Spicule Content in Larvae of Two Species of Demosponge(Porifera)

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The present study focuses on spicule number, length, and positioning in larvae of two confamilial species of demosponge, Halichondria coerulea Bergquist, 1967 and Hymeniacidon heliophila (Parker, 1910). The anatomy and spiculation of newly emergent larvae were examined. On hatching, larvae of Halichondria coerulea are approximately one-half as long as larvae of Hymeniacidon heliophila. The spicules of adults and larvae of Halichondria coerulea are oxeas whereas those of Hymeniacidon heliophila adults and larvae are styles. Oxeas and styles are straight or slightly curved, and needle-shaped. In both species, spicules in larvae are significantly shorter (in mean length) than spicules of adults. This observation parallels previous reports on other species of demosponge. Mean spicule number per larva was significantly different between the two species, but the respective mean spicule lengths were indistinguishable ; some overall constraints may dictate spicule size independently of larval size. In contrast, within-species comparisons of adult spicule length versus larval length, larval spicule number versus larval length, and larval spicule number versus spicule length yielded no pairwise correlations. These data indicate that broad plasticity exists in spiculation patterns of newly hatched larvae in both species. Finally, the spicular mass of Hymeniacidon heliophila is asymmetrically positioned in the posterior region of the larva whereas the spicules of Halichondria coerulea are situated in the central region. This difference in the distribution of spicules may affect the swimming properties of the larvae of the two species differently and, possibly, also determine their positioning in the water column. It is proposed that the architecture of the flagellated epithelium governs the exclusion of spicules from the posterior region of Halichondria coerulea but is not similarly restricting in Hymeniacidon heliophila.