Siphonariid development: Quintessential euthyneuran larva with a mantle fold innovation (Gastropoda; Panpulmonata).

Recent phylogenetic revisions of euthyneuran gastropods ("opisthobranchs" and "pulmonates") suggest that clades with a planktotrophic larva, the ancestral life history for euthyneurans, are more widely distributed along the trunk of the euthyneuran tree than previously realized. There is some indication that the planktotrophic larva of euthyneurans has distinctive features, but information to date has come mainly from traditional "opisthobranch" groups. Much less is known about planktotrophic "pulmonate" larvae.

Muscle and nerve net organization in stalked jellyfish (Medusozoa: Staurozoa).

Staurozoan cnidarians display an unusual combination of polyp and medusa characteristics and their morphology may be informative about the evolutionary origin of medusae. We studied neuromuscular morphology of two staurozoans, Haliclystus 'sanjuanensis' and Manania handi, using whole mount immunohistochemistry with antibodies against FMRFamide and α-tubulin to label neurons and phalloidin to label muscles. All muscles appeared to lack striations.

The other gastropod larvae: larval morphogenesis in a marine neritimorph.

Two of the three major gastropod clades with feeding larvae are sister groups and larval morphogenesis for members of these clades, the Caenogastropoda and Heterobranchia, has been well studied. The third clade, the Neritimorpha, has an unstable phylogenetic position and little is known about development of their planktotrophic larvae. Information about larval morphology of neritimorphs and resolution of their controversial phylogenetic placement is critically important for understanding evolution of larval feeding within the Gastropoda.

Metamorphic remodeling of a planktotrophic larva to produce the predatory feeding system of a cone snail (Mollusca, Neogastropoda).

I used histological sections and 3D reconstructions to document development through metamorphosis of the foregut and proboscis in the conoidean neogastropod Conus lividus. A goal was to determine how highly derived features of the post-metamorphic feeding system of this gastropod predator develop without interfering with larval structures for microherbivory. A second goal was to compare foregut development in this conoidean with previous observations on foregut development in the buccinoidean neogastropod Nassarius mendicus.

Developmental modularity and phenotypic novelty within a biphasic life cycle: morphogenesis of a cone snail venom gland.

The venom gland of predatory cone snails (Conus spp.), which secretes neurotoxic peptides that rapidly immobilize prey, is a proposed key innovation for facilitating the extraordinary feeding behaviour of these gastropod molluscs. Nevertheless, the unusual morphology of this gland has generated controversy about its evolutionary origin and possible homologues in other gastropods.

Embryonic toxin expression in the cone snail Conus victoriae: primed to kill or divergent function?

Predatory marine cone snails (genus Conus) utilize complex venoms mainly composed of small peptide toxins that target voltage- and ligand-gated ion channels in their prey. Although the venoms of a number of cone snail species have been intensively profiled and functionally characterized, nothing is known about the initiation of venom expression at an early developmental stage. Here, we report on the expression of venom mRNA in embryos of Conus victoriae and the identification of novel α- and O-conotoxin sequences.

Molluscan larvae: Pelagic juveniles or slowly metamorphosing larvae?

Asking the right questions about evolution of development, larval morphology, and life history requires knowledge of ancestral state. Two hypotheses dominate current opinion about the ancestral life cycle of bilaterians: the "larva-first" and the "intercalation" hypotheses. Until recently, the larva-first hypothesis was preeminent.

Shrinking to fit: fluid jettison from a haemocoelic hydrostatic skeleton during defensive withdrawals of a gastropod larva.

Although most of the basic animal body plans are supported by hydrostatic skeletons consisting of fluid maintained at constant volume, studies on how animals have solved biomechanical scaling dilemmas during evolution of large body size have emphasized cases where skeletons are formed by rigid solids. Larvae of gastropod molluscs swim using ciliated velar lobes supported by a constant volume hydrostatic skeleton. Defensive behaviour involves rapid withdrawal of the velar lobes and foot into a protective biomineralized shell.

