Paired fin skeletons and relationships of the fossil group Porolepiformes (Osteichthyes: Sardcopterygii)

The endoskeletal girdles, anocleithrum and paired fin supports of the porolepiform fish Glyptolepis (Osteichthyes: Sarcopterygii: Porolepiformes) are figured and described. The pectoral fin skeleton is known from the proximal part only and the pelvic fin skeleton is fragmentary, but the scapulocoracoid, anocleithrum and pelvic girdle can be reconstructed in their entirety. The anocleithrum is entirely subdermal. The pectoral fin skeleton in shown to be biserial, with a large number of axial mesomeres, whereas the pelvic fin contains fewer mesomeres and is strongly asymmetrical with very few postaxial radials. The scapulocoracoid is essentially similar to a reconstruction figured by Jarvik (1980), but has a more elongate glenoid; this has functional implications. The pelvic girdle consists of two separate halves as in Eusthenopteron, but differs from that genus in lacking dorsolateral rami. A brief survey of the evidence of paired fin structure in other porolepiform genera is carried out to establish whether the structures seen in Glyptolepis are likely to be representative for the Porolepiformes. A study of the morphology and muscle attachments of the paired fin skeletons indicates that the pattern of fin movement was significantly different from that in Neoceratodus. The fin supports and girdles of Glyptolepis are compared with those of other sarcopterygian groups as well as with actinopterygians, placoderms and sharks, in order to establish evolutionary polarities. Glyptolepis is shown to display a number of derived characters. The information gained from the comparison is used to construct a maximum parsimony cladogram, which places coelacanths as the sister group of porolepiforms + lungfishes, with the rhizodonts + tetrapods and osteolepiforms as successive sister groups of this clade. Characters of uncertain polarity are considered in the light of this cladogram. A comparison with recently published cladograms shows that none are completely compatible with the results from this study.     

Clasper morphology of skates of the tribe Riorajini (Chondrichthyes: Rajiformes: Arhynchobatidae) and its systematic significance

Claspers of adult specimens of the skate tribe Riorajini, family Arhynchobatidae, comprising Atlantoraja and Rioraja , are described, compared, and systematically reinterpreted based on material collected off southeastern and southern Brazil. For the first time the external components and musculature of the clasper of members of this tribe are described and related to internal (skeletal) structures. The component pecten is present in all species of Atlantoraja but absent in Rioraja . The new external component grip , an autapomorphy of A. cyclophora fully developed in adults, is described. Rioraja presents dorsal terminals 1 and 2, ventral marginal distally extended and ventral terminal cartilages. Dorsal terminals 1 and 2, ventral marginal distally extended, accessory terminals 2 and 3, and ventral terminal cartilages occur in Atlantoraja . A new interpretation of the ventral marginal distally extended is discussed. The dorsal terminal 1 of Atlantoraja has an inverted U shape but is triangular in Rioraja . The accessory terminal 2 cartilage is reported for the first time in Atlantoraja cyclophora . The accessory terminal 3 is present only in A. platana and A. cyclophora , and absent in Rioraja and A. castelnaui . Many of our findings concerning the clasper skeleton do not agree with previous interpretations. The arrangement, distribution and systematic significance of many of the terminal clasper components are discussed among rajoids.     

Plasticity of the skeleton and skeletal deformities in zebrafish (Danio rerio) linked to rearing density

The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studies concerning the effect of rearing density on the skeletal phenotype are lacking. This study analyses the response of the skeleton to different rearing densities and describes the skeletal deformities. Wild-type zebrafish were reared up to 30 dpf (days post-fertilization) in a common environment. From 30 to 90 dpf, animals were reared at three different densities: high density (HD), 32 fish l^–1; medium density (MD), 8 fish l^–1 and low density (LD), 2 fish l^–1. Animals at 30 and 90 dpf were collected and whole-mount stained with Alizarin red S to visualize mineralized tissues. The entire skeleton was analysed for meristic counts and 172 types of deformities. The results showed that the rearing density significantly influenced the specimens’ average standard length, which decreased with the increase in the rearing density. Differences in meristic counts among the three groups were not observed. Rearing density–independent malformations affected the ribs, neural arches and the spines of the abdominal region, as well as vertebrae of the caudal complex. The HD group showed the highest number of deformities per specimen, the highest number of observed types of deformities and, together with the MD group, the highest frequency of specimens affected by severe deformities. In particular, the HD group showed deformities affecting arches, spines and vertebral centra in the caudal region of the vertebral column. This study provides evidence of an effect of the rearing density on the development of different skeletal phenotypes.     

