Callidictyon abyssorum, gen. et sp. nov. (Rhodophyta), A New Deep-water Net-forming Alga from Hawai'i

Abstract

Callidictyon abyssorum, gen. et sp. nov., an unusual, net-forming red alga, is described from deep-water Pacific collections made from the research submersible Makati'i at 80-m depths on Penguin Bank, off the island of Moloka'i, Hawai'i. Though no reproductive structures were found, the new genus shares vegetative similarities with three tribes of the Ceramiaceae. The vegetative structure of C. abyssorum is similar to that of genera of the tribe Antithamnieae in having: (1) distinct basal cells on all primary lateral branches that are isodiametric and smaller than other cells of the primary laterals; (2) a central axis that is prostrate except for the portions near the apices of branches; and (3) axes that are completely without cortication. Some characters of C. abyssorum also suggest affinities to genera of the Callithamnieae, including: (1) the oblique apical cell division resulting in a strictly alternate branching pattern; (2) the absence of gland cells; and, (3) the presence of short, branching rhizoids on the basal cells of the primary lateral branches and long slender rhizoids on the main axial cells. Finally, the regularly alternate branching pattern, blunt apices, formation of anastomoses, and different .types of rhizoidal filaments, all characteristics of C. abyssorum, are also features present in members of the Compsothamnieae. Based on vegetative features, Callidictyon is tentatively placed in the Ceramiaceae until reproductive structures are found.