THE REPRODUCTIVE SYSTEM IN THE BLASTOIDEA (ECHINODERMATA)

Blastoids (Echinodermata) are the longest-lived and most diverse members of Blastozoa, a major component of the great Ordovician biodiversification event. There is significant potential for understanding the phylogeny of this reasonably well-constrained clade, but this potential is diminished because many of their key functional systems, located internally, remain poorly constrained. We have been studying internal features by digitizing the legacy collection of acetate peels of serially sectioned blastoids from the Naturalis Biodiversity Center (NCB). The digitized peels were registered, clipped from the background and stacked in Photoshop to virtually recreate the blastoid that had been serially sectioned. The digital images were then segmented in Spiers, public domain 3D imaging software, to produce models, which were manipulated in Rhino, a commercial 3D modeler.

Here we present the initial results of our study of the blastoid reproductive system. Details of the reproductive system were first revealed by the recognition of a gonopore in fissiculate blastoids. When present externally, the gonopore is located in the anal interarea, situated between the mouth and anus. If internal, the gonopore pierces the epideltoid and opens directly into the anal cavity.

The reproductive system of spiraculate blastoids is less well known with evidence of a gonoduct reported in a single taxon. Reports of fossilized eggs in the anal hydrospires of Pentremites suggest an alternative configuration for the reproductive system. No evidence of a gonopore or other reproductive structures were reported in the egg-bearing specimen. The gonopore presumably connected to an internal gonad by a canal termed the gonoduct, but previous studies have found no evidence of a gonad.

Based on our study of the peels from NCB, the Permian blastoid Deltoblastus has a well-developed reproductive system consisting of a gonopore, gonoduct and gonad. This is the first report of a preserved gonad from a blastoid. Adorally, the gonopore is located within the anispriacle, forming the external opening of a sinuous gonoduct which pierces the epideltoid and connects to a gonad located in the anal interray between the mouth and anispiracle. The reduction in anal ray hydrospires seen in many blastoid genera may reflect the positioning of the gonad.