Amélie H. Scheltema

A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale.

Odontogriphus omalus was originally described as a problematic non-biomineralized lophophorate organism. Here we re-interpret Odontogriphus based on 189 new specimens including numerous exceptionally well preserved individuals from the Burgess Shale collections of the Royal Ontario Museum. This additional material provides compelling evidence that the feeding apparatus in Odontogriphus is a radula of molluscan architecture comprising two primary bipartite tooth rows attached to a radular membrane and showing replacement by posterior addition. Further characters supporting molluscan affinity include a broad foot bordered by numerous ctenidia located in a mantle groove and a stiffened cuticular dorsum. Odontogriphus has a radula similar to Wiwaxia corrugata but lacks a scleritome. We interpret these animals to be members of an early stem-group mollusc lineage that probably originated in the Neoproterozoic Ediacaran Period, providing support for the retention of a biomat-based grazing community from the late Precambrian Period until at least the Middle Cambrian.

Discrimination and phylogeny of solenogaster species through the morphology of hard parts (Mollusca, Aplacophora, Neomeniomorpha)

Ten species in five genera and three families from continental shelf and deep-sea collections of neomenioid Aplacophora (Mollusca) are described, emphasizing external anatomy and hard parts--body shape, radula, epidermal spicules, and copulatory spicules--as well as the reproductive system. One genus and seven species are new: Plawenia n.g., Plawenia sphaera, P. argentinensis, Dorymenia tortilis, Eleutheromenia bassensis, E. mimus, Kruppomenia levis, and K. delta. Also included are redescriptions of three published species, emphasizing hard parts for comparisons with the new species and genus: Dorymenia sarsii (Koren & Danielssen), Simrothiella margaritacea (Koren & Danielssen), and Plawenia schizoradulata (Salvini-Plawen). A cladistic analysis of species described here demonstrates the usefulness of hard parts for phylogeny. Specimens came from collections made in the southwest Pacific and the southwest and northeast Atlantic.

Natural history of a solenogaster mollusc from Papua New Guinea, Epimenia australis (Thiele) (Aplacophora: Neomeniomorpha)

Epimenia australis (Thiele) is a large, tropical, shallow-water neomenioid aplacophoran, or solenogaster, of the west Pacific. More than 30 individuals were collected during January and February by diving off Madang, Papua New Guinea, where they occurred in aggregations with their cnidarian prey underneath overturned coral slabs at 15–24 m depth in a steeply sloping coral rock area with swift currents. Animals were kept alive for several weeks in large aquaria with running sea water and fed Scleronephthya. Like other species of Epimeniidae, E. australis is brightly coloured, with iridescent green and blue pactches on a reddish-brown background. Madang specimens were up to 11 cm long and 6 mm in width and were in reproductive condition with brooding embryos in the mantle cavity. Some individuals contained embryos in several stages of development. Epimenia fed on Scleronephthya by clamping onto the soft coral with the hook-shaped radular teeth while sucking in the polyps. They move by ciliary action of the ...

Pelagic larvae of New England intertidal gastropods

SummaryThe egg case, pelagic larva and postlarva ofNassarius trivittatus Say are described and figured from specimens reared in the laboratory. Similarities and differences in the larvae of New England and European species ofNassarius are indicated.ZusammenfassungDie Arbeit beschreibt die Eierkapseln, die pelagischen Larven und die Postlarven vonNassarius trivittatusSay. Abbildungen von Examplaren, die im Laboratorium aufgezogen wurden, werden wiedergegeben.

Falcidens halanychi, a new species of Chaetodermomorpha (=Caudofoveata) (Mollusca) from the northwest Atlantic Ocean

Abstract During a cruise with R/V Oceanus out of Woods Hole organized by the National Science Foundation project WormNet, a new species of chaetodermomorph aplacophoran was found in the northwestern Atlantic on the continental rise, between 1100 and nearly 2900 m. An investigation into the material of older collections revealed that the species had previously been collected on numerous occasions but remained undescribed. We here describe the species under the name Falcidens halanychi sp. nov. The species is compared with F. limifossorides Salvini-Plawen 1992 that has the most similar overall morphology, but occurs in the eastern Pacific at lower slope and abyssal depths between 3700 and 4300 m. We illustrate the radula of limifossorides and the birefringent colours of the sclerites photographically for the first time. We also include two DNA barcodes of F. halanychi (cytochome oxidase I) to aid future molecular identification.

The radula of the chaetodermatidae (Mollusea, Aplaeophora)

Summary1.Members of the aplacophoran family Chaetodermatidae (genera Falcidens and Chaetoderma) have a radula consisting of a single cone-shaped structure associated with a pair of teeth. In the genus Falcidens there also occurs a plate with two pairs of apophyses that wrap around the paired teeth.2.One species of each genus is known to feed on foraminifera.3.The buccal mass bears many similarities to the gastropod buccal mass: it lies in a buccal cavity; it is covered distally by a membrane connected to the radula, apparently the subradular membrane; it contains a pair of bolsters, from which run muscles to the radula and subradular membrane; and it has a blood sinus surrounding a sac of epithelial cells which secrete the cone-shaped radula. This sac appears to be homologous to the radula gland of other mollusks. It lies above and between the bolsters, and at its ventral, blind end are four large cells, the odontoblasts.4.The cone-shaped median structure appears to be a fused, permanent, continuously secreted radula. The structures seen with scanning electron microscopy, the increase in size with size of animal, and the indication of tanning by the radula gland support this view.

