Trunk Myomeres Research Articles

Reconstructing the subcephalic musculature in Pucapampella and Ichthyostega.

We present new reconstructions of subcephalic musculature for the stem chondrichthyan Pucapampella, the tetrapodomorph fish Eusthenopteron, and the Devonian tetrapod Ichthyostega. These reconstructions are based on macroscopic dissections of the head muscles of an archaic shark Heptranchias and an archaic actinopterygian Polypterus, that are combined with functional considerations and a reappraisal of not widely known theoretical concepts from the past. The subcephalic, as well as the supracephalic, musculature is formed by four anterior myomeres. They are continuous with subsequent myomeres of the trunk, but are innervated by ventral nerve roots of the medulla oblongata and thus belong to the head. The fourth subcephalic myomere ends with its posterior myoseptum on the occiput in osteichthyans, but on the first vertebra in chondrichthyans. The original function of subcephalic and supracephalic muscles in basal gnathostomes supposedly was to hold together anterior and posterior parts of the neurocranium during interaction with prey, such as the backward-ripping prey dissection, hypothesized for Pucapampella. In sarcopterygian osteichthyans, subcephalic musculature is involved in active depression of the anterior part of the neurocranium; specialization of this mechanism resulted in a complete separation of m. subcephalicus from trunk myomeres in Latimeria. Fusion of anterior and posterior parts of the neurocranium has resulted in reduction of the subcephalic musculature in the majority of cartilaginous and bony fishes. However, hexanchid sharks retain three posterior subcephalic myomeres for backward-ripping prey dissection. Polypterus and Chauliodus have retained the subcephalic musculature, but its function has shifted to a depression of the whole neurocranium.

Invasion of the European River Lamprey Lampetra fluviatilis in the Upper Volga

The European river lamprey came to the Upper Volga from the Baltic Sea most probably via a system of shipways developed in the 18th and 19th centuries. The Vyshnii Volochek, Tikhvin, and Mariinskaya water systems are possible invasion pathways for this species. Dispersal and colonization of the Caspian Basin was likely a combination of upstream and downstream migrations. Analysis of museum and our own samples showed that lamprey possibly migrated upstream (for spawning) along rivers of the Baltic Basin until they reached the watershed boundary from which they could disperse downstream (in the juvenile period) into rivers of the Caspian Basin. Dispersal in the Volga River could occur in accordance with the migration cycle of this opportunistic lamprey species and lead to the present distribution. Key features (dentition and number of trunk myomeres) showed that lamprey from the studied area are similar to lampreys from the Baltic basin, although specimens in each population have their own peculiarities in morphology (size and coloration). Genetic data (Cyt-b) support the idea of a relatively recent invasion of lamprey into the Upper Volga. The haplotype, found in three rivers, is one of the most widespread in Europe and is found along the supposed route of invasion.

Morphology-based taxonomic re-assessment of the Arctic lamprey, Lethenteron camtschaticum (Tilesius, 1811) and taxonomic position of other members of the genus.

The lamprey genus Lethenteron Creaser & Hubbs, 1922 is widespread across Eurasia and North America, but the number and distribution of its constituent species is not firmly established. After a morphological examination of extant type material of the currently recognized species and their synonyms, Lethenteron mitsukurii (Hatta, 1901) is resurrected with Le. matsubarai Vladykov & Kott, 1978 as its junior synonym. Amongst nonparasitic species Le. reissneri (Dybowski, 1869) and Le. mitsukurii are confirmed as present in Japan and the former is also present on Sakhalin. An in-depth study of large samples of nonparasitic lamprey adults from Japan and Sakhalin Island is needed to determine whether the lower trunk myomere (< 66) individuals from these areas represent one or more undescribed species, or Le. mitsukurii, or Le. reissneri, or a mixture of these three alternatives. The material from the Anadyr Estuary identified by Berg (1931, 1948) as Lampetra japonica kessleri has been re-identified as Le. camtschaticum and there is no evidence that Le. kessleri occurs there. Lethenteron reissneri is reported from the Angara River system, Yenisei River drainage, Russia. Lethenteron alaskense Vladykov & Kott, 1978 is provisionally considered to be a junior synonym of Le. kessleri (Anikin, 1905). Petromyzon ernstii Dybowski, 1872, Ammocoetes aureus Bean, 1881, Petromyzon dentex Anikin, 1905, Lampetra mitsukurii major Hatta, 1911, and Lampetra japonica septentrionalis Berg, 1931 are junior synonyms of Petromyzon marinus camtschaticus Tilesius, 1811. A key is provided to adults of the six species recognized as belonging in the genus Lethenteron.