Musculoskeletal morphology of the pelvis and pelvic fins in the lungfish Protopterus annectens

The West African lungfish (Protopterus annectens) performs benthic, pelvic fin‐driven locomotion with gaits common to tetrapods, the sister group of the lungfishes. Features of P. annectens movement are similar to those of modern tetrapods and include use of the distal region of the pelvic fin as a “foot,” use of the fin to lift the body above the substrate and rotation of the fin around the joint with the pelvis. In contrast to these similarities in movement, the pelvic fins of P. annectens are long, slender structures that are superficially very different from tetrapod limbs. Here, we describe the musculoskeletal anatomy of the pelvis and pelvic fins of P. annectens with dissection, magnetic resonance imaging, histology and 3D‐reconstruction methods. We found that the pelvis is embedded in the hypaxial muscle by a median rostral and two dorsolateral skeletal projections. The protractor and retractor muscles at the base of the pelvic fin are fan‐shaped muscles that cup the femur. The skeletal elements of the fin are serially repeating cartilage cylinders. Along the length of the fin, repeating truncated cones of muscles, the musculus circumradialis pelvici, are separated by connective tissue sheets that connect the skeletal elements to the skin. The simplicity of the protractor and retractor muscles at the base of the fin is surprising, given the complex rotational movement those muscles generate. In contrast, the series of many repeating segmental muscles along the length of the fin is consistent with the dexterity of bending of the distal limb. P. annectens can provide a window into soft‐tissue anatomy and sarcopterygian fish fin function that complements the fossil data from related taxa. This work, combined with previous behavioral examination of P. annectens, illustrates that fin morphologies that do not appear to be capable of walking can accomplish that function, and may inform the interpretation of fossil anatomical evidence. J. Morphol. 275:431–441, 2014. © 2013 Wiley Periodicals, Inc.     

First observation on the mating behaviour of the marbled ray, <Emphasis Type="Italic">Taeniurops meyeni,</Emphasis> in the tropical Eastern Pacific

Elasmobranch reproductive behaviour remains understudied, particularly for batoids (rays). Most of the information available originates from opportunistic observations of mating scars in the wild and/or from individuals held in captivity. Here we describe the first complete mating sequence of the marbled ray (Taeniurops meyeni) in the wild. The event was filmed at Isla del Coco National Park in Costa Rica, in the Tropical Eastern Pacific. The complete sequence lasted approximately 3 hrs and is defined by the following behaviours: (1) close following or chasing: a group of males swim in a close formation chasing an individual female; (2) pre-copulatory biting: oral grasping of the female’s posterior pectoral fin by the males, with anterior bending of one clasper and rotation of the pelvic region towards the female’s cloaca; (3) copulation/ insertion of the male’s clasper followed by ‘ventral to ventral’ position and energetic thrusting of the male’s pelvic region; (4) post-copulatory behaviour: the male removes its clasper from the female’s cloaca while releasing her posterior pectoral fin and (5) separation: the male sets the female free and separates himself from the group. The mating behaviour described here shares some similarities with the few other studies of batoids in the wild and highlights the need to further understand their mating system to guide conservation plans for this vulnerable species.     

Senegalese sole bone tissue originated from chondral ossification is more sensitive than dermal bone to high vitamin A content in enriched Artemia

