Comprehensive Description
provided by Smithsonian Contributions to Zoology
Alasmidonta (Decurambis) varicosa (Lamarck, 1819)
Unio varicosa Lamarck, 1819:78–79. [Type-locality: “la riviere de Schuglkill, pres de Philadelphie…aussi dans le lac Champlain.” Holotype in Geneva Museum, Geneva, Switzerland (Johnson, 1953:95).]
Alasmodon corrugata DeKay, 1843:198, pl. 24: 259. [Type-locality: Passaic River. Type material not in Museum of Comparative Zoology (Johnson, 1956) and probably lost.]
THE SHELL
DESCRIPTION.—Shell kidney-shaped, up to 70 mm long, 40 mm high, and 30 mm wide, thin-shelled, slightly thickened anteriorly (up to 2 mm thick) but approximately equally strong throughout. Anterior margin abruptly curved, ventral margin long and a little concave centrally, posterior margin roundly biangulate below and obliquely flattened or flatly curved above, and dorsal margin long and gently convex. Maximum inflation at the posterior ridge near the center of the shell. Beaks narrow and bluntly pointed, located about 1/4 the distance from anterior to posterior, and barely projecting above the hinge line. Posterior ridge conspicuous, broad, inflated, and rounded. Posterior slope flattened, and somewhat concave. Growth increments marked by concentric ridges and grooves, especially anteriorly. Additional post-juvenile sculpturing consisting of numerous, short, low, poorly-developed corrugations on the posterior slope and at right angle to the lines of growth. The posterior slope corrugations may be virtually absent, principally adapical, generally distributed, or arranged in transverse bands just within lines that apparently mark previous annual growth rests. Periostracum smooth centrally but roughened elsewhere, yellowish and partly or wholly covered by greenish rays in juveniles, brownish and with rays partially obscured in adults. Ligament moderate in length, rather thick, strong, and in longitudinal section clearly exhibiting numerous annual growth rests.
Hinge teeth poorly developed, variable, and incomplete. Pseudocardinal teeth rather small, rounded, and variously developed or rudimentary, 1 in the right valve and 1 in the left. In some specimens the left valve also bears a vestigial tooth anterior to the major denticle. Interdental projection clearly defined or indicated only by a swelling, which may be barely perceptible, in one or both valves. Lateral teeth vestigial or entirely lacking.
Beak cavity excavated but shallow. Anterior muscle scars impressed, pallial line well marked, especially anteriorly, posterior muscle scars shallow but well-defined, and scars within beak cavity consisting of a few short, low, irregular ridges and grooves behind the hinge plate and subparallel with it, and two shallow, radial grooves directed anterior-ventrally and posterior-ventrally. Nacre glossy, bluish white anteriorly, bluish posteriorly, and yellowish tan olive, or pinkish centrally and in the beak cavity.
Beak sculpture coarse, variable, and composed of a few single-looped or double-looped ridges. The ridges are rarely preserved, however, except in very young individuals.
TOPOGRAPHIC ANATOMY
SPECIMEN DESCRIBED.—From Rocky River, 11 mi (17.6 km) N of Sanford, U.S. Hwy. 15 bridge, Chatham Co., N.C., collected 22 June 1978 (USNM 794929, A. H. Clarke Station 1583); anaesthetized with nembutol, fixed in 10% formalin, preserved in 70% ethyl alcohol; shell length 57.0 mm, sex male (inferred).
DESCRIPTION.—Mantle grayish white, translucent, and with color of the branchiae showing through. A broken band of mostly widely-separated, brown, rectangular pigment spots occurs along the mantle edge from the mid-ventral area posteriorly and dorsally to near the posterior end of the ligament. The pigmented band is separated from the posterior mantle openings by a lip. The incurrent opening is 11 mm long and with groups of small papillae, pale gray and orange-brown in color, 2 or 3 rows deep, just within the opening. The central portion (4 mm long) is without papillae. The separation of incurrent and anal openings appear to be achieved by the diaphragm entirely, without appression of mantle edges. The anal opening has smooth but irregular edges, without papillae, and is 8 mm long. The mantle edges between the anal and supra-anal openings are not connected but are simply appressed during life; this area is 5 mm long. The supra-anal opening is slit-like, without papillae, and also 5 mm long.
Demibranchs of preserved specimen pale brown. Outer demibranch 36 mm long, 12 mm high, with anterior portion narrowed and subtruncate, ventral and posterior margins broadly but irregularly rounded, with broad radial wrinkles throughout, and with about 1.0 water tube per mm. Inner demibranch about 40 mm long and 15 mm high, anterior portion broad and truncated, ventral margin more or less evenly convex, and posterior margin sharply rounded; all margins extend beyond the outer demibranch and especially so (5 mm beyond) near the labial palps. Broad radial wrinkles also cover the surface of the inner demibranchs and there is also about 1.0 water tube per mm. Gravid specimens were not seen. The inner lamina of the inner demibranch is completely attached to the visceral mass.
