Studyon Morphology Of Onchidiidae In Eastern Coast Of China

Onchidiidae (Mollusca Gastropoda) is a hermaphrodite and there are at least four species of Onchidiidae in eastern coastal areas of China, respectively Onchidium struma,Platevindex mortoni,Paraoncidium reevesii,Peronia verruculata of which the last three species are new record ones in mainland China. Their ecological habits and external morphology were observed through field investigation and laboratory culture. The main indicators of biological characteristics were measured for statistical analysis. The results indicate that the living habitats of these four species show a gradient which are respectively from a low tide zone to the high tide zone of the intertidal zone and then to supratidal zone. Their living habits and the ways of breathing are different because of different habitats. The differences on the external morphology of the four species are significant of which the color of feet and dorsal are different. Platevindex mortoni has no dorsal eyes with a gray black or grey white foot and only Peronia verruculata has dendritic gills. Foot length and foot width are found as typical indicators in the analysis of biological data of four species. The ratio of the length of pneumostome to posterior and anus to pneumostome is a significant observation indicator in comparison of genera and species. It is correct to divide them into four species after morphological comparison. The special external structure and differences of the internal structure can be one of the main basis for classification in Onchidiidae. The comparative study of four species in eastern coastal areas of China has great significance to basic research in amending new type species and morphological re-description of Onchidiidae.Onchidiidae are hermaphroditism animals of Gastropoda Mollusca, the structure of reproduction system can be one of the auxiliary basis for the classification of the Onchidiidae. their reproductive system consist of mating organs, genital groove and genital organs.The mating organs are composed of penis, love dart, dart sac, spermaduct, female gonopore, male gonopore, male accessory gonad and penis traction muscle; The genital organs are composed of hermaphroditic gland, vitelline gland, albumin gland, diverticulum and spermatheca. In breeding season, the experimental samples of Onchidium struma, Platevindex mortoni, Paraoncidium reevesii and Peronia verruculata were vivisected to observe and compare the reproductive systems of the four Genus. The tissue used in the experiments which need histological observation were fixed using Bouin,s Solution for 24 hours. The results showed that the furcation of love dart of Onchidium struma,Platevindex mortoni,Peronia verruculata is penis traction muscle which connect abdominal muscles, bifurcation to the other side is spermaduct. The penis traction muscle of Onchidium struma,Peronia verruculata is connected with the muscle in the back of the abdomen while FJH is connected with the front of the abdomen . Paraoncidium reevesii has no penis traction muscle. The dart sac and spermaduct of Platevindex mortoni,Paraoncidium reevesii are connected. The spermathecas of Platevindex mortoni,Paraoncidium reevesii,Peronia verruculata are located in the lower left and next to hermaphroditic gland while the Onchidium struma are in the right lower side and not next to hermaphroditic gland. Mating organs are not directly connected with genital organs in four Genus and genital groove is the main canal connecting genital organs with penis, indicating that the transportation of sperm in the individual self is mainly done through genital groove during reproduction season, which has important signification in fertilization mechanism of Onchidiidae .Tissue slice show that hermaphroditic gland which can produce sperm and eggs is composed of supporting cells and reproductive cells;Albumin gland contains large amounts of rough endoplasmic reticulum;Vitelline gland is composed of white fat cells,which are rich in oil droplets.Onchidium struma is a hermaphrodite. Mating behavior and mechanism of Hermaphrodite animals has diversity characteristics. Using the relationship of body size and mating behavior is an important way to speculate mating laws of hermaphrodite animals . By laboratory observations and mathematical analysis showed that: the courtship behavior of Onchidium struma is two or three individuals to chase, chasing behavior has randomness. Mating behavior is complex ,there has not only the individual of similar body size but also different size individual to mating, smaller individuals more tend to play a role of male and larger individual as female. During the breeding season, Onchidium struma has several mating peak and different mating behavior in every mating peak. Onchidium struma has qualify for the reciprocal mating.Study on digestive system and nervous system of Onchidiidae in eastern coast of China shows: digestive system of Onchidiidae composed of the digestive tract, stomach and digestive gland. Digestive tract including the mouth ball, esophagus, intestines, and anus; Stomach has cardiac stomach and pyloric stomach; Digestive gland composed of salivary glands, hepatopancreas and anal gland,Paraoncidium reevesii and Peronia verruculata have no anal gland except Onchidium struma and Platevindex mortoni in four species Onchidiidae. Section shows esophagus, stomach and intestines tract all composed of mucous membrance, submucosa, lamina muscularis and adventiitia, submucosa and mucous membrance form a ruffle together in lumen, lamina muscularis is circular muscle, submucosa is looseconnective tissue. Hepatopancreas contains large amounts of conductor connected with intestine and stomach; salivary glands were clustered by the acinas and conductor. Nervous system of Onchidiidae is compsed of a esophageal nerve ring and mouth ball ganglia, and on the esophageal nerve ring attached to a thin white vagina fibrosa with connective tissue. The nerve ring composed of five ganglias, respectively are, one brain ganglion, two pleural ganglias, one foot and one visceral ganglion. Mouth ball ganglion connected to and controlled by brain ganglion, is divided into a left and right one with cable to connected. Mouth ball ganglia were connected with the pharyngeal nerve, salivary gland nerve, labellum nerve, tongue nerve and so on.