Several studies have evaluated the effects of dietary vitamin A (VA) on the incidence of skeletal deformities during early ontogeny of fish, but little is known about its effects on bones depending on their process of ossification (dermal or chondral). We examined the incidence of skeletal deformities along development (30 and 48 dph) by double staining technique, in dermal (haemal and caudal vertebral bodies) and chondral (neural and haemal spines, epural, parahypural and hypurals) bones in Senegal sole post metamorphosed larvae fed with different dietary VA levels (37 000, 44 666, 82 666 and 203 000 UI total VA kg^?1 DW) during Artemia feeding phase (6–37 dph, at 18°C). Results obtained in this study showed that dietary VA disrupted the skeletogenesis in Senegalese sole post metamorphosed larvae by increasing the incidence of skeletal deformities in the axial skeleton and caudal fin complex, which were dependent on both bone morphogenesis and ossification processes. Fish fed with the highest dietary VA content showed the highest incidence of skeletal deformities and its value increased along ontogeny. However, when we compared the incidence of deformities in skeletal structures considering their ossification process, most skeletal structures derived from chondral ossification showed a significant higher increase in deformity incidences in fish fed an excess of VA (44 666, 82 666 and 203 000 UI kg^?1 DW), however within chondral bones, hypurals deformity incidence only increased in sole larvae fed Artemia highest VA content. In contrast, this dietary dose‐response effect was only noted in dermal bones from fish fed the highest dose of VA (203 000 UI kg^?1 DW). In addition, the incidence of deformities in chondral bones increased even when the dietary imbalance of VA was corrected, whereas dermal bones were not affected at later ages. These results indicated that depending on the ossification process from which different skeletal structures are derived, bones might be differentially affected by high dietary VA content. Those directly originated from the connective tissue with a preliminary cartilage stage were more sensitive to dietary VA excess than those formed by intramembranous ossification.     

Skeletal and muscular pelvic morphology of hillstream loaches (Cypriniformes: Balitoridae)

The rheophilic hillstream loaches (Balitoridae) of South and Southeast Asia possess a range of pelvic girdle morphologies, which may be attributed to adaptations for locomotion against rapidly flowing water. Specifically, the connectivity of the pelvic plate (basipterygium) to the vertebral column via a sacral rib, and the relative size and shape of the sacral rib, fall within a spectrum of three discrete morphotypes: long, narrow rib that meets the basipterygium; thicker, slightly curved rib meeting the basipterygium; and robust crested rib interlocking with the basipterygium. Species in this third category with more robust sacral rib connections between the basipterygium and vertebral column are capable of walking out of water with a tetrapod-like lateral-sequence, diagonal-couplet gait. This behavior has not been observed in species lacking direct skeletal connection between the vertebrae and the pelvis. The phylogenetic positions of the morphotypes were visualized by matching the morphological features onto a novel hypothesis of relationships for the family Balitoridae. The morphotypes determined through skeletal morphology were correlated with patterns observed in the pelvic muscle morphology of these fishes. Transitions towards increasingly robust pelvic girdle attachment were coincident with a more anterior origin on the basipterygium and more lateral insertion of the muscles on the fin rays, along with a reduction of the superficial abductors and adductors with more posterior insertions. These modifications are expected to provide a mechanical advantage for generating force against the ground. Inclusion of the enigmatic cave-adapted balitorid Cryptotora thamicola into the most data-rich balitorid phylogeny reveals its closest relatives, providing insight into the origin of the skeletal connection between the axial skeleton and basipterygium.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

Musculoskeletal determinants of pelvic sucker function in hawaiian stream gobiid fishes: Interspecific comparisons and allometric scaling

Gobiid fishes possess a distinctive ventral sucker, formed from fusion of the pelvic fins. This sucker is used to adhere to a wide range of substrates including, in some species, the vertical cliffs of waterfalls that are climbed during upstream migrations. Previous studies of waterfall‐climbing goby species have found that pressure differentials and adhesive forces generated by the sucker increase with positive allometry as fish grow in size, despite isometry or negative allometry of sucker area. To produce such scaling patterns for pressure differential and adhesive force, waterfall‐climbing gobies might exhibit allometry for other muscular or skeletal components of the pelvic sucker that contribute to its adhesive function. In this study, we used anatomical dissections and modeling to evaluate the potential for allometric growth in the cross‐sectional area, effective mechanical advantage (EMA), and force generating capacity of major protractor and retractor muscles of the pelvic sucker (m. protractor ischii and m. retractor ischii) that help to expand the sealed volume of the sucker to produce pressure differentials and adhesive force. We compared patterns for three Hawaiian gobiid species: a nonclimber (Stenogobius hawaiiensis), an ontogenetically limited climber (Awaous guamensis), and a proficient climber (Sicyopterus stimpsoni). Scaling patterns were relatively similar for all three species, typically exhibiting isometric or negatively allometric scaling for the muscles and lever systems examined. Although these scaling patterns do not help to explain the positive allometry of pressure differentials and adhesive force as climbing gobies grow, the best climber among the species we compared, S. stimpsoni, does exhibit the highest calculated estimates of EMA, muscular input force, and output force for pelvic sucker retraction at any body size, potentially facilitating its adhesive ability. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

