Fine structure of the spermatozoon of Diopatra neapolitana (Polychaeta, Onuphidae)

Abstract

The identification of Diopatra species lacks of clear diagnostic features of taxonomic importance and the knowledge of their reproductive characters is scant. The spermatozoa of Diopatra neapolitana were ultrastructurally investigated by electron microscopy in order to correlate the mode of reproduction with sperm cells morphology. The mature male gamete has a depressed subspherical nucleus, a cone-like acrosome, and a long flagellum. The acrosome is conical in shape and radially symmetrical, with a base diameter twice the height. Within the acrosome vesicle, the basal region includes a very electron-dense thickened ring composed of paracrystalline substances. The subacrosomal space is filled with a poorly electron-dense material, with straight filaments axially arranged to form a perforatorium. The nucleus contains the complete axial canal, holding the hind perforatorium region. The middle piece consists of five mitochondria with well-distinct membranes and tubulo-vesicular cristae. Two centrioles are located perpendicularly to each other. The proximal one lies in the central fossa and the distal one, slightly eccentric to the sperm axis, anchors to the plasma membrane by nine satellite rays of the pericentriolar complex. The axoneme has a 9+2 arrangement of microtubules. In general, the spermatozoon of D. neapolitana conforms exteriorly to the typical ect-aquasperm; the acrosome complex ultrastructure, however, shows noticeable modifications from the basic form. This finding agrees with the previously observed reproductive pattern (broadcast spawning-free-swimming larvae) of D. neapolitana belonging to Santa Gilla population, and may be helpful to solve the taxonomic problems of the D. neapolitana complex as well.

Redescription and biology of Diopatra neapolitana (Annelida: Onuphidae), a protandric hermaphrodite with external spermaducal papillae

“…Conti et al (2005) described the mature sperm of D. neapolitana from the Santa Gilla population (Sardinia, Central Mediterranean) as having a long tail attached to a spherical, short and rounded head and consistent with the typical ect-aquasperm type (as defined by Jamieson and Rouse (1989)), which closely agrees with our …”

“…Cazaux (1970) artificially fertilised D. neapolitana eggs from Arcachon Bay (France) on the Atlantic Ocean that were green in colour and found that the lecithotrophic larvae had a brief pelagic phase before they settled, indicating that they are broadcast spawners. These findings were confirmed with studies by Conti et al (2005) who described the sperm of D. neapolitana as a typical ect-aquasperm as defined by Jamieson and Rouse (1989). Dagli et al (2005) carried out a one-year study of a population in Izmir Bay (Aegean Sea, eastern Mediterranean).…”

The spermatozoon ofLumbrineris (Scoletoma) impatiens(Claparède, 1868) (Polychaeta, Lumbrineridae)

“…from Grappler Inlet, Vancouver Island (Leander et al 2003), compared with those of the species so far studied (Rouse 1988;Messina et al 2005), differs greatly in external morphology, in size of the nucleus, which is rather elongated, and in number and shape of mitochondria. These findings highlight the considerable variability of form and structure of sperm in similar polychaetes species which inhabit distant seas and oceans, as noted also by our previous studies (Conti et al 2005).…”

One‐year observation on the population structure of Diopatra neapolitana Delle Chiaje (Polychaeta: Onuphidae) in Izmir Bay (Aegean Sea, eastern Mediterranean)

“…Conti et al (2005) also reported that this species is a free spawner and uses external fertilization. Conti et al (2005) reported that the external morphology of the mature male gamete of D. neapolitana conforms to that of a typical ect-aquasperm by having a short, rounded head with a conical acrosome, five mitochondria and a long tail. Our observation on the spermatozoo of D. neapolitana from Izmir Bay agrees with the Conti's findings.…”

“…In the group IV, eggs are believed to release in a jelly mass that immediately dissolves in seawater, as occurred in D. cuprea (Paxton 1993). Conti et al (2005) also reported that this species is a free spawner and uses external fertilization. Conti et al (2005) reported that the external morphology of the mature male gamete of D. neapolitana conforms to that of a typical ect-aquasperm by having a short, rounded head with a conical acrosome, five mitochondria and a long tail.…”