Abstract

The genus Protopalythoa Verrill, 1900 (family Sphenopidae) is defined and its status discussed. As with other zoanthid genera, species are difficult to separate by traditional methods. We have developed a rigorous approach to quantitative data derived from measurements and meristic characters. In support of genetic evidence, we have utilised the relationship between number of septa and polyp column diameter, and the capsule length of nematocysts (holotrichs and p-mastigophores), together with the presence or absence of basitrichs in the cnidom. Using this approach, the species Pr. mutuki (Haddon & Shackleton, 1891b) and Pr. heliodiscus, sp. nov. are separated, described and illustrated. Protopalythoa mutuki is interpreted as a normal micro-carnivore with autotrophic capability, while Pr. heliodiscus sp. nov. is an obligate autotroph with little ability to capture prey. The latter is the only zoanthid known to have vertical transmission of zooxanthellae.