The immunoglobulin (Ig) level in serum from Atlantic cod, Gudus morhua L. (Teleostomi, Gadiformes), was measured using ELISA. Cod serum contains 5.62k0.19 mg Igml I , which constitute 17.2% of the total serum proteins.Polyclonal and monoclonal antibodies (Ab) against cod-Ig were used for cross-reactivity studies in sera from other species. The cross-reaction with polyclonal Ab was high in gadifom fish, and low or absent in the other tested species. Immunoprecipitation showed that the Ab only binds to the Ig of the serum from the other species. The results within the gadiform group indicate that (1) Gadidae and Lotidae are more closely related to each other than to Merluccidae, (2) Phycidae is more distant related to Lotidae than earlier considered, (3) Zoarcidae seem to be more distant related to Gadus than other species of Gadiformes. These results support recent revisions of the systematics of Gadiformes.Monoclonal Ab against the heavy chain of cod-Ig show no, or small (< 15%) cross-reactions with serum from gadiform species. One monoclonal Ab against the light chain shows high crossreaction and also binds to Ig from species outside the Gadiformes, indicating that the light chain of Ig might be more conserved than the heavy chain.

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.