Pinna deltodes Menke newly described and differentiated from P. bicolor Gmelin (Bivalvia, Pterioida)

Abstract Pinna deltodes Menke is a valid Indo-Pacific species of Pinnidae morphologically similar to P. bicolor Gmelin. It can be distinguished from P. bicolor in Australia by the presence of regular, sharply defined, pinkish-buff lateral bands of subepithelial gland cells along the inner fold of the posterior mantle margin and by the position of the posterior adductor muscle scar at the posterior edge of the dorsal nacreous layer. The subepithelial gland cells are coarsely granular; they are not acid or neutral muco-polysaccharides (mucins) or muco-glycoproteins (mucoids). The preferred habitat of P. deltodes is a hard substrate, either within cobble flats or beneath boulders, coral blocks, and bombies. The species extends off eastern Africa to eastern Australia and as far north as Pakistan and probably the Red Sea, from the intertidal zone to 14 0m.

The original molluscan radula and progenesis in Aplacophora revisited

Radulae of two Middle Cambrian Burgess Shale stem molluscs Odontogriphus and Wiwaxia have recently been imaged by new techniques. Images show both species had a central, or rhachidian, tooth and mirror-image, separately articulating lateral teeth as found in the radulae of Polyplacophora and Conchifera. The hypothesis from earlier radula images of these two fossil genera is that their radulae were like those of Aplacophora (Solenogastres [or Neomeniomorpha] + Caudofoveata [or Chaetodermomorpha]) where there is no central tooth. From these earlier fossil images it was concluded that Aplacophora, often considered basal molluscs, had retained the condition of the original molluscan radula. Support for considering that the early mollusc radula lacked a central tooth rested on embryogenesis in several Polyplacophora and many Gastropoda species in which the rhachidian tooth develops after the first lateral teeth. Recent molecular studies and fossil vermiform chitons indicate that Aplacophora, rather than being basal to Mollusca, branched from chitons in the Ordovician, after development of the rhachidian tooth in molluscs. The arrested development in Aplacophora of a central tooth supports the hypothesis that Aplacophora are progenetic, rather than reflecting the earliest molluscan radula. As a vermiform, shell-less taxon, Aplacophora appears to be preadapted to a deep-sea floor turbidite, changed from the prevalent biomats of Precambrian and Cambrian times.

Hard and soft anatomy in two genera of Dondersiidae (Mollusca, Aplacophora, Solenogastres).

Phylogenetic relationships and identifications in the aplacophoran taxon Solenogastres (Neomeniomorpha) are in flux largely because descriptions of hard parts––sclerites, radulae, copulatory spicules––and body shape have often not been adequately illustrated or utilized. With easily recognizable and accessible hard parts, descriptions of Solenogastres are of greater use, not just to solenogaster taxonomists, but also to ecologists, paleontologists, and evolutionary biologists. Phylogenetic studies of Aplacophora, Mollusca, and the Lophotrochozoa as a whole, whether morphological or molecular, would be enhanced. As an example, morphologic characters, both isolated hard parts and internal anatomy, are provided for two genera in the Dondersiidae. Five species are described or redescribed and earlier descriptions corrected and enhanced. Three belong to Dondersia: D. festiva Hubrecht, D. incali (Scheltema), and D. namibiensis n. sp., the latter differentiated unambiguously from D. incali only by sclerites and copulatory spicules. Two species belong to Lyratoherpia: L. carinata Salvini-Plawen and L. californica (Heath). Notes are given for other species in Dondersiidae: L. bracteata Salvini-Plawen, Ichthyomenia ichthyodes (Pruvot), and Heathia porosa (Heath). D. indica Stork is synonymized with D. annulata. A cladistic morphological analysis was conducted to examine the utility of hard parts for reconstructing solenogaster phylogeny. Results indicate monophyly of Dondersia and Lyratoherpia as described here.

Heart, pericardium, coelomoduct openings, and juvenile gonad in Chaetoderma nitidulum and Falcidens caudatus (Mollusca, Aplacophora)

Summary1.The single auricle of Chaetoderma nitidulum originates as double invaginations of pericardial epithelium; these invaginations lie laterally at the base of an intrapericardial channel and receive blood from a capacious gill sinus into which empty the dorsally situated efferent vessels of the gills. The ventricle and aortal bulb with its strong sphincter change shape markedly during systole and diastole. The auriculo-ventricular valve is a cup-shaped check valve, the blind end facing posteriorly toward the auricle. It is attached medially both dorsally and ventrally to the wall of the auriculo-ventricular opening, thus forming a double passage. The heart of Falcidens remains to be described in detail. The ventricle in neither genus is open to the dorsal sinus.2.The pericardium in Falcidens caudatus and Chaetoderma nitidulum divides medially around the dorsal gill retractors, forming an intrapericardial channel connecting the gill sinus and dorsal sinus. The pericardium is completely closed off from the dorsal sinus. A pair of lateral V-shaped extensions open ventrally into the coelomoducts.3.The male coelomoduct openings into the mantle cavity of C. nitidulum and F. caudatus pass through strong sphincters, which may or may not be protruded into papillae. The female openings are slits also surrounded by sphincters. Paired funnel-shaped areas of the mantle wall epithelium of females only are produced into columnar gland cells and surround the openings; their function is not known.4.The gonad primordium of juvenile C. nitidulum is paired; the anlagen lie in paired coelomic lumina. As in Bivalvia, adults do not distinctly show a paired condition in the ripe gonad.5.The shape of the heart, the supposed number of auriculo-ventricular openings, and the type of coelomoduct openings into the mantle cavity are not useful taxonomic characters for species differentiation in the family Chaetodermatidae.