Bastard

Arcidens (Arcidens) confragosus (Say, 1829)

Alasmidonta confragosus Say, 1829:339; 1831, pl. 21. [Type-locality: “A side stream of the Wabash, called Fox River [Indiana]…[and near] New Orleans [Louisiana].” The latter locality was emended by Say in 1832 to “Bayou Teche in the Parish of St. Mary, Louisiana” [see Binney, 1858:195]. Type-material not in Academy of Natural Sciences of Philadelphia (Johnson and Baker, 1973) and presumably lost.]

Arcidens confragosa jacintoensis Strecker, 1931. [Type-locality: San Jacinto River, Texas. Type material in Baylor University Museum, Waco, Texas.]

THE SHELL

DESCRIPTION.—Shell moderately heavy, inflated, and ovate-rhomboid, up to about 144 mm long, 95 mm high, and 66 mm wide, slightly thickened anteriorly (up to 10 mm thick) and about half as thick posteriorly. Anterior margin round, ventral margin flattened or slightly concave posteriorly, posterior margin broadly and roundly pointed below and obliquely flattened above, and dorsal margin long and flatly curved. Maximum width near the center of the shell. Beaks inflated, full, located about 30% to 32% the distance from anterior to posterior, and projecting well above the hinge line. Posterior ridge variable, angular or rounded, and well defined above but becoming obscure below. Posterior slope covered with narrow and wide, low radial ridges perpendicular to the lines of growth. Growth increments marked by wide, concentric, dark bands and by crowded, fine, ridges and grooves. Additional post-juvenile sculpturing very heavy and variable consisting of two radial rows of nodules extending to the middle of the shell (continuations of the beak sculpturing, see below), 4 to 6 broad, diagonal folds extending across the central third of the shell, and numerous, short, rounded radial ridges over nearly the whole surface. Only the lower part of the anterior disc is principally unsculptured. Periostracum greenish and obscurely rayed in juveniles and becoming dark brown (chestnut colored) in adults. Ligament long, thick, and dark brown.

Hinge teeth thick, strong, and dorsoventrally compressed. Pseudocardinal tooth in right valve protuberant, rounded on the lower surface, flattened on the upper, and buttressed below. Anterior pseudocardinal tooth in left valve compressed and sharp, flatly rounded or rounded on the lower surface, flat on the upper, serrated, and also buttressed below. Posterior pseudocardinal tooth coalesced with interdental projection and forming a single, irregular, heavy, and sharp projection under the beak. Lateral teeth of moderate thickness but variable, short, indistinct and incomplete, numbering 1 to 3 in each valve. Beak cavity broad, excavated, and deep. Anterior muscle scars impressed but shallow, pallial line also shallowly impressed, wavy, and intersected from above or crossed by crowded, fine radial grooves; posterior muscle scars shallow and poorly defined; and scars within beak cavity consisting of 2 or 3 small, variable, deep pits located principally, or entirely, deep within the cavity and on the back of the hinge plate. Nacre silvery white and lustrous throughout but not iridescent. A broad yellowish or greenish band occurs along the margin where the nacre becomes thin.

Beak sculpture very heavy and composed of two radial rows of heavy, raised loops (in the form of V-shaped tubercles) that extend far out on the shell and numerous, narrow, radial grooves and ridges posterior to the tubercles and extending onto the posterior slope. Early ridges obliterated in old specimens but distal elements of beak sculpture that continue onto the disc are perennial features.

VARIATION.—A. confragosus is quite constant in its morphology. There is some variation in hinge plate thickness (see Table 23) and in the strength and extent of sculpturing. Specimens from Pigeon Creek, Chandler, Indiana (USNM 677485) are heavily sculptured with plicae and irregular, mostly radial, ridges over the whole outer surface whereas some specimens from the Mississippi River (e.g. from Lynxville, Wisconsin, USNM 745921) are nearly smooth. Young specimens tend to be decidedly greenish and more mature specimens are brownish or nearly black. Baker (1928:198) has pointed out that, as in other species, specimens from small streams tend to be more compressed than those from large rivers. The largest specimen, a single left valve from near Burlington, Iowa, is 144.20 mm long, 94.75 mm high, 33.10 mm in single valve convexity, and 38.00 mm in B-A measurement.

