Zoological Journal of the Linnean Society 

Abstract: Muscular-hydrostats, muscular organs which lack typical systems of skeletal support, include the tongues of mammals and lizards, the arms and tentacles of cephalopod molluscs and the trunks of elephants. In this paper the means by which such organs produce elongation, shortening, bending and torsion are discussed. The most important biomechanical feature of muscular-hydrostats is that their volume is constant, so that any decrease in one dimension will cause a compensatory increase in at least one other dimension. Elongation of a muscular-hydrostat is produced by contraction of transverse, circular or radial muscles which decrease the cross-section. Shortening is produced by contraction of longitudinal muscles. The relation between length and width of a constant volume structure allows amplification of muscle force or displacement in muscular-hydrostats and other hydrostatic systems. Bending requires simultaneous contraction of longitudinal and antagonistic circular, transverse or radial muscles. In bending, one muscle mass acts as an effector of movement while the alternate muscle mass provides support for that movement. Torsion is produced by contraction of muscles which wrap the muscular-hydrostat in a helical fashion.

Abstract: 1. Lyell and Hooker’s own letter of introduction explaining the extraordinary circumstances; 2. An excerpt from Darwin’s unpublished draft, part of a chapter titled, “On the Variation of Organic Beings in a State of Nature; on the Natural Means of Selection; on the Comparison of Domestic Races and True Species”; 3. An abstract of Darwin’s 1857 letter to Harvard University botanist, Prof. Asa Gray; 4. Wallace’s manuscript, “On the Tendency of Varieties to Depart Indefinitely From the Original Type.”

Abstract: Morphological (including ultrastructural) and developmental characters utilized in recent literature are critically reviewed as the basis to reassess the phylogenetic relationships of gastropods. The purpose of this paper is to provide a framework of characters for future studies and a testable phylogenetic hypothesis. This is one of the first attempts to use such characters to assess the relationships of all major clades using parsimony methods. The analysis uses 117 characters and includes 40 taxa, predominantly ‘prosobranchs’. Five outgroup taxa are included, representing four conchiferan groups and Polyplacophora. Of the 117 characters reviewed and included in the analyses, nine are shell characters (four of these are shell structure), two opercular, two muscular, four ctenidial, 12 renopericardial and 24 reproductive (including 17 based on sperm and spermatogenesis), 27 of the digestive system, 32 of the nervous system and sense organs; the remainder are developmental (3) and of the foot and hypobranchial gland. In the initial analysis the data set included a mixture of binary and multistate characters with all characters unordered. These data were also analysed after scaling so that each character had equal weight. A third data set was constructed in which all characters were coded as binary characters. These analyses resulted in some implausible character transformations, mainly involving the regaining of lost pallial structures. Additional analyses were run on all three sets of data after removing five characters showing the most unlikely transformations. These analyses resulted in generally similar topologies. The robustness of the clades was tested using clade decay. The adaptive radiation of gastropods and their life history traits are briefly described and discussed and the terminology for simultaneous hermaphroditism refined. A scenario for the evolution of torsion equated with the fossil record is proposed and the effects of torsion and coiling on gastropods are discussed along with asymmetry imposed by limpet-shaped body forms. It is suggested that the first gastropods were ultradextral. The idea that heterochrony has played a major part in gastropod evolution is developed and discussed, particularly the paedomorphic stamp imposed on the apogastropods. The veliger larvae of caenogastropods and heterobranchs are contrasted and found to differ in many respects. The evolution of planktotrophy within gastropods is discussed. Recent phylogenetic hypotheses for gastropods based on molecular data are generally in broad agreement with the present results. On the basis of our analyses we discuss the major monophyletic groups within gastropods. Gastropods appear to be a monophyletic clade, and divide into two primary groups, the Eogastropoda (incorporating the patellogastropods and their (probably sinistrally coiled) ancestors and the Orthogastropoda — the remainder of the gastropods. Orthogastropoda comprises several well defined clades. The vetigastropod clade encompasses most of the groups previously included in the paraphyletic Archaeogastropoda (fissurellids, trochoideans, scissurelloideans, haliotoideans pleurotomarioideans) as well as lepetodriloidean and lepetelloidean limpets and seguenzids. The location of the hot vent taxa Peltospiridae and Neomphalidae varies with each analysis, probably because there is a lack of ultrastructural data for these taxa and parallelism in many characters. They either form a paraphyletic or monophyletic group at or near the base of the vetigastropods or a clade with the neritopsines and cocculinoideans. The neritopsines (Neritoidea etc.) consistently form a clade with the cocculinoidean limpets, but their position on the tree also differs depending on the data set used and (in the case of the scaled data) whether or not the full suite of characters is used. They are either the sister to the rest of the orthogastropods or to the apogastropods. Caenogastropods [Mesogastropoda (+ architaenioglossan groups) + Neogastropoda] are consistently monophyletic as are the heterobranchs (‘Heterostropha’ + Opisthobranchia + Pulmonata). The caenogastropods and heterobranchs also form a clade in all the analyses and the name Apogastropoda is redefined to encompass this group. New taxa are proposed, Sorbeoconcha for the caenogastropods exclusive of the architaenioglossan taxa, and Hypsogastropoda for the ‘higher caenogastropods’ — the Sorbeoconcha exclusive of the Cerithioidea and Campaniloidea.

Abstract: The history of ostariophysan classification is summarized and it is noted that traditional concepts of relationships have never been supported by characters found to be unique to the taxa. We present a new hypothesis of relationships among four of the five major ostariophysan lineages: Cypriniformes, Characiformes, Siluroidei, and Gymnotoidei (Otophysi). Cypriniforms are the sister-group of the remaining three (Characiphysi), and characiforms are the sister-group of siluroids plus gymnotoids (Siluriformes). Placement of the Gonorynchiformes as the sister-group of the Otophysi is supported by additional evidence. Each of the five lineages is monophyletic. Analysis was concentrated upon species thought to be the least specialized within each lineage; choices of these species are discussed. Chanos is determined to be a relatively primitive gonorynchiform morphologically and the sister-group of all other Recent members of the order. Opsariichthys and Zacco are found to be morphologically primitive cypriniforms. We propose that a monophyletic group comprising the Citharinidae and Distichodontidae forms the sister-group of all other characiforms. Within the two families, Xenocharax is the least specialized. We suggest that Hepsetus, the erythrinids, and the ctenoluciids are more derived than the distichodontids and citharinids, and may form a monophyletic group within die characiforms. The traditional hypothesis that Diplomystes is the primitive sister-group of all Recent siluroids is substantiated. Our evidence suggests that Sternopygus is the most primitive gymnotoid morphologically; but rather than being the sister-group of all other gymnotoids, it is the primitive sister-group within a lineage called the Sternopygidae by Mago-Leccia. Previous explanations of otophysan distribution have been based on notions of relationships which are unsupported by the evidence presented herein. Our own analysis of relationships serves primarily to make clear the extent of sympatry, and therefore the probability of dispersal, among the major ostariophysan lineages. The extent of sympatry, together with the widespread distribution of ostariophysans, suggests that the group is older than previously supposed, and our hypotheses of relationships among the characiforms implies that many of the extent characiform lineages evolved before the separation of Africa and South America. Further understanding of ostariophysan distribution must await phylogenetic analysis within each of the five major lineages so that distributions linked with vicariance patterns and dispersal events can be sorted out.