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Thelxiope palaeothalassia

A rare spiny arthropod

Image of Thelxiope palaeothalassia.

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Thelxiope palaeothalassia (GSC 74990). Articulated specimen (close up to the right), associated with several individuals of the arthropod Canadaspis perfecta. Specimen length = 29 mm. Specimen dry – polarized light. Walcott Quarry.

© Geological Survey of Canada. Photos: Jean-Bernard Caron

Media 1 of 2 for Thelxiope palaeothalassia Photo
Media 2 of 2 for Thelxiope palaeothalassia Photo







Unranked clade (stem group arthropods)


The affinity of Thelxiope has not been considered in detail because the appendages are unknown.

Species name:

Thelxiope palaeothalassia

Described by:

Simonetta and Delle Cave

Description date:



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.

Type Specimens:

Holotype –USNM144914 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

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Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

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Principal localities:

The Walcott Quarry on Fossil Ridge.

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History of Research

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.

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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.

Maximum size:

43 mm

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Life habits:

Nektobenthic?, mobile

Feeding strategies:


Ecological Interpretations:

Thelxiope is too poorly known to allow detailed studies of its ecology.

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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.

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