A study on spermatogenesis of three Mediterranean serpulid species

Abstract

Sperm ultrastructure and some steps of spermatogenesis of the serpulids Hydroides dianthus, Serpula vermicularis and Vermiliopsis infundibulum are reported. In all the species examined the germinal cells originated from a germinative epithelium associated to blood vessels in the intersegmental septa. The spermatocytes were irregular in shape with a large nucleus and a thin cytoplasmic layer. In early spermatids in which the nucleus gradually condensed, a developed endoplasmic reticulum and some electron-dense bodies were observed. The nucleus was dehydrated in the late spermatids and assumed a cylindrical shape. In all the examined species, the morphology of the ripe spermatozoa can be ascribed to the ect-aquasperm type. The acrosome had a simple cup shape in V. infundibulum, whilst it was more developed extending laterally to the nucleus in H. dianthus, and cup-shaped with a swelling towards the nucleus in S. vermicularis. When the morphology of the serpulid spermatozoa was superimposed on a phylogenetic scheme, some trends could be highlighted. Although the paucity of data on serpulid spermatozoa ultrastructure at present prevents any phylogenetic inference, the comparison of acrosome ultrastructure within a group having similar reproductive strategies showed an increase in the internal complexity of the acrosome.

Ultrastructural investigation and in vitro recapitulation of spermatid differentiation in a potential bio-indicator species – The marine invertebrate Galeolaria gemineoa (Polychaeta: Serpulidae)

“…gemineoa exhibited a cap-like appearance, which is similar to the acrosomal morphology observed in several other closely related polychaete species with ect-aquasperm (e.g. Hydroides dianthus , Serpula vermicularis , Vermiliopsis infundibulum [ 36 ] and Spirobranchus tetraceros [ 35 ]).…”

Detailed analysis of the male reproductive system in a potential bio-indicator species – The marine invertebrate Galeolaria caespitosa (Polychaeta: Serpulidae)

“…fertilisation strategy and sperm structure) with G . caespitosa , sperm detachment may happen after the completion of mitotic divisions due to the absence of spermatogonia in the coelomic cavity and similarly, no cytoplasmic bridge has been detected between spermatocytes [44]. Either way, these studies demonstrate that a significant portion of the spermatogenic process, occurs in the testicular lumen/coelomic cavity in these polychaete species.…”

“…Nevertheless, they have been neglected or mistakenly recognised as sperm flagella in some polychaetes, as the histological sections presented in association with these studies do demonstrate the existence of ciliary structures (e.g. Pomatoceros lamarckii [28] and Serpula vermicularis [44]).…”