Early differentiating neuron in larval abalone (Haliotis kamtschatkana) reveals the relationship between ontogenetic torsion and crossing of the pleurovisceral nerve cords.

Crossing of the pleurovisceral nerve cords in gastropods has supported the view that gastropods evolved by 180 degrees rotation between the ventral and dorsal body regions. Indeed, a rotation of this type occurs as a dramatic morphogenetic movement ("ontogenetic torsion") during the development of basal gastropods. According to a long-standing hypothesis, ontogenetic torsion in basal gastropods preserves an ancient developmental aberration that generated the contorted gastropod body plan.

Modern insights on gastropod development: Reevaluation of the evolution of a novel body plan.

More than a century of speculation about the evolutionary origin of the contorted gastropod body plan has been inspired by adult anatomy and by long-standing developmental observations. The result has been a concept of gastropod torsion that I call the "rotation hypothesis." Under the rotation hypothesis, gastropods originated when all components of the visceropallium (shell, mantle, mantle cavity with contained structures, and viscera) rotated by 180° relative to the head and foot.

Anti-tubulin labeling reveals ampullary neuron ciliary bundles in opisthobranch larvae and a new putative neural structure associated with the apical ganglion.

This investigation examines tubulin labeling associated with the apical ganglion in a variety of planktotrophic and lecithotrophic opisthobranch larvae. Emphasis is on the ampullary neurons, in which ciliary bundles within the ampulla are strongly labeled. The larvae of all but one species have five ampullary neurons and their associated ciliary bundles.

Development of foregut and proboscis in the buccinid neogastropod Nassarius mendicus: evolutionary opportunity exploited by a developmental module.

This article extends previous descriptions of foregut development and metamorphosis in neogastropods by providing data on the buccinid Nassarius mendicus, a species with a feeding larva. Histological sections showed that, like many other gastropods, the postmetamorphic buccal cavity and radular sac of N. mendicus differentiate during the larval stage from a ventral outpocketing of the distal larval esophagus.

Gastropod ontogenetic torsion: developmental remnants of an ancient evolutionary change in body plan.

A dramatic morphogenetic movement ('ontogenetic torsion') during the development of gastropods has been proposed as a recapitulation of the original developmental departure that established the novel gastropod body plan. Nevertheless, speculative literature about ontogenetic torsion and its evolutionary significance has far outstripped empirical observations and recent results suggest that the developmental process may be somewhat different than the traditional description. I used scanning electron microscopy, immunohistochemistry, phalloidin labeling, and histological sections to monitor displacements of five components of the visceropallium with respect to axial coordinates of the cephalopodium in developing embryos of the caenogastropod, Trichotropis cancellata.

Ontogenetic torsion in two basal gastropods occurs without shell attachments for larval retractor muscles.

Results of this study on two species of vetigastropods contradict the long-standing hypothesis, originally proposed by Garstang (1929), that the larval retractor muscles power the morphogenetic movement of ontogenetic torsion in all basal gastropods. In the trochid Calliostoma ligatum and the keyhole limpet Diodora aspera, the main and accessory larval retractor muscles failed to establish attachments onto the protoconch (larval shell) when the antibiotics streptomycin sulfate and penicillin G were added to cultures soon after fertilization. Defects in protoconch mineralization were also observed.

Apical sensory organ in larvae of the patellogastropod Tectura scutum.

The apical sensory organ in veliger larvae of a patellogastropod, a basal clade of gastropod molluscs, was studied using ultrastructural and immunohistochemical techniques. Immediately before veligers of Tectura scutum undergo ontogenetic torsion, the apical sensory organ consists of three large cells that generate a very long apical ciliary tuft, two cells that generate a bilateral pair of shorter ciliary tufts, and a neural ganglion (apical ganglion). Putative sensory neurons forming the ganglion give rise to dendrites that extend to the apical surface of the larva and to basal neurites that contribute to a neuropil.