Rudolf S. Scheltema

Feeding habits and growth in the mud-snailNassarius obsoletus

Nassarius obsoletus is primarily a deposit-feeder. The microflora to be found on the surface of sediment of intertidal flats serves as its major source of food. Living bivalves do not form part of the diet as previously reported. Dead organisms such as molluscs, crustacea, and fish are eaten when available but are not a principal item of food. Occasionally thallus algae are probably also utilized. Ecologically,Nassarius obsoletus may be regarded largely as a herbivorous species and deposit-feeder. In the strict sense, however, it is an omnivore and a facultative scavenger.

Evidence for trans-Atlantic transport of gastropod larvae belonging to the genus Cymatium

Abstract Many tropical and semi-tropical species of gastropods are geographically distributed in a manner such as to suggest that their larvae may be transported across the ocean. Direct evidence from plankton tows shows that veliger larvae, probably referable to Cymatium parthenopeum (von Salis), are commonly found throughout the Gulf Stream and North Atlantic drift. The average rate of transport of surface waters between the Bahamas and the Azores, computed from drift-bottle records, is 0·4 knots. Living veliger larvae caught in plankton samples were kept in the laboratory for a period longer than that required for their transport in the Gulf Stream to the eastern Atlantic. The distribution of C. parthenopeum in the western Atlantic extends from the coast of Brazil northward, throughout the West Indies, to Bermuda; in the eastern Atlantic it ranges from the Azores and the western Mediterranean southward along the west coast of Africa to the Cape of Good Hope. This distribution could be accounted for by transport of veliger larvae in the warm currents of the North Atlantic. Computations based on drift bottle data and from estimates of larval survival show that trans-Atlantic drift of veliger larvae is probably a common phenomenon. If the estimates are reasonably correct, considerable gene flow must occur between the populations of the western and eastern Atlantic.

Growth Stasis and Limited Shell Calcification in Larvae of Cymatium parthenopeum During Trans-Atlantic Transport

Larvae of the shallow-water marine gastropod Cymatium parthenopeum show no appreciable shell calcification and no demonstrable growth as they disperse across the Atlantic Ocean. Evidence of what appears to be physiological specialization for prolonged delay of metamorphosis was found in larvae of this prosobranch gastropod.

Semper's (zoanthid) larvae: pelagic life, parentage and other problems

Sempers larvae were obtained from <300 out of ∼1800 plankton tows taken in the worlds oceans (1964–1993). Zoanthellae (larvae of Sphenopidae) occurred at 217 stations and zoanthinae (larvae of Zoanthidae) at 86, the two larval types showing distributions clearly delimited by a minimum sea temperature (∼22 °C for zoanthellae, ∼18 °C for zoanthinae; a statistically significant difference, P<0.001). Length of formalin-fixed zoanthellae was ∼2–8.6 mm and of zoanthinae ∼1.5–5.9 mm. Endodermal zooxanthellae were present in 9/24 zoanthinae but in no zoanthellae (of 19). Three larvae contained an endo-commensal/parasitic amphipod. Septa were externally visible in larger zoanthinae and were counted in transverse sections of other larvae, a majority of which (both kinds) had 12 septa, the normal maximum. The pattern was brachycnemic in 40/43 larvae and anomalous (but non-macrocnemic) in three. If macrocnemic genera reproduce by Sempers larvae, they should have been represented in such a large sample. The distribution of adult Epizoanthus was examined: many species are deep sea (recorded down to ∼5000 m) but shallow-water species are relatively plentiful in, for example, the Adriatic and North Seas. No Sempers larva has ever been recorded from either. Some Parazoanthus species also occur in shallow water, especially associated with western Atlantic reef sponges. If they produce Sempers larvae, these have never been found. It is probable that macrocnemic zoanthids settle from planulae that do not develop into recognizable zoanthellae or zoanthinae.

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.

Life history of the Antarctic sea star Labidiaster annulatus (Asteroidea: Labidiasteridae) revealed by DNA barcoding

Labidiaster annulatus, Sladen (1889) is a multi-rayed (9–50) voracious Antarctic sea star with numerous large, conspicuous crossed pedicellariae. An active and opportunistic predator, it commonly preys upon euphausiids, amphipods, and small fish in the water column (Dearborn et al. 1991). Labidiaster annulatus is distributed around the Antarctic, Kerguelen, South Orkney, South Sandwich Islands, South Georgia, and Shag Rocks, at recorded depths of 30–440 m (Fisher 1940, unpublished data).

Pelagic larvae of New England intertidal gastropods II. Anachis avara

SummaryThe egg case, pelagic larvae, and young juvenile of Anachis avara Say, a species of prosobranch gastropod belonging to the family Columbellidae, are described and figured from specimes reared in the laboratory.ZusammenfassungDie Arbeit beschreibt die Eierkapseln, die pelagischen Larven und die Jugendformen von Anachis avara Say, einer prosobranchen Gastropoden-Spezies, die zur Familie der Columbelliden gehört. Abbildungen von Exemplaren, die im Laboratorium aufgezogen wurden, werden wiedergegeben.