2 research outputs found
An unexpectedly sophisticated, V-shaped spermatozoon in Demospongiae (Porifera): Reproductive and evolutionary implications.
14 páginas, 7 figuras.The demosponge Crambe crambe shows a peculiar spermatogenesis, hard to be reconciled with the basal
position of sponges in the animal phylogeny. Early spermatogenesis stages showed most of the simple features
expected in sponges. However, spermiogenesis departed from the anticipated process. Spermatids lengthened
remarkably, forming a deep cytoplasmic pit around the cilium insertion, with the proximal axoneme bending to
produce a V-shaped spermatozoon surprisingly similar to that known in the phylum Phoronida. The cytology
was unexpectedly complex, with a needle-like nucleus of helically condensed chromatin, a conical acrosome with
a subacrosomal rod, and a mitochondrion connected to the basal body by striated rootlets. These findings
establish that the spermatozoon of broad-casting demosponges occurs in two structural categories (‘primitive’
and ‘modified’ type). This dualistic condition must necessarily have pre-dated the evolutionary apparition of
higher metazoans, if we are to keep regarding sponges as the most primitive animals. We hypothesize that
internal fertilization in C. crambe – and incidentally other demosponges – may depart from the general model
assumed for spermcasting sponges. The V-shape of this spermatozoon suggests a design to favour autonomous
penetration through the dense mesohyl to reach the oocytes, rather than engulfment and transportation by
carrier cells towards the oocyte.The research was supported
by two grants from the Spanish Ministry for
Science and Education (MEC-CTM2005-05366/MAR;
MCI-BFU2008-00227/BMC). The work conducted in
this study complies with the current laws of Spain.Peer reviewe