Vertigo rowellii

Vertigo (Staurodon) rowellii (Newcomb, 1862)
Threaded Vertigo

  • Pupa rowellii Newcomb 1862: 146.
  • “Hoko Vertigo” of authors.
Vertigo rowellii.

Identification. Vertigo rowellii is readily distinguished from all other Vertigo species likely to be found in coastal forests by the combination of its relatively large size, expanded palatal lip, and shell sculpture. No other Vertigo species in BC are so strongly arboreal.

In the area near the Sooke Basin, specimens with the palatal lamellae fused and enlarged are not uncommon. These appear to be the same as the “Hoko Vertigo” (an informal name for a taxon believed to be a new species; see Burke 2012). However, Nekola et al. (2018) treated this form as within the variation of V. rowellii.

Habitat. Mostly on the trunks of bigleaf maples (Acer macrophyllum Pursch), up to at least 2 m above the ground, both in crevices of the bark and in moss, but also fully exposed on smooth, bare bark such as on younger trees. Less commonly on other tree and shrub species and occasionally in leaf litter. All known occurrences in BC are not far from the ocean and below 200 m (COSEWIC 2010).

Global range. Coastal British Columbia south to Monterey County, California (COSEWIC 2010, Roth and Sadeghian 2003).

Canadian range. Southwestern British Columbia: around the Georgia Depression (east and south coasts of Vancouver Island, the Gulf Islands, the Sunshine Coast, and Keats Island, Howe Sound; on the south coast of Vancouver Island at least to the Sooke area (COSEWIC 2010, https://www.inaturalist.org/observations/10280030). Cameron (1986) first reported this species from BC, although specimens collected many years earlier exist in museum collections.

Etymology. Named for the Reverend Joseph Rowell (1820–1918), Californian naturalist and conchologist (Coan 1889).

Remarks. See comments for the subgenus Staurodon.

The species name is often spelled rowelli, but according to the ICZN (1999), the original spelling Rowellii should be emended to rowellii (Article 32.5.2.5), but the -ii termination must not be changed to a single-i (Article 33.4). For two decades, following Turgeon et al. (1998), this species had been thought to require a new name; however, this was in error and V. rowellii is the valid name for the taxon (Nekola et al. 2018).

Along the Strait of Juan de Fuca on Vancouver Island, the strange, informally named “Hoko Vertigo” occurs together with the typical form on the same tree trunks. The form was first recognized from the Olympic Peninsula in Washington, USA, and was thought to be a putative unnamed species (Burke 2013). However, Nekola et al. (2018) treated Hoko Vertigo as a synonym of V. rowellii, noting that the two shared identical habitat requirements and that the lamellae development is within the range of variation seen in other species of west coast Staurodon.