Kunio Sasaki

Homologies of the adductor mandibulae muscles in Tetraodontiformes as indicated by nerve branching patterns

Homologies of the adductor mandibulae muscles in eight families of Tetraodontiformes were hypothesized from the branching patterns of ramus mandibularis trigeminus. Insertions of the muscles to the upper or lower jaw were weak indicators of homology, migrations of the sites occurring frequently in A1, A2α, A2β, and A3. In monacanthids, tetraodontids, and diodontids, A1 tended to be split into numerous subsections, whereas in aracanids and ostraciids, A3 was highly developed, comprising three or four subsections. In tetraodontids, A2β was found to be a composite of A1 subsection and A2β. The methods of and limits to applying nerve branching patterns to muscle homology are discussed. A new naming system that reflects both muscle homologies and insertions is proposed.

Lateral line system and its innervation in Tetraodontiformes with outgroup comparisons: descriptions and phylogenetic implications.

The lateral line system and its innervation in ten tetraodontiform families and five outgroup taxa were examined. Although some homology issues remained unresolved, tetraodontiforms were characterized by having two types (at least) of superficial neuromasts (defined by the presence or absence of supporting structures) and accessory lateral lines and neuromasts (except Molidae in which “accessory” elements were absent). The preopercular line in Tetraodontiformes was not homologous with that of typical teleosts, because the line was innervated by the opercular ramule that was newly derived from the mandibular ramus, the condition being identical to that in Lophiidae. Within Tetraodontiformes, the number of neuromasts varied between 70 and 277 in the main lines and between 0 and 52 in accessory elements. Variations were also recognized in the presence or absence of the supraorbital commissure, mandibular line, otic line, postotic line, ventral trunk line, and some lateral line nerve rami, most notably the dorsal branch of the opercular ramule, being absent in Aracanidae, Ostraciidae, Tetraodontidae, Diodontidae, and Molidae. Morphological characteristics derived from the lateral line system and its innervation provided some support for a sister relationship of tetraodontiforms with lophiiforms. J. Morphol., 2010.

Description and innervation of the lateral line system in two gobioids, Odontobutis obscura and Pterogobius elapoides (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.

Fluorescent dye staining of neuromasts in live fishes : an aid to systematic studies

The lateral line system is unique to fishes and some amphibians, functioning to sense water flow and vibrations in aquatic environments (Coombs and Braun 2003). The system comprises mechanoreceptors (neuromasts), their associated components including hair cells, support cells, mantle cells and cupula (Coombs et al. 1988). Neuromasts are classified as either canal or superficial, the former being incorporated into the lateral line canals and the latter exposed on the skin (Coombs et al. 1988). Their number and distribution patterns are important in the diagnoses of fish taxa at various levels, ranging from species to order (see Webb 1989), and for phylogenetic considerations (e.g., Nelson 1972; Bergman 2004; Nakae and Sasaki 2010). However, confirmation of the numbers and positions of neuromasts under a stereomicroscope is difficult and time consuming, owing to their small size and pale opaque color. Although methylene blue (e.g., Roper 1981; Puzdrowski 1989; Peleshanko et al. 2007) and cyanine blue (e.g., Saruwatari et al. 1997; Shibukawa et al. 2001; Akihito et al. 2002; Bergman 2004) have been traditionally used to dye neuromasts (producing blue spots) in both live and dead fishes, the contrasts of such spots to the epidermis are usually weak. Accordingly, some neuromasts, particularly those occurring in ‘‘unexpected’’ positions, are often overlooked. To clearly visualize living motor nerve terminals using fluorescent dyes, Magrassi et al. (1987) evaluated the efficacy of 18 cationic mitochondrial dyes, with 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (4-Di-2-ASP) being recognized as the most effective. Subsequently, that dye has been used for staining neuromasts by developmental biologists and neurologists (e.g., Collazo et al. 1994; Alexandre and Ghysen 1999; Gompel et al. 2001; Sapède et al. 2002; Starr et al. 2004; Wada et al. 2008; Nuñez et al. 2009; Wada et al. 2010), with its application in fishes generally being limited to larval and juvenile (or small-sized) specimens. During attempts to visualize the superficial neuromasts in cyprinid and gobioid fishes, we recognized that the dye was surprisingly effective for that purpose, even in large (adult) fishes. Subsequently, we realized that emitted light from canal neuromasts could also be detected, passing through the bones and skin. Thus, the potential of the dye for improving descriptions of the lateral line system in systematic studies became apparent. Because the staining protocol has previously been noted only very briefly, and may have differed significantly in earlier studies (e.g., concentration of 4-Di-2-ASP solution ranging between 5 lM to 5 mM), a standardized method is presented here, such being universally applicable for small to moderately large [ca. 150 mm total length (TL)] individuals. Procedure The fluorescent dye utilized in this staining method was 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (4-Di-2-ASP; Aldrich, D3418; 485 nm excitation k and 603 nm emission k in methanol). Living fish specimens M. Nakae (&) Department of Zoology, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan e-mail: nakae@kahaku.go.jp

Branchial arch muscle innervation by the glossopharyngeal (IX) and vagal (X) nerves in Tetraodontiformes, with special reference to muscle homologies

Branchial arch muscle innervation by the glossopharyngeal (IX) and vagal (X) nerves in 10 tetraodontiform families and five outgroup taxa was examined, with special reference to muscle homologies. Basic innervation patterns and their variations were described for all muscle elements (except gill filament muscles). In the tetraodontids Takifugu poecilonotus and Canthigaster rivulata, diodontid Diodon holocanthus, and molid Mola mola, levator externus 4 was innervated by the 3rd vagal branchial trunk (BX3) in addition to BX2, owing to strong posterior expansion of the muscle. Based on nerve innervation, migrations of the muscle attachment sites (i.e., origins and insertions) were recognized in levator internus 2 (in Mola mola), obliquus dorsalis 3 (in Ostracion immaculatus and Canthigaster rivulata), and obliquus ventralis 2 (in Stephanolepis cirrhifer), muscle topologies not necessarily being indicative of homologies. Embryonic origin of the retractor dorsalis and parallel attainment of the swimbladder muscle within the order were also discussed. J. Morphol., 2008.

