Echinarachnius

Abstract: Dividing eggs of Echinarachnius parma, Hydractinia echinata, Cerebratulus fuscus and Mytilus edulis were subjected to experiments designed to yield additional information concerning the cytoplasm in the cleavage plane. Answers to the following questions were sought: (1) Will the base of the furrow cut itself upon a needle placed in its path at right angles to the cleavage plane? (2) What part of the surface is responsible for the constricted shape of the partly divided egg? (3) Does completion of furrowing depend upon a specific subsurface cytoplasmic arrangement? It was found that in no case could the base of the furrow cut itself upon a needle. The constricted shape of the partly divided Echinarachnius egg depends on the integrity of the surface at the base of the furrow. The eggs of all four species completed division despite drastic stirring and mixture of subsurface cytoplasm which was begun during early stages of furrowing and continued until the blastomeres were separated.

Abstract: Thirteen species of sand dollar echinoids, representing six north Pacific genera, are reported from middle Miocene through the Recent in Alaska. Miocene records are from around the Gulf of Alaska in the Lituya and Yakataga areas, on Kodiak Island and on the western Alaska Peninsula. Pliocene sand dollars are known only on the Alaska Peninsula and Pleistocene occurrences are from the Pribilof Islands and northern Seward Peninsula. Echinarachnius parma lives in the Pacific as far east as the central Gulf of Alaska and Dendraster excentricus ranges as far north as the Juneau area. Phyletic relationships between the Alaska Tertiary fauna and those of Japan and of Oregon and California are evident. Only one Alaskan echinoid, Echinocyamus cf. E. pusillus, appears to have migrated into the north Pacific since middle Miocene time. New species described are Kewia kannoi, K. kehoei, K. lituyaensis, K. tachilniensis, Echinarachnius astrodapsoides, E. plafkeri, E. ungaensis and Remondella waldroni.