| Onchidiidae is one of the higher clades of pulmonates. Most of themare marine organism and live in the intertidal zone, in rocky, sandy, ormuddy habitats, including mangroves. In China, previous studies onOnchidiidae mainly focused on Onchidium struma.The reproductive system of Platevindex mortoni has been observedand studied in detail. The reproductive system is mainly composed ofhermaphroditic reproductive system and male reproductive system. Thehermaphroditic reproductive system were consisted of hermaphroditicgland, albumen gland, mucous gland, hermaphroditic duct, seminal vesicle,spermatheca and vagina, and the male reproductive system was includedvas deferens, penial sheath and penis. Compared with the reproductivesystem of Onchidium struma, find that they have some difference in themale reproductive system, the O. struma have a spiral penis with accessorypenial gland while the Platevindex mortoni have a straight penis withoutany accessory gland. The anatomy of un-copulation individuals, find thattheir seminal vesicle were full of slender spermatozoa, while thespermatheca without any spermatozoa. The result shows that the matureown-spermatozoa were store in seminal vesicle. Anatomy of thecopulationed individuals which act as a female role, their spermatheca werefull of moving stubby spermatozoa, the result shows that the spermathecawere the place where donor-spermatozoa store. Vas deferens and malemating organ were observed in detail, and the transportation route ofspermatozoa was also analyzed. The mature spermatozoa were transferred by hermaphrodite duct from hermaphroditic gland to seminal vesicle, thenconvey via vas deferens to penis, during the copulation, penis transport thespermatozoa to the vagina, finally enter spermatheca, when ova matured,transferred by oviduct to spermatheca, the sperm fertilized ova in thespermatheca.The structural characteristics of mature spermatozoa of Platevindexmortoni were observed by light and transmission celectron microscopy. P.mortoni sperm is of the modified type, the mature spermatozoon containsthree parts: head, mid-piece and end-piece. The head comprised anacrosome and a nucleus. The acrosome is nipple-shaped，about0.7μm inlength. The acrosome contents is uniform, and the electron concentration isless than the electron concentration in nucleus. We find that there was noclearance between the acrosome and nucleus. The nucleus is chili-shaped,about3.8μm in length and1.0μm in width. There was no vesicle found innucleus, and the caryoplasm of nucleus is highly condensed. There existeda posterior nuclear fossa at the end of nucleus. The elongated mid-piecewas more complex. The filar mitochondria formed into chondriosomalmantle, and enwraps the elongated middle piece. The end-piece of thesperm consists of the axoneme and its surrounding cytoplasm，and theaxoneme has a typical “9+2” structure. The similarities and differences ofthe sperm ultruastructure between P.mortoni and some other relatedgastropods are discussed. The main difference between different species liein the existence or not of acrosome, the feature of acrosome, the shape andthe length of nucleus, the number, morphology and the arrangement ofmitochondria in the mid-piece.Platevindex mortoni and Paraoncidium reevesii are new record onesin mainland China. Their embryonic development process composed ofseven stages: cleavage, blastula, gastrula, intracapsular trochophore, veligerin capsule and free-swimming veliger stage. The embryonic developmentof Platevindex mortoni and Paraoncidium reevesii were observed and described. The morphological characteristics of every period of larvae wererecorded under microscopic observation, the time series table of embryonicand larval development was confirmed and compared with Onchidiumstruma. Results showed: different species Onchidiid have significantdifferences in zygote biological parameters and the time required forfertilized eggs hatch. At the average water temperature of28℃and salinityof15, the time from the fertilized eggs hatching to the free-swimmingveliger stage required of three species Onchidiid was210h,253h and270hrespectively. We have not observed The larvae develop for they all died increeping larva stage. More work still needs to be done to ascertain thecondition and process of metamorphosis for pelagic veliger. |
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