Thomas R. Waller

Unprotected larval development in the Antarctic scallop Adamussium colbecki (Mollusca: Bivalvia: Pectinidae)

Most Antarctic bivalves are small and protect their young by holding fertilized eggs or larvae in their mantle cavities for varying periods. Nourishment for these early growth stages is provided by yolk reserves rather than by planktotrophy. The anomalously large Antarctic scallop, Adamussium colbecki, has unprotected planktotrophic larvae that are spawned during the austral spring. Successful recruitment of these larvae, in populations which are most abundant in oligotrophic habitats, may be associated with episodic pulses of organic material. Reasons why planktotrophy persists in A. colbecki are suggested by acomparison with another large Antarctic bivalve, Laternula elliptica. The latter has protected lecithotrophic larvae that are released at the beginning of the austral winter. This comparison suggests that unprotected larval development persists in A. colbecki because of unusual anatomical and ecological adaptations among the adults of the Adamussium lineage that have been evolving in the Southern Ocean since the early Oligocene.

Chapter 1 New phylogenies of the pectinidae (Mollusca: Bivalvia): Reconciling morphological and molecular approaches

Publisher Summary This chapter examines the phylogenetic relationship of scallop species of commercial interest. The evolutionary relationships among commercial scallops on the basis of shared derived morphological characters are postulated and a phylogeny scaled against geologic time using data from the fossil record is produced by Waller. The phylogenetic results of the molecular genetic studies are reviewed and the new data phylogenetic interpretations from an extensive study of the worldwide fossil record of the Pectinidae beginning at the dawn of the Cenozoic Era are presented. The new phylogenies resolve some of the conflicts between morphological and molecular approaches. They also provide new hypotheses for further testing by both approaches. The new phytogenies indicate that extant pectinid genera comprise four subfamilies: Camptonectinae, Chlamydinae, Palliolinae, and Pectininae. One of the major results is a new phylogeny of the Palliolinae, demonstrating the importance of this group in Cenozoic pectinid evolution in both hemispheres. Study of a stratigraphic succession of Pectininae in the Oligocene and Miocene of Central America reconfirms the phylogenetic independence of the American genus Euvola and the European-Indo-Pacific genus Pecten.

MIDDLE TRIASSIC PTERIOMORPHIAN BIVALVIA (MOLLUSCA) FROM THE NEW PASS RANGE, WEST-CENTRAL NEVADA: SYSTEMATICS, BIOSTRATIGRAPHY, PALEOECOLOGY, AND PALEOBIOGEOGRAPHY

Abstract The parautochthonous Anisian and Ladinian rocks of the New Pass Range previously referred to as the Augusta Mountain Formation have a unique, endemic assemblage of pteriomorphian bivalves with Triassic Northern Hemisphere biogeographic relationships, especially to the Carnian cratonal faunas of northeastern British Columbia as well as to Ladinian faunas of the Shoshone Mountains and the Gillis Range. A new suborder Prospondyloidina is described, as well as three new genera, Promysidiella, Loxochlamys, and Nevadapecten, a new subgenus, Gervillaria (Baryvellia), and 17 new species either named or referred to by letters: Promysidiella planirecta, P. desatoyensis, Bositra favretensis, Enteropleura species a, Gervillaria (Baryvellia) ponderosa, Atrina sinuata, Antiquilima ladinica, Palaeolima newpassensis, Plagiostoma acutum, Leptochondria shoshonensis, Asoella? species a, b, and c, Oxytoma (Oxytoma) grantsvillensis, Pleuronectites newelli, Loxochlamys corallina, and Nevadapecten lynnae. Promysidiella aff. otiosa is a new combination for Mytilus otiosus McLearn; Mysidiella newtonae n. sp., Norian, Wallowa terrane, is based on Krumbeckiella cf. timorensis (Krumbeck) of Newton, 1987. Triassic “Posidonia” is placed in Bositra de Gregorio, 1886, regarded as a senior synonym of Peribositria Kurushin and Trushchelev, 1989. The morphological and stratigraphic sequence Bositra-Enteropleura-Daonella-Aparimella-Halobia is rooted in Paleozoic Caneyella and Posidonia and indicates declining dependence on and eventual loss of byssal attachment as well as a possible shift from low to high dispersal ability (between Bositra and Enteropleura). There is no evidence for trans-Panthalassan dispersal of bivalves in low latitudes within the interval of Ladinian coral beds. So-called Tethyan and Muschelkalk species are endemics in slowly evolving genera or are phylogenetically convergent on west Tethyan species.

