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

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.

A new genus and species of clingfish from the Rangitāhua Kermadec Islands of New Zealand (Teleostei, Gobiesocidae)

Flexorincus, new genus and species, is described from 15 specimens (14.0–27.2 mm SL) collected from shallow (0–9 meters) intertidal and sub-tidal waters of the Rangitāhua Kermadec Islands, New Zealand. The new taxon is distinguished from all other members of the Gobiesocidae by a combination of characters, including a heterodont dentition comprising both conical and distinct incisiviform teeth that are laterally compressed with a strongly recurved cusp, an oval-shaped opening between premaxillae, a double adhesive disc with a well-developed articulation between basipterygia and ventral postcleithra, and many reductions in the cephalic lateral line canal system. The new taxon is tentatively placed within the subfamily Diplocrepinae but shares a number of characteristics of the oral jaws and the adhesive disc skeleton with certain members of the Aspasminae and Diademichthyinae.

Proliferation of superficial neuromasts during lateral line development in the Round Goby, Neogobius melanostomus

ABSTRACTMembers of the family Gobiidae have an unusual lateral line morphology in which some of the lateral line canal segments do not develop or enclose. This loss of lateral line canal segments is frequently accompanied by proliferation of superficial neuromasts. Although the proliferation of superficial neuromasts forms intricate patterns that have been used as a taxonomic tool to identify individual gobiid species, there has never been a detailed study that has documented the development of the lateral line system in gobies. The Round Goby, Neogobius melanostomus, is the focus of this study because the absence of the lateral line canal segments below the eye are accompanied by numerous transverse rows of superficial neuromasts. Our results suggest that the origin of some of these superficial neuromast lines could be the result of single presumptive canal neuromasts that have proliferated after canal enclosure is arrested. Many of the intricate patterns of neuromasts observed in gobiids develop from a simplified pattern of neuromast that is very similar among different species of gobies. The proliferation of superficial neuromasts has evolved several times in fish families such as the tetras, gobies, and sculpins, and may provide an adaptive advantage to ‘tune’ the lateral line system for different environments and prey types.SIGNIFICANCE STATEMENTUnderstanding the development of different lateral line morphologies can provide insights into how these morphologies have convergently evolved in many fish taxa. This is the first study to document the progression of the development of the reduced lateral line morphology. This study shows evidence that the developmental origins of orthogonal lines of superficial neuromasts posterior to the eye are not neomorphic lines, but in fact arise from precursor neuromasts that seem to be analogous to presumptive canal neuromasts.

A case of mistaken identity: ‘Latvius’ obrutus and new dipnoans from the Frasnian of Stolbovo, Russia

The village of Stolbovo, western Russia, has previously yielded a dipnoan fauna comprising the long-snouted form 'Rhinodipterus' stolbovi, but also a three-dimensionally preserved otoccipital region of a skull previously identified as the osteolepiform ‘Latvius’ obrutus. This identification was made from the density of lateral line canal pores in the skull roof bones in addition to what Vorobyeva (1977) described as the post-parietal, tabular and extratabular bones. Reexamination of this specimen does not recognise the osteolepiform dermal elements previously identified but rather a dipnoan configuration including a characteristic B-bone, lateral dermal elements and a dipnoan parasphenoid. rhinodipterid and dipterid dipnoans. Phylogenetic analysis resolves ‘Latvius’ obrutus as the primitive sister taxon to the ‘phaneropleurid-fleurantiid’ clade – a clade comprising derived Middle–Upper Devonian lungfishes. 'Rhinodipterus' stolbovi resolves among the more primitive griphognathids, typical Gondwanan forms, and is not a rhinodipterid. Additional isolated dipnoan skeletal elements from the site include tooth plates, parasphenoids, shoulder girdle elements and dermal elements and indicate at least an additional three lungfish taxa from Stolbovo. Of particular note is a ctenodiform tooth plate more characteristic of Carboniferous lungfishes. The new material and analyses not only demonstrate increased lungfish diversity from the Frasnian of Baltica but also probable interchange between Gondwana and Baltica during this time. Most importantly, Carboniferous-like forms appear more common in the Devonian than previously realised indicating that Carboniferous lungfishes likely represent a survival assemblage in addition to a new radiation of lungfish.

A case of mistaken identity: ‘Latvius’ obrutus and new dipnoans from the Frasnian of Stolbovo, Russia

The village of Stolbovo, western Russia, has previously yielded a dipnoan fauna comprising the long-snouted form 'Rhinodipterus' stolbovi, but also a three-dimensionally preserved otoccipital region of a skull previously identified as the osteolepiform ‘Latvius’ obrutus. This identification was made from the density of lateral line canal pores in the skull roof bones in addition to what Vorobyeva (1977) described as the post-parietal, tabular and extratabular bones. Reexamination of this specimen does not recognise the osteolepiform dermal elements previously identified but rather a dipnoan configuration including a characteristic B-bone, lateral dermal elements and a dipnoan parasphenoid. rhinodipterid and dipterid dipnoans. Phylogenetic analysis resolves ‘Latvius’ obrutus as the primitive sister taxon to the ‘phaneropleurid-fleurantiid’ clade – a clade comprising derived Middle–Upper Devonian lungfishes. 'Rhinodipterus' stolbovi resolves among the more primitive griphognathids, typical Gondwanan forms, and is not a rhinodipterid. Additional isolated dipnoan skeletal elements from the site include tooth plates, parasphenoids, shoulder girdle elements and dermal elements and indicate at least an additional three lungfish taxa from Stolbovo. Of particular note is a ctenodiform tooth plate more characteristic of Carboniferous lungfishes. The new material and analyses not only demonstrate increased lungfish diversity from the Frasnian of Baltica but also probable interchange between Gondwana and Baltica during this time. Most importantly, Carboniferous-like forms appear more common in the Devonian than previously realised indicating that Carboniferous lungfishes likely represent a survival assemblage in addition to a new radiation of lungfish.