Acanthotretella spinosa

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A brachiopod covered in long, slender spines

Reconstruction of Acanthotretella spinosa.

Acanthotretella spinosa (GSC 134788). Specimen attached to the antenna of a disarticulated specimen (presumably a moult) of the arthropod Sidneyia inexpectans (close up to the right). Specimen length (shell only) = 8 mm. Specimen dry – polarized light (both images). Walcott Quarry.

Acanthotretella spinosa (ROM 57750) – Part and counterpart. Specimen showing the pedicle attached to the putative algae Dictyophycus. Specimen length (shell only) = at least 5 mm, incomplete. Specimen dry– polarized light. Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Brachiopoda

Higher Taxonomic assignment: Lingulata (Order: Siphonotretida, stem group brachiopods)

Species name: Acanthotretella spinosa

Remarks:

Acanthotretella spinosa is probably related to a primitive group of brachiopods of the Order Siphonotretida (Holmer and Caron, 2006).

Described by: Holmer and Caron

Description date: 2006

Etymology:

Acanthotretella – from the Greek akantha, “thorn,” and tretos, “perforated,” and the Latin diminutive ella, describing the small, perforated, spiny shell.

spinosa – from the Latin spinosus, referring to the exterior spines.

Type Specimens: Holotype –ROM57749 in the Royal Ontario Museum, Toronto, Canada.

Other species:

Burgess Shale and vicinity: none.

Other deposits: Acanthotretella decaius from the early Cambrian Guanshan fauna, China.

Age & Localities:

Age:

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

Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Specimens were first illustrated as Lingulella sp. by Jin, et al. (1993), and formally described as Acanthotretella spinosa by Holmer and Caron (2006). New characters preserved in a related species from China (Acanthotretella decaius, Zhifei et al., 2010) reinforce the probable position of this genus within the Order Siphonotretida.

Description:

Morphology:

The shell of Acanthotretella is mainly organic in composition with probably only minor organo-phosphatic mineralization, and is ventri-biconvex. Both valves are covered in long, slender spines that penetrate the shell and are posteriorly inclined, angled obliquely away from the anterior margin. A long, flexible pedicle emerges from an external tube that extends from the pedicle foramen along the ventral valve. The pedicle is at least three to four times the length of the valves. The visceral area of both valves is short and triangular, and does not extend to mid-valve. Other interior features are poorly known.

Abundance:

Most specimens come from the Walcott Quarry and represent one of the rarest brachiopods with less than 0.05% of the entire fauna (Caron and Jackson, 2008).

Maximum Size:

8 mm

Ecology:

Life habits: Epibenthic, Sessile

Feeding strategies: Suspension feeder

Ecological Interpretations:

The long, thin pedicle and overall shell shape probably preclude an infaunal habit. Pedicles of several specimens were found attached at the terminal bulb to organic structures, suggesting that Acanthotretella spinosa was epibenthic. The pedicle was likely able to maintain the shell in an upright position well above the sediment-water interface. Extraction of food particles from the water would have been possible thanks to a filter-feeding apparatus (located between the shells) called a lophophore.

References:

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

HU, S. X., Z. F. ZHANG, L. E. HOLMER AND C. B. SKOVSTED. 2010. Soft-part preservation in a linguliform brachiopod from the lower Cambrian Wulongqing Formation (Guanshan Fauna) of Yunnan, South China. Acta Palaeontologica Polonica, 55: 495-505.

HOLMER, L. E. AND J.-B. CARON. 2006. A spinose stem-group brachiopod with pedicle from the Middle Cambrian Burgess Shale. Acta Zoologica (Stockholm), 87: 273-290.

JIN, Y. G, X. G. HOU. AND H. Y. WANG. 1993. Lower Cambrian pediculate lingulids from Yunnan, China. Journal of Paleontology, 67: 788-798.