Andrea L. Meireles

Comparative study of shell choice by the southern endemic hermit crab Loxopagurus loxochelis from Brazil and Argentina

Este estudio tuvo por objetivo determinar la forma de eleccion de conchas de caracoles por el cangrejo ermitano endemico del Atlantico sudoccidental Loxopagurus loxochelis proveniente de dos provincias biogeograficas de Brasil y Argentina. Se determinaron las tallas y las preferencias de conchas entre los dos tipos de caracoles mas ocupados (Olivancillaria urceus y Buccinanops gradatum) en la region de Caraguatatuba (Brazil) y en Mar del Plata (Argentina). La composicion de las conchas fue analizada por las caracteristicas biometricas y ocurrencia de los tipos de conchas y la seleccion por la preferencia del cangrejo ermitano en relacion a la especie de concha mas ocupada. Las muestras fueron tomadas usando redes de arrastre en las areas infralitorales de ambas regiones y los animales capturados fueron medidos y pesados. Las conchas de caracoles fueron identificadas, pesadas, medidas y calculado el volumen interno. Las experiencias fueron realizadas en acuarios donde los cangrejos ermitanos fueron ubicados con un numero suficiente y adecuado de conchas de caracoles. En el laboratorio, L. loxochelis de Argentina no presentaron diferencias entre las dos especies de conchas ofrecidas, mientras los especimenes de Brasil prefirieron conchas de B. gradatum en forma significativa. Se observo que las relaciones de las dimensiones y los pesos de las conchas fueron aquellas que mejor reflejaron la asociacion con los cangrejos ermitanos. Teniendo en consideracion que los especimenes de Argentina fueron mas grandes, se puede inferir que ello puede ser uno de los factores influenciando en las diferencias por las preferencias de los tipos de conchas halladas

Pattern of shell occupation by the hermit crab Pagurus exilis (Anomura, Paguridae) on the northern coast of São Paulo State, Brazil

The purpose of this study was to determine the shell occupation pattern of Pagurus exilis using the percentage of shell types that were occupied and the morphometric relationship between hermits and occupied shells. Specimens were collected monthly from July 2001 to June 2003. A total of 1737 individuals were collected, occupying 19 gastropod shell species. Buccinanops gradatum (82%) was the most occupied shell, followed by Natica isabelleana (6.4%), Stramonita haemastoma (3.2%), and Cymatium parthenopeum (2.2%). There was a differential shell utilization pattern between sexes; males occupied larger and heavier shells while the non‐ovigerous females occupied the lightest ones. Pagurus exilis occupied more bare shells instead of incrusted ones. Buccinanops gradatum was the most occupied shell species as a function of its availability in the survey, and this occupation is strongly associated with the higher internal volume presented by these shells.

Bio-ecological aspects of the hermit crab Paguristes calliopsis (Crustacea, Diogenidae) from Anchieta Island, Brazil

In southern Atlantic studies on hermit crab biology are scanty considering the local biodiversity. In this way, some population features of Paguristes calliopsis Forest and Saint Laurent, 1968 such as size frequency distribution, sex ratio and shell occupation in the natural environment were studied. Specimens were collected by means of scuba methods in the infralittoral area of the Anchieta Island. A total of 116 individuals were analyzed. Size measurements (minimum; maximum; mean shield length +/- sd, respectively) were 0.8; 4.5; 2.76 +/- 0.79 mm for males and 2.28 +/- 0.36 mm for females. The sex ratio was 1.47:1 in favor of males which prevailed in the largest size classes. The hermit crabs occupied shells from eleven gastropod species and Cerithium atratum (Born 1778) was significantly the most occupied one (75.86%). Significant correlations were not obtained in all regression analysis, demonstrating sexual differences on fitting of the occupied shells. In the studied area P. calliopsis population is small if compared with the other hermit crab populations. The shell utilization varies as a function of shell availability and hermit crabs interspecific competition, in relation to the other coexistent species.