Gamet development and ultrastructure in Patella (Mollusca:Gastropoda) living in Antalya Bay

The purpose of the present investigation is to describe the process of gametogenesis and gametic structures in Patella species common in Turkish seawaters. Three species of limpet; Patella rustica, P. caerulea, P. ulyssiponensis were collected from rocky shores of Antalya Bay. Small portions of the ovary and testis were excised from animals and fixed in Bouin's fixative for light microscopy, double fixed in glutaraldehyde and osmium tetroxide for transmission (TEM) electron microscopy. Paraffin sections were stained in hematoxylin eosin. Semi-thin sections were stained in 1% toluidine blue and the thin sections with aqueous uranyl acetate followed by lead citrate. The ultrastructural stages of male and female gametogenesis were described in three Patella species. Firstly, the gonadal development in reproduction cycles is analyzed and secondly gametic formations are discussed. According to the present observations shell or soft body structures are not significant cues to differentiate sex characters of Patella, except their gonads. Regardless of the species and the gender of the organisms the gonads of limpets showed four stages (1) "partially ripe", (2) "ripe", (3) "partially spawned" and (4) "spawned" stages. During the process of spermatogenesis in P. rustica, P. caerulea, P. ulyssiponensis; spermatogonium, primer-secondary spermatocytes, spermatids and mature sperms were observed. The spermatozoa of examined Patella species are of a primitive type which generally developed in organisms that spawn their gametes free laying to the water where fertilization occurs. There are some variations in the morphology of the mid piece of the sperms of three species but there are considerable differences in the head regions. The sperm consist of a head of variable length, which is composed of a nucleus and acrosome, a simple mitochondrial midpiece and a flagellum with a 9+2 arrangement of microtubules. The acrosomal forms are these Patella species are different from each others. The P. rustica's spermatozoan head was determined the longest among three species. Their spermatozoa are characterized by an elongated nucleus. The mid-piece of all species examined found similar and consists of a ring of four spherical mitochondria with well developed cristae. In the centre of the mitochondrial ring are the proximal and distal centrioles, the proximal lying in a small posterior nuclear fossa and the distal giving rise to the axoneme. During the process of oogenesis in P. rustica, P. caerulea, P.ulyssiponensis; oogonia, vitellogenic and mature oocytes were observed. So-called early and late stages of vitellogenic oocytes were recognized. Mature oocytes diameters were determined different in oogenesis process in examined Patella species. Cytoplasmic inclusions such as cortical granules, lipid droplets, mitochondria and yolk granules constituted the fundamental components of the late vitellogenic and mature oocyte. The cortical granules were arranged beneath the oolemma at the cortex of the oocyte. Each oocyte is surrounded by a vitelline layer, a thick jelly coat. Jelly coat was found the thickest in P. caerulea's oocytes. Numerous microvilli were embedded in the jelly coat. The present results obtained on structural elements of the reproductive cycle of three Patella species examined provide basic information for further studies on the subject. So, results from the present study should be considered when morphological data sets are assembled for advanced research such as phylogenetic analysis. This work proposes the expansion of research via approach to hybridization applications which would strengthen our understanding of how gametic structural factors drive interspecific variations. In recent years some ecological factors such as climatic and pollutions affected species' gamete structure and reproductive cycle and cause that these species' populations decline.