The composition of the caudal skeleton of teleosts (Actinopterygil: Osteichthyes)

The diural caudal skeleton of teleostean actinopterygians develops phylogeneticaily and ontogenetically from a polyural skeleton. The reduction of the polyural anlage to four, three, two or fewer centra in the adult caudal skeleton takes different pathways in different genera (e.g. compare Elops and Albula) and groups of teleosts. As a result, ural centra are not homologous throughout the teleosts. By numbering the ural centra in a homocercal tail in polyural fashion, one can demonstrate these and the following differences. The ventral elements (hypurals) always occur in sequential series, whereas the dorsal elements (epurals and uroneurals) may alter like the ural centra. The number of epurals, five or four in fossil primitive teleosts, is reduced in other primitive and advanced teleosts, but the same epurals are not always lost. The number of uroneurals, seven in fossil teleosts, is reduced in living teleosts, but it has not been demonstrated that the first uroneural is always derived from the neural arch of the same ural centrum. The landmark in the homocercal tail is the preural centrum I which can be identified by (1) bifurcation of the caudal artery and vein in its ventral element, the parhypural, (2) its position directly caudal to the preural centrum (PU2) which supports the lowermost principal caudal ray with its haemal spine, (3) carrying the third hypaxial element ventral to the course of arteria and vena pinnalis, and (4) by carrying the first haemal spine (parhypural) below the dorsal end of the ventral cartilage plate. The study of the development of the vertebral column reveals that teleosts have different patterns of centrum formation. A vertebral centrum is a complete or partial ring of mineralized, cartilaginous or bony material surrounding at least the lateral sides of the notochord. A vertebral centrum may be formed by arcocentrum alone, or arcocentral arcualia and chordacentrum, or arco-, chorda- and autocentrum, or arcocentral arcualia and autocentrum. This preliminary research demonstrates that a detailed ontogenetic interpretation of the vertebral centra and of the caudal skeleton of different teleosts may be useful tools for further interpretations of teleostean interrelationships.     

Histochemical study of jaw muscle fibers in the American alligator (Alligator mississippiensis)

The ontogenetic development of caudal vertebrae and associated skeletal elements of salmonids provides information about sequence of ossification and origin of bones that can be considered as a model for other teleosts. The ossification of elements forming the caudal skeleton follows the same sequence, independent of size and age at first appearance. Dermal bones like principal caudal rays ossify earlier than chondral bones; among dermal bones, the middle principal caudal rays ossify before the ventral and dorsal ones. Among chondral bones, the ventral hypural 1 and parhypural ossify first, followed by hypural 2 and by the ventral spine of preural centrum 2. The ossification of the dorsal chondral elements starts later than that of ventral ones. Three elements participate in the formation of a caudal vertebra: paired basidorsal and basiventral arcocentra, chordacentrum, and autocentrum; appearance of cartilaginous arcocentra precedes that of the mineralized basiventral chordacentrum, and that of the perichordal ossification of the autocentrum. Each ural centrum is mainly formed by arcocentral and chordacentrum. The autocentrum is irregularly present or absent. Some ural centra are formed only by a chordacentrum. This pattern of vertebral formation characterizes basal teleosts and primitive extant teleosts such as elopomorphs, osteoglossomorphs, and salmonids. The diural caudal skeleton is redefined as having two independent ural chordacentra plus their arcocentra, or two ural chordacentra plus their autocentra and arococentra, or only two ural chordacentra. A polyural caudal skeleton is identified by more than two ural centra, variably formed as given for the diural condition. The two ural centra of primitive teleosts may result from early fusion of ural centra 1 and 2 and of ural centra 3 and 4, or 3, 4, and 5 (e.g., elopomorphs), respectively. The two centra may corespond to ural centrum 2 and 4 only (e.g., salmonids). Additionally, ural centra 1 and 3 may be lost during the evolution of teleosts. Additional ural centra form late in ontogeny in advanced salmonids, resulting in a secondary polyural caudal skeleton. The hypural, which is a haemal spine of a ural centrum, results by growth and ossification of a single basiventral ural arococentrum and its haemal spine. The proximal part of the hypural always includes part of the ventral ural arcocentrum. The uroneural is a modification of a ural neural arch, which is demonstrated by a cartilaginous precursor. The stegural of salmonids and esocids originates from only one paired cartilaginous dorsal arcocentrum that grows anteriorly by a perichondral basal ossification and an anterodorsal membranous ossification. The true epurals of teleosts are detached neural spines of preural and ural neural arches as shown by developmental series; they are homologous to the neural spines of anterior vertebrae. Free epurals without any indication of connection with the dorsal arococentra are considered herein as an advanced state of the epural. Caudal distal radials originate from the cartilaginous distal portion of neural and haemal spines of preural and ural (epurals and hypurals) vertebrae. Therefore, they result from distal growth of the cartilaginous spines and hypurals. Cartilaginous plates that support rays are the result of modifications of the plates of connective tissue at the posterior end of hypurals (e.g., between hypurals 2 and 3 in salmonids) and first preural haemal spines, or from the distal growth of cartilaginous spines (e.g., epural plates in Thymallus). Among salmonids, conditions of the caudal skeleton such as the progressive loss of cartilaginous portions of the arcocentra, the progressive fusion between the perichondral ossification of arcocentra and autocentra, the broadening of the neural spines, the enlargement and interdigitation of the stegural, and other features provide evidence that Prosopium and Thymallus are the most primitive, and that Oncorhynchus and Salmo are the most advanced salmonids respectively. This interpretation supports the current hypothesis of phylogenetic relationships of salmonids. © 1992 Wiley-Liss, Inc.     

