Reproductive biology of Perkinsiana antarctica (Kinberg) (Polychaeta, Sabellidae) in the Straits of Magellan (south America): Systematic and ecological implications

Abstract

Reproductive biology and larval development of the polychaete Perkinsiana antarctica (Kinberg, 1867) (Sabellidae) are described of a population sampled in October 1994 and March 1997 in the type locality of this species, the Straits of Magellan (Southern Chile). Perkinsiana antarctica is a simultaneous hermaphrodite. Eggs are present in the thorax and in the anterior part of the abdomen, while sperm cells occur in the posterior abdomen. Spermatids are grouped in tetrads; mature sperm cells present an oval nucleus (length of major axis about 3 μm) and the acrosome is about 2.5 μm long with a conoid shape. Mature eggs have a mean diameter of 235 μm; embryos and larvae are incubated within the branchial crown of specimens exceeding 10 mm in length. Hatching larvae have a mean length of 420 μm, with 4 segments, each bearing two notochaeta; two ocular spots and a well-developed prototroch are present at the anterior end. Both number of embryos and larvae per individual showed a relatively high range of variation (embryos from 54 to 374, mean=173; larvae from 18 to 222, mean=101). The features of reproductive biology in P. antarctica do not seem to be related to the size of the species itself, as P. antarctica represents one of the largest-sized sabellids that are brooding eggs, and producing a relatively high number of offspring. These reproductive and developmental traits seem more related to the colonization of harsh and selective habitats, such as the intertidal and shallow subtidal of the Subantarctic areas. Comparisons with the reproductive biology of other species of Perkinsiana demonstrate a high degree of variability within the genus regarding reproduction and the apparent lack of synapomorphies.