The innervation of head neuromast rows in eleotridine gobies (Teleostei: Gobioidei)

The innervation of free neuromast (sensory papillae) rows is described from Sihler wholemount preparations of four species of eleotridine gobies, one ( Perccottus glenii ) representing the 'longitudinal' type of neuromast arrangement, the others ( Butis buits, Bostrychus urophthalmus, B. marmoratus ) the 'transverse' arrangement. In the latter, the characteristic transverse cheek rows (1–7) are innervated from the infraorbital trunk of the anterior lateral-line nerve. Longitudinal cheek rows b and d , and the three opercular rows, ot, os and oi , common to all species, are innervated by rami of the hyomandibular trunk of the same nerve. Two neuromast groupings are shown to have a mixed nerve supply. For the median preorbital snout rows, there is innervation from the infraorbital ( s ³ and r ) as well as the supraorbital ( s ¹ and s ²) trunks of the anterior lateral line nerve. The anterior dorsal rows are supplied both by the posterior lateral-line supratemporal ramus (rows g and m ) and the anterior lateral-line supraorbital trunk (rows o and n ). The neuromast rows, under the designations of Sanzo, are tabulated according to innervation and their putative origin in the phyletic replacement of a complete head canal system seen in more generalized percomorph fishes.     

Organization of the superficial neuromast system in goldfish, Carassius auratus

Distribution, morphology, and orientation of superficial neuromasts and polarization of the hair cells within superficial neuromasts of the goldfish (Carassius auratus) were examined using fluorescence labeling and scanning electron microscopy. On each body side, goldfish have 1,800-2,000 superficial neuromasts distributed across the head, trunk and tail fin. Each superficial neuromast had about 14-32 hair cells that were arranged in the sensory epithelium with the axis of best sensitivity aligned perpendicular to the long axis of the neuromast. Hair cell polarization was rostro-caudal in most superficial neuromasts on trunk scales (with the exception of those on the lateral line scales), or on the tail fin. On lateral line scales, the most frequent hair cell polarization was dorso-ventral in 45% and rostro-caudal in 20% of the superficial neuromasts. On individual trunk scales, superficial neuromasts were organized in rows which in most scales showed similar orientations with angle deviations smaller than 45 degrees . In about 16% of all trunk scales, groups of superficial neuromasts in the dorsal and ventral half of the scale were oriented orthogonal to each other. On the head, most superficial neuromasts were arranged in rows or groups of similar orientation with angle deviations smaller than 45 degrees . Neighboring groups of superficial neuromasts could differ with respect to their orientation. The most frequent hair cell polarization was dorso-ventral in front of the eyes and on the ventral mandible and rostro-caudal below the eye and on the operculum.     

Swim bladder and posterior lateral line nerve of the nurseryfish, Kurtus gulliveri (Perciformes: Kurtidae)

The morphology of the swim bladder and inner ear of the nurseryfish, Kurtus gulliveri, appear adapted for enhanced pressure wave reception. The saccule is enlarged and surrounded by very thin bone and two large fontanelles that would present reduced resistance to pressure waves. The swim bladder is elaborate, with six dorsolaterally projecting pairs of lobes that are tightly encased in ribs and an additional caudally projecting pair of lobes encased in the first hemal spine. The ribs and musculature surrounding the swim bladder laterally are very thin, so that four or five "rib windows" are readily apparent on back-lit specimens. This swim bladder-rib configuration would also present reduced resistance to pressure waves to enhance function as a peripheral auditory structure. However, high-resolution X-ray computed tomography and dissection reveal no anterior projections of the swim bladder that could serve as a mechanical coupling to the inner ear. The posterior lateral line nerve is well developed and lies directly over the tips of the ribs encasing the swim bladder lobes. This nerve is not, however, associated with a lateral line canal and a lateral line canal is absent on most of the body. We hypothesize that the posterior lateral line nerve transmits mechanosensory information from the swim bladder.     

The lateral line system in larvalIchthyophis (Amphibia: Gymnophiona)

Summary The lateral line systems of larval caecilians of the genusIchthyophis possess two types of elements, free neuromasts and ampullary organs. Free mechanoreceptive neuromasts are typical of those found in other vertebrates, and are arranged in series roughly homologous to neuromast groups in many other fishes and amphibians. In contrast to other amphibians,Ichthyophis larvae possess only one paired, dorsal body series of neuromasts. Regional specialization of neuromasts is evident inIchthyophis. Premaxillary and anterior head neuromasts are the largest in size and total cell number. Overall, size and total cell numbers are correlated with depth of epidermis. Neuromasts on the anterior sides of the head occur in slight grooves and have apical tips situated farther below the level of the epidermis and with greater apical indentation. These features probably provide increased protection against abrasion. Apparently abnormal neuromasts are frequently found among the neuromast series. Such neuromasts contain fewer cells that lack normal apical extension, producing a sunken effect similar to that of the ampullary organ elements. The ampullary organs ofIchthyophis are morphologically similar to those found in various freshwater fishes and known to function as electroreceptors. These organs are not observed in the lateral line systems of members of other amphibian orders (Urodela and Anura), and we suggest that they function as electroreceptors. The sunken neuromasts of theIchthyophis lateral line system may parallel the possible evolutionary development of pit organs from normal neuromasts.     