Actinotrichia collagens and their role in fin formation

The skeleton of zebrafish fins consists of lepidotrichia and actinotrichia. Actinotrichia are fibrils located at the tip of each lepidotrichia and play a morphogenetic role in fin formation. Actinotrichia are formed by collagens associated with non-collagen components. The non-collagen components of actinotrichia (actinodins) have been shown to play a critical role in fin to limb transition. The present study has focused on the collagens that form actinotrichia and their role in fin formation. We have found actinotrichia are formed by Collagen I plus a novel form of Collagen II, encoded by the col2a1b gene. This second copy of the collagen II gene is only found in fishes and is the only Collagen type II expressed in fins. Both col1a1a and col2a1b were found in actinotrichia forming cells. Significantly, they also expressed the lysyl hydroxylase 1 (lh1) gene, which encodes an enzyme involved in the post-translational processing of collagens. Morpholino knockdown in zebrafish embryos demonstrated that the two collagens and lh1 are essential for actinotrichia and fin fold morphogenesis. The col1a1 dominant mutant chihuahua showed aberrant phenotypes in both actinotrichia and lepidotrichia during fin development and regeneration. These pieces of evidences support that actinotrichia are composed of Collagens I and II, which are post-translationally processed by Lh1, and that the correct expression and assembling of these collagens is essential for fin formation. The unique collagen composition of actinotrichia may play a role in fin skeleton morphogenesis.     

Observations of mating behavior of the manta ray,manta birostris, at the ogasawara islands, japan

On 11 July 1997, the mating behavior of wild manta rays,Manta birostris, was observed while skin diving off Chichijima. Ogasawara Islands, Japan, and recorded with 49 underwater photographs and about 20 minutes of video tape. The female manta ray involved was estimated as being approximately 5 m in dise width (DW) and the two males involved, approximately 4 m DW. Copulatory behavior of the two males appeared to be almost the same, copulation itself being of the abdomen-to-abdomen type. Initially, the males chased the female for 20–30 minutes, all animals swimming at approximately 10 km/h. Each copulation event occurred within one meter of the surface, during which time the participating male grasped the tip of the female's left pectoral fin with his mouth. The clasper was inserted for 90 seconds (Male No. 1) and 60 seconds (Male No. 2), respectively. The mating behavior sequence of the manta rays involved following five steps. 1.: Male chases behind the tail of the female, attempting (several times) to grasp the latter's pectoral fin (chasing behavior). 2.: Male bites the tip of the female's pectoral fin, before positioning itself against the latter's underside (biting behavior). 3.: Male inserts a clasper into the cloaca of the female (copulating behavior). 4.: Male removes the clasper from the cloaca of the female, but continues biting the latter's pectoral fin (post-copulating behavior). 5.: Male releases the pectoral fin of the female, setting her free (separating behavior).     

Abnormalities in flatfishes of the south‐west Atlantic Ocean

Five adult paralichthyid specimens with various kinds of abnormalities are reported from the south‐west Atlantic Ocean. These abnormal flatfish specimens represent the first records of wholly ambicoloured Paralichthys orbignyanus specimens having a deep notch between the eye and dorsal fin and a partially albinistic specimen having skeletal deformities and only the second record of an almost totally ambicoloured specimen. We also report the first observation of reversal in Paralichthys patagonicus and an almost totally ambicoloured, reversed Xystreurys rasile.     

Osteology of Paedocypris,a miniature and highly developmentally truncated fish (Teleostei: Ostariophysi: Cyprinidae)