TOPOGRAPHIC ANATOMY

SPECIMENS DESCRIBED.—From Mississippi River, 1 mi (1.6 km) S of Burlington, Iowa in Henderson Co., Ill. (OSUM 13128, D. H. Stansbery, et al!); preserved in 70% ethyl alcohol; shell removed, body length 93.0 mm, sex female, gravid.

DESCRIPTION.—Mantle of preserved specimen pale brown and somewhat translucent. A narrow, brown pigmented band occurs along the posterior edge and, in the vicinity of the posterior mantle openings, it is adjacent to their edges. The incurrent opening is 17 mm long and surrounded just within by a dark, pigmented band and about 3 ranks of narrow, pale brown, pyriform or filiform papillae, the inner papillae the longest, i.e., up to 1.5 mm long. The separation of the incurrent and anal openings is achieved in life both by the diaphragm and by appression of the mantle edges over a short (0.5 mm) distance. The anal opening is 6 mm long, with darkly pigmented areas within, and surrounded below the edge by a single row of very short (0.2–0.3 mm) rounded papillae. The mantle connection between the anal and supra-anal openings is short (3.0 mm) and the supra-anal opening is long (15 mm), without papillae, and bordered by lamellate mantle edges that extend 7 mm anterior-dorsally beyond the opening.

Demibranchs of preserved specimen pale brown. Gravid outer demibranch 68 mm long, 26 mm high, and 7 mm thick, fragile, padlike, with free margins rounded anteriorly and posteriorly and more flatly curved centrally and with low radial wrinkles. Outer membrane with about 10 double radial filaments and three horizontal cross-filaments per mm; glochidia-filled radial water tubes about 1 per mm. Inner demibranch 64 mm long, 26 mm high, subtruncated and somewhat oblique anteriorly, flatly curved ventrally, and obliquely narrowing posteriorly to a point. Inner demibranch extending 4 mm beyond the outer demibranch anteriorly but posteriorly it is overlapped by the outer demibranch. Outer membrane also with about 10 double radial filaments and 3 horizontal cross-filaments per mm. Inner lamina of inner demibranch attached to visceral mass only along its anterior third. Diaphragm strongly ridged and perforated by the open ends of the water tubes.

Labial palps pale brown, distally overlapping both the inner and outer demibranchs, broadly curved ventrally, more or less straight dorsally, and with a posterior-dorsal point; outer distal edges rolled outward. Outer surfaces smooth and inner surfaces of opposing members radially furrowed (about 5 furrows per mm). Outer member diagonally attached to the mantle for about half its length and subdorsally attached to the inner member for half of its free length.

VARIATION.—Since only two specimens with soft parts are available little can be said about variation. In the figured specimen the labial palpi do not touch the inner demibranchs. Otherwise, the specimens examined agree with the descriptions by Ortmann (1912:284–5) and Baker (1928:197).

GLOCHIDIUM

DESCRIPTION.—Glochidium pyriform, asymmetrical, 0.360 mm high, 0.359 mm long, 0.115 mm single valve convexity. The posterior margin is much more protuberant and rounded than the anterior, but the posterior portion of the glochidial shell, seen in basal view, is markedly less inflated than the anterior. The apex is located about 44% of the distance from anterior to posterior (measured parallel to the hinge axis). The surface is finely malleated (depressions irregular or subcircular and about 4–12 μm wide) and even more finely pitted (pits 1–4 μm wide and located within the depressions) except for the distal apical areas (about 40 μ high) and the edges of the valves that are slightly irregular but not pitted. The apex is also sculptured with concentric curved lines subparallel with the apical margin. Hinge 0.234 mm long, convex centrally but flattened near each end. Ligament narrow (about 5 μm wide) and about 0.220 mm long and apparently in two sections, the posterior portion about 0.100 mm long and separated from the 0.060 mm long anterior section by an interligamental space about 0.060 mm long. It is actually continuous, however, but the central part is hidden by the convex edge of the shell.