Molecular phylogeny of basal gobioid fishes: Rhyacichthyidae, Odontobutidae, Xenisthmidae, Eleotridae (Teleostei: Perciformes: Gobioidei)

Morphological character analyses indicate that Rhyacichthyidae, Odontobutidae, Eleotridae, and Xenisthmidae are the basal families within the perciform suborder Gobioidei. This study uses DNA sequence data to infer the relationships of genera within these families, as well as determine the placement of more derived gobioids (family Gobiidae) and the identity of the outgroup to Gobioidei. Complete sequences of the mitochondrial ND1, ND2, COI, and cyt b genes (4397 base pairs) are analyzed for representatives of 27 gobioid genera and a variety of perciform and scorpaeniform outgroup candidates; the phylogeny is rooted with a beryciform as a distal outgroup. The single most parsimonious tree that results indicates that, of the outgroups sampled, the perciform family Apogonidae is most closely related to Gobioidei. Gobioidei is monophyletic, and Rhyacichthys aspro is the most basal taxon. The remainder of Gobioidei is resolved into clades corresponding to the families Odontobutidae (plus Milyeringa) and Eleotridae+Xenisthmidae+Gobiidae. Within Eleotridae, the subfamily Butinae (minus Milyeringa) is paraphyletic with respect to Gobiidae, and Eleotrinae is paraphyletic with respect to Xenisthmidae. Other than these groupings, the primary disagreement with the current morphology-based classification is that the molecular data indicate that the troglodytic Milyeringa should be placed in Odontobutidae, not Butinae, although support for this placement is weak. The most basal lineage of Gobioidei is known from the freshwaters of the Indo-Pacific, with marine-dwelling lineages arising several times independently in the group. The phylogeny also indicates that different gobioid lineages are distributed in Asia, Africa, Madagascar and the Neotropics. Five sister pairs of basal gobioid species inhabit Atlantic and Pacific drainages of Panama, with widely varying divergences.     

Description and innervation of the lateral line system in two gobioids, <Emphasis Type=Italic>Odontobutis obscura</Emphasis> and <Emphasis Type=Italic>Pterogobius elapoides</Emphasis> (Teleostei: Perciformes)

Components of the lateral line system and their innervation were studied in Odontobutis obscura (Odontobutidae) and Pterogobius elapoides (Gobiidae), which are benthic and pelagic species, respectively. Innervation of the superficial neuromasts constituting the trunk lateral line system by way of three continuous longitudinal series (dorsal, middle, and ventral series: ld, lm, and lv series, respectively) became apparent for the first time. Innervation patterns indicated that the ld and lv series represented a mixture of displaced rows (from lm series) and new additional rows. In O. obscura, the ld and lv series were poorly developed, whereas both series were well developed in the pelagic P. elapoides, possibly as an adaptation to receive stimuli from above and below. Two extremely elongated nerve branches derived from the lateral ramus of the posterior lateral line nerve innervated the ld and lv series, respectively, in P. elapoides. Homologies of the neuromast rows on the head and body were discussed on the basis of their innervation patterns.     

Lateral line system in the triplefin Enneapterygius etheostomus (Perciformes: Tripterygiidae): new implications for taxonomic studies

The lateral line system, including the distribution and counts of canal and superficial neuromasts, in a Japanese tripterygiid Enneapterygius etheostomus was studied. Although the basic topography of the lateral line canals was typical of teleosts, preopercular, mandibular, parietal, predorsal and caudal fin groupings of superficial neuromasts were recognized for the first time in addition to the previously reported groupings in Tripterygiidae. Comparisons of neuroanatomical characteristics with those of New Zealand tripterygiids previously reported revealed significant differences, thereby indicating that detailed examination of the lateral line system could provide new information useful for taxonomic studies.     

