Abstract
The position of brachiopods in the animal system remains controversial, with morphological data often being inconsistent with the results of molecular phylogenetic analysis. In this study, we investigated the structure of the spermatozoa and determined the combined sequences of the 18S and 28S rRNA genes of the articulate brachiopod Coptothyris adamsi (Davidson, 1871). The spermatozoa of C. adamsi are similar to those of other articulate brachiopods. Two types of sperm structure can be distinguished within Brachiopoda: the first type is characteristic of the articulate brachiopods (Rhynchonelliformea), the second type, the inarticulate brachiopods (Linguliformea and Craniiformea). Rhynchonelliformea spermatozoa are similar to those of the deuterostome animals, in particular to the sperm of the Echinodermata, whereas Linguliformea and Craniiformea spermatozoa are similar to the typical sperm of the Trochozoa, such as annelids and mollusks. Molecular phylogenetic analysis has shown that the brachiopods and phoronids form two monophyletic groups within the group Brachiozoa, where phoronids are united in a separate basal clade, while brachiopods are divided into two clades.
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