Gregory S. Herbert

Influence of alternative shell‐drilling behaviours on attack duration of the predatory snail, Chicoreus dilectus

Edge drilling is a form of predation in which a predatory snail excavates a hole at a point along the margin of the closed valves of a bivalved animal. We tested the hypothesis that edge-drilling attacks by the predatory snail Chicoreus dilectus on its clam prey Chione elevata shorten the duration of the predation process relative to the alternative behaviour of drilling through the preys shell wall away from its edges. The time required to complete an edge-drilling attack was on average about three times less than when prey were attacked through the shell wall. This improvement in predation speed was a function of the thickness of the preys shell at the point of attack. We suggest that owing to the shorter length of time required to kill prey, the edge-drilling behaviour may be selectively advantageous in environments where enemies are abundant, especially competitors that might attempt to steal prey. Behaviours that speed up the predation process may create opportunities for more effective exploitation of available prey resources in highly competitive environments.

Reconstructing early 17th century estuarine drought conditions from Jamestown oysters

Oysters (Crassostrea virginica) were a central component of the Chesapeake Bay ecosystem in 1607 when European settlers established Jamestown, VA, the first permanent English settlement in North America. These estuarine bivalves were an important food resource during the early years of the James Fort (Jamestown) settlement while the colonists were struggling to survive in the face of inadequate supplies and a severe regional drought. Although oyster shells were discarded as trash after the oysters were eaten, the environmental and ecological data recorded in the bivalve geochemistry during shell deposition remain intact over centuries, thereby providing a unique window into conditions during the earliest Jamestown years. We compare oxygen isotope data from these 17th century oyster shells with modern shells to quantify and contrast estuarine salinity, season of oyster collection, and shell provenance during Jamestown colonization (1609–1616) and the 21st century. Data show that oysters were collected during an extended drought between fall 1611 and summer 1612. The drought shifted the 14 psu isohaline above Jamestown Island, facilitating individual oyster growth and extension of oyster habitat upriver toward the colony, thereby enhancing local oyster food resources. Data from distinct well layers suggest that the colonists also obtained oysters from reefs near Chesapeake Bay to augment oyster resources near Jamestown Island. The oyster shell season of harvest reconstructions suggest that these data come from either a 1611 well with a very short useful period or an undocumented older well abandoned by late 1611.

A developmental perspective on evolutionary innovation in the radula of the predatory neogastropod family Muricidae

The neogastropod family Muricidae includes a diverse set of radular bauplane, including a beaked, three-dimensional form, a flattened-pentacusped form, and a third “dagger” type in which the central rachidian cusp is massive and elongate. Examination of the radular ontogenies of representatives of five muricid subfamilies reveals that several species undergo changes in radular form during ontogeny on a scale comparable to the evolutionary differences between higher taxa. The species Concholepas concholepas (Bruguière, 1789) (Rapaninae) and Trophon geversianus (Pallas, 1774) (Trophoninae) begin ontogeny with a three-dimensional rachidian characteristic of the Ocenebrinae or Muricopsinae but end with the dagger rachidian typical of their respective subfamilies. Young individuals of Vitularia salebrosa (King and Broderip, 1832) (Muricopsinae?) also have a three-dimensional rachidian but shift to a double-dagger morphology by adulthood. Chicoreus (Phyllonotus) pomum (Gmelin, 1791) (Muricinae) has a typical flattened muricine rachidian as an adult but possesses a “buccinoid”-like rachidian just after hatching. Urosalpinx cinerea (Say, 1822) (Ocenebrinae), was unique among the species examined in exhibiting no ontogenetic changes in radular form. The occurrence of two radular bauplane within the same individual snail during ontogeny suggests great potential for rapid, convergent evolution of adult features through simple changes in developmental timing. A three-dimensional rachidian, for example, could be retained into adulthood through paedomorphosis in any lineage possessing the three-dimensional-to-dagger ontogeny. Systematic assignments of muricids based solely on radular features should be reexamined.