西伯利亚鲟仔鱼侧线系统的发育

鲟鱼属软骨硬鳞鱼,在电感受器的进化中占据着极为重要的地位。该文以光镜和扫描电镜手段研究了西伯利亚鲟侧线系统早期发育,包括侧线基板发育及感觉嵴的形成、侧线感受器的发育和侧线管道的形成。1日龄,听囊前后外胚层增厚区域出现6对侧线基板;除后侧线基板细胞向躯干侧面迁移外,其他侧线基板均形成感觉嵴结构;每一侧线基板中均有神经丘原基形成。7日龄,壶腹器官在吻部腹面两侧出现,壶腹器官的发育比神经丘晚一周左右。9日龄,神经丘下的表皮略有凹陷,侧线管道开始形成。29日龄,在吻部腹面两侧可见少数个别的壶腹器官表皮细胞覆盖壶腹器官中央区域留下3～4个小的开口;壶腹管内可见大量的微绒毛存在,在其他鲟形目鱼类、软骨鱼类中也存在类似的结构。57日龄,躯干侧线管道已完全埋于侧骨板中;壶腹器官主要分布在吻部腹面,3～4个聚集在一起,呈"梅花状",分布紧密,并且该部分皮肤表面凹陷,形成花朵状凹穴;侧线系统发育完善。     

Intraspecific divergence in the lateral line system in the nine-spined stickleback (Pungitius pungitius)

The mechanosensory lateral line system of fishes is an important organ system conveying information crucial to individual fitness. Yet, our knowledge of lateral line diversity is almost exclusively based on interspecific studies, whereas intraspecific variability and possible population divergence have remained largely unexplored. We investigated lateral line system variability in four marine and five pond populations of nine-spined stickleback (Pungitius pungitius). We found significant differences in neuromast number between pond and marine fish. In particular, three of seventeen lateral line regions (viz. caudal peduncle superficial neuromasts; canal neuromasts from the anterior trunk and caudal peduncle) showed strong divergence between habitats. Similar results were obtained with laboratory-reared individuals from a subset of populations, suggesting that the patterns found in nature likely have a genetic basis. Interestingly, we also found habitat-dependent population divergence in neuromast variability, with pond populations showing greater heterogeneity than marine populations, although only in wild-caught fish. A comparison of neutral genetic (F(ST)) and phenotypic (P(ST)) differentiation suggested that natural selection is likely associated with habitat-dependent divergence in neuromast counts. Hence, the results align with the conclusion that the mechanosensory lateral line system divergence among marine and pond nine-spined sticklebacks is adaptive.     

Convergent evolution of the lateral line system in Apogonidae (Teleostei: Percomorpha) determined from innervation

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.     

The origin and fate of spermatophores in the viviparous teleost Cymatogaster aggregata (Perciformes: Embiotocidae)

The sperm of the shiner surfperch are packaged into high density aggregations which are introduced into the female genital tract at insemination. Germ cell differentiation occurs within cysts formed by nongerminal Sertoli cells. In late spermiogenesis, spermatozoa within the cysts come to lie parallel to each other and become more densely packed. These sperm packets (spermatophores), containing approximately 600 spermatozoa, then are released into the efferent sperm ducts. The exact nature of the spermatophore binding material is not known, but a major component is proteinaceous and is synthesized in the rough endoplasmic reticulum of the efferent sperm duct epithelial cells. The mechanism by which the spermatophores pass from cysts into ducts is not clear. It appears that whereas many Sertoli cells degenerate causing the cyst wall to break down, many Sertoli cells do not degenerate, but rather assume the configuration of columnar duct cells. The spermatophores remain intact within the testicular ducts, but rapidly dissolve within the female ducts in response to increased pH.     

Two new species of Cryptocephalum n. gen. (Monogenoidea: Dactylogyridae) from the cephalic lateral line of Percichthys trucha (Perciformes: Percichthyidae) in Patagonia, Argentina

Two new species of Monogenoidea were found parasitizing the cephalic lateral line canals of Percichthys trucha (Valenciennes) (Perciformes: Percichthyidae). These species are described as members of a newly proposed genus of Dactylogyridae. Cryptocephalum n. gen. is characterized by the site of infection and the combination of the several features: ventral and dorsal anchor/bar complexes, anchors with strongly elongated shaft and recurved point, shaft and point of dorsal anchors protruding laterally from haptor, hooks with 2 subunits and with pair 5 smaller than the others; gonads overlapping; coiled male copulatory organ with counterclockwise rings, accessory piece formed by 2 distinct parts, and a tubular, sclerotized ventral vagina. C ryptocephalum petreum n. sp. is characterized by having both anchor pairs protruding laterally from haptor, male copulatory organ with a coil of 2-1/2 rings, accessory piece tweezers-shaped, and sclerotized vaginal vestibule. Cryptocephalum spiralis n. sp. has ventral anchors protruding ventrally and dorsal ones protruding laterally, male copulatory organ with a coil of 1-1/2 rings, the antero-dorsal part of the accessory piece saddle-shaped, vaginal vestibule not present, and coiled vagina. This is the first record of Dactylogyridae species parasitizing the cephalic lateral line of fishes.     