Ontogeny,variation, and homology in Salvelinus alpinus caudal skeleton (Teleostei: Salmonidae)

The ontogeny of the caudal skeleton in the Arctic charr, Salvelinus alpinus was examined using an extensive series of cleared and stained specimens. We demonstrate the presence of skeletal components never reported previously within the Salmonidae. In contrast to the generalized condition for salmonids, seven hypurals (instead of six), and four uroneurals (instead of three) have been found in some specimens. Variation in the number and condition of epurals is documented. New hypotheses are proposed concerning (1) relationships among centra and their associated elements, (2) phylogenetic distribution of caudal characters within the Salmonidae, and (3) homology of caudal components. Using the published phylogenetic hypotheses, we provide evidence, that a seventh hypural and a fourth uroneural are taxic atavism in salmonids. The development of the salmonid homocercal fin is discussed in the light of a polyural scheme based on evidences of a one‐to‐one relationship among ural centra and their associated elements. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

New osteological and morphological data of four species of Aphaniops (Teleostei; Aphaniidae)

Aphaniops dispar, widespread around the Arabian Peninsula, was recently separated in four species (A. dispar, A. hormuzensis, A. kruppi, A. stoliczkanus) by molecular results and colour patterns, but the morphological differences are small and call for more studies. Here we report differences in skeleton and median fin osteology of these species. In addition, we introduce the term 'modified caudal vertebra' to describe caudal vertebrae that are not directly associated with caudal ray support but are visibly modified from a 'usual' caudal vertebra. Aphaniops hormuzensis, an endemic species to southern Iran, has a significantly higher number of modified caudal vertebrae compared to the more widespread A. stoliczkanus and A. dispar, and also to A. kruppi. This is a surprising result as the caudal skeleton and related structures of the posterior caudal vertebral column have yielded successful results in separating between families or genera, but there are only a few studies that have examined these structures for their role in species diagnosis. Our study also highlights that state-of-the-art methods in X-raying and improved staining procedures assist in the discrimination of superficially similar species.     

