Showing papers in "Veliger in 1997"

List of the Worldwide Food Habits of Nudibranchs

Abstract: List of the Worldwide Food Habits of Nudibranchs by Gary McDonald The list of the worldwide food habits of nudibranchs was originally available on the web as a supplement to two articles published in the Veliger: McDonald & Nybakken, 1997 & 1999. On 5 November 2014, it was brought to my attention that the list is no longer available on the web, so I have uploaded it to eScholarship in order to make it available once again. References M C D ONALD , G. R., & J. W. N YBAKKEN . 1997. A worldwide review of the food of nudibranch mollusks. I. Introduction and the suborder Arminacea. Veliger 40(2):157-159. M C D ONALD , G. R., & J. W. N YBAKKEN . 1999. A worldwide review of the food of nudibranch mollusks. II. The suborder Dendronotacea. Veliger 42(1):62-66.

Comparative Survivorship of Sympatric Native North American Gastropods (Anguispira, Mesodon, Physella, Pleurocera) and an Introduced Bivalve {Dreissena) Exposed to Freezing Temperatures

Abstract: Seventy-four specimens from four genera of native gastropods were cooled from 2.0°C to — 3.3°C over a 3 hour period under laboratory conditions. The taxa examined included two terrestrial pulmonates {Anguispira alternata and Mesodon inflecta), a pulmonale known to occupy both permanent and ephemeral aquatic habitats {Physella mtegra), and an aquatic prosobranch {Pleurocera canaliculatum) . There was no mortality in the pulmonates, but 39% mortality occurred in the prosobranch Pleurocera. Additionally, a sample of 43 zebra mussels {Dreissena polymorpha), a non-native but recently introduced species, were aerially exposed to the same temperature cycle. Of the 43 mussels, 20 had been acclimated to 2°C, and 23 acclimated to 15°C. Mortality occurred in both treatments (35% mortality in the 15°C acclimated and 25% in the 2°C acclimated) and did not differ significantly between the two groups. No mortality occurred among controls. INTRODUCTION invertebrates, terrestrial arthropods, and both terrestrial and aquatic vertebrates (Storey & Storey, 1988). Freeze The most common ways in which organisms survive in a tolerance, although less common, has also been reported subfreezing environment are avoidance (including superfor such animals as some marine invertebrates and some cooling) and/or freeze tolerance. Supercooling, the extenvertebrates (Storey & Storey, 1988). sion of the liquid phase below the equilibrium freezing Illinois gastropods occur in a wide variety of habitats point of tissue fluids, has been documented in a diversity and include terrestrial, aquatic, and semi-aquatic species, of animal groups including various mollusks and intertidal These forms may all be periodically exposed to subfreezing Page 68 The Veliger, Vol. 40, No. 1 temperatures, particularly during the spring and fall months when ambient temperatures can vary widely within a 24 hour period. However, there is little information available on how these species tolerate periodic and short-term exposure to subfreezing temperatures. The purposes of this study were twofold: (1) to examine the effects of a temperature cycle that would expose four species of native moUusks to freezing temperatures, and (2) to determine whether an introduced moUusk is more or less able to withstand exposure to subfreezing temperatures compared to the native mollusks we studied. Our study was not intended to determine mortality curves or to investigate the eflficacy of freezing as a control method for the zebra mussel Dreissena polymorpha. We selected a prosobranch, Pleurocera canaliculatum (Say, 1821), which is strictly aquatic and occupies large rivers (Burch, 1982). We also included three pulmonates. One, Physella integra (Haldeman, 1841), Family Physidae, is a basommatophoran pulmonate that occupies both permanent and ephemeral aquatic habitats (Te, 1978). Additionally, two terrestrial stylomatophoran species, Anguispira alternata (Say, 1816), Family Endodontidae, and Mesodon inflecta (Say, 1821), Family Polygyridae, were included. The two terrestrial species are active during spring and fall months and are readily obtained during these seasons. As such, individuals are likely to encounter subfreezing temperatures under natural conditions. We also included specimens of an introduced bivalve, the zebra mussel Dreissena polymorpha (Pallas, 1771), in this study. Zebra mussels attach themselves with a byssus to firm substrates. Included among these substrates are the shells of various species of native unionid bivalves (Nalepa & Schloesser, 1993; Tucker et al., 1993) and species of native gastropods including P. canaliculatum (Tucker,