Pycnoclavella (Tunicata: Ascidiacea) species from the West Indian Ocean

Abstract

Three new Pycnoclavella species, recorded from a number of locations in Algoa and Plettenberg bays, suggest an unusual diversity for this genus in South African waters and indicate the extent to which the fauna of this part of the world is incompletely explored and documented. One of the species, with sandy thread-like zooids forming loose aggregates, is in the stanleyi species-group; another has zooids partially embedded in solid test as do other species of the aurilucens group to which it belongs; and a third species is in the detorta group with the thoraces of its separated zooids turned at right angles to the longitudinal axis of the zooids and larvae that closely resemble those of Euclavella Kott, 1990. In the latter species the pharyngeal wall is reduced to a scaffolding of longitudinal and transverse branchial sinuses framing large perforations similar to those that in many abyssal species replace the small stigmata of most shallow water taxa of the Ascidiacea. The environmental pressures selecting for this remarkable adaptation are not known. A key to Pycnoclavella spp. recorded from the western Indian Ocean is included.