Retracted: Evolution and development of the homocercal caudal fin in teleosts

The vertebrate caudal skeleton is one of the most innovative structures in vertebrate evolution and has been regarded as an excellent model for functional morphology, a discipline that relates a structure to its function. Teleosts have an internally‐asymmetrical caudal fin, called the homocercal caudal fin, formed by the upward bending of the caudal‐most portion of the body axis, the ural region. This homocercal type of the caudal fin ensures powerful and complex locomotion and is thought to be one of the most important evolutionary innovations for teleosts during adaptive radiation in an aquatic environment. In this review, we summarize the past and present research of fish caudal skeletons, especially focusing on the homocercal caudal fin seen in teleosts. A series of studies with a medaka spontaneous mutant have provided important insight into the evolution and development of the homocercal caudal skeleton. By comparing developmental processes in various vertebrates, we propose a scenario for acquisition and morphogenesis of the homocercal caudal skeleton during vertebrate evolution.     

Anatomical and Histological Investigations on the Caudal Skeleton of Apteronotus leptorhynchus (Apteronotidae,Gymnotoidei)

The caudal skeleton of Apteronotus leptorhynchus was studied at various stages from hatching to the adult stage using anatomical and histological techniques. The caudal skeleton that supports the lepidotrichia is reduced to a rhomboid caudal plate (caudal cartilage) that extends the vertebral axis. This cartilage appears for the first time in 8 day old fish, postero-ventral to the notochord. During its growth, perichondral and endochondral ossification occurs, beginning at the anterior end of the cartilage. Comparison with the anatomy and ontogeny of the typical caudal skeleton of teleosts allows us to interpret the caudal cartilage of A. leptorhynchus as an hypuro-opisthural component that is homologous to the cartilage that occurs at the tip of the axial skeleton in Eigenmannia virescens.     

The colour pattern of the caudal fin, a useful criterion for identification of two species of Tilapia and their hybrids

The present work reports on some chromatic characters and their change with size in two species of Tilapia ( T. zillii and T. guineensis ) and their first generation hybrids. Successful reciprocal hybridizations between T. zillii and T. guineensis were performed in concrete tanks. The hybrids obtained were viable. The colour patterns of the hybrids and their parents were registered during a rearing cycle of 12 months. Between 2 and 13 cm standard length ( L _S), the hybrids were found to be heterogeneous and three phenotypes were observed. The type (1) phenotype had a fully yellowish caudal fin without dots, the type (2) phenotype had a bicoloured caudal fin with the upper part clear yellowish and the lower part dark yellowish and without dots and the type (3) had a similar bicoloured caudal fin, but with dots. Above 13 cm L _S, the hybrid population was homogenous and all specimens had a bicoloured caudal fin with dots. In T. zillii , all specimens >14 cm L _S had a greyish caudal fin with dots while all T. guineensis >13 cm L _S were characterized by a bicoloured caudal fin without dots. A multivariate analysis of the morphometric and meristic characters did not allow a clear separation of all groups. The study showed that the external morphology of the hybrids was intermediate to that of the parental species.     

The evolution of sexually dimorphic tail feathers is not associated with tail skeleton dimorphism

Sexual selection can influence the evolution of sexually dimorphic exaggerated display structures. Herein, we explore whether such costly ornamental integumentary structures evolve independently or if they are correlated with phenotypic change in the associated skeletal system. In birds, elongate tail feathers have frequently evolved in males and are beneficial as intraspecific display structures but impart a locomotor/energetic cost. Using the sexually dimorphic tail feathers of several passeriform species as a model system, we test the hypothesis that taxa with sexually dimorphic tail feathers also exhibit sexual dimorphism in the caudal skeleton that supports the muscles and integument of the tail apparatus. Caudal skeletal morphology is quantified using both geometric morphometrics and linear morphometrics across four sexually dimorphic passeriform species and four closely related monomorphic species. Sexual dimorphism is assessed using permutational MANOVA. Sexual dimorphism in caudal skeletal morphology is found only in those taxa that exhibit active functional differences in tail use between males and females. Thus, dimorphism in tail feather length is not necessarily correlated with the evolution of caudal skeletal dimorphism. Sexual selection is sufficient to generate phenotypic divergence in integumentary display structures between the sexes, but these change are not reflected in the underlying caudal skeleton. This suggests that caudal feathers and bones evolve semi‐independently from one another and evolve at different rates in response to different types of selective pressures.     