Lampetra soljani, a new brook lamprey from the southern Adriatic Sea basin (Petromyzontiformes: Petromyzontidae).

Lampetra soljani, new species, is described from the lower Neretva River in the Adriatic Sea basin. Previously it was identified as L. zanandreai. Based on morphological similarity and mitochondrial genetic data, it is related to L. lanceolata and L. ninae from the Black Sea basin. Lampetra soljani is distinguished from all other species of Lampetra by having a marmorate flank pattern in live, fully grown ammocoetes, and in some adults (vs. plain colour pattern). Lampetra soljani is distinguished from other Lampetra species by having three velar tentacles, 54-57 trunk myomeres between the last branchial opening and the anus, no posterial teeth and a bicuspid middle endolateral tooth. Lampetra soljani is also well distinguished by COI barcode data from its congeners. The new species is widespread in the Neretva River drainage and lampreys from Lake Skadar basin are likely to belong to this species also.

Distribution and ecology of lampreys Lethenteron spp. in interior Alaskan rivers.

This study describes phenetic characteristics and examines the life history of anadromous Arctic lamprey Lethenteron camtschaticum and freshwater-resident Alaskan brook lamprey Lethenteron alaskense in two tributaries of the middle Yukon River, Alaska. Larval lampreys could not be identified to species using pigmentation density patterns or trunk myomere counts, but adults could be identified to species based on colouration, body size and oral-disc dentition. Although larvae were patchily distributed in both rivers, there was a greater proportion of sample locations where Lethenteron spp. were absent in upper reaches than in middle and lower reaches. Relative abundance, density and median and maximum total length (LT ) of larvae were highly variable among sampling locations. Current velocity, substratum type and coarse woody debris were most strongly correlated with larval Lethenteron spp. density; velocity and substratum size was negatively correlated, whereas woody debris was positively correlated. Water depth, dissolved oxygen levels and specific conductance did not influence habitat selection. Length-frequency distributions, diet composition (organic detritus ≥ 98%), assimilation efficiency (>70%) and gut fullness (<0·2 mg diet ash-free dry mass) were similar for larvae, regardless of river or sampling location. These results increase understanding of Lethenteron spp. biology and ecology in interior Alaska drainages and add to the existing literature on Lethenteron spp. life history.

The mystery of the two‐unit skull of the Sarcopterygii: a trap for functional morphologists

AbstractThis is an analytical study which presents a rigorous biomechanical interpretation of the well known but poorly understood two‐unit skull of extant Latimeria and extinct non‐dipnoan sarcopterygian fishes. The two units, anterior ethmosphenoid and posterior otoccipital, are hinged, dorsally, by intracranial syndesmosis between parietal and postparietal bones of the skull roof, and interconnected, centrally, by intracranial segment of the notochord and, ventrally, by a very strong paired subcephalic muscle unique to these fishes. This muscle depresses the anterior unit with the upper jaw, and this movement is kinematically coupled, in Latimeria, with the mandible elevation and, in basal sarcopterygians, with narrowing of the jaws and the oropharyngeal cavity. However, the muscular antagonist able to raise the anterior unit was never found. Neither manipulations on thawed Latimeria nor modern techniques of CT scanning and computer modeling helped to solve the puzzle. To find the way out, researchers were forced to rely, implicitly, on various fantastic mechanisms, such as strut‐like action of ligaments, positive mechanical work of elongating muscles, mechanical force action without opposite reaction and depression of the snout without elevation, etc. An accurate analysis of statics of the head of Latimeria shows that all of the most important muscles (m. subcephalicus, m. levator arcus palatini, m. coracomandibularis and m. adductor mandibulae) are synergists in respect of snout depression. I suggest a new idea that their antagonist, which is only possible, is parietal musculature acting via notochord. Indeed, the longitudinal contraction of the trunk myomeres causes some shortening of postcranial segment of the notochord, and consequently, forward protrusion of its liquid‐filled intracranial segment. Thus, the last pushes, as a hydraulic drive, the anterior skull unit. The problem is posed, whether the cranial muscles depressing the snout are able to counteract the pressure force in the notochord produced by powerful parietal musculature during undulatory swimming of the fish. Otherwise, the skull mechanism could be broken. Calculation of physiological cross‐sectional areas of major muscles involved allows to state that the m. subcephalicus is strong enough to counteract myomeric contraction. In basal sarcopterygians, the m. adductor mandibulae did not yet participate in this struggle because the hyomandibular suspension of the jaws was not shifted from the jaw joint onto the retroarticular process of the mandible. The biomechanic‐based explanation is suggested of how this shift could occur gradually in the evolution of coelacanths. The second novelty of Latimeria and its relatives, the forward shift of the intracranial syndesmosis relative to the notochordal apex, is explained too, as a means to engage ligamentous suspension of the intracranial notochord under prootic bones in stopping the snout elevation under the pressure of the notochord. The new idea on adaptive significance of the neurocranial kinesis of sarcopterygian fishes is suggested: this mechanism allows the recruitment of powerful parietal musculature into prey suction with water by oropharyngeal expansion.