The Genus Strombus (Mollusca: Caenogastropoda: Strombidae) in the Neogene of the Bocas del Toro Area, Panama, with the Description of Three New Species

Abstract In contrast to the immense effort that has been put into the geological survey and stratigraphic study of the Neogene of Bocas del Toro region (Panama), little research has been done on the systematics of this regions rich gastropod assemblages. This is the first paper dealing primarily with the Bocas Neogene gastropod assemblages (Strombidae) since the pioneer work of Olsson (1922). Neogene strombid assemblages of the Dominican Republic have recently been reviewed and updated, and, therefore, the Strombidae are a suitable starting point for the revision of the gastropod assemblages from the Neogene of Bocas del Toro. Six species of Strombus are described, three of them new: S. acanthospira n. sp., S. pugiloides, S. gatunensis, S. elegantissimus n. sp., S. vermeiji n. sp. and S. cf. floridanus.

A molecular phylogenetic framework for the subfamily Ocenebrinae (Gastropoda, Muricidae)

The Ocenebrinae is a subfamily of marine predatory gastropods known as oyster and mussel drills. Their current phylogenetic framework is traditionally based on shell and radular characters, but a consensus on relationships among genera is still lacking. We investigated the molecular phylogeny of Ocenebrinae using 50 species and DNA data from one nuclear (28S) and two mitochondrial (COI and 16S) genes, the largest data set so far assembled for this subfamily. We found support for the monophyly of the Ocenebrinae, and species were divided into four major lineages. Within groups, genera had similar geographic distributions, suggesting that except in a few cases, species diversification within clades occurred without range expansions. We discuss the phylogenetic distribution of a labral tooth and a sealed siphonal canal, two characteristic ocenebrine features. We also show that Ocinebrina species in the north‐eastern Pacific are not monophyletic with north‐eastern Atlantic and Mediterranean species, and that the Ocinebrina edwardsii species complex belongs to Ocenebra.

DESCRIPTION OF ARGENTHINA EMILYAE, A NEW GENUS AND SPECIES OF OCENEBRINE MURICID GASTROPODS FROM THE EARLY MIDDLE MIOCENE OF ARGENTINA

Abstract Argenthina emilyae is a new genus and species of extinct muricid gastropods from the early Middle Miocene of southern Argentina. Most of its shell features are consistent with those of the Acanthina-clade of Thais-like ocenebrines, including a broad, rounded body whorl, a large aperture lacking ornamentation, and a short, open siphonal canal, although other characters are consistent with the Ocinebrina-like ocenebrines, such as the differentiation of axials into varices and intervaricals and complex spiral sculpture. This combination of traits is unique in the Ocenebrinae. It is not yet clear whether this new taxon represents an episode of morphological experimentation by a stem group of Thais-like ocenebrines resulting in convergence on the Ocinebrina-like shell form or an evolutionarily intermediate step between Thais-like and Ocinebrina-like ocenebrines. Intermediates are expected from previously published phylogenetic hypotheses for the Ocenebrinae that suggest Ocinebrina-like ocenebrines have evolved multiple times from Thais-like ocenebrines. Until now, however, such intermediates have not been reported from the fossil record.

MEXFUSUS ROTUNDICOSTATUS, A NEW GENUS AND SPECIES OF NEOGASTROPOD FROM THE LATE CRETACEOUS OF SOUTHERN MEXICO

Abstract Mexfusus rotundicostatus new genus and species is a neogastropod of uncertain affinities from the Late Cretaceous (Early Maastrichtian) Mexcala Formation of southern Mexico. It is characterized by strong, rounded, axial ribs, fine spinelets at the intersection of axial ribs and sharp spiral cords, subsutural cord, strong simple spiral cords, and an apparently smooth, glazed columellar lip. A possible second species is Peristernia conica Riedel, 1932 from the Coniacian of Cameroon.

Morphological Development of the Radula of Four Species of the Neogastropod Family Muricidae

ABSTRACT Radular ontogenies of four species of the neogastropod family Muricidae are described through comparisons of early post-metamorphic and adult developmental stages, with specific focus on the rachidian (central) tooth. The degree of rachidian transformation during ontogeny varies from minor shape change to addition or loss of structural features important for assigning taxa to subfamilies. Changes include: flattening of the rachidian base and a switch from a short, beak-like to a long, flattened central cusp in the rapanine Stramonita biserialis; a switch from variable, asymmetric to regular, symmetric expression of inner lateral denticles in the basal muricid Timbellus phyllopterus; curvature of the rachidian base at the margins and separation of the pointed base endpoint from the radular membrane to form a marginal cusp in the muricine Chicoreus dilectus; and moderate straightening of the rachidian base in the ocenebrine Vokesinotus perrugatus. From these observations and previous work, we propose a plesiomorphic developmental sequence for the Muricidae and provide supporting evidence for the developmental origins of novel features of the muricid radula.