Intraspecific variation in the postcranial skeleton morphology in African clariids: a case study of extreme phenotypic plasticity

Taxonomic relationships within the Clariidae, especially within the anguilliform species, are currently ambiguous due to the lack of a reliable structure of valid generic and specific characteristics. Based on the information available, it is difficult to properly diagnose the different elongated genera and species; this is due in part to a high degree of variability of certain traits generally considered to be important taxonomically. For example, the caudal skeleton is often considered to be an important diagnostic trait. However, the degree of phenotypic plasticity has not hitherto been adequately assessed. This paper deals with interspecific variation of the caudal skeleton of Clarias gariepinus , Platyallabes tihoni , Platyclarias machadoi , Gymnallabes typus , Channallabes apus and Dolichallabes microphthalmus . The caudal skeleton of C. apus is studied, using specimens from three regions in Gabon. Hypural fusions and haemal and neural spines show most variation. The observed morphological variation appears to be geographically independent, in contrast to other morphological features such as vertebrae.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 437–446.     

Oreoglanis infulatus, a new species of glyptosternine catfish (Siluriformes: Sisoridae) from central Vietnam

A new species of glyptosternine catfish, Oreoglanis infulatus , is described from the Lam River drainage in central Vietnam. The new species is distinguished from all its congeners by possessing the following combination of characters: a dark band running across the anal fin, a lunate and uniformly dark caudal fin, the lower lip lacking a medial notch and with a lobulate posterior margin, maxillary barbel with a rounded tip, length of caudal peduncle 19·0–22·6 % L _S, depth of caudal peduncle 2·6–3·2 % L _S, post-adipose distance 6·8–8·0 % L _S, eye diameter 10·5–12·1 % L _H, 12 principal caudal-fin rays.     

Grammatonotus ambiortus sp. nova: A new species of callanthiids (perciformes) from the western tropical pacific

A new species of the genus Grammatonotus from the western part of the Pacific Ocean (the region of the Hawaiian Islands) is described. From all previously known species of this genus, G. ambiortus sp. nova differs in multiserial teeth and the absence of canine teeth on praemaxillaria. The structure of its caudal skeleton is also different from most species (except G. macrophthalmus from the Kyusyu-Palau Ridge); moreover it is differentiated by a large eye.     

Skeletal structure as taxonomic tool for identification of mullet species (Teleostei: Mugilidae) from Aceh waters,Indonesia

Many members of the mullets (family Mugilidae) are very similar morphologically, hence the possibility of taxonomic misidentification. This study involved the use of skeleton structure to distinguish four species of mullets, including Cremugil crenilabis, Liza macrolepis, Moolgarda engelii, and Mugil cephalus, harvested from Aceh waters, Indonesia. The mullets samples were collected from 10 locations, and a total of 10 samples were taken randomly as representatives of each species. The skeletal sample was prepared using the dry method. The results showed the presence of 8 pairs of ribs in C. crenilabis and L. macrolepis, while M. engelii had 9, with 10 in M. cephalus. In addition, the origin of the haemal canal of C. crenilabis is at the 12th vertebrae, extends to the 23rd, while for the other three species it starts at the 10th and extends to the 23rd. In addition, C. crenilabis possesses 12 haemal canals, but the rest have 14. The haemal canal is present in the last precaudal vertebrae of all specimens, except C. crenilabis, whose epural bone in the caudal skeleton is small and located far from the preural, while a larger and distinctly attached form is observed in the rest. Furthermore, L. macrolepis possess a pair of diapophyses, which laterally extend in the 2nd vertebrae. This bone is absent in the three other species. The presence of diapophyses, the number of ribs and haemal canals and the location of the epural bone in the caudal skeleton, and the condition of frontal attachment to the sphenotic are the important characters in distinguishing the four investigated species of mullets.     

