The affinity of Thelxiope has not been considered in detail because the appendages are unknown.
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.
Burgess Shale and vicinity: none.
Other deposits: none.
The Walcott Quarry on Fossil Ridge.
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.
SIMONETTA, A. M. 1964. Osservazioni sugli arthropodi non trilobiti della “Burgess Shale” (Cambriano medio). Monitore Zoologico Italiano, 72 (3-4: III Contributo: I Generi Molaria, Habelia, Emeraldella, Parahabelia (Nov.) Emeraldoides (Nov.): 215-231.
SIMONETTA, A. M. AND L. DELLE CAVE. 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.
WALCOTT, C. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6):145-228.