Labial palps pale brown (paler than the demibranchs), wide and hemilunate, broadly curved below and meeting the flattened upper margin in a rounded point, with outer surfaces smooth and lower portion of inner surfaces radially furrowed (about 6 furrows per mm at margin). Each palpus is fused to its corresponding member at its base, but not along its dorsal margin.
VARIATION.—Table 19 indicates that normal anatomical variation occurs in A. varicosa. A-SA tends to be longer in this species than in A. marginata and the incurrent and anal openings are also longer; in fact in all of these features A. varicosa resembles A. undulata. As in A. undulata a geographic trend is also suggested in regard to the position of the labial palpi; in the northern population the palpi do not touch the inner demibranchs but in the southern populations the palpi tend to touch or overlap these demibranchs.
As in A. marginata, the inner lamina of the inner demibranch was fully connected with the visceral mass in all of the specimens examined.
GLOCHIDIA
Glochidia have not been available for study. According to Ortmann (1919:191) they are identical to those of A. marginata.
LIFE HISTORY
The period of gravidity for A. varicosa spans the interval from August 9 to May 3 in Pennsylvania (Ortmann, 1919:191). A specimen from Rocky River near Sanford, North Carolina, collected on 22 June 1978 had stretched but empty marsupial demibranchs. The host fish is unknown.
“As in A. marginata, A. varicosa is usually found in rapids or riffles on rock and gravel substrates and also in sandy shoals. It is more abundant in small rivers and creeks, whereas A. marginata is more abundant in larger streams. The two species often occur together [in the Susquehanna River System], however, and are readily separable” (Clarke and Berg, 1959:29).
This habitat description applies to populations throughout the range of the species. The species most commonly found associated with it are Elliptio complanata and, less frequently, Strophitus undulatus, Alasmidonta undulata, and (in New England and the Canadian Maritime Provinces) Margaritifera margaritifera.
GEOGRAPHICAL RECORDS
Atlantic Coastal Drainages
NOVA SCOTIA RIVER SYSTEMS.—Cumberland Co., Wallace River: 9 mi (14.4 km) S of Pugwash (1960, A. H. Clarke, L. R. Clarke, and A. R. Clarke! (NMC)); Lunenburg Co.: La Have River above Bridgewater (ANSP); Guysborough Co.: St. Mary River, Sherbrooke; Annapolis Co.: Annapolis River, Lawrencetown; Colchester Co.: Stewiacke River, 5 mi (8.0 km) E of Stewiacke (all Athearn and Clarke, 1962).
PETITCODIAC RIVER SYSTEM, NEW BRUNSWICK.—Petitcodiac River, Petitcodiac, Westmoreland Co. (1967, D. H. Stansbery! (OSUM)); 2 mi (3.2 km) above Salisbury, Westmoreland Co., New Brunswick (1951, H. D. Athearn! (MCZ)).
RENOUS RIVER SYSTEM, NEW BRUNSWICK.—Renous River, Northumberland Co. (MCZ).
DENNYS RIVER SYSTEM, MAINE.—Dennys River, Washington Co. (MCZ).
MACHIAS RIVER SYSTEM, MAINE.—Upper Machias River (1961, D. Cameron! (OSUM)).
PENOBSCOT RIVER SYSTEM, MAINE.—Molunkus Stream, 2.4 mi (3.8 km) above Macwahoc, Aroostook Co. (1954, H. D. Athearn! (MCZ)). Mattawamkeag River at Haynesville, Aroostook Co. (1952, A. H. Clarke! (NMC)); and Mattawamkeag, Penobscot Co. (1953, H. D. Athearn! (MCZ)).
MERRIMAC RIVER SYSTEM.—Beaver Creek, 2.5 mi (4.0 km) NNE of Pelham, Hillsboro Co., N.H. (1952, H. D. Athearn and A. H. Clarke! (OSUM)). Spicket River, Lawrence, Essex Co., Mass. (MCZ). Shawsheen River, Andover, Essex Co., Mass. (MCZ).
EASTERN MASSACHUSETTS.—Woburn and Nonesuch Pond, Weston, both Middlesex Co., (both MCZ). Gates Pond, Berlin, Worcester Co. and Abbott Run, North Attleboro, Bristol Co. (both MCZ).