First report of Litomosa spp. (Nematoda: Filarioidea) from Malagasy bats; review of the genus and relationships between species

The presence of the filarial genus Litomosa in Malagasy bats is demonstrated by the finding of L. goodmani n. sp. from Miniopterus gleni and Litomosa sp. (male unknown) from M. manavi, both in the Special Reserve of Ankarana. These materials are compared to the 22 Litomosa species, including two Indian species originally placed in the genus Litomosoides, L. fotedari (Gupta and Trivedi, 1989) n. comb. and L. tewarii (Gupta and Trivedi, 1989) n. comb., and the new taxon L. seurati n. sp. (= L. beaucournui Bain, 1966 pro parte), type-host Rhinolophus ferrum-equinum, Algeria, distinguished by the narrow area rugosa and the female caudal extremity with two conspicuous points, instead of several small ones. The Malagasy material belongs to a group of species close to the type, L. filaria, which have a male area rugosa composed of cuticular bosses and microfilariae folded within the sheath, and which are parasitic in Vespertilionidae, Hipposideridae and Rhinolophidae from Africa and Europe. The two Malagasy species resemble L. seurati n. sp., L. beshkovi Jancev, 1971, L. chiropterum Ortlepp, 1932, L. adami Petit, 1980 and L. ottavianii Lagrange et Bettini, 1948, with the enlarged third segment of the buccal capsule. L. goodmani n. sp. is distinct with its small size and female caudal extremity with a single point, which is suppressed in old mature worms; the females of Litomosa sp. have two conical points. Relationships among Litomosa species appear to be dependent upon both the chiropteran host groups and the geographical region.     

Redescription of a rare bothid,Asterorhombus bleekeri (Macleay), and description of a new species ofAsterorhombus from northwestern Australia (Teleostei: Pleuronectiformes)

A rare Australian bothid flounder.Asterorhombus bleekeri (Macleay), is redescribed from the holotype and ten additional specimens from the east coast of Qeensland, Gulf of Carpentaria and Rowly Shoal (Western Australia). The species is transferred fromArnoglossus Bleeker toAsterorhombus Tanaka because of the lack of obvious sexual dimorphism in the interorbital width and pectoral fin length, the lack of rostral and orbital spines, the yellow-white blind side body coloration, and the deeply cleft parhypural and hypural plates. The definition ofAsterorhombus was emended as follows: the first dorsal fin ray continuous with or separated from remaining fin rays and gill rakers slender or stubby, with or without serrations.Asterorhombus osculus sp. nov., formerly briefly described in the literature as unidentified species ofEngyprosopon, was described from eight specimens from the northwestern coast of Australia. The new species is most similar toA. bleekeri in lacking sexual dimorphism, and having the caudal skeleton with deep clefts, two or three rows of teeth on the upper jaw and a pair of conspicuous black spots on the caudal fin, in addition to a similar general appearance, but is distinguished from the latter by shorter gill rakers, a very small mouth and feebly ctenoid scales on the ocular side. Both species clearly differed fromA. intermedius andA. fijiensis in having two (or three) rows of teeth on the upper jaws, slender gill rakers without serrations, first dorsal fin ray continuous with the other fin rays, and a pair of conspicuous black spots on the caudal fin.     

A fossil osteoglossoid fish from Tanzania (E. Africa)

A new genus and species ( Singida jacksonoides ) and a new family (Singididae) of osteoglossoid fishes are described from the lacustrine deposits in Tanzania which have already yielded the primitive clupeomorph Palaeodenticeps. Singida differs from all Osteoglossomorpha in being toothless. Although it shows some affinity with the living Asiatic genus Scleropages , it also exhibits certain characters, particularly in the caudal skeleton, which are usually associated with the recent and fossil Hiodontoidei of North America. Singida shows little affinity with either of the living African genera of Osteoglossoidei. The age of the Singida deposits is unknown, but the fish fauna suggests a Palaeogene (? Oligocene) age.     

Nomenclature of cartilaginous elements in the caudal skeleton of teleostean fishes

Nomenclature and abbreviations are proposed for the cartilaginous elements of the caudal skeleton of teleostean fishes. These were developed on the basis of examination of 510 species within 198 families of 31 orders and the determination of the positional relationship between these structures and the bony elements. A review of the most important relative literature is also provided.