Review of the Lampreys of Iran (Family Petromyzontidae)

The systematics, morphology, distribution, biology, economic importance and conservation of the lamprey of Iran are described, the species is illustrated, and a bibliography on this fish in Iran is provided. There is one native and endemic species in the Caspian Sea basin, Caspiomyzon wagneri . The genus Caspiomyzon is characterised by having 2 dorsal fins, an oral disc narrower than the body, teeth are generally low and blunt, the supraoral lamina is small, oval and sometimes has 2 tubercles and rarely 2 teeth, the infraoral lamina has 4-6, usually 5, teeth which may be bicuspid at their tips; there are about 8 small teeth of equal size in the transverse lingual lamina, the exolaterals, anterials and posterials are strong and close together, anterior and endolateral circumorals 9-11, usually 11, and 3 long, papillose velar tentacles are present. Characters of the species are the same as the genus. Trunk myomeres number of C. wagneri are 53-68 in ammocoetes, and 68-69 in adults.

Polymorphism of spawners of the resident form of European river lamprey Lampetra fluviatilis (Petromyzontidae)

Data on polymorphism (plastic and meristic characters) are obtained for spawners of resident nonparasitic form of European river lamprey Lampetra fluviatilis from the Serebristaya River. The new data verify the diagnosis of this species and contribute to the formulation of a hypothesis on the presence of several phenotypic groups: dwarf, small-sized, and common. Analysis of plastic characters and of the number of trunk myomeres demonstrated that the values of these characters reliably depend on position of lampreys in a certain discerned group. Some aspects of biology of this species are discussed: spawning and interaction between resident nonparasitic river and migrating parasitic lampreys.

Validity of Lampetra pacifica (Petromyzontiformes: Petromyzontidae), a brook lamprey described from the lower Columbia River Basin

The Pacific Brook Lamprey, Lampetra pacifica Vladykov, 1973 was described from the lower Columbia River Basin near Portland, Oregon. Subsequently, L. pacifica has generally been treated as a junior synonym of the Western Brook Lamprey, L. richardsoni Vladykov and Follett, 1965, a species described from the Fraser River Drainage east of Vancouver, British Columbia. We reexamine the available morphological data used by previous authors (trunk myomere counts), report on recent collections from the Columbia Basin, and reinterpret the trunk myomere data in the context of recent genetic sampling from the same populations. Populations of L. pacifica are distinguished from those of L. richardsoni by trunk myomere counts of 53–60 (means 59), respectively, and by genetic sequence divergence (cyt b) of 2.85 to 3.20%. We find no support for placing L. pacifica in the synonymy of L. richardsoni and recognize L. pacifica as a valid species. However, we recognize that there is considerable unresolved diversity in the western North American lampreys and recommend restriction of L. pacifica to the Columbia Basin, suggesting that unresolved populations of Lampetra brook (non-parasitic) lampreys outside the basin with mean trunk myomere counts below 59 be referred to as L. cf. pacifica, until further systematic information is available.

