Juliana Giménez

EXPLOITATION OF THE VOLUTE SNAIL ZIDONA DUFRESNEI IN ARGENTINE WATERS, SOUTHWESTERN ATLANTIC OCEAN

Abstract Zidona dufresnei (fine snail) is a common gastropod species in the Southwestern Atlantic Ocean, which has been exported to Asian countries for human consumption since 1988. Landings of Z. dufresnei increased from 1974 to a maximum record of 1,300 mt (whole shelled animal) in 1997, followed by a steady decline through 2002. No resource management effort have been applied to this species since the beginning of its catch history, about 30 y ago. Information provided in this work, together with previous studies on the reproductive biology and population dynamics of Z. dufresnei, will contribute to establish effective precautionary polices to manage this resource. We suggest that Z. dufresnei is in a phase of over-exploitation since 1988 until present, we propose a rational management as size selectivity, with a minimum capture size of 16 cm, closure of the fishery during the reproductive season, from September to December and to rotate the fishing areas. This study provides historical and updated information as an attempt to implement corrective measures towards a better management of the fishery on the Argentine Continental Shelf.

Sperm morphology of two species of Olivancillaria (Gastropoda: Olividae) from the south-western Atlantic

Sperm ultrastructure in two species of the marine snail family Olividae is examined. Euspermatozoa of both species are composed of a conical, membrane-bound acrosomal vesicle; an axial rod and a basal plate similar in both species; a solid and highly electron-dense nucleus; an elongate midpiece consisting of the axoneme sheathed by helical mitochondrial elements; an elongate glycogen piece; a double electron-dense ring at the junction of the midpiece and glycogen piece; and a free tail region. The slight narrowing in the acrosomal vesicle invagination is situated in different levels between Olivancillaria deshayesiana and Olivancillaria carcellesi. This morphology could be considered as a specific character. The length of the nucleus in O. carcellesi and in O. deshayesiana is shorter than that of other neogastropods, and could be diagnostic at family level.

Spermatogenesis and sperm morphology in Trophon geversianus (Gastropoda: Muricidae)

Fil: Gimenez, Juliana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biologia Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biologia Experimental; Argentina

Spawn and Reproduction of the Gastropod Trochita pileus (Lamarck, 1822) from the Southwestern Atlantic Ocean

ABSTRACT Specimens and eggs masses of the gastropod Trochita pileus were collected during a research cruise by bottom trawling at depths between 82 m and 120 m. Adult T. pileus were found attached to such hard substrata as the shells of scallops and oysters. The egg mass of T. pileus is composed of 7–8 transparent, triangular-shaped egg capsules fixed to the substratum with stalks. Four egg masses collected from brooding females, with a total number of 241 embryos, were examined. Trochita pileus is a protandrous hermaphrodite, and histological studies of the male, transitional, and female gonads were performed. The testicular portion of the gonad in both male and transitional individuals and the ovary of the female were studied by histological techniques. Spermatogenesis was observed for males and transitional individuals.

Morphology and Cyclic Activity of the Digestive Gland of Zidona dufresnei (Caenogastropoda: Volutidae)

ABSTRACT Zidona dufresnei is a carnivorous snail that plays an important role in the trophic web as a top predator. It is a threatened species due to high levels of fisheries exploitation. In this study, we describe the morphology of the digestive gland of Z. dufresnei from Mar del Plata, Argentina, and discuss the function and the cycle of activity of the different cell types. Histological analysis reveals two types of tubules: type 1 tubules composed of digestive and basophilic cells and type 2 tubules lined by basophilic cells only. Pyramidal basophilic cells contain lipofuscin and a large amount of rough endoplasmic reticulum, which suggests that these cells are responsible for the secretion of digestive enzymes that initiate the extracellular digestion of the food. Columnar digestive cells exhibit large membrane-bound vesicles that contain proteoglycans, neutral glycosaminoglycans and small amounts of lipid and lipofuscin. The presence in digestive cells of many endocytic vesicles and residual lysosomal bodies, as evidenced by the presence of lipofuscin pigments in the apical region, indicate that digestion is completed intracellularly within these cells. The digestive cells are subject to cyclical changes involving four phases: initial, digestion, fragmentation, and disintegration stages.

Reproductive strategy of Brachidontes rodriguezii (Bivalvia: Mytiloida) in the South-western Atlantic Ocean

This study consisted in the characterization of reproductive aspects such as oocytes morphology, temporal variation in size and frequency of oocytes and the reproductive cycle of the mussel Brachidontes rodriguezii. This species dominates the rocky intertidal coast of Buenos Aires province, Argentine and is a prey item of several exploited species; however, due to the introduction of piers and seawalls, as a consequence of anthropogenic activities, the species also inhabits sandy coasts. Mussels were collected from May 2011 to May 2013. Gonad tissue samples were processed according to standard histological procedures. Four gonadal development stages were described for males and females. According to the significant decrease in the frequency of mature oocytes, the spawning events were detected between February and May. However, some evacuation events were recorded in June-July. This study reports the first record of two modalities of hermaphrodites in this species; individuals with male and female gonads and individuals with both types of gametes within a gonad.