Martín I. Brogger

Echinoderms from Argentina: Biodiversity, Distribution and Current State of Knowledge

This chapter reviews the research on echinoderms that occur in the waters of Argentina. One hundred and thirty-four echinoderm species have been recorded. Two species of Crinoidea, 58 Asteroidea, 32 Ophiuroidea, 16 Echinoidea, and 26 species of Holothuroidea. The variety of marine environments and the main oceanographic processes in the region are described. Comprehensive information regarding historical and recent echinoderm research is included. A review of the biological, ecological, and chemical research of species inhabiting the Argentine Sea is also presented. Until recently studies on echinoderms in Argentina were very limited. Further studies should be carried out to increase knowledge of the biology and ecology of the fauna. In addition, systematic and phylogenetic studies of Asteroidea, Ophiuroidea and Holothuroidea are needed. Echinoderm fisheries have been sporadic occurring only in the Beagle Channel, especially for the local market. Benthic disturbance resulting from bottom trawling fisheries at various localities seems to be a major threat to echinoderms in the Argentine Sea.

Reproduction of the sea urchin Arbacia dufresnii (Echinoidea: Arbaciidae) from Golfo Nuevo, Argentina

Arbacia dufresnii is a common and abundant sea urchin in Argentinean waters. The gonad index cycle was studied for this species in Golfo Nuevo, Patagonia, from May 2001 to March 2003. Comparative studies of gonad index and gonad histology were performed for the three years of 2001, 2002 and 2003. The gonad index reflects gonadal stages, and the results showed two spawning peaks for the studied period. The first spawning event occurred during spring and a second major spawning occurred in summer. Proliferation and differentiation of gametes, and the presence of mature gonads were synchronous among males and females. Male and female individuals spawned synchronically. Gonad resorption was observed for males and females. Histological examination data reflected gonad index analysis, providing together a good estimation of the reproductive cycle of A. dufresnii. Statistical analyses showed a positive correlation between gonad index and photoperiod. The mean fresh oocyte diameter observed was 8 7 . 1 μm (SD = 1 . 3 μm) with a jelly coat of 12.7 μm (SD = 0.9 μm), which corresponds to planktotrophic larval development.

Life History Parameters in the Edible Snail Adelomelon ancilla from Patagonian Waters

ABSTRACT Life history parameters, including size-age, production, mortality and size at reproductive maturity, were studied on the edible snail Adelomelon ancilla to provide useful management data. Stable oxygen isotope ratios confirmed semiannual formation of internal growth marks. Adelomelon ancilla can reach up to 18 years at a size of 150 mm, fitting to a Gompertz growth model. Size at which 50% of the population matured was 73.5 mm in males (7 years) and 93.5 mm in females (9 years). The long lifespan of this species is comparable to other large gastropods, in particular volutids from southern Atlantic Ocean. Longevity, low somatic production, low population density, late reproductive maturity and direct development with few embryos, makes A. ancilla a vulnerable resource that will require a proper management approach incorporating estimates of these life history parameters.

Ultrastructural and cytochemical aspects of the germarium and the vitellarium in Syndesmis patagonica (Platyhelminthes, Rhabdocoela, Umagillidae)

The cytoarchitecture of the female gonad of the endosymbiont umagillid Syndesmis patagonica has been investigated using electron microscopy and cytochemical techniques. The female gonad consists of paired germaria and vitellaria located behind the pharynx in the mid‐posterior region of the body. Both the germaria and the vitellaria are enveloped by an outer extracellular lamina and an inner sheath of accessory cells which contribute to the extracellular lamina. Oocyte maturation occurs completely during the prophase of the first meiotic division. Oocyte differentiation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be involved in the production of round granules, about 2–2.5 μm in diameter, with a homogeneous electron‐dense core surrounded by a granular component and a translucent halo delimited by a membrane. These egg granules migrate to the periphery of mature oocytes, are positive to the cytochemical test for polyphenol detection, are unaffected by protease and have been interpreted as eggshell granules. The mature oocytes also contain a small number of yolk granules, lipid droplets, and glycogen particles scattered throughout the ooplasm. The vitellaria are branched organs composed of vitelline follicles with vitellocytes at different stages of maturation. Developing vitellocytes contain well‐developed rough endoplasmic reticulum and small Golgi complexes involved in the production of eggshell and yolk globules. Eggshell globules are round, measure 4–5 μm in diameter, and have a mosaic‐like patterned content which contains polyphenols. The yolk globules, 2–3 μm in diameter, show a homogeneous protein content of medium electron density, devoid of polyphenols, and completely digested by protease. The mature vitellocytes also contain glycogen as further reserve material. The presence of polyphenolic eggshell granules in the oocytes and of polyphenolic eggshell globules with a mosaic‐like pattern in the vitellocytes have been considered apomorphic features of the Rhabdocoela + Prolecithophora. J. Morphol. 275:703–719, 2014.