Variability, function and phylogenetic significance of periostracal microprojections in unionoid bivalves

Zieritz, A. and Checa, A. G. and Aldridge, D. C. and Harper, E. M. (2010) Variability, function and phylogenetic significance of periostracal microprojections in unionoid bivalves. Journal of Zoological Systematics and Evolutionary Research. ISSN 1439-0469 DOI

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Microprojections of unionoid shells are virtually unstudied but could be important characters for resolving questions on the phylogeny and ecology of these bivalves. By investigating 26 unionoid and three species of their closest living relatives, the Trigonioida, using scanning electron microscopy, we identified three types of periostracal microprojections. (1) Microridges were present only in one species from each of the two unionoid families Mycetopodidae (Anodontites trapesialis) and Iridinidae (Chambardia bourguignati) and may represent a synapomorphy for the mycetopodid-iridinid clade. In A. trapesialis, microridges were additionally equipped with (2)ensp;flag-like projections (microfringes), possibly a synapomorphic character for the Mycetopodidae. Examination of partially bleached specimens indicated that both microridges and microfringes are predominantly or purely organic. In contrast, previously undescribed (3) spicule-like spikes represent calcifications within the periostracum. These were found in 20 of the 29 species and four of the six unionoid families. Spikes were particularly large and abundant in umbonal (juvenile) shell regions and species characteristic of fast-flowing habitats. These structures may thus serve in protecting the periostracum and shell underneath, and/or stabilizing life position by increasing shell friction. Microfringes and microridges, on the other hand, possibly aid in the orientation of the mussel within the sediment.

Item Type: Article
Uncontrolled Keywords: 2010AREP; IA61;
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Journal of Zoological Systematics and Evolutionary Research
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 24 Sep 2010 17:07
Last Modified: 23 Jul 2013 10:00

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