Syncytial organization of acanthors of Polymorphus minutus (Palaeacanthocephala), Neoechinorhynchusrutili (Eoacanthocephala), and Moniliformis moniliformis (Archiacanthocephala) (Acanthocephala)

Abstract

The fine structures of immature and of developed shelled acanthors of three species belonging to the three subgroups of the Acanthocephala were investigated. Acanthors are surrounded by four eggshells (embryonic envelopes) and are composed of three syncytia: a frontal syncytium, a central syncytium, and an epidermal syncytium. Neither a sense organ nor a nervous system has been found. The central syncytium shows a mass of condensed nuclei and 12 decondensed nuclei and gives rise to 10 anterior/posterior subepidermal myofibrillar systems and 2 oblique retractor muscles. Circular muscles are missing. A single decondensed nucleus can be assigned to each of the 12 muscular systems. The epidermal syncytium embeds the other two syncytia and forms the wrinkled epidermis, which shows an extracellular glycocalyx and intrasyncytial condensations. Prominent recurved hooks, which mark the anterior end of each acanthor, and body spines are intraepidermal differentiations. Partly branched tubular infoldings of the epidermal plasma membrane of the acanthor exist and represent precursors of the pore ducts typical of the adult epidermis. Autapomorphies in the ground pattern of the monophylum Acanthocephala are the four eggshells, the early development of three syncytia, the condensed nuclei in the central syncytium, and the differentiation of ten longitudinal muscle bands and two muscle retractors and of intraepidermal hooks and spines. The syncytial organization of the epidermis with intraepidermal skeletal condensations and infoldings of the apical plasma membrane are characteristics inherited from a stem species common to Acanthocephala, Seison, and Rotifera.

Cryptic species and their utilization of indigenous and non-indigenous intermediate hosts in the acanthocephalanPolymorphus minutus sensu lato(Polymorphidae)

“…Accordingly, no recent taxonomic studies were published for this species. Furthermore, P. minutus has been frequently used as a model organism in various fields throughout the last decades, including studies about tegumental structure of adults (Crompton and Lee, 1965) and acanthor-larvae (Albrecht et al 1997) or the relation of the parasite with its intermediate and final hosts (Hynes and Nicholas, 1963; Itämies et al 1980; Bollache et al 2001; Bauer et al 2005; Haine et al 2005; Médoc et al 2006; Tain et al 2006; Jacquin et al 2014). If the hypothesis holds true that several cryptic species are subsumed in a presumed ‘ P. minutus -complex’, this will have consequences for the conclusions drawn from behavioural or structural studies, especially if different intermediate host species were involved.…”

Ultrastructure of the acanthella of Paratenuisentis ambiguus (Acanthocephala)

“…The acanthor was described following an ultrastructural examination by Albrecht et al (1997, see also Taraschewski 2000. A shelled acanthor is enveloped by ®ve eggshells, and consists of three syncytial layers: frontal, central and epidermal.…”