the head of the apogonids, with three additional branches that were absent in L. japonicus, innervating 1,117 SNs in F. variegata and 1,928 in O. doederleini. In the apogonids, the additional anterodorsal branch of the MDR coursed parallel to the buccal ramus anteriorly (on the interorbital space) and to the supratemporal ramus posteriorly (on the temporal region). The two parallel portions supplied numerous SN rows forming a characteristic crosshatch pattern, the branch and two rami distributing to transverse and longitudinal rows, respectively. In the two groups, the trunk lateral line scales each housed a canal neuromast (CN; partly replaced by an SN in F. variegata). In addition, one to four (in L. japonicus) and three to 55 (in the apogonids) SNs occurred on each lateral line scale, the pattern of SN innervation being identical in having two types of branches; one innervated a CN and SNs, and the other SN(s) only. The latter type extended only to a limited number of scales in L. japonicus, but to nearly all or all scales in the apogonids. Compared with F. variegata, branches of the respective types were more finely ramified with greater number of SNs in O. doederleini.