Huenellidae

Huenella cf. texana, from Holtedahl (1880).

Belongs within: Pentamerida.

The Huenellidae
Published 4 April 2022

Researchers who deal with the modern marine fauna are used to thinking of brachiopods as a marginal group, their diversity greatly overshadowed on a global scale by the superficially similar bivalves. However, modern brachiopods are but a shadow of their former selves; for much of the Palaeozoic era, their relationship with the bivalves was the inverse of today. Many are the brachiopod lineages that came and went over this time.

External views of ventral (left) and dorsal valves of Huenella triplicata, from Walcott (1924).

The Huenellidae were an assemblage of brachiopods that lived during the late Cambrian and early Ordovician (Amsden & Biernat 1965). They represent early representatives of the Pentamerida, a Palaeozoic order of fairly generalised-looking brachiopods. Within the Pentamerida, they fall within the suborder Syntrophiidina. Syntrophiidinans as a whole are rarely found in the fossil record and as a result remain poorly known. Members of the suborder share a distinctive shape with biconvex valves marked by a dorsal fold and ventral sulcus. That is, the midline of the shell is raised above either side with the ventral valve forming a ‘valley’ to match the raised ‘hill’ of the dorsal valve. What, if anything, was the purpose of this arrangement I wouldn’t know but modern brachiopods often inhabit locations with a lot of organic silt and/or fine sediment. Perhaps the uneven level of the syntrophiidinan shell helped protect it from burial by a shifting substrate.

Interior view of ventral valve of Radkeina taylori, from Laurie (1997), with scoop-shaped spondylium at upper midline.

Families of Syntrophiidina may be distinguished based on the development of the spondylium, an internal projection at the base of the ventral valve that provided an attachment site for the shell muscles. Members of the Huenellidae possessed either a sessile spondylium or a pseudospondylium, a spondylium-type structure rising from the internal surface of the valve itself rather than from the hinge. Amsden & Biernat (1965) recognised a division of the huenellids between two subfamilies based on the development of the brachiophore plates, projections on the inside of the dorsal valve that would have supported the lophophore. Members of the Huenellinae possessed more developed brachiophores than members of the Mesonomiinae. Outer ornament of the huenellid shell varied from more or less smooth with weak concentric ridges to costate with distinct radiating ridges.

Phylogenetic relationships within the Syntrophiidina do not seem to have been established in detail but the early appearance in the fossil record of huenellids at least raises the question of whether they included the ancestors of later families. As well as other families of the Syntrophiidina, candidates for descent would include members of the suborder Pentameridina as well as of the related order Rhynchonellida. This latter order includes species which survive to the present day so the possibility exists that while the huenellids themselves may be long gone, their legacy may yet live on.

Systematics of Huenellidae
<==HuenellidaeAB65
| i. s.: Rectotrophia globularis Bates 1968HB93
| Radkeina Laurie 1997L97
| `--*R. taylori Laurie 1997L97
|--MesonomiinaeAB65
| |--Glyptotrophia Ulrich & Cooper 1936AB65
| | |--*G. imbricata Ulrich & Cooper 1936AB65
| | `--G. rotunda Cooper 1952C52
| `--Mesonomia Ulrich & Cooper 1936AB65
| |--*M. iophon (Walcott 1924) [=Eoorthis iophon]AB65
| `--M. magna Cooper 1952C52
`--Huenellinae [Palaeostrophiinae]AB65
|--Huenellina Schuchert & Cooper 1931AB65
| `--*H. triplicata (Walcott 1924) [=Huenella triplicata]AB65
|--Palaeostrophia Ulrich & Cooper 1936AB65
| |--*P. orthia (Walcott 1905) [=Syntrophia orthia]AB65
| `--P. elax (Clark 1924) [=Syntrophia elax]C52
|--Plectotrophia Ulrich & Cooper 1936AB65
| |--*P. bridgei Ulrich & Cooper 1936AB65
| `--P. laticosta Cooper 1952C52
`--Huenella Walcott 1908AB65
|--*H. texana (Walcott 1905) [=Syntrophia texana]AB65
|--H. abnormis (Walcott 1912)HB93
|--H. icetas Walcott 1924L97
|--H. juba Walcott 1924L97
`--H. lesleyi Walcott 1908L97

*Type species of generic name indicated

References

[AB65] Amsden, T. W., & G. Biernat. 1965. Pentamerida. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt H. Brachiopoda vol. 2 pp. H523–H552. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas Press: Lawrence (Kansas).

[C52] Cooper, G. A. 1952. New and unusual species of brachiopods from the Arbuckle Group in Oklahoma. Smithsonian Miscellaneous Collections 117 (14): 1–35, 4 pls.

[HB93] Harper, D. A. T., C. H. C. Brunton, L. R. M. Cocks, P. Copper, E. N. Doyle, A. L. Jeffrey, E. F. Owen, M. A. Parkes, L. E. Popov & C. D. Prosser. 1993. Brachiopoda. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 427–462. Chapman & Hall: London.

[L97] Laurie, J. R. 1997. Silicified Late Cambrian brachiopods from the Georgina Basin, western Queensland. Alcheringa 21: 179–189.

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