FIRST PALEONTOLOGICAL RECORD OF LARVAL BROODING IN THE CALYPTRAEID GASTROPOD GENUS CREPIDULA LAMARCK, 1799

Studies of larval development in the calyptraeid gastropod genus Crepidula Lamarck, 1799 have greatly enhanced the ability of systematists to delineate the Recent species in this challenging group. Although the simple, limpetlike growth form and near absence of surface ornamentation in adult Crepidula provide few diagnostic characters, larval developmental strategies (i.e., feeding or planktotrophic vs. nonfeeding or lecithotrophic larvae) appear to be stable within species and evolve rapidly, making them useful taxonomic tools. Molecular phylogenetic analyses of several species previously believed to possess multiple developmental modes—a condition known as poecilogony—found that these “species” are instead clades comprised of multiple cryptic species distinguishable only by larval type (e.g., Gallardo, 1977, 1979; Hoagland, 1977, 1984, 1986; Collin, 2000a, 2001). Until now, however, attempts to apply larval taxonomic criteria to fossil Crepidula have been unsuccessful. Larval development of extinct species and populations cannot be studied in the lab, and larval shell features that might indicate developmental mode are usually worn away on shells longer than a few millimeters (Collin, 2000a). One solution is to examine larval shells directly from fossilized larval broods. The peculiar combination of life habits of calyptraeids, including the brooding of young underneath the caplike shell of the female (Hoagland, 1979, 1986; see also Penchaszadeh et al., 2002: figs. 1–6) and a sedentary existence with the aperture of the shell held tightly against a hard substrate (see Marshall, 2003: figs. 7–10), is highly conducive to brood preservation in the fossil record. Lines of evidence attesting to this potential include: 1) Crepidula fossil shells are not uncommonly found still attached to their original substrates [Hoagland, 1977; Smith, 1986; Miller and DuBar, 1988; Woods, 1989; Campbell, 1976, 1993; Warren Blow (USNM), personal commun., 2002; …

Evidence for intense biotic interactions in the eastern Gulf of Mexico after a two million year hiatus: inferences from muricid edge-drilling behaviour

Edge drilling by the muricid gastropods Chicoreus dilectus and Phyllonotus pomum has been observed in the laboratory under conditions simulating an enemy-rich environment, and evidence for it is found in Florida’s Pliocene fossil record. However, this behaviour has never been observed in the wild and was presumed to be ecologically extinct for the last two million years. This study documents for the first time expression of enemy-induced edge-drilling behaviour in the wild by C. dilectus and P. pomum. These observations are based on a multi-year survey between 2002 and 2015 in St Joseph Bay, Florida, a coastal lagoon in the northeastern Gulf of Mexico. Edge drilling was not recorded in 2002 in St Joseph Bay, but expression of edge-drilling behaviour was confirmed by direct observation for both species and two stations in the bay between 2007 and 2011. Edge-drilling predation traces produced by C. dilectus and P. pomum accounted for more than half of all their drilling attacks in bulk samples collected in 2007, with the frequency of occurrence in bulk samples declining at both stations over time. Intensive sampling along the west Florida shelf over the same time interval failed to find any other unambiguous evidence for expression of edge drilling by these species. St Joseph Bay has the highest densities of predators and lowest prey survival rates in the region and also highest secondary productivity in any seagrass habitat globally, confirming the use of edge drilling by C. dilectus and P. pomum as an indicator of Florida’s ‘enemy hotspots’ and their fates in modern times and in the fossil record. The re-emergence of enemy-induced edge drilling by C. dilectus and P. pomum in Florida after two million years, but only in St Joseph Bay, suggests the presentday ecology of the bay is unique on geological time scales.