Comparative Study On Traits Of Reproductive Evolution From Four Species Of Family Arcidae (Mollusca: Acridae)

Tegillaren granosa Scapharca subcrenata Scapharca broughtoni and Subclass virescens are all belongs to Family Arcidae (Mollusk, Class Bivalve. Subclass Pteriomorphia, Superfamily Arwcea). Tegillaren granosa (Genus Tegillarca), Scapharca subcrenata(Germs Scapharca) ^ Scapharca broughtoni (Genus Scapharca), Subclass virescens (Genus Barbatia),are marine mollusks that have high economic significance. There are few reports about these mollusks' reproductive biology and evolution traits. Zheng jia-sheng(1995) reported gonadic development and reproductive periods of Tegillaren granosa; Sun hui-ling(2000) > Zhu jun-quan(2001) investigated the ultrastructure of mature spermatozoon in Tegillaren granosa. Sun hui-ling(2000) observed the fertilization biology of Tegillaren granosa. Zhu jun-quan(2000) studied on the spermatogenesis in Scapharca subcrenata. Transmission electron microscopy was used to study the morphological structures of these mature spermatozoa as well as the characteristic changes of spermatocytes, spermatids and spermatozoa structure during spermatogenesis and spermatoleosis. Reproductive evolution traits of these four seashells and other mollusks were analyzed. The results show that the morphological structures of spermatozoa are the important characters of reproductive evolution; and the similarity of spermatozoa morphology can explicate the relationships of interspecies; The special features in the course of spermatogenesis and spermatid formation can be an important basis on phylogenesis research. Through this research, we can not only enrich the reproductive biology of mollusk, but also accumulate the phylogenesis dataof the mollusk.. The main results are as follows: 1. SpermatogenesisSpermatogonium stage The structure characters of spermatogonium of Tegillaren granosa and Scapharca subcrenata are very similar.?The cell and nucleus are oval-shaped; Many chromatin granules disperse in karyotin or the inner karyotheca. There is a high electron-density nucleolus in the karyotin.@The ribosome is very abundant in the cytoplasm. In this stage, the mitochondrias scatter in the cytoplasm. The number of mitochondria is scarce, and the ridges are not developed. Endoplasmic reticulum and other cell organs are not observed.Spermatocyte stage The structure characters of spermatocyte of Tegillaren granosa and Scapharca subcrenata are very alike. The cell is oval- or elongated oval-shaped; (2)The nucleus is round or elongated round. The double karyothecas can be clearly observed. Vesicles may be seen on the karyotheca. The chromatin hi the nucleus is distributed in granules or small conglomeration. ㏕he typical Golgi body and excreted vesicle can be seen in the cytoplasm . The mitochondrias with developed ridges are plentiful, and polar-distribution, gradually fuse and migrate. @In the anaphase of spermatocyte of Scapharca subcrenata, cytolysin accumulate inclusion and evolve into proacrosome.Spermatozoa stage Spermatids of Tegillaca granosa?Scapharca subcrenata and Scapharca broughtoni are developed through the following three main stages, that is, the early stage, middle stage and end stage. During these series of proceeds, the inner changes in the spermatozoon cell can be described as follows:瓼ormation of spermatozoon cell organisms. The proacrosome migrates to the prenuclear in advance and developed into acrosome; Mitochondrias get infusion and migration to form the middle piece of spermatozoon; proximal centriole appears in the posterior nuclear fossa, and axonemes are elongated from distal centriole. 〤hanges in nuclear. Chromatins begin condense and congregate. The nuclear is composed of high and even electron-density till the formation of spermatozoon nuclear. At the same time, the nuclear transform from oval-shape to cylindric shape. 〤ytoplasm are discarded with exocytosis, and only a thin stratum can be observed between nuclear envelopand plasma membrane or axoneme and plasma membrane. The spermatozoon developed from spermatid cell has specific in species. 2.ultrastructure...