CONNECTICUT RIVER SYSTEM.—Connecticut River at Turner's Falls, Franklin Co., Mass. (USNM) and Hadley, Hampshire Co., Mass. (MCZ). Westfield River, Westfield, Hampden Co., Mass. (MCZ). Tributary of the South Branch Connecticut River, West Hartford, Hartford Co., Conn. (MCZ).
PASSAIC RIVER SYSTEM, NEW JERSEY.—Near Morris Plains, Morris Co. (USNM). Stony Brook, Princeton, Mercer Co. (Ortmann, 1919).
RARITAN RIVER SYSTEM, NEW JERSEY.—North Branch Raritan River, Somerset Co. (ANSP).
DELAWARE RIVER SYSTEM.—Delaware River Drainage: Delaware River at Columia, Warren Co., N.J. (ANSP); Shawnee, Monroe Co., Pa.; Delaware Water Gap, Monroe Co.; and Northampton Co., Pa. (all Ortmann, 1919); Trenton, Mercer Co., N.J. (ANSP); Bucks Co., Pa. (MCZ; Ortmann, 1919). Paulins Kill, Marksboro, Warren Co., N.J. (ANSP). Lehigh River, Bethlehem, Northampton Co., Pa. (Ortmann, 1919). Big Neshaming Creek near Edderton, Bucks Co., Pa. (ANSP). Pennypack Creek below Valley Falls and near Bethayres, both Montgomery Co., Pa., and Holmesburg, Philadelphia Co., Pa. (all ANSP). Frankford Creek, Philadelphia Co., Pa. (ANSP). White Clay Creek, Avondale, Chester Co., Pa. (Ortmann, 1919). Pickering Creek, Chester Co., Pa. (ANSP, MCZ). Ridley Creek, Delaware Co.; Princess Creek, Kunkletown, Monroe Co.; Lizard Creek, Mantz, Schuylkill Co.; Mahoning Creek, Lehighton, Carbon Co., all Pa. (all Ortmann, 1919). Head of Red Clay Creek, New Castle Co., Del. (ANSP).
Schuylkill River Drainage, Pennsylvania: Manatawny Creek near Earlville, Berks Co.; Maiden Creek, Berks Co.; and Swamps Creek, Zieglerville, Montgomery Co., (all ANSP and Ortmann, 1919).
SUSQUEHANNA RIVER SYSTEM.—Upper Susquehanna River Drainage, New York: Unadilla River at Leonardsville, Madison/Otsego Co. (1965, C. B. Stein! (OSUM)); 15 mi (24.0 km) NE of Norwich, Otsego/Chenango Co. (1965, C. B. Stein! (OSUM)). Otselic River, Whitney Point, Broome Co. (1965, E. J. Karlin and C. O. Berg!). Chenango River, Chenango Forks, Broome Co. (Clarke and Berg, 1959). West Branch Tioughnioga River, just N of Homer, Cortland Co., N.Y. (1965, C. B. Stein! (OSUM)); 5.5 mi (8.8 km) N of Cortland, Cortland Co., (Clarke and Berg, 1959). Catatonk Creek below Spencer Lake, Spencer, Tioga Co., (MCZ; Clarke and Berg, 1959); 7 mi (11.2 km) SE of Candor, Tioga Co. (1955, C. O. Berg! (MCZ)); Owego, and 4.5 mi (7.2 km) W of Candor, both Tioga Co. (both Clarke and Berg, 1959).
Lower Susquehanna River Drainage, Pennsylvania: Wyalusing Creek, Stevensville, Bradford Co. (MCZ). Conodoquinet Creek, Carlisle, Cumberland Co. (USNM). Conewago Creek, 10 mi (16.0 km), 8 mi (12.8 km) and 7.5 mi (12.0 km) above Gettysburg, Adams Co. (MCZ; 1957: D. R. Franz! (ANSP)); 1.5 mi (2.4 km) S of, and “near,” Boulder, Adams Co. (Ortmann, 1919 and 1952, H. D. Athearn! (MCZ, OSUM)). Muddy Creek, Lancaster Co., Pa. (MCZ). Sinnemahoning Creek, Driftwood, Cameron Co. (Ortmann, 1919); Round Island, Clinton Co. (ANSP). Lancaster, Lancaster Co.; Cush Cushion Creek, Indiana Co. (both Ortmann, 1919). Susquehanna River at Selinsgrove, Snyder Co.; York Haven and “York Furnace,” [York], both York Co. (all Ortmann, 1919). Juniata River at Everett, Mount Dallas and Bedford, all Bedford Co., Pa. (all Ortmann, 1919); 1 mi (1.6 km) E of Hollidaysburg, Blair Co. (MCZ). Raystown Branch Juniata River, Huntingdon Co., Pa. (ANSP).
