Unranked clade (stem group arthropods)
The affinity of Thelxiope has not been considered in detail because the appendages are unknown.
Simonetta and Delle Cave
Thelxiope – from the Greek thelx meaning “enchanting,” and ops, meaning “voice,” referring to the muse-like appearance of the animal.
palaeothalassia – from the Greek palaios, meaning “ancient,” and thalassios, meaning “marine,” in reference to the age and environment where the animal lived.
Holotype –USNM144914 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott Quarry on Fossil Ridge.
Brief history of research:
Walcott (1912) figured two fragmentary specimens as Mollisonia? rara; these were first reinterpreted by Simonetta (1964) within a new genus Parahabelia rara, along with three additional specimens that he thought were related. However, Simonetta and Delle Cave (1975) considered that among those five specimens, the two originally figured by Walcott as M? rara had to be synonymized with M. symmetrica and the other three had to be placed within a new genus and species called Thelxiope palaeothalassia, a name in use since then.
This species has a relatively wide cephalon and seven segments and resembles Habelia in overall shape. However, in T. palaeothalassia, each segment bears a single prominent spine pointing dorsally. The last segment is armed with a very long pointed telson.
Thelxiope is extremely rare, with only four known specimens.
Thelxiope is too poorly known to allow detailed studies of its ecology.