Quadrula fragosa

Shell subcircular to pentagonal, solid, inflated; anterior end broadly rounded from dorsum to terminus of medial ridge; ventral margin between termini of medial and posterior ridges concave; posterio-ventral junction bluntly biangulate; posterior margin truncated, may be a slight concavity above the posterio-ventral biangulation; dorsal margin generally straight, concave lunule before beak; beak subcentral, elevated, relatively narrow, inclined anteriorly, sculpted by fine irregularly arched ridges and pustules; anterior third of shell surface generally lacks pustules, termini of annual growth increments elevated; maximum shell inflation along a medial ridge, sculpted by a narrow row of medium-sized pustules; medial and posterior ridges separated by a narrow sulcus; posterior ridge relatively low, bluntly angular, sculpted by a single row of prominent, widely spaced pustules; posterior slope concave, broad, expanded into moderately-developed wing, transversed by relatively heavy costations curved posterio-dorsally, a faint radial ridge and sulcus posterior to posterior ridge; periostracum with a cloth-like texture, greenish to brown, occasionly with wide, indistinct green rays. Pseudocardinal teeth heavy, serrated, triangular, double in left valve, single in right but with lamellar denticle adjacent to contiguous sulci; interdentum short, moderately wide; lateral teeth rather lamellar, roughened with striations, double in left valve, single in right but accessary lamella may develop ventrally; anterior muscle scars distinct, rather small, impressed, smooth; pallial line impressed, lighter posteriorly; posterior muscle scars lightly impressed, confluent; beak cavaties deep, compressed; nacre white, somewhat iridescent posteriorly.

This species is quite similar to and has often been confused with Quadrula quadrula. In outline, Q. fragosa more resembles the shape of Q. nodulata. With respect to Q. quadrula, Q. fragosa is more rounded and pentagonal in outline, the medial sulcus is narrower and more centrally positioned, the beak is narrower and appears more elevated, beak sculpture is finer and less developed, and the posterior slope is broader and more alate. The costations across the posterior slope are relatively thick, fairly smooth, and well-separated. In Q. quadrula, costations are more closely packed and tend to be composed of small pustules. Additionally, Q. quadrula is more quadrate in appearance, tends to be posteriorly elongated, has a yellowish and shiny periostracum, and may be highly rayed. Height: 84mm.

This species appears to have inhabited medium-sized and large rivers. Baker (1928) lists its habitat as "mud bottom in water 2m or more in depth". Locality records indicate that it also inhabited riffle areas with substantially shallower water depths and substrates ranging from sand and gravel to mixture including some cobble and boulder sized particles. The remnant population in the St. Croix River is found in riffles with clean gravel, sand, or rubble substrates and in clear water of high water quality but this may not reflect ideal habitat (USFWS, 1997). Information on substrate, flow, current, sediment, temperature, oxygen, alkalinity, nitrogen, phosphorus, conductivity, and toxics in the St. Croix River can be found in USFWS (1997).

Other than what was listed by Baker (1928) and the above speculation on habitat, nothing is known of this species.

Heath et al. (2000) observed winged mapleleaf in the St. Croix River for 3 years before they described it as a late season, short-term (~5 weeks) brooder that typically released its glochidia as water temperature decreased to ~15 C in early autumn. Most other Quadrula species are reported to brood and release glochidia over longer periods during spring and summer (Oesch, 1995; Heath et al., 2000). Steingraeber et al. (2007) provided evidence for a thermal cue (17-20 C) that presumably is needed to trigger peak juvenile excystment with glochidial metamorphosis time ranging from 28 to 37 d at constant 19C, 70 d in varied 12-19C, and 260-262 d in simulated natural thermal 0-21C. Therefore, the winged mapleleaf may be a host overwintering mussel (Watters and O'Dee, 2000) throughout much of its range. The channel catfish, Ictalurus punctatus, may be a suitable glochidial host (Hove et. al., 2000; 2001). Recently, channel catfish, Ictalurus punctatus, has been confirmed as the host fish for this species (Schwebach et al., 2003). Steingraeber et al. (2004; 2007) have confirmed blue catfish (Ictalurus furcatus) and channel catfish (Ictalurus punctatus) as suitable fish hosts, but blue catfish are a more prolific host. Oetker et al. (2005) also successfully reared this species on channel catfish.