Choia carteri

Overview

Choia carteri is a sponge with spicules radiating from a flat oval disc. Fine central structures are distinguished from thicker, longer outer spicules. The arrangement spreading outward from a small disc is striking.^[1]

Key facts

The long outer spicules connect to the central disc. Looking separately at the center and outside reveals differences between fine and thick structures. The connection between a large disc and small hard parts survives as evidence of the same body.^[1]

Time and place

The lectotype USNM 66482 and complete specimen USNM 200634 of Choia carteri are material from the Walcott Quarry. This is on Fossil Ridge in present-day British Columbia, Canada. The Cambrian as a whole was roughly 540–490 million years ago.^{[1][2][3][4][5]}

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The central disc is a flat oval, with radial spicules extending beyond the body. Fine radial structures in the center are distinguished from longer, thicker outer spicules. You can examine how the construction changes from center to edge.^[1]

The museum account gives a diameter of up to about 5cm including the long spicules. The central disc itself is described as reaching 2cm in diameter.^[6]

Habitat and reproduction

Which side of a flattened fossil faced upward in life? In 2025, researchers proposed that the concave side of Choia may have faced up. This interpretation seeks the body’s three-dimensional orientation from clues in flat fossils.^[2]

Fossil discovery

Institutional species descriptions and the 2025 study convey the connection between the disc and spicules. Later research discussed not only form but also the body’s orientation. The same outline led to a broader set of questions.^[1][2]

References

1. The Burgess Shale: Choia carteri
2. 2025 study — Morphology and classification of Choia
3. International Commission on Stratigraphy (2024) — Geological time chart
4. Royal Ontario Museum — The Burgess Shale locality today
5. Royal Ontario Museum — Waptia fieldensis
6. Royal Ontario Museum — Choia carteri
7. The Burgess Shale: Eiffelia globosa

Research questions

Why compare the fine central structures with the long outer spicules? It helps reveal how different parts of the body connect. A radial outline grasped at a glance can be reread as a combination of several structures.^[1]

Observation

Follow the long spicules outward from the center of the oval disc. Alternating between the fine central structures and thick outer spicules reveals several features of the radial body.^[1]