The Origin of the Bony Shell of Turtles as a Unique Evolutionary Model in Reptiles

Generally, the bony armor of reptiles consists of separate osteoderms which develop in the dermis independently from the internal skeleton. Such a dermal armor is characteristic of ancient pareiasaurs that are closely related to Testudines. On the basis of this fact it has been assumed that the turtle shell is built up as the fusion of the osteoderms with some elements of the internal skeleton. However, this concept is not confirmed by morphogenetic data. During turtle ontogeny the reduction of the trunk myomeres leads to sinking of the vertebrae and ribs into the dermis. The neural and costal plates of the dorsal disk form as the outgrowths of these endoskeletal bones on inside the dermis. There are no independent superficial ossicles over the general plastral bony primordia in the ventral region of the body. Each plastral plate develops only from a single primordium like the clavicles, interclavicle and gastralia of other reptiles. Most likely, Testudines progressed in a unique evolutionary direction. Their bony shell is mainly the result of modification and consolidation of internal skeletal elements. The real osteoderms develop only on the body margins as connections between the dorsal and the ventral discs.

Morphological analysis of geographic variation of sea lamprey ammocoetes in Portuguese river basins

The main objective of this study was to compare the morphological variability of sea lamprey (Petromyzon marinus L.) larvae from the main Portuguese river basins. Samples were collected in rivers Minho, Lima, Cavado, Vouga, Mondego, Tejo and Guadiana. Specimens were analysed in terms of morphometric (linear body measures) and meristic (number of myomeres) characters to investigate the hypothesis of population fragmentation between river basins caused by some degree of homing behaviour. The discriminant analysis showed a morphological segregation of the studied populations based on the characters head, tail and branchial length. The discriminatory power of the meristic characters was comparatively weaker, with the number of trunk myomeres, and to some extent the head myomeres, being responsible for the reduced separation between groups. Both analyses were consistent in identifying the cephalic region as the most important morphological feature to discriminate populations of sea lamprey larvae in the Portuguese territory. The largest cephalic region of the ammocoetes sampled in the northern river basins may be responsible for a better feeding efficiency and, consequently, higher values of condition factor.

Taxonomy and molecular phylogeny of Lethenteron lampreys in eastern Eurasia

Allozyme analyses of lampreys (genus Lethenteron) in eastern Eurasia showed that samples of L. reissneri from the upper Amur River, Russia, possessed the diagnostic alleles of L. kessleri(MDH‐3*‐93). These samples were closely related to L. kessleri samples in the Ob, Lena and middle Amur Rivers and on Sakhalin and Hokkaido Islands. On the other hand, they were distantly related to samples of the northern and southern forms of L. reissneri in the Japanese Archipelago and the southern Korean Peninsula. The number of trunk myomeres in L. reissneri from the upper Amur (63–76) strongly overlapped the number in L. kessleri(64–73), but were markedly displaced from those of the northern (51–66) and southern forms (49–62). These results suggest that L. reissneri in the upper Amur basin is likely to be the same taxonomic entity as L. kessleri reported from eastern Eurasia. The genetic and morphological divergences from L. reissneri in the type locality make it appropriate to regard the northern and southern forms as distinct species, L. sp. N and sp. S. Despite the close relationships found among L. japonicum, the L. reissneri complex and L. sp. N, L. sp. S was highly divergent from other species of Lethenteron, Lampetra and Entosphenus. In the monophyletic group comprising L. japonicum, the L. reissneri complex and L. sp. N, the direction of life‐history evolution presumed from the most parsimonious character reconstruction on the molecular tree was inconsistent with the previous hypothesis that nonparasitic species arise from parasitic species, indicating the necessity of detailed assessment of characteristics. On the other hand, L. sp. S may be a relict species of the coancestor of Lethenteron, Lampetra and Entosphenus.

