The ultrastructure of spermatozoa and spermiogenesis in pyramidellid gastropods, and its systematic importance

Abstract

Ultrastructural observations on spermiogenesis and spermatozoa of selected pyramidellid gastropods (species of Turbonilla, ~gulina, Cingufina and Hinemoa) are presented.During spermatid development, the condensing nucleus becomes initially anterio-posteriorly compressed or sometimes cup-shaped. Concurrently, the acrosomal complex attaches to an electrondense layer at the presumptive anterior pole of the nucleus, while at the opposite (posterior) pole of the nucleus a shallow invagination is formed to accommodate the centriolar derivative. Midpiece formation begins soon after these events have taken place, and involves the following processes: (1) the wrapping of individual mitochondria around the axoneme/coarse fibre complex; (2) later internal metamorphosis resulting in replacement of cristae by paracrystalline layers which envelope the matrix material; and (3) formation of a glycogen-filled helix within the mitochondrial derivative (via a secondary wrapping of mitochondria). Advanced stages of nuclear condensation {elongation, transformation of fibres into lamellae, subsequent compaction) and midpiece formation proceed within a microtubular sheath ('manchette'). Pyramidellid spermatozoa consist of an acrosomal complex (round to ovoid apical vesicle; column-shaped acrosomal pedestal), hehcally-keeled nucleus (short, 7-10 ~m long, shallow basal invagination for axoneme/coarse fibre attachment), elongate helical midpiece (composed of axoneme, coarse fibres, paracrystalline and matrix materials, glycogen-filled helix}, glycogen piece (length variable, preceeded by a dense ring structure at junction with midpiece). The features of developing and mature spermatozoa observed in the Pyramidelhdae are as observed in opisthobranch and pulmonate gastropods indicating that the Pyramidelloidea should be placed within the Euthyneura/Heterobranchia, most appropriately as a member group of the Opisthobranchia.

Ultrastructure of euspermatozoa and paraspermatozoa in the marine gastropod Adelomelon beckii (Caenogastropoda, Volutidae)

“…The annulus of A. beckii is similar to that found in other neogastropods and in many neotaenioglossans (BucklandNicks et al 1982a, b;Koike 1985;Healy 1986aHealy , 1988bHealy and Jamieson 1993) and diVers from the single ring annulus observed in basal caenogastropods (Healy 1982(Healy , 1983. The glycogen piece and the end-piece do not diVer from the conWgurations shown in other caenogastropods (Koike 1985).…”

Ultrastructure of the Sperm of Aplysia Californica Cooper

“…The structure of the sperm of the few members of the Anaspidea that have been studied, however, appears similar to that for members of other orders of this class (Healy & Willan, 1984;Healy, 1988). For example, Vita et al (2001) studying the structure of sperm of A. depilans found features that have been recognized as typical for a related order, the Notaspidea; these include the presence of an acrosome, a nucleus that spirals about the flagellum, a mid piece consisting of one or more glycogen helices, a complex mitochondrial derivative, course fibers in the axoneme, and a dense ring structure and glycogen piece near the terminus of the flagellum.…”

“…The nucleus elongates concurrent with its spiraling about the flagellum thus forming a helix (Beeman, 1977). The flagellar base (centriolar derivative or analog ;Healy, 1988Healy, , 1990Vita et al, 2001) inserts into a posteriordepression in the nucleus (the nuclear fossa, Hodgson et al, 1990). The midpiece mitochondria become highly modified into a paracrystaline structure, the mitochondrial derivative (Healy, 1996), with the loss of the appearance of individual mitochondria and their cristae.…”

“…Another vacuole develops either concurrent with the mitochondrial derivative, directly from it or just distal to its termination and it can overlap with the spiraled nucleus. This vacuole generally contains glycogen, is spiraled about the flagellum and is termed the glycogen helix (Healy, 1988(Healy, , 1991. In this paper, the spiraled nucleus and glycogen vacuole are termed nuclear and glycogen helices respectively.…”

“…The flagellum and glycogen helix were enclosed by a common microtubular basket. Healy (1988) describes, however, that the glycogen helix in several pyramidellid gastropods developed concurrent with or just distal to the termination of the mitochondrial derivative. Healy (1991) reports the absence of a glycogen helix in the sperm of the gastropod, Architectonica perspectiva, while Beeman (1977) for A. californica and Kubo and Ishikawa (1981) for A. kurodai report not only the presence of a glycogen helix but also the presence of a second helical structure.…”