Peripheral nervous system of the ocean sunfish Mola mola (Tetraodontiformes: Molidae)

Dissection of peripheral nerves in the ocean sunfish Mola mola showed the lateral line system to comprise 6 cephalic and 1 trunk lateral lines, all neuromasts being superficial. The trunk line was restricted to the anterior half of the body, the number of neuromasts (27) being fewer than those previously recorded in other tetraodontiforms. The lateral ramus of the posterior lateral line nerve did not form a “serial collector nerve” along the body. The number of foramina in the neurocranium, serving as passages for the cranial nerves, was fewer than in primitive tetraodontiforms, the reduction being related to modifications in the posterior cranium. Some muscle homologies were reinterpreted based on nerve innervation patterns. The cutaneous branch innervation pattern in the claval fin rays was clearly identical with that in the dorsal and anal fin rays, but differed significantly from that in the caudal fin rays, providing strong support for the hypothesis that the clavus comprises highly modified components of the dorsal and anal fins.

The lateral line system and its innervation in the boxfish Ostracion immaculatus (Tetraodontiformes: Ostraciidae): description and comparisons with other tetraodontiform and perciform conditions

The lateral line system and its innervation were examined in the ostraciid Ostracion immaculatus (Tetraodontiformes), and compared with those in the triacanthodid Triacanthodes anomalus (Tetraodontiformes) and the acropomatid Malakichthys wakiyae (Perciformes). The carapace of O. immaculatus was composed of 6 cephalic and 2 trunk lateral lines, all neuromasts being categorized as “superficial.” Triacanthodes anomalus was identical with O. immaculatus in the absence of the mandibular line and its innervating ramus, whereas in M. wakiyae the line and ramus were present. All neuromasts were “superficial” in the former two, but “canal” in the latter. Judging from the essentially identical lateral line topography and innervation patterns in all three species, the superficial neuromasts in the two tetraodontiforms were considered to have resulted from replacement of canal neuromasts. The number of neuromasts in the cephalic lateral lines of O. immaculatus (106) and T. anomalus (91) were similar, being significantly higher than in M. wakiyae (30). However, the reverse was true for the trunk lateral lines, the two tetraodontiforms having fewer neuromasts (39 in O. immaculatus, 47 in T. anomalus) compared with M. wakiyae (59).

The innervation and adaptive significance of extensively distributed neuromasts in Glossogobius olivaceus (Perciformes: Gobiidae)

Components of the lateral line system and their innervation were examined in Glossogobius olivaceus (Gobiidae), with almost all of the trunk scales bearing a row of superficial neuromasts, the latter comprising some 2,900 of the total (ca. 4,800) neuromasts on the body. The relationship between orientation and innervation of the superficial neuromasts on the head showed the buccal and mandibular rami to be clearly separated. On the trunk, the lateral ramus detached a number of branches, typically comprising dorsal, lateral and ventral ramules, to innervate neuromasts. Extensively distributed neuromasts were considered as an adaptation to a nocturnal habit, compensating for reduced vision.

Monophyletic origin of the dorsally arched lateral line in Teleostei: evidence from nerve innervation patterns

Branching patterns of the horizontal septum lateral line nerves (HSN) were studied in 123 teleostean species (including literature records) assigned to 96 families in 28 orders, primarily to indentify the group characterized by the presence of the dorsal longitudinal collector nerve (DLCN) for innervation of the trunk lateral line. In nonacanthomorphs, DLCN was absent, the trunk lateral line being mostly innervated by branches directly detached from HSN or those derived from the collector nerve running parallel to the former. In acanthomorphs, the dorsally arched trunk lateral line, typical of the group, was uniformly innervated by DLCN, indicating that presence of the latter was a synapomorphy of the group. Within the latter, DLCN was absent in Gasterosteiformes (Fistularia and Macroramphosus), Mugilidae, Atherinomorpha, Champsodontidae, Blenniidae, Callionymidae, Gobioidei, Istiophoridae, Gempylidae, Cynoglossidae, Ostraciidae, and Molidae. Monophyly of the Mugilidae plus Atherinomorpha was discussed based on the specialized innervation pattern.

The occurrence of two species of Macroramphosus (Gasterosteiformes : Macroramphosidae) in Japan : morphological and ecological observations on larvae, juveniles, and adults

Earlier opinions that Macroramphosus is monotypic are refuted, with two species apparently occurring in Japan (tentatively identified as M. gracilis and M. scolopax). In postsettlement young and adults, the former is characterized by a dark slender body (vs. red-orange and deep) and short second dorsal fin spine with a smooth posterior margin (vs. long spine with a serrated margin). Food habits also differ between the two species, which are either plankton or benthos feeders. Two types of Macroramphosus larvae and juveniles occurring at the surface were recognized, one having a straight ventral body profile of the body (identified here as M. gracilis) and the other having a notch in the anal region. The dark body of postsettlement M. gracilis is considered to be a retention of the character suited to the neustonic distribution of the larval and juvenile stages, the species remaining to ca. 40 mm in standard length (SL) in that habitat (vs. to ca. 12 mm SL in M. scolopax).