New species of Camptochlamys and Chlamys (Mollusca; Bivalvia; Pectinidae) from near the Cretaceous/Tertiary boundary at Ocean Point, North Slope, Alaska

Two new species of pectinid bivalves, Camptochlamys alaskensis and Chlamys aquilonia , are present in shallow-marine deposits near Ocean Point, northeastern Alaska, at about 70°N latitude. The precise age of these deposits is debatable, but paleontological and isotopic age estimates indicate placement near the Cretaceous–Tertiary boundary. The occurrence of Camptochlamys extends the chronostratigraphic and geographic range of this genus, previously unknown from any strata above the uppermost Jurassic (Tithonian) of Europe and unknown from any strata in North America. In contrast, the new Chlamys species represents an evolutionary advance beyond its nearest relative in the Maastrichtian of northern Europe and resembles Cenozoic members of its clade in certain features of shell microstructure. These new species are thus a microcosm of the debate regarding the age of these deposits and strengthen the hypothesis that the Ocean Point fauna lived in an Arctic Ocean basin that was isolated from the world ocean.

THE EVOLUTIONARY AND BIOGEOGRAPHIC ORIGINS OF THE ENDEMIC PECTINIDAE (MOLLUSCA: BIVALVIA) OF THE GALÁPAGOS ISLANDS

Abstract New phylogenies of endemic Pectinidae of the Galápagos Islands allow their endemic status to be assessed relevant to the relict theory of insular endemism. Nodipecten magnificus and Leopecten isabelensis n. sp. are neoendemic species that evolved in the Pliocene from ancestors in the tropical eastern Pacific and more remote ancestors in the Tertiary Caribbean Province before closure of transisthmian seaways. Spathochlamys vestalis, an eastern Pacific species whose incipiently neoendemic Galápagos representatives have diverged only slightly from the mainland stock, is related to an extant, broadly distributed western Atlantic sister species, S. benedicti, which has an ancestry traceable back to the Miocene in the Tertiary Caribbean Province. Euvola galapagensis is a paleoendemic whose ancestral lineage is extinct on mainland coasts. Veprichlamys incantata is a paleoendemic with an exclusively Pacific history, with its probable immediate ancestor occurring in the Pliocene of Ecuador and its more remote Miocene ancestors in the cooler waters of the southeastern Pacific. The high frequency of endemism and the evidence that originations are Pliocene or later are consistent with the high rates of morphological evolution attained by the Pectinidae relative to many other bivalves. New species described are L. isabelensis of the Galápagos Islands and L. cocosensis of Cocos Island. Leopecten is shown to be restricted to the Americas and to differ morphologically from Flabellipecten, an extinct Neogene European genus that is phylogenetically not closely related. Based on a new phylogeny, the genus Lyropecten is extinct, and living representatives of the Lyropecten-Nodipecten clade are all in the genus Nodipecten.

Bridging the gap between the Eastern Atlantic and Eastern Pacific; a new species of Crassadoma (Bivalvia; Pectinidae) in the Pliocene of Florida

Crassadoma monroensis new species (Mollusca: Bivalvia: Pectinidae), from the lower upper Pliocene Ochopee Limestone Member of the Tamiami Formation of southern Florida, is the first undoubted member of the genus Crassadoma Bernard, 1986, to be discovered in the Neogene on the eastern side of the Americas. The new species was likely byssate, not cemented, and fills the geographic gap between ancestral members of the tribe Crassadomini in the eastern Atlantic and Crassadoma gigantea, the giant cemented species that lives along the western shores of North America.

Morphology, Phylogeny, and Systematic Revision of Genera In the Dimyidae (Mollusca, Bivalvia, Pteriomorphia)

Abstract Differences in the mineralogy of hinge teeth and inner shell layers in the family Dimyidae form the basis for a revision of genera. The stem genus Atreta (Late Triassic to Late Cretaceous) has aragonitic denticulate hinge teeth on the right valve articulating with pitted sockets on the left valve. The same arrangement is present in Neoatreta n. gen. (Paleocene? Miocene to Recent) but with the appearance of extensive calcitic overarching of the resilifer. In Dimyella (Eocene to Recent), aragonitic teeth and sockets are still present but are modified into hook shaped denticulate teeth with corresponding sockets. All three of these genera have inner aragonitic crossed-lamellar shell layers that extend well outside the pallial line. In contrast, Dimya (Eocene to Recent) and Basiliomya (Pliocene to Recent) comprise a second clade in which aragonitic hinge teeth are absent and hinge articulation is calcitic, derived from the calcitic rim. Dimya has only weak hinge articulation and has an aragonitic inner shell layer delimited by the pallial line; in Basiliomya calcitic hinge teeth are more prominent and the entire inner shell layer inside the pallial line is foliated calcite. Diploschiza (Cretaceous, Albian to Maastrichtian), here reinstated from synonymy with Atreta, is probably a precursor of the Dimya-Basiliomya clade based on incipient calcitic hinge teeth. Predation pressures probably drove the evolution of this cemented family from its original habitat on hardgrounds in moderately deep water into much greater depths or into cryptic habitats, including submarine caves. New combinations are Dimyella malnatrensis (Corselli and Bernocchi), D. molokaia (Dall, Bartsch, and Rehder), D. similis (v. Koenen), Neoatreta dissimilis (Tate), N. filipina (Bartsch), N. kaiparaensis (Laws), N. phaidra (Woodring), and N. plana (Martin).