Tectarius

Abstract: The littorine gastropods Cenchritis muricatus, Nodilittorina mespillum, N angustior, N dilatata, N riisei, N ziczac and Tectarius antonii from a natural limestone platform on the north coast of Jamaica were evaluated according to several ecological parameters in an effort to define their respective niches on this shore Distributions along transects perpendicular to the shore demonstrated that distance from the sea is one, albeit not always consistent, ecological criterion which serves to delineate these species N riisei generally occupies that region of the shore frequently wetted by wave splash, N mespillum is usually found within frequently refreshed tidepools and C muricatus always occupies the highest regions of the shore most distant from the sea There is, however, considerable overlap between these and other species and, along much of the rock platform, N angustior, N dilatata, T antonii and C muricatus are sympatric N dilatata has the broadest range on this low profile limestone platform A comparison of body temperatures and substratum temperatures taken from adjacent rock surfaces revealed that the body temperatures of T antonii generally reflect that of the ambient environment On the other hand, C muricatus, N dilatata, N riisei and N angustior seem to thermoregulate, maintaining body temperatures above ambient at temperatures below 29 °C and below ambient at temperatures above 33 °C Data were also compiled for most species with respect to resting posture (whether hanging suspended or resting aperture-down), resting site (whether within the shelter of a crevice or upon an exposed rock surface), shell orientation and the relative frequency (presence or absence) of a mucous holdfast Size-frequency analyses indicate that N riisei and N angustior re-populate the shore from the meroplankton at least sometime between January and March

Abstract: The distribution and abundance of the littorinid gastropod Cenchritis (Tectarius) muricatus were determined on an exposed shore at Lee Stocking Island, Bahamas in July/August 1995 and June 1999. Activity patterns were observed on two occasions shortly before a hurricane passed near the island in 1995. C. muricatus extended from the low water mark to 3.6 m vertical height above it. Highest densities (20/m2) were found just above the high tide mark but the animal remained relatively abundant (8/m2) at the highest point. Small animals were only found at high shore levels. With the exception of animals very near to the water's edge C. muricatus was inactive by day and on dry nights. Many individuals of the high shore populations became active at night during periods of high humidity and rainfall, moving distances of up to 4 m overnight. At lower levels, extensive pairing and copulation was associated with these periods of rainfall. Abundance changed dramatically after the passage of the hurricane. At the level of maximum abundance numbers were reduced from 20/m2 to 2.8/m2. Long-term experimental studies of water loss rate and haemolymph concentration showed that both water loss rate and increase in haemolymph concentration are greatest in the early period of desiccation. The concentration of the blood after 20 weeks is 250% of the original and the water lost is of the order of 22.5%. After an initial increase there appears to be evidence of regulation of haemolymph concentration possibly by exchange with free water in the shell itself. The considerable reserve capacity in tolerance is no doubt in part due to the structure and functioning of the kidney. Adaptive features of the excretory system identified from ultrastructural examination include the replacement of podocyte-containing filtration chambers in the auricle by extracellular tubules permeating the walls of both auricle and ventricle, which suggests a reduction in the rate of primary urine formation. This is also indicated by a reduced surface area of the nephridial gland, which resorbs organic solutes from the urine. Excretory cells contain single large vacuoles in which arise large multi-layered concretions composed of phospholipids and calcium salts typical of prosobranchs in which excretory products may be stored for long periods.