Species of the cyprinid genus Paedocypris are among the smallest and most developmentally truncated fishes and vertebrates. Our analysis of their skeletal structure reveals a puzzling combination of extreme developmental truncation and an increased morphological complexity in sexually dimorphic characters. The skeleton of Paedocypris is characterized by reduction and loss and resembles in many aspects that of a larval/early juvenile stage of its close relatives. We found 61 characters that have been affected by developmental truncation. A comparison with the skeletal development of a close relative, the zebrafish Danio rerio, demonstrates that the majority of the absent bones or skeletal structures in Paedocypris are those that appear late in the ossification trajectory of the zebrafish. Thus, their absence in Paedocypris seems to be due to the simple developmental truncation of terminal stages in the ossification sequence. Our study of the sexually dimorphic structures in Paedocypris demonstrates that predominantly the male exhibits the more complex state. In relation to the female, male Paedocypris uniquely possess a cleithrum with a pointed posterior process that covers the scapula laterally, and a more medially situated posterior flange that contacts the dorsal area of the coracoid; a massive and heavily ossified uppermost pectoral radial tightly bound to the scapula; thickened and enlarged three uppermost pectoral‐fin rays; a large triangular, dorsolaterally directed process on the outer arm of the massive os suspensorium; and a enlarged and shovel‐like anterodorsally directed basipterygium; and a hypertrophied first pelvic‐fin ray with additional anterior flanges that support keratinized pads of skin. Female Paedocypris show only one structure that is better developed than in males: the first proximal‐middle radial and the anteriormost fin ray of the dorsal fin are more massive and more heavily ossified. Although the function and biological role of these dimorphisms is still unknown, we hypothesize that they are related to a special reproductive behavior. Paedocypris is a prime example for the recent claim that miniaturization among cyprinids is associated with evolutionary novelty only in developmentally truncated miniatures and not in proportioned dwarfs. Paedocypris offers a strong challenge to Schindleria as the most extreme example of developmental truncation known among fishes. We highlight the difficulties that developmentally truncated taxa frequently pose to the resolution of their phylogenetic position and propose an approach to overcome this problem. Our phylogenetic comparison to determine the systematic position of Paedocypris among cyprinids reveals that it shares not only a number of unique absences, but also highly unusual progressive characters with Sundadanio and Danionella, two other Asian miniature cyprinids. We hypothesize that the three genera form a monophyletic group. We further found that Paedocypris and Danionella share a number of uniquely derived characters pointing to a sister group relationship of the two. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

Venous drainage of the pelvic fins of rays (subclass elasmobranchii: Superorder Batoidea)

A contrast radiographic study of pelvic fin drainage in rays reveals considerable differences in patterns of drainage among the species studied. The “typical” shark pattern of drainage, to the lateral abdominal vein, is also found in rays with shark-like morphology. However, variation in the connections of pelvic fin veins to muscular and cutaneous vessels of the pectoral fin occurs in the more “derived” batoid groups, with marked differences between rays of similar external morphology and mode of locomotion. There is a positive association between the pattern of fin drainage and the number of radial cartilages in the posterior (metapterygial) lobe of the pectoral fin. Variation in shark pelvic fin drainage may also be related to differences in pectoral fin morphology.     

Redescription of †Paralycoptera wui Chang & Chou, 1977 (Teleostei: Osteoglossoidei) from the Early Cretaceous of eastern China

?Paralycoptera wui Chang & Chou, 1977 from the Early Cretaceous of China is redescribed herein through a re‐examination of the original materials, as well as observations on some newly collected specimens. The use of the peeling method has revealed much of the new or revised information on its osteology, e.g. aspects of the nasal, infraorbitals, retroarticular, preopercle, extrascapular, basihyal toothplate, epineural, pelvic fin, caudal skeleton and scales. The phylogenetic relationships of ?Paralycoptera and other osteoglossomorphs are re‐evaluated. The cladistic analysis largely agrees with the previous hypothesis that ?Paralycoptera is not a ?lycopterid, but rather a stem osteoglossoid. ?Paralycoptera is excluded from notopteroids and exhibits the following derived characters of the Osteoglossoidei: (1) palatal area behind and below orbit completely covered by infraorbitals; (2) jaw articulation under posterior portion of orbit; (3) opercle depth twice or more its width; (4) first pectoral fin ray much enlarged and long, extending posteriorly beyond origin of pelvic fin. ?Singida and ?Phareodus are regarded as different levels of osteoglossoids above ?Paralycoptera. ?Singida shares the following derived characters with ?Phareodus plus extant osteoglossoids: (1) jaw articulation posterior to orbit; (2) anterior process of hyomandibula in contact with entopterygoid; (3) subopercle small and anterior to opercle. ?Phareodus shares the following derived characters with extant osteoglossoids: (1) supraorbital and otic sensory canals connected; (2) one uroneural; (3) reticulate furrows present over entire scale.