Vascular anatomy of the lateral musculature of the flathead,Platycephalus bassensis (Teleostei: Perciformes)

Summary The vascular anatomy of the lateral musculature of the flatheadPlatycephalus bassensis, was studied by scanning electron microscopy of corrosion casts. Arteries and veins showed an alternating pattern in neighbouring vertebral segments. The red muscle was supplied by five major branches of the intermuscular artery, and the white muscle by infrequent branches of the intermuscular artery, dorsal segmental artery and ventral segmental artery. Venous drainage of the red and white muscles broadly mimicked the arterial supply. The functional unit of the trunk vasculature can be considered as an artery, a vein and connecting fine blood vessels. There appear to be 2 over-lapping types leading to alternating clockwise and counter-clockwise flows of blood. Small satellite vessels were observed running parallel to most of the larger blood vessels. No anatomical A-V shunt vessels, or series vascular connections between the red and white muscle, were observed. The irregular, alternating adult system is postulated to have developed from an earlier system showing strict bilateral symmetry and equal arterial and venous development in each vertebral segment.     

The ontogeny of the lateral line system in Telmatobius atacamensis (Anura,Telmatobiidae)

The lateral line system in anurans is functional during aquatic stages and therefore could provide characters related to larval morphological variation. However, few studies have addressed its components in an integrated overview, and little is known about its ontogenetic variation. This study describes the postembryonic trajectory of the lateral system in Telmatobius atacamensis up to its metamorphic regression. This includes structure, number, topography, and innervation of neuromasts, to contribute new and complete information about its larval organization and its temporal sequence of regression. The arrangement and innervation of lateral lines in T. atacamensis resembles those described for other Type IV tadpoles. Its distinctive features are the orientation of the neuromast stitches in the lateral lines, the presence of supraotic neuromasts, and the first-described case of asymmetry of the ventral trunk line. The temporal sequence of regression during metamorphosis differs between the lateral lines and the lateral line nerves, which remain myelinated into postmetamorphic stages. This asynchronous pattern between different components of the system has also been described for Pseudis paradoxa, which shares with T. atacamensis a remarkably long larval period. This long larval period and gradual metamorphosis could also be related to the constitutive metamorphic regression of the system, in spite of the aquatic lifestyle of these frogs.     

Molecular phylogeny of the antitropical genus Pseudolabrus (Perciformes: Labridae): evidence for a Southern Hemisphere origin

The genus Pseudolabrus comprises 11 species of marine nearshore fishes which are antitropically distributed: two species occur in East Asia, the remaining nine species being distributed in the Southern Hemisphere, mainly in the temperate Pacific. The distributions of their closely allied genera, collectively called "pseudolabrines" are, however, restricted to the Australia-New Zealand region. The molecular phylogeny of six of the 11 Pseudolabrus species from both Hemispheres and four of the five other pseudolabrine genera was reconstructed from nucleotide sequence data from mitochondrial DNA 12S rRNA, tRNAVal, and 16S rRNA genes. Both parsimony and Bayesian analyses were performed. Results are not consistent with a previous phylogenetic hypothesis based on osteological data, particularly in the relationship between Pseudolabrus and Notolabrus, indicating a probable need for reviewing the status of Notolabrus (or the delimitations of both Pseudolabrus and Notolabrus). The two Northern Hemisphere species of Pseudolabrus were monophyletic and nested deep into the clade of the Southern Hemisphere pseudolabrines, which indicates that both pseudolabrines and Pseudolabrus originated in the Southern Hemisphere. A dispersal rather than vicariance explanation for the antitropical distribution of Pseudolabrus is more parsimonious given the number of dispersal events, extinctions, and evolutionary adaptations required under the phylogeny. Based on molecular clock calibrations, the transequatorial divergence was suggested to be early to mid Pliocene at the earliest.     

Building the posterior lateral line system in zebrafish

The posterior lateral line (pLL) in zebrafish has emerged as an excellent system to study how a sensory organ system develops. Here we review recent studies that illustrate how interactions between multiple signaling pathways coordinate cell fate,morphogenesis, and collective migration of cells in the posterior lateral line primordium. These studies also illustrate how the pLL system is contributing much more broadly to our understanding of mechanisms operating during the growth, regeneration, and self-organization of other organ systems during development and disease.