POTOMAC RIVER SYSTEM.—Upper Potomac River Drainage: Raystown Creek, 1 mi (1.6 km) W of Breezewood, Bedford Co., Pa. (OSUM). Sideling Creek, Alleghany Co., Md. (ANSP). Wills Creek, Ellerslie, Alleghany Co., Md. (Ortmann, 1919). Lost River, Wardensville, Hardy Co., W. Va. (USNM). Birch Run, Adams Co., Pa. (ANSP). Conococheaque Creek at Greencastle, Scotland, and Mercersburg Junction, Franklin Co., Pa. (all Ortmann, 1919); and Williamsport, Washington Co., Md. (1959, F. W. and G. F. Grimm! (NMC) and 1973, C. B. Stein! (OSUM)). Great Tonoloway Creek, Fulton Co., Pa. (Ortmann, 1919). Tom's Creek, 6.5 mi (10.4 km) and 7.1 mi (11.4 km) SE of Emmitsburg, Frederick Co., Md. (1960, F. W. Grimm! (NMC)). Monocacy River, 12 mi (19.2 km) NNE Frederick, Frederick Co., Md. (1968, H. G. Lee! (OSUM)); 0.5 mi (0.8 km) W of Bridgeport, Frederick/Carroll Co., Md. (1973, C. B. Stein! (OSUM)). South Branch Potomac River, Southbranch, Hampshire Co., W. Va. (Ortmann, 1919). Potomac River at Hancock, Washington Co., Md. (ANSP; 1973, C. B. Stein! (OSUM)); Cherry Run, Morgan Co., W. Va. (ANSP); Harpers Ferry, W. Va. (ANSP) and between Harpers Ferry and Fishers Island, Jefferson Co., W. Va. (1962–65, C. B. Stein! (OSUM)).
Shenandoah River Drainage: North Fork of Shenandoah River, E of Woodstock, Shenandoah Co., Va. (MCZ); 2 mi (3.2 km) SE of Strasburg, Shenandoah Co. (1968, W. J. Clench and D. H. Stansbery! (MCZ)). South River, Waynesboro, Augusta Co., Va. (Ortmann, 1919). South Fork Shenandoah River, Elkton, Rockingham Co., Va. (Ortmann, 1919) and Riverton, Warren Co., Va. (MCZ). Shenandoah River, Clarke Co., Va. (USNM); Milleville, Power Dam, Jefferson Co., W. Va. (USNM); Harpers Ferry, Jefferson Co., W. Va. (ANSP).
Lower Potomac River Drainage: Potomac River at Seneca Falls, Montgomery Co., Md. (USNM); several localities near Great Falls, Maryland and Virginia (MCZ, USNM); High Island, D.C. (USNM). Broad Run, Fairfax Co., Va. (Johnson, 1970). Bull Run, Sudley Church, Prince William Co., Va. (USNM). Occoquan Creek, Prince William Co., Va. (USNM) and 3 mi (4.8 km) W of Manassas, Prince William Co., Va. (Johnson, 1970).
JAMES RIVER SYSTEM, VIRGINIA.—Calf Pasture River (Ortmann, 1919).
CAPE FEAR RIVER SYSTEM, NORTH CAROLINA.—Haw River, 4 mi (6.4 km) ENE of Pittsboro, Chetham Co., Bear Creek, 7 mi (11.2 km) SSW of Pittsboro, (both OSUM). Rocky River, 11 mi (17.6 km) N of Sanford, Chetham (MCZ; Johnson, 1970; 1978, A. H. Clarke and J. J. Clarke (USNM)).
YADKIN RIVER SYSTEM.—Uwharrie River, N.C. (ANSP).
COOPER-SANTEE RIVER SYSTEM.—Catawba River, Bridgewater, Burke Co., N.C. (Ortmann, 1919).
SAVANNAH RIVER SYSTEM.—Turkey Creek, 8 mi (12.8 km) NW of Edgefield, Edgefield Co., S.C. (UMMZ; Johnson, 1970).
Gulf of Mexico Coastal Drainage
COOSA RIVER SYSTEM.—Etowah River, Georgia (ANSP, ex C. M. Wheatley Collection). Locality probably incorrect.
Ohio-Mississippi River Drainage
KANAWAH RIVER SYSTEM.—Greenbrier River, 1 mi (1.6 km) below Fort Spring, Greenbriar Co., W. Va. (1974, K. G. Borror! (OSUM).
- bibliographic citation
- Clarke, Arthur Haddleton. 1980. "The tribe Alasmidontini (Unionidae, Anodontinae), Part I: Pegias, Alasmidonta and Arcidens." Smithsonian Contributions to Zoology. 1-101. https://doi.org/10.5479/si.00810282.326.1
