The Burgess Shale

Spartobranchus tenuis

A tiny worm living in a tube

Spartobranchus tenuis, ROMIP 65137


Kingdom: Animalia
Phylum: Hemichordata
Higher Taxonomic assignment: Enteropneusta
Species name: Spartobranchus tenuis

Spartobranchus is considered a stem-group enteropneust (acorn worm), and shares many similarities with modern acorn worms (Caron et al. 2013; Nanglu et al. 2020). It shows the tripartite body characteristic of this group, consisting of an acorn-shaped proboscis, cylindrical collar, and elongate trunk.

Described by: Walcott
Description date: 1911 (redescribed in 2013)

Spartobranchus — from the Greek “sparte,” for cord or rope (made from the Spartium shrub), and “brankhia” for gills.

tenuis — from the Latin, meaning thin or delicate.

Type Specimens: USNM 108494; Paralectotype – USNM 553526.
Other species:

Burgess Shale and vicinity: None
Other deposits: None

Age & Localities:

Middle Cambrian, Wuliuan stage, Burgess Shale Formation (around 507 million years old).
Principal localities:

Walcott Quarry

History of Research:

Brief history of research:

Spartobranchus tenuis was first reported by Walcott in 1911 as a priapulid worm named Ottoia tenuis. It was removed from the genus Ottoia by Conway Morris in 1979, and formally redescribed as Spartobranchus tenuis, an acorn worm, by Caron et al. in 2013.



Spartobanchus is a small worm with a maximum length of 10 cm. The three major components of its body are a proboscis, a collar, and a long, thin section called the trunk. The proboscis is oval or “acorn” shaped, hence the common name of the group: acorn worms. The trunk is a relatively short cylindrical section behind the proboscis. The trunk comprises roughly 90%-95% of the total body length of the animal. The entire body is highly flexible, with the trunk often being recurved onto itself. The anterior part of the trunk is known as the pharynx. Inside the pharynx are presumably collagenous bars known as gill bars, which give the pharynx a strongly striated appearance. The posterior part of the trunk is where the gut is located and is relatively featureless. It is often preserved darkly compared to the rest of the body. At the most posterior end of the trunk is a bulbous structure, which may have served as an anchor for the animal. Roughly one quarter of Spartobranchus specimens are found associated with fibrous, collagenous tubes that the worms produced. These tubes have a corrugated appearance, and can take many forms including: straight tubes, forked, spiral, and circular.


More than 9000 specimens, making it one of the most abundant species in the Walcott Quarry.

Maximum Size:
About 10 cm.


Life habits: Endobenthic, Epibenthic
Feeding strategies: Deposit feeder
Ecological Interpretations:

Spartobranchus was likely a deposit feeder, as this is the most common mode of life of extant acorn worms that are morphologically highly similar. The presence of a pre-oral ciliary organ on the proboscis also suggests that food particles were transported from the proboscis to the mouth. It may have also been able to filter feed, given the ability of some burrowing hemichordates to draw in food from interstitial water. The tubes Spartobranchus is associated with would have served as a protective dwelling and were secreted by the proboscis. These worms shared this trait with their close relatives, the graptolites. Some large tubes from the Raymond Quarry (located roughly 20m above the Walcott Quarry) appear to also contain undescribed acorn worms similar in morphology to Spartobranchus (Nanglu and Caron 2021). These tubes also possessed polychaetes, suggesting a symbiotic relationship between these worms.


  • CARON, J.-B., CONWAY MORRIS, S., AND C. B. CAMERON. 2013. Tubicolous enteropneusts from the Cambrian period. Nature 495: 503-506
  • CONWAY MORRIS, S. 1979. The Burgess Shale (Middle Cambrian) fauna. Annual Review of Ecology, Evolution, and Systematics 10: 327–349.
  • NANGLU, K. AND J.-B. CARON. 2021. Symbiosis in the Cambrian: enteropneust tubes from the Burgess Shale co-inhabited by commensal polychaetes. Proceedings of the Royal Society B 288 (1951): 20210061.
  • NANGLU, K., J.-B. CARON, AND C. B. CAMERON. 2020. Cambrian tentaculate worms and the origin of the hemichordate body plan. Current Biology 30 (21): 4238-4244
  • WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109-145.
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