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Studies on the Comparative Anatomy of Four Marine Bivalve Molluscs Gastropods and Byssus

Author: HuangChaoMin
Tutor: ShiYaoHua
School: Hainan University
Course: Aquaculture
Keywords: pearl oyster Perna viridis byssus byssal gland microstructure ultralstructure
CLC: S917.4
Type: Master's thesis
Year: 2011
Downloads: 10
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Abstract

Some marine bivalve species can attach to hard surfaces by byssus, one kind of secreted proteins fibers with some characteristics in water environment, such as stable, difficult to break down, renewable. These proteins, called adhesive protein or foot protein, are very excellent biomedical materials. Now, study on these proteins is one of the focus. It is helpful for extraction and utilization of mollusc foot protein to reveal morphological structure and mechanism of byssus Thus, in this study, the fundamental process of byssus secretion, microstructure of byssus gland, and ultrastructure of byssus and gastropods were studied with three kinds of pearl oyster (Pinctada martensii, P.margaritifera, Pteria penguin) and one kind of mussel(Perna viridis). Differences among these mollusc and development mechanism of byssus were also discussed.Three species of these domesticated shellfish, including P. martensii, P. penguin and P. viridis, could regenerate new byssus in the stud while no new byssus could be observed in P. margaritifera. The number of new byssus regenerated by P. martensii and P. penguin are less than that of P. viridis during the same period. The average number of new byssus regenerated by each individual were 58.63 and 12.13 respectively for P. viridis and P. martensii 48h later after old byssus being cut. The average weight of new byssus regenerated by P. penguin was about 1.95g with a mortality rate of 23% 120h later after old byssus being cut. Although mortality rate was as high as 70%, there was not any new byssus regenerated in. P. margaritifera during the same time of P. penguin.SEM analysis showed that although there were observious differences of byssal external shape between P. martensii, P. margaritifera and P. penguin, the basic units of internal structure is similar. The fundamental structure units was original fiber protein which diameter were variable among different species. Original fiber diameter was approximately 0.6-0.9μm, 1-1.5μm and 1.2-1.5μm respectively for P. martensii, P. penguin and P. margaritifera byssus. Protein fibers were arranged more tightly in pearl oyster byssus than in P. viridis.Results of study on gastropods by paraffin sections and TEM showed that it was different for the volume ratio of byssal gland to gastropod in these four shellfish. It was P. penguin which owned the largest volume ratio, and followed by P. viridis. All these four mollusc byssal gland were consisted of a variety of cells. For these two species of genus Pinctada, P. martensii and P. margaritifera, morphology and staining results of byssal gland cell was quite similar to each other. Most of their proximal gland cells were eosinophils, although there were a few basophilic cells in P. martensii. According to the study of paraffin sections, there were both morphological similar eosinophilic and basophilic cells in proximal byssal gland of P. penguin. These cells had obviously nucleus and were separated. Besides, two kinds of gland secretory cells, in which the morphology and staining of granules are quite different, could also be observed under TEM.From the observation of byssus regeneration, paraffin sections, and ultrastructure studies of SEM and TEM, a reasonable byssal developmental mechanism of these bivalve may be as following. Firstly, secretory granules came into being in gland cells of the gastropods. Then, these secretory granules moved to one side to develop into one dense core, in which inclusions secreted outward and developed into secretion beads. Many secretion beads integrated together to form larger secretion granules by outer membrane contacting each other. Subsequently, material of the large secretion granules was usually extruded into cavity of gastropods muscle, looking like liquid adhesive. Liquid adhesive, which included lots of proteins and other material that would make up of byssal thread and disc, accumulated little by little and finally polymerized into linear structure, which extended along gastropod and protruding outside. Finally, when adhesive protein liquid was secreted out the gastropod and contacted with hard material, it could transferred from liquid adhesive into solid resilient byssus rapidly.

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