River, 1 mi S of Burlington, Iowa (abbreviations same as Table 4)

Each apical stylet is flatly reflexed and is about 0.100 mm long, 0.024 mm wide at the base and spatulate in form, with a blade-like rounded apex. It is supported on each side, for about ¾ of its length, by a lamellate cartilagenous structure, an expansion of the narrower membrane that projects inward from the whole free edge of each valve. Except for the distal extremity the exposed surface of the stylet is covered with about 75 major microstylets oriented in oblique rows and overlapping somewhat in the manner of shingles on a roof, directed toward the distal end of the stylet, and each about 12 μm in length. The microstylets are principally pyramidal in shape but a few located near the point of the stylet exhibit one or two longitudinal ridges. Other, smaller, pyramidal microstylets (about 2 μm high) occur near the base of the stylet and continue as micropoints (<0.5 μm) onto the ventral edge of the valves and on the supporting membrane.

The glochidium described is from an adult collected in the Mississippi River, 1 mi (1.6 km) S of Burlington, Iowa, on 15 September 1964 by D. H. Stansbery, J. J. Jenkinson, and T. A. Balding (OSUM 13128). In another glochidium from the same adult the microstylets are somewhat less numerous and appear soft, as if in a stage of incomplete development.

LIFE HISTORY

BREEDING SEASON.—“Bradytictic, probably [gravid] from September to June. ‘Gravid with active glochidia the latter part of January and with late embryos in the middle of March. Sterile in July and August’ (Utterback)” (Baker, 1928: 197).

The gravid specimens reported in this paper were collected on 15 September 1964.

NATURAL HOSTS.—Fuller (1974) gives the following fishes as hosts for Arcidens confragosus: American eel, Anguilla rostrata (Lesueur); gizzard shad, Dorosoma cepedianum (Lesueur); rock bass, Ambloplites rupestris (Rafinesque); white crappie, Pomoxis annularis (Rafinesque); and freshwater drum, Aplodinotus grunniens (Rafinesque).

HABITAT.—According to Baker (1928:197) this species occurs on sand or mud bottoms, in water a few feet deep, in rapid currents. The species is characteristic of, but not restricted to, large rivers.

GEOGRAPHICAL RECORDS

Interior Basin River Systems

OHIO RIVER SYSTEM.—Green River Drainage, Kentucky: Green River at Glenmore, 12 mi (19.2 km) N of Bowling Green, Warren Co. (1972, D. H. Stansbery, et al! (OSUM)); 16 mi (25.6 km) ESE of Morgantown, Butler/Warren Co. (1969, D. H. Stansbery and C. B. Stein! (OSUM)).

Rough River Drainage: Rough River at Dundee, Ohio Co., Ky. (MCZ).

Mud River Drainage, Kentucky: Mud River, 3 mi (4.8 km) W of Diamond Spring, Logan Co. (OSUM); Rectors Bridge, 3 mi (4.8 km) E of Dunmar, Muhlenberg Co. (MCZ).

Pigeon Creek Drainage, Indiana: Pigeon Creek, Chandler, Warrick Co. (USNM); Evansville, Vanderburgh Co. (USNM).

Wabash River Drainage: White River at Martin Co., Ind. (1964, C. B. Stein! (OSUM)); West Fork White River, Marysville, Davies Co., Ind. (1967, C. B. Stein! (OSUM)); East Fork White River, 0.5 mi (0.8 km) below Shoals, Martin Co., Ind. (OSUM). Fox River, Richland Co., Ill.; Little Wabash River, Carmi, White Co., Ill. (both MCZ). Wabash River, 7 mi (11.2 km) N of Mt. Carmel, Ill. in White River Township, Knox Co., Ind. (OSUM); New Harmony, Posey Co., Ind. (USNM, MCZ).

Sangamon River Drainage: Sangamon River at Springfield, Sangamon Co., Ill. (MCZ).

TENNESSEE RIVER SYSTEM.—Kentucky Lake of Tennessee River, 6 mi (9.6 km) above New Johnsville, Benton Co., Tenn. (1964, D. H. Stansbery! (OSUM and MCZ)).

