Microstructure of octocoral sclerites for diagnosis of taxonomic features
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ORIGINAL PAPER
Microstructure of octocoral sclerites for diagnosis of taxonomic features Dafna Aharonovich & Yehuda Benayahu
Received: 26 April 2011 / Revised: 1 September 2011 / Accepted: 1 September 2011 / Published online: 28 September 2011 # Senckenberg, Gesellschaft für Naturforschung and Springer 2011
Abstract The octocoral family Xeniidae constitutes a major faunistic component of Indo-Pacific coral reefs, particularly in the Red Sea. The sclerites of several common genera, among which Xenia, are composed of minute platelets, or corpuscle-like forms, with a surface that appears almost smooth at light microscope magnification. Scanning electron microscopy (SEM) revealed the fine microstructure of the xeniid-sclerites, leading to the establishment of several new taxa, including the genus Ovabunda, whose spheroid sclerites are composed of aggregations of minute microscleres rather than the Xeniastyle platelets. The present study applied for the first time high-resolution environmental SEM (ESEM) in order to examine the detailed structure of these octocoral sclerites. It determines whether and how the microstructural features in three type specimens of O. biseriata, O. faraunensis and O. impulsatilla play a role in determining their structural stability: namely, how the corpuscular microscleres adhere together and maintain the sclerites’ spheroid shape. The study revealed the surface of the microscleres to be constructed of coarse granular crystals, and the adjacent microscleres to be interconnected by various microstructural means. It is suggested that these microstructural features are diagnostic for the genus. Future examination of type specimens of other Ovabunda species, as well as additional xeniid genera, will also enable a better evaluation of the taxonomic importance of high-resolution images in relation to other genera.
D. Aharonovich : Y. Benayahu (*) Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel e-mail: [email protected]
Keywords Octocorallia . Xeniidae . Sclerites . Microstructure . Taxonomy . Electron microscopy
Introduction Soft corals (Octocorallia) are common members of the benthic communities of Indo-Pacific coral reefs (Benayahu and Loya 1981; Fabricius and Alderslade 2001). Unlike reef-building stony corals (Scleractinia), octocorals do not produce a massive skeleton but sclerites, which are internal polycrystalline aggregates of calcite-composed skeletal elements. Sclerites demonstrate a high variability in shape and size, and constitute an important trait in octocoral taxonomy (e.g., Bayer 1981; Fabricius and Alderslade 2001; Tentori and Ofwegen 2011). Species of the octocoral family Xeniidae Wright and Studer (1889), form a major benthic component of shallow coral-reef communities throughout the tropical Indo-West Pacific (e.g., Reinicke 1997; Fabricius and Alderslade 2001), and in the Red Sea in particular (e.g., Benayahu 1985, 1990; Reinicke 1997). Xeniid colonies harbor zooxanthellae and comprise mostly
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