Morphometric discrimination of early life stage Lampetra tridentata and L. richardsoni (Petromyzonidae) from the Columbia River Basin

The effectiveness of morphometric and meristic characteristics for taxonomic discrimination of Lampetra tridentata and L. richardsoni (Petromyzonidae) during embryological, prolarval, and early larval stages (i.e., age class 1) were examined. Mean chorion diameter increased with time from fertilization to hatch and was significantly greater for L. tridentata than for L. richardsoni at 1, 8, and 15 days postfertilization. Lampetra tridentata larvae had significantly more trunk myomeres than L. richardsoni; however, trunk myomere numbers were highly variable within species and deviated from previously published data. Multivariate examinations of prolarval and larval L. tridentata (7.2-11.0 mm; standard length) and L. richardsoni (6.6-10.8 mm) were conducted based on standard length and truss element lengths established from eight homologous landmarks. Principal components analysis indicated allometric relationships among the morphometric characteristics examined. Changes in body shape were indicated by groupings of morphometric characteristics associated with body regions (e.g., oral hood, branchial region, trunk region, and tail region). Discriminant function analysis using morphometric characteristics was successful in classifying a large proportion (> 94.7%) of the lampreys sampled.

New discovery of the Ukrainian brook lamprey in Croatia

The Ukrainian brook lamprey Eudontomyzon mariae was collected in two streams belonging to the Sava river basin in Croatia. The great variation in morphological characters of this species is emphasized and its description is augmented. Clinal variation in the trunk myomeres, total length and the oral disc dentition is detected.

A giant conodont with preserved muscle tissue from the Upper Ordovician of South Africa

AN exceptionally preserved new specimen of the giant conodont Promissum pulchrum reveals details of the trunk musculature, feeding apparatus and eyes. High-fidelity resolution of ultrastruc-tural features of the trunk myomeres provides the first conclusive evidence of muscle-fibre organization and orientation in an extinct agnathan. The presence of fibrous extrinsic eye muscles confirms the degree of encephalization of the conodonts and is consistent with a cladistic position crownwards of the myxinoids. The soft tissues are uniquely preserved as illite and mixed-layer clay minerals.

The Timing of Muscle Strain and Activation During Steady Swimming in a Salamander, Ambystoma Mexicanum

Muscle function during undulatory swimming is commonly described by the relative timing of muscle activity (EMG) in the strain cycle and has been studied for several fish species, ranging from anguilliforms to carangiforms. This paper supplies the basic data for steady swimming at an intermediate speed in a salamander (Ambystoma mexicanum). The strain cycle of the swimming muscles is estimated using high-speed video recordings (500 frames s-1) of an animal swimming in a flow tank. Synchronously, EMG signals of six epaxial myomeres were recorded using bipolar electrodes inserted unilaterally along the body. The neural stimulation pattern is a head-to-tail travelling wave with a higher speed than the kinematical propulsive wave. The resultant phase delay causes a different muscle recruitment pattern along the body axis, similar to reports for anguilliform fishes like the lamprey (WILLIAMS et al., 1989) and the eel (GRILLNER & KASHIN, 1976). The anterior trunk myomeres (up to 45% of the total body length L) are activated purely concentrically (i.e., while shortening). Caudal to the 45% L position, the muscles show an increasing proportion of eccentrical activation. This pattern suggests that there is gross positive work delivery along the body axis, with a limited amount of negative work in the tail tip. This is in agreement with the general conclusions for fish of WARDLE & VIDELER (1994), where this recruitment pattern is associated with a body shape without a distinct tail blade and with direct and continuous thrust production along the body.

Comparative morphology of the myomeres and axial skeleton in four genera of centrarchid fishes.

