Structure of the nervous system of Myzostoma cirriferum (Annelida) as revealed by immunohistochemistry and cLSM analyses

Abstract

The nervous systems of juvenile and adult Myzostoma cirriferum Leuckart, 1836, were stained with antisera against 5-HT (5-hydroxytryptamine, serotonin), FMRFamide, and acetylated ␣-tubulin in combination with the indirect fluorescence technique and analyzed by confocal laser scanning microscopy. The central nervous system consists of two small cerebral ganglia, connected by a dorsal commissure, a ventral nerve mass, and a pair of long circumesophageal connectives joining the former to the latter. The two neuropil cords within the ventral nerve mass curve outward and are joined to one another anteriorly and posteriorly. They are connected by 12 commissures, forming a ladder-like system. A single median nerve runs along the midventral axis. In addition to the circumesophageal connectives, 11 peripheral nerves arise from each main cord. The first innervates the anterior body region. The others form five groups of two nerves each, the first and thicker nerve of which is the parapodial nerve, innervating the parapodium and two corresponding cirri. Except for those in the most posterior group, the second nerves innervate the lateral organs and the body periphery. Serotonergic perikarya are arranged in six more or less distinct clusters, the first lying in front of and the other five between the main nerve cords. The distribution pattern of the FMRFamidergic perikarya is less clear and the somata lie between and outside the cords. One pair of dorsolateral longitudinal nerves was visualized by tubulin staining. Peripheral nerves and the commissures, in particular, demonstrate a segmental organization of the nervous system of M. cirriferum. Furthermore, their arrangement indicates that the body consists of six segments, the first of which is identifiable only by the first pair of peripheral nerves, the first two commissures, and the anteriormost ventral ganglion. The nervous system M. cirriferum thus exhibits several structures also found in the basic plan of the polychaete nervous system.

The interrelationships of metazoan parasites: a review of phylum- and higher-level hypotheses from recent morphological and molecular phylogenetic analyses

“…In conclusion, myzostomes are platyzoans that exhibit a complicated mixture of annelid-like (Rouse andFauchald 1997a, b, Müller andWestheide 2000), basal spiralian (Haszprunar 1996b, Zrzavý et al 1998), and platyzoan/prosomastigozoan (Mattei and Marchand 1987, 1988, Eeckhaut et al 2000, Zrzavý et al 2001 characters, as well as unique features possibly linked with their parasitic lifestyle. These results suggest that major body-plan characters (segmentation, parapodia) might have been independently lost or gained in different animal phyla (see Eeckhaut et al 2000).…”

“…The characters supporting annelid origin of the myzostomes (Nielsen 1995, Rouse and Fauchald 19951997a, b, Rouse 1999, Müller and Westheide 2000 are usually either symplesiomorphic (e.g., spiral cleavage, trochophora-like larva, multiciliary epithelial cells) or convergent (e.g., annelid-like chaetae are present in most annelids, myzostomes, echiurids, and some brachiopods, in the ectoproct gizzard armature, and in the cephalopod Kölliker organs; see Lüter andBartolomaeus 1997, Lüter 2000). Myzostomes possess metameric paired organs like protonephridia and parapodia (five pairs), but numbers of so-called "lateral organs" (of uncertain homology), of marginal cirri, and of gut diverticles do not accord with the protonephridial and parapodial numbers.…”

“…Myzostomes lack epithelial organisation of the musculature, metanephridia, a circulatory system, a true coelom and the eucoelomic anatomy of the gonads (Haszprunar 1996b). The only myzostomid body system which exhibits obvious segmentation traits is their polychaete-like nervous system indicating that the body of Myzostoma is formed by six segments (Müller and Westheide 2000). Importantly, cladistic analysis of the morphology of polychaete families (Rouse and Fauchald 1997a) placed myzostomes either amongst polychaetes with a hypertrophied eversible axial pharynx (Phyllodocida), or, together with spongeparasitic spintherids, at the base of their annelid tree.…”

Metameric organisation of the nervous system in developmental stages of Urechis caupo (Echiura) and its phylogenetic implications

“…Immunohistochemical methods and confocal laserscanning microscopy were used to study the development of the nervous system in B. viridis (Hessling 2001(Hessling , 2002Hessling and Westheide 2002). This combination of methods has proven to be very informative in the study of neurogenesis and in many cases has revealed previously unreported details in neuronal structures of various invertebrate taxa (see, for example, Harzsch et al 1997;Müller and Westheide 2000). The present study is the first application of these techniques in a species of Echiura with planktotrophic larval development.…”

The plastic nervous system of Nemertodermatida

“…immunoreactivity is known to be widespread in protostome stomatogastric NS, e.g. in Gnathostomulida (Müller and Sterrer 2004), Annelida (Müller and Westheide 2000; and catenulid and rhabditophoran flatworms (Reuter and Halton 2001;Reuter et al 2001a;Kotikova et al 2002), and it is present also in post-metamorphic cnidarians (Grimmelikhuijzen 1983a(Grimmelikhuijzen , 1938b. Both 5-HT-and FMRFamide immunoreactivity was detected in the gut of tornaria larvae of enteropneusts (Nezlin and Yushin 2004), while it is absent in cnidarian, polyclad and lophotrochozoan larvae (Ruppert 1978;Hay-Schmidt 1995;Dickinson et al 1999;Hessling 2002;Voronezhskaya et al 2002;Wanninger and Haszprunar 2003).…”