PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 108(3):401-435. 1995. Loven's law and adult ray homologies in echinoids, ophiuroids, edrioasteroids, and an ophiocistioid (Echinodermata: Eleutherozoa) Frederick H. C. Hotchkiss 26 Sherry Road, Harvard, Massachusetts 01451, U.S.A. Abstract. —Lov en's law, which is summarized by an AABAB rule, is found to apply to the structure of Stromatocystites and Astrocystites (edrioasteroids) and Gillocystis (an ophiocistioid) and was previously known in echinoids and in Paleozoic ophiuroids. Chance coincidence and convergent evolution are not likely explanations. Loven's law is interpreted from edrioasteroids as a man-ifestation of 2-1 -2 symmetry, and in echinoids, ophiuroids and ophiocistioids it is interpreted as a vestige of 2-1 -2 symmetry. Thus, Loven's law is a ple-siomorphic character that indicates ray homologies. Roman numerals as used by Loven for echinoids are applied to edrioasteroids, ophiuroids and ophio-cistioids. The anterior ray in exocyclic echinoids is ray III, whereas it is ray II in edrioasteroids. This is reconciled by noting that ray II was anterior in the elongate tests of the Ordovician echinoids Ectinechinus and Eothuria. In echi-noids the anterior-posterior axis of the bilateral larva lines up with ray II in the imago [von Ubisch's axis of primordial symmetry]. This relation is used to deduce that the anterior-posterior axis of edrioasteroids coincided with the axis of their larvae. Studies by Fell, Strathmann, and Smith are used to speculate that the larval type of Ordovician ophiuroids was a bilateral planktotroph but not yet an ophiopluteus. Loven's law is a distinctive and fundamental feature of the body plan that validates the Subphylum Eleutherozoa. There are at least two distinct constructions of 2-1-2 symmetry (Eleutherozoa and Blastozoa) and possibly a third (crinoids). This paper investigates the value of Lov-The program for this research was laid en's law in establishing ray homologies out in the earlier paper (Hotchkiss 1978). among echinoderms. Loven's law of het-1 . Attempt to determine which, if any, of erotropy describes an AABAB pattern of the conflicting propositions for designating relative sizes of echinoid basicoronal plates, ray homologies may be the correct propo-In an earlier paper (Hotchkiss 1978), my a sition. 2. Investigate the location of the plane priori hypothesis was that demonstration of of hydrocoele closure and the orientation of the AABAB pattern of Loven's law in the the embryological or developmental axes as ambulacra of Paleozoic ophiuroids would part of this analysis. 3. Attempt to decide establish either the madreporite or the anus whether Loven's law independently evolved as the landmark for homologous orientation in echinoids and ophiuroids, or whether it of echinoderms. The unexpected finding was is indicative of a recent common ancestry that possibly neither the madreporite nor between echinoids and ophiuroids [review the anus is reliable. Several a posteriori hy-also the embryological evidence], or wheth-potheses came out of that work, including er it is fundamental to the ground plan of the possibility that Loven's law may be fun-the phylum. 4. Investigate whether Loven's damental to the echinoderm ground plan. law is expressed in other echinoderm groups
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