Two small groups of tiny marine parasites are listed in Table 30.1 but are not depicted in the phylogeny in Figure 30.1: the orthonectids and the rhombozoans. Recent genomic analyses suggest that these groups may be among the closest surviving relatives of the bilaterians, although their exact phylogenetic placement is uncertain. Both groups are highly reduced parasites that lack many of the structures that traditionally have been used to study animal relationships. As their genomes become more completely known, the relationships of these two groups to other animals should become clearer. Two other small groups (also listed in Table 30.1 but not shown in Figure 30.1) have been proposed as also falling just outside the bilaterians: the xenoturbellids and acoels. Some genomic analyses, however, suggest that these animals are actually highly specialized deuterostomes.