The most remarkable anatomical specialization of threadfins (Percomorphacea: Polynemidae) is the division of their pectoral fin into an upper, unmodified fin and a lower portion with rays highly modified into specialized filaments. Such filaments are usually elongate, free from interradial membrane, and move independently from the unmodified fin to explore the environment. The evolution of the pectoral filaments involved several morphological modifications herein detailed for the first time. The posterior articular facet of the coracoid greatly expands anteroventrally during development. Similar expansions occur in pectoral radials 3 and 4, with the former usually acquiring indentations with the surrounding bones and losing association with both rays and filaments. Whereas most percomorphs typically have four or five muscles serving the pectoral fin, adult polynemids have up to 11 independent divisions in the intrinsic pectoral musculature. The main adductor and abductor muscles masses of the pectoral system are completely divided into two muscle segments, each independently serving the pectoral-fin rays (dorsally) and the pectoral filaments (ventrally). Based on the innervation pattern and the discovery of terminal buds in the external surface of the filaments, we demonstrate for the first time that the pectoral filaments of threadfins have both tactile and gustatory functions.
The Polynemidae is a family of primarily marine fishes with eight genera and 42 extant species. Many aspects of their morphology are largely unknown, with few reports about their osteology and barely any information on their myology. This paper describes and illustrates in detail all facial and branchial muscles of representative species of polynemids. Our analysis demonstrates the existence of several remarkable and previously unknown specializations in the polynemid musculature. The aponeurotic and completely independent origin of the pars promalaris of the adductor mandibulae is apparently unique among percomorphs. The differentiation of this section into lateral and medial subsections; the total separation of the promalaris from the retromalaris; the differentiation of the pars primordialis of the levator arcus palatini into external and internal subsections are also uncommon features of polynemids that are shared by sciaenids, thus supporting the hypothesis of a closer relationship between these families. K E Y W O R D S anatomy, morphology, myology, Polynemidae, threadfin
The distinction of squid species in the genus Doryteuthis is not easy due to their morphological similarity, lack of conspicuous specific characters, and overlap geographical occurrence. This difficulty has leading to an almost exclusive molecular approach, and a premature neglect of the morpho-anatomy. To emphasize that the squid phenotypic features can be useful to identify, as well as to perform any comparative analyses (such as taxonomy and phylogeny), two close species were selected as outset. Doryteuthis pleii and D. sanpaulensis are common sympatric squids in Brazilian waters, commonly used in fisheries, not so difficult to distinguish by external features of the adult specimens. The samples were analyzed from biometric data to dissections, and the found most expressive characters to distinguish them are the mantle-fin ratio; morphology of the tentacle club, its ratio compared to the mantle length; hectocotylus morphology and nidamental gland morphology.
Threadfins are primarily marine bony fishes that have part of the pectoral fin modified into specialized sensitive filaments. They compose the Polynemidae, a family with eight genera and 42 extant species. The internal relationships and phylogenetic position of Polynemidae within Percomorphacea are controversial, with highly conflicting hypotheses proposed by both molecular and phenotypic analyses. We performed a cladistic analysis of threadfins based on the most comprehensive sampling of morphological data ever done. The final dataset included 197 characters from external morphology, the laterosensory system, osteology, myology and neurology in representatives of all valid polynemid genera. More than half of the characters are reported here for the first time, notably the myological ones. A sensitivity analysis of 11 different weighting schemes (equal weighting and extended implied weighting parsimony) resulted in a fully resolved tree. Sciaenidae, not Pleuronectiformes, is recovered as sister to Polynemidae. All polynemid genera are resolved as monophyletic except Polydactylus, which is polyphyletic. Filimanus, Pentanemus and Polydactylus s.s. appear as successive sister taxa of all remaining threadfins. Leptomelanosoma, Parapolynemus and Polynemus form a monophyletic group. Eleutheronema and Galeoides appear intercalated with other species of Polydactylus in the apical portions of the polynemid tree.
Polynemidae is a family of primarily marine fishes with eight genera and 42 extant species. The phylogenetic allocation of polynemids within Percomorphacea as well as its internal relationships are uncertain as highly conflicting hypotheses has been proposed in the literature. Many aspects of the polynemid morphology are largely unknown, with little reports in the literature about their osteology, barely any information on their myology, and no studies on the ontogeny of their skeleton. This project aimed to study different aspects of the musculoskeletal system of Polynemidae and understand its internal relationships. The most remarkable feature of polynemids is their pectoral fin divided into an upper, unmodified fin and a lower portion with rays highly modified into specialized filaments. The present analysis reveals that the main adductor and abductor muscles masses of the pectoral fin involved in such intricate structure are completely divided into two muscle segments that serve separately the pectoral-fin rays, dorsally, and pectoral filaments, ventrally. Interestingly, it is herein demonstrated that the pectoral filaments receive massive nerves specialized in gustatory reception, indicating that the polynemid pectoral filament have not only tactile but also tasting functions. Several unique specializations in the mandibular, hyopalatine and branchial musculature of polynemids are herein reported for the first time. A comprehensive cladistic analysis based on 162 morphological characters and all valid polynemid genera was performed and resulted in fully resolved new hypothesis of relationships. All genera were recovered as monophyletic except Polydactylus, which is polyphyletic. Lastly, a survey of the skeletogenesis of polynemids reveals remarkable changes during their ontogeny, such as the shifting in pectoral radial 3 and the expansion of pectoral radial 4, both transformations associated with the differentiation of the pectoral filaments. The saddle-like ossification pattern of vertebral centra 1-4 of polynemids is only shared with sciaenids and additionally supports the hypothesis of a closer relationship between these families.
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