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18 December 2017
Scientists discover mysterious marine worm without an anus
Researchers in Japan have discovered a bizarre new species of worm that could shed light on the origin of complex structures inside animals’ bodies. The strange pale-orange creature dwells on the floor of the western Pacific Ocean, and lacks a number of features – including an anus. Scientists say the species comes from a group of worms that holds a ‘controversial’ place in the tree of life, as a sister group of that which contains most complex animals.
These creatures dwell hundreds or thousands of meters beneath the surface, making them difficult to study. But, the researchers say the latest discovery could now offer a solution. Xenoturbella japonica was found in the western Pacific, in a region easily accessible from marine stations.
From the University of Tsukuba in Japan:
Mysterious new seafloor species sheds light on early animal evolution
December 18, 2017
Summary: Researchers have described a new species of the enigmatic marine worm Xenoturbella, named Xenoturbella japonica. Two specimens of this new species were dredged from the seafloor of the western Pacific. These primitive worms, lacking a centralized nervous system, kidneys, and anus, are important for understanding the early evolution of the Bilateria. MicroCT scanning revealed previously unknown structures, and molecular genomic analysis suggested that features of this species may be ancestral to Xenoturbella. This newly identified species is promising for further research on early bilaterian evolution.
Japanese researchers have discovered a new species of the enigmatic marine worm Xenoturbella, which they have named Xenoturbella japonica, as reported in a new study published in BMC Evolutionary Biology.
Xenoturbella lacks certain features common among more complex animals, such as a centralized nervous system, kidneys, and an anus (i.e., its digestive system has only one opening). Thus, these primitive worms are important for understanding the origins of these structures. The classification of Xenoturbella in the tree of life has been controversial, but it is generally regarded as a basal member or sister group of the Bilateria, a group that includes most complex animals.
The researchers, centered at the University of Tsukuba, described two specimens of X. japonica dredged from the seafloor of the western Pacific: a female about 5 cm in length, and a juvenile about 1 cm in length. Both specimens are pale orange in color, with an oval-shaped mouth and a glandular network on the ventral (bottom) surface.
MicroCT scanning, a method not previously applied to Xenoturbella, revealed the specimens’ internal structures, and a new feature not visible using conventional methods: the frontal pore.
“We also extracted DNA and sequenced the mitochondrial genome and partial Histone H3 gene sequences,” co-author Hideyuki Miyazawa explains.
“Molecular phylogenetic analysis confirmed that X. japonica is distinct from previously described species of Xenoturbella.” DNA contamination from several species of bivalve was also detected, which indicates that, like other species of Xenoturbella, X. japonica likely feeds on marine bivalves.
“Species within this genus have previously been divided into ‘shallow’ and ‘deep’ subgroups, and our results place X. japonica in the ‘shallow’ subgroup,” lead author Hiroaki Nakano says. “Interestingly, X. japonica shares features with both subgroups, however. Thus, features of this species may be ancestral for this genus, and this new species may be particularly important for unraveling the ancestry of Xenoturbella and the early history of the Bilateria.”
Research on Xenoturbella has been limited by the inaccessibility of specimens in their seafloor habitats hundreds or thousands of meters below the surface. This new discovery may offer a solution. As co-author Hisanori Kohtsuka explains, “because one habitat where X. japonica was found is easily accessible from a marine station, this new species promises to be valuable for future research on bilaterian and deuterostome evolution.”
The longest animal in the world, the bootlace worm, which can be up to 55 meters long, produces neurotoxins that can kill both crabs and cockroaches. The toxins could be used in agricultural insecticides, among other things: here.