File:American malacological bulletin (1987) (17968663548).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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TAN TIU AND PREZANT: GEUKENSIA SHELL MICROSTRUCTURE 175 mussels. Some emerged mussels had elevated borders of con- tinuous ridges, beads (Plate 2, Fig. C) or granules that par- tially or completely surrounded one or more tablets along their 001 faces. These circumferential ridges resemble those struc- tures attributed to shell formation and growth in Pinctada martensii (Dunker) (Wada, 1960, 1961), ring nacre of Mytilimeria nuttalli Conrad and Lyonsia californica Conrad (Prezant, 1981) and those attributed to shell dissolution in Geukensia demissa (Wilkes and Crenshaw, 1979; Rhoads and Lutz, 1980). Emerged mussels that exhibited these shell microstructures have fragmented and pitted tablets pre- dominating in their internal shell surface (Table 1). The predominance of erosive remnants of nacre, both inside and outside the pallial line of emerged mussels (Table 1), indicates shell dissolution. Contrary to expectations, the warming trend in the weather inhibited shell formation in emerged mussels (absence of crystal nuclei, growing tablets and smooth sur- faced tablets, etc.). Possibly a short cold spell following the day mussels were transplanted could have increased stress associated with the emerged habitat. One could speculate that the circumferential beads (Plate 2, Fig. C) are anlages to mature microstructures if one assumes that the emerged mussels were at a stage of recovery from shell dissolution (shell formation being initiated in response to changing Table 1. Internal shell surface microstructures of Geukensia demissa granosissima after field experiment (1985) (- = absent, + to + + + + = degree of presence of microstructure in internal shell, where + = 1-25%, + + = 26-50%, + + + = 51-75%, + + + + = 76-100%). Emerged Submerged Mussels Mussels A. OUTSIDE THE PALLIAL LINE 1. anterior region —crystal nuclei and growing tablets + —smooth surface tablets + —pitted tablets + + + + + —ridged, beaded and granulated tablets + 2. posterior region —crystal nuclei and growing tablets + —smooth surface tablets + —pitted tablets + + + + + —ridged, beaded and granulated tablets B. INSIDE THE PALLIAL LINE 1. anterior region —erosive remnants of nacre + + + + + + —homogeneous (granules shape and size) variable uniform 2. posterior region —erosive remnants of nacre + + + + + + —homogeneous (granules shape and size) variable uniform
Text Appearing After Image:
Plate 2. A. Internal shell surface consists of elongated solitary and fusing polygonal tablets (Posterior region of submerged mussels, area O, March 1984). Horizontal field width = 22.8 urn. B. Internal shell surface consists of typical hexagonal tablet in various states of fusion (Posterior region of emerged mussels, area O, March 1984). Horizontal field width = 22.8 ^m. C. Internal shell surface consists of peripherally beaded tablets (Anterior region of emerged mussel, area O, February 1985). Horizontal field width = 22.8 nm.

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