Theses and Dissertations

Defense Date

6-2000

Document Type

Thesis

Degree Name

M.S. Marine Biology

First Advisor

Charles G. Messing

Second Advisor

Andrew Rogerson

Third Advisor

Richard Mooi

Abstract

Several genera in the comatulid family Mariametridae are currently ambiguously distinguished on the basis of variations in length and robustness of oral pinnules. Previous descriptions have suggested that at least the genera Stephanometra and Lamprometra are imperfectly distinguishable. A detailed re-examination of morphology coupled with principal component analyses of morphometric data and cladistic analyses provide support for a monophyletic Stephanometra distinct from Lamprometra. A preliminary morphological analysis suggests that Dichrometra and Liparometra should be synonymized with Lamprometra. The six currently recognized species of Stephanometra uniquely share at least one pair of oral pinnules characterized by enlarged size, reduced ambulacral groove and flat, almost featureless articular facets that together produce a large, stiff, spinelike pinnule. Additional features distinguishing Lamprometra from Stephanometra include oral pinnular proportions, distribution of cirri and the nature of the adambulacral margin along the brachitaxes and arm bases.

Within Stephanometra, two groups of species are currently recognized. Those of the first group, S. echinus and S. tenuipinna, have long sharp aboral spines on distal cirrals and a spinelike fIrst pinnule. Those in the second group, S. spinipinna, S. indica, S. spicata and S. oxyacantha, lack aboral cirral spines and are differentiated by oral pinnule features. The latter three have a slender, flexible first pinnule and are distinguished by the number of enlarged spinelike pinnules that follow. In S. spinipinna, the first pinnule is also spinelike. Twenty percent of the specimens examined in the indica-spicata-oxyacantha series are intermediates that cannot be satisfactorily assigned to species based on current diagnoses. Cladistic analyses suggest that these three form a continuum and should be synonymized (under S. indica), that S. spinipinna should be assigued to S. indica, and that S. echinus and S. tenuipinna are synonymous (with S. tenuipinna the senior name). Likewise principal component analysis illustrates distinct groupings for these two species.

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