We used X-rays and dissection of myotomes to quantify the axial morphology of four species of centrarchid fishes (Micropterus salmoides, Ambloplites rupestris, Pomoxis nigromaculatus, and Lepomis macrochirus). Proceeding from dorsal to ventral, we designated the two epaxial and two hypaxial protions of the myomeres AB, BC, CD, and DE, respectively. For each of 11 myomeres, spaced at 10% increments along the length of the fish, a total of 14 variables described the length and orientation of each portion, the dorsalventral symmetry, and the overall height and longitudinal span of the entire myomere. Nine variables described the lengths, orientation, and symmetry of the vertebral centra, neural and hemal spines, and ribs. Analysis of variance revealed that, with one exception, all 23 morphological variables varied significantly both among species and among longitudinal locations within a species. However, the extent of longitudinal and interspecific variance differed considerably among different variables. Maximal myomeric height ranged from about 45% of the standard length (SL) in Lepomis to 27% SL in Micropterus. Longitudinal and interspecific increases in overall height of the trunk myomeres resulted primarily from greater lengths of CD. Compared to other portions of the myomere, the length of BC was most conservative both longitudinally and interspecifically. Dorsal-ventral symmetry of the myomeres and axial skeleton was greater in the caudal region than in the trunk in all species, and the myomeric morphology diverged least among species in the posterior caudal region. The overall longitudinal span of superficial myomeric landmarks varied from 6% to 18% SL, and, including the deep portions of the myomeres, the longitudinal span varied from about 7 to 10 vertebrae. Within each of the species, myomeric and skeletal variables were often not significantly correlated, but for the pooled data of all species there were usually highly significant correlations between myomeric and skeletal morphology. For example, strong correlations existed between BC and the underlying neural spines, and between CD and the underlying ribs and hemal spines. In contrast, the longitudinal spans of entire myomeres and underlying axial skeletal segments were only weakly associated. © 1994 Wiley-Liss, Inc.

A multivariate morphometric and meristic description of a population of freshwater-feeding river lampreys, Lampetra fluviatilis (L.), from Loch Lomond, Scotland

Adults of a freshwater-feeding population of Lampetra fluviatilis (L.) in Loch Lomond, Scotland, were trapped on their upstream (spawning) migration in the main inflow to the loch, the Endrick Water. These animals could be distinguished from the more typical anadromous upstream migrant L. fluviatilis, from the Endrick Water and the nearby catchment of the River Forth, principally by their smaller total length, greater disc, snout and eye size and much darker pigmentation. These, and other morphometric and meristic characteristics have been compared for populations of L. fluviatilis and Lampetra planeri (Bloch) from the Lomond and Forth catchments using univariate and multivariate statistics. The Endrick Water ‘dwarf’L. fluviatilis was found to differ significantly from the other Lampetra studied, in a number of body proportions in addition to those traits mentioned above, and also in mean numbers of trunk myomeres and teeth. These differences are likely to be due to a combination of the effects of genetic isolation, and the short (freshwater) feeding phase of the ‘dwarf’L. fluviatilis, which may, therefore, represent the intermediate stage between parasitic and non-parasitic forms in the L. fluviatilis/L. planeri species pair.

Morphological variation among widely dispersed larval populations of anadromous southern hemisphere lampreys (Geotriidae and Mordaciidae)

Larvae of all three southern hemisphere anadromous parasitic lampreys were collected from rivers in Australia, New Zealand and South America. Body intervals were measured, trunk myomeres counted and the frequency of pigmentation in different body regions recorded. Morphometric data were subjected to multiple group principal components analysis (MGPCA) which took into account changes during growth. The components (together with myomere counts) and the pigmentation data were both subjected to discriminant analysis. Ordination and rank correlation tests revealed no evidence for either latitudinal clines or a continuum of circumpolar change amongst larval lamprey populations. Clustering of population centroids clearly distinguished between Mordacia lapicida (Gray) from Chile and M. mordax (Richardson) from south-eastern Australia. Populations of Geotria australis Gray divided into groups representing three geographical regions, namely Argentina, Chile and Australasia (Western Australia, Tasmania and New Zealand). Ammocoetes from Argentina were the most divergent, possessing a more posterior cloaca, taller dorsal fins, a greater gap between dorsal fins, and distinctive pigmentation on the head and caudal fin. Within the Australasian group, Western Australian and New Zealand populations clustered closer than either did with those from Tasmania. The cluster analyses for larval populations of G. australis suggest that, during their marine trophic phase, the adults of this species originating from Argentinian and Chilean rivers follow different migratory routes, whereas those from Western Australia, New Zealand and, to a lesser extent, Tasmania intermix.

Descriptions and Keys for Ammocoetes of Lampreys from British Columbia, Canada

Characters useful for the identification of ammocoetes of lampreys found in British Columbia were verified by rearing ammocoetes through metamorphosis to specifically identifiable adults. We developed a key that employs new as well as some previously published features. We showed that published descriptions previously thought to be characteristic of species are unreliable for taxonomy. Counts of trunk myomeres and body proportions were not useful for separating species.Key words: ammocoetes, taxonomy, identification criteria