Nerve cells of Xenoturbella bocki (phylum uncertain) and Harrimania kupfferi (Enteropneusta) are positively immunoreactive to antibodies raised against echinoderm neuropeptides

Abstract

The phylogenetic position of Xenoturbella spp. has been uncertain since their discovery in 1949. It has been recently suggested that they could be related to Ambulacraria within Deuterostomia. Ambulacraria is a taxon that has been suggested to consist of Hemichordata and Echinodermata. The hypothesis that X. bocki was related to Ambulacraria as well as the hypothesis of a monophyletic Ambulacraria is primarily based on the analysis of DNA sequence data. We tested both phylogenetic hypotheses using antibodies raised against SALMFamide 1 and 2 (S1, S2), neuropeptides isolated from echinoderms, on X. bocki and the enteropneust Harrimania kupfferi. Both species showed distinct positive immunoreactivity against S1 and S2. This finding supports the Ambulacraria-hypothesis and suggests a close phylogenetic relationship of X. bocki to Ambulacraria. In particular, the presence of immunoreactivity against S2 can be interpreted as a synapomorphy of Enteropneusta, Echinodermata, and Xenoturbella spp.

The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis

“…Instead, Xenoturbella was variably grouped to enteropneusts or holothurians (Reisinger, 1960), to bryozoans (Zrzavy et al, 1998), and to molluscs (Israelsson, 1997(Israelsson, , 1999. The immunoreactivity of X. bocki nerve cells to antibodies raised against echinoderm neuropeptides suggested a close phylogenetic relationship to Ambulacraria (Stach et al, 2005). Other authors advocated a basal position within the metazoa (Jägersten, 1959;Ehlers and Sopott-Ehlers, 1997a;Raikova et al, 2000).…”

After all: Xenoturbella is an acoelomorph!

“…There has been confusion about the nature of the developmental stages found inside Xenoturbella , and it seems most safe to state that its embryology is presently unknown. Only some TEM studies of the extracellular matrix (Pedersen and Pedersen 1986) and immune reactions of the nervous system (Stach et al 2005) hint to a closer relationship to enteropneusts. A formal cladistic analysis of morphological characters (Haszprunar 1996) placed Xenoturbella with the acoelomorphs.…”

PCR survey of Xenoturbella bocki Hox genes

“…The simple body plan, the diffuse nerve net without centralization and the unusual morphology, with an epithelial epidermis and gastrodermis, but without anus and only a ''statocyst'' as distinct organ (Ehlers,'91), led to highly divergent phylogenetic interpretations. All available molecular data, namely authentic nuclear SSU rDNA sequences (Bourlat et al, 2003), mitochondrial proteincoding gene sequences (Israelsson and Budd, 2005;Bourlat et al, 2006;Perseke et al, 2007), expressed sequencing tags (Bourlat et al, 2006) and immunohistochemical evidence (Stach et al, 2005;Israelsson, 2006) place Xenoturbella in a basal position among the Deuterostomia, albeit so far an even more basal position among the Bilateria cannot be ruled out with certainty (Perseke et al, 2007).…”