UPPER MISSISSIPPI RIVER SYSTEM.—Main Mississippi River Drainage: Mississippi River at Red Wing, Goodhue Co., Minn. (USNM); Vermilion Slough, 7 mi (11.2 km) NW of Red Wing (USNM); Dreshback, Winona Co., Minn. (USNM); 2 mi (3.2 km) SSW of La Crosse, La Crosse Co., Wisc. (1977, M. Havlik! (OSUM)); Prairie du Chien, Crawford Co., Wisc. (1976, M. Havlick! (OSUM; USNM); Baker, 1928); Mouth of Harper's Slough, Crawford Co., Wisc. (USNM); Lynxville, Crawford Co., Wisc. (USNM); Prescott, Pierce Co., Wisc. (USNM); Genoa, Vernon Co., Wisc. (USNM); Feuley's Landing; Grant Co., Wisc. (USNM); 8 mi (12.8 km) below Lansing, Allamakee Co., Iowa (USNM); McGregor Island, Clayton Island, York Landing, N of Marquette, and opposite Sny Magill (all Clayton Co.), Iowa (all USNM); 7 mi (11.2 km) SE of Guttenberg, Clayton Co., Iowa; Pine City and Wilkins Island, both Dubuque Co., Iowa (all USNM): 1.2 mi (1.9 km) N of Bellevue, Jackson Co., Iowa (1977, E. Perry! (OSUM)); Eroys Landing, Jackson Co., Iowa; Savanna, Carroll Co., Ill.; Mouth of Elk River, Clinton Co., Iowa (all USNM); Clinton Co., Iowa (MCZ); Lyons, Clinton Co., Iowa and Albany, Whiteside Co., Ill. (both USNM); Davenport, Scott Co., Iowa (ANSP); Princeton, Scott Co., Iowa (USNM and 1968, I. Baumgarth! (OSUM)); Muscatine, Muscatine Co., Iowa (OSUM; USNM); Rock Island, Rock Island Co., Ill. (1976, E. Perry, et al! (OSUM)); Moline, Rock Island Co., Ill. (MCZ, USNM); near Cordova, Rock Island Co., Ill. (OSUM); New Boston, Mercer Co., Ill. (USNM); Parker's Landing, Louesa Co., Iowa (USNM); Burlington Island, Des Moines Co., Iowa (USNM); rapids, 1.5 mi (2.4 km) S. of Montrose, Lee Co., Iowa (USNM); Dallas, Hancock Co., Ill. (USNM); 2 mi (3.2 km) N of Nauvoo Island, Hancock Co., Ill. (USNM); below Burlington, Des Moines Co., Iowa (1964, D. H. Stansbery, et al! (MCZ)); Benton Slough, Henderson Co., Ill. (MCZ); Warsaw, Hancock Co., Ill. (MCZ); Quincy, Adams Co., Ill. (MCZ); 3 mi (4.8 km) S of Hannibal, Ralls Co., Mo (USNM); ¼ mi (0.4 km) below Peark, Pulaski Co., Ill. (USNM); Baton Rouge, E. Baton Rouge Parish, La. (MCZ).

Minnesota River Drainage: Minnesota River, 2.8 mi (4.5 km) SSW of Bloomington, Hennepin Co., Minn. (1977, D. H. Stansbery, et al! (OSUM)).

Rock River Drainage: Pecotonica River, Ill. (MCZ).

Illinois River Drainage: Illinois River at Peru, La Salle Co. (MCZ); many sites between Peoria, Peoria Co. and junction with Mississippi River (1966, W. Starrett, et al!; Starrett, 1971); Peoria, Peoria Co. (OSUM); Liverpool, Fulton Co. (USNM; Starrett, 1971); Quiver Lake and Havana, both Mason Co. (both Starrett, 1971); Frederick, Schuyler Co. (Starrett, 1971); Meredosia, Morgan Co. (MCZ); Naples and Pearl, both Pike Co. (both Starrett, 1971); below Hardin, Calhoun Co. (USNM).

Kaskaskia River Drainage, Illinois: Flat Branch of Kaskaskia River, Humbolt, Coles Co. (OSUM). Kaskaskia River, Washington Co. (MCZ).

Grand River Drainage: Grand River, Clinton, