Comparative sperm ultrastructure of Neodasys ciritus and Musellifer delamarei, two species considered to be basal among Chaetonotida (Gastrotricha)

Abstract

The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 92+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 92+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.

Diuronotus aspetos (Gastrotricha): new morphological data and description of the spermatozoon

“…The presence of supernumerary membranes is a feature shared by D. aspetos and M. delamarei, while the structure of the accessory fibres and a similar geometry of the connections to the doublets are synapomorphies of D. aspetos, M. delamarei and the Xenotrichulidae. The thin, oblique striation of the dense material of the accessory fibres is similar in D. aspetos and the Xenotrichulidae (Ferraguti et al 1995;Guidi et al 2003).…”

“…Species of three families of Chaetonotida Paucitubulatina have been spermatologically studied: Heteroxenotrichula squamosa, Xenotrichula punctata and X. intermedia (Xenotrichulidae; Ferraguti et al 1995), Musellifer delamarei (Muselliferidae; Guidi et al 2003), Lepidodermella squamata and Chaetonotus maximus (Chaetonotidae ;Hummon 1984;Balsamo 1992). The spermatozoa of the latter two species consist of nothing but rods of condensed chromatin enclosed in a cellular membrane, so they are very different from the filiform and complex spermatozoa of the other Chaetonotida.…”

“…On the contrary, the phylogenetic relationships within Chaetonotidae and between Chaetonotidae and Xenotrichulidae are still unclear, due in part to the uncertain status of the genus Musellifer, originally assigned to the Chaetonotidae. A sister-group relationship between Xenotrichulidae and Musellifer was hypothesized based on the similarity of the spermatozoa ultrastructure (Guidi et al 2003;Marotta et al 2005). However, the muscular architecture of Musellifer greatly differs from species of both Chaetonotidae and Xenotrichulidae (Leasi and Todaro 2008).…”

Unusual spermatozoa and reproductive modalities ofXenodasys eknomios(Gastrotricha: Xenodasyidae)

“…Hochberg & Litvaitis 2001b); since genuine spermatophores are know to also occur in Neodasys (see Guidi et al 2003), the supposedly most basal taxon in Chaetonotida, the sister group of Macrodasyida, a possible sperm transfer modality by means of spermatophores might be hypothesized in the common ancestor of both taxa. The presence of spermatophores also in another basal taxon such as Xenodasys may support this hypothesis.…”

Sperm ultrastructure in Bathypolypus bairdii and B. sponsalis (Cephalopoda: Octopoda)

“…Furthermore, it can be used as a complementary 30 phylogenetic-taxonomic character (Tuzet, 1950). For these reasons, sperm morphology has attracted considerable interest in many different groups of organisms (Jamieson, 1991;Guidi et al, 2003;Michalik, 2007). Comparative analysis from sperm structure has proved to be useful helping to define the taxonomic position and phylogenetic relationships between many groups of gastropod and molluscs (Franzén, 1955(Franzén, , 1970Giusti et al, 1990;Healy, 1988Healy, , 19901995;Zhu and Yang, 2004).…”