endemic to a single state or province
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (<100 square km (less than about 40 square miles)) Pleurobema athearni is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al., 2006; Williams et al., 2008).
Length: 9.3 cm
From Gangloff et al. (2006):
Pleurobema athearni is typically more compressed and round in outline than Pleurobema georgianum. It is less elongate and more compressed than Pleurobema decisum and Pleurobema hanleyianum. Larger specimens of P. athearni may exhibit slight corrugations approximately parallel to the posterior ridge along the posterior-dorsal shell slope that are not found in P. georgianum and Fusconaia cerina. Additionally, the umbo cavity in P. athearni is typically intermediate in depth between that of P. georgianum (shallower) and F. cerina (deeper). Pleurobema athearni conglutinates are elongate and red to dark pink and similar in appearance to those of F. cerina. Pleurobema georgianum conglutinates are lighter and appear less elongate. Further, P. georgianum conglutinates appear to consist of a clear central core with glochidia encrusted on the outer surface, whereas those of P. athearni appear to be darker at their core with a lighter outer covering suggesting glochidia retained within the conglutinate. Historically it was misidentified as Fusconaia cerina, but it is the only Pleurobema with a deep umbo cavity (Williams et al., 2008).
Catalog Number: USNM 1078388
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Collector(s): M. Gangloff et al.
Year Collected: 2001
Locality: Big Canoe Creek, 1 KM downstream of St. Clair County Road 36, near mouth of Mukleroy Creek, St. Clair County, Alabama, United States
- Holotype: Gangloff, M., et al. 2006. A new species of freshwater mussel (Bivalvia: Unionidae), Pleurobema athearni, from the Coosa River Drainage of Alabama, USA. Zootaxa. 1118: 43-56.
Habitat Type: Freshwater
Comments: Pleurobema athearni is known only from the Big Canoe Creek watershed, a western tributary of the Coosa River, northeast Alabama (Gangloff et al., 2006). It occurs in shoal habitat in a medium to large Coosa River tributary and its preferred substrate is gravel (Williams et al., 2008).
Habitat and Ecology
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 1 - 20
Comments: Pleurobema athearni appears to be restricted to one small (<500 km2) watershed in a single creek in northeast Alabama in St. Clair Co. (Williams et al., 2008). Only 19 specimens are known (fewer than a half dozen sites) but only one-third of these were recent collections. Four specimens were found alive between 2000-2004. One gravid individual was found on 26 May 2004, indicating that P. athearni remains reproductively viable (Gangloff et al., 2006).
Life History and Behavior
Inner gills approximately 1.5 times larger in surface area than outer gills. No mature or developing glochidia observable in individuals collected in September and October, conglutinates present in late May, suggesting species tachytictic (i.e., short-term brooder). Conglutinates elongate, length 10-15 mm, width ~12 mm, red or dark pink (Gangloff et al., 2006). The glochidial host is not known.
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: This recently described species has an extremely limited distribution and range with few recently collected specimens; and habitat degradation is a continuing threat. Although declining, the extent of the decline is not known because the species is known from fewer than two dozen specimens, only one-third of which are recent.
Intrinsic Vulnerability: Unknown
Comments: newly described
Environmental Specificity: Unknown
Comments: newly described
IUCN Red List Assessment
Red List Category
Red List Criteria
Global Short Term Trend: Decline of 10-30%
Comments: Newly described but only known from 19 specimens, and only one-third of these are recent collections (Gangloff et al., 2006).
Global Long Term Trend: Unknown
Comments: newly described
Degree of Threat: Very high - high
Comments: From Gangloff et al. (2006), below, it appears habitat loss/modification is the greatest threat:
The Coosa River ecosystem has been reduced to a number of highly fragmented tributary refugia. Only five tributary sub-basins were found to have mollusk speciesrichness levels that approach historic reports (Gangloff 2003). These watersheds, along with tributaries of the Black Warrior, Tombigbee, Cahaba and Conasauga drainages, represent most of what remains of a unique and species-rich aquatic ecosystem (Williams et al. 1992; Lydeard and Mayden 1995; McGregor et al. 2000). Protection of these few remaining fragments is critical to preserving populations of mussels and other aquatic species in the Mobile Basin (USFWS 1989; 2000).
Biological Research Needs: Life history virtually unknown; recently described.
Global Protection: None. No occurrences appropriately protected and managed
Needs: Because of its rarity, this species may qualify for endangered status under the Endangered Species Act.
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