Convergent discoidal sand dollars from isolated regions: A geometric morphometric analyses of Dendraster and Arachnoides

Robert E Swisher

doi:10.3319/tao.2021.10.19.02

Abstract

Convergent discoidal sand dollars from isolated regions: A geometric morphometric analyses of <i>Dendraster</i> and <i>Arachnoides</i>

Highlights

Though the group has a wide history of analysis, including examination of the morphology of Dendraster, minimal work examines or focuses on underlying morphological variation within the group, utilizing statistically robust methodologies like geometric morphometric analysis
Larger degrees of morphological variation are reported through the principal component analysis (PCA) results of the Dendraster data set of the aboral landmark and semilandmark analysis when compared with the Arachnoides data set
clypeasteroids provides exciting avenues for future work. This analysis and its results demonstrate that discoidal ambitus outlines is derived from a disparate and distinct ontogenetic pathway, with distinct variation in where and how shape changes in during ontogeny and with disparately positioned loci for morphological variation in the assessed clypeasteroid genera Arachnoides and Dendraster

Summary

Introduction

The Clypeasteroida (Agassiz 1835) genus Dendraster, family Scutellidae (Gray 1825), is well documented, among the most common macrobenthic invertebrates of the northeastern Pacific Ocean of the United Stated, and has a rich history of study due to a relatively high species diversity, restricted paleogeographic distribution along the Western North American coast line, and abundance of specimens from the Gulf of California to southeastern Alaska (Mooi 1989, Beadle 1989, Beadle 1991, Mooi 1997). The extensive Dendraster literature covers a wide range of analyses ranging from descriptive, population analyses, and examination of morphological variation and functionality (O’Neill 1978, Seilacher 1979, Beadle 1995, Nakamura 1995, Collin 1997, Mooi 1997). As observed in other clypeasteroids, Dendraster has developed a distinctive discoidal/circular morphology along the perimeter curvature or ambitus; though research continues it appears that this distinctive morphology may be adaptive for the high-energy, shallow intertidal settings and a burrowing/current filter feeding life habitat that many clypeasteriods inhabit (O’Neill 1978, Seilacher 1979, Stanton et al 1979, Telford 1981, Brown 1983, Kanazawa 1992, Cabanac and Himmelman 1996, Saitoh and Kanazawa 2012). Height (camber), and population density all effect the efficiency of the inclined suspension/filter feeding position (O’Neill 1978)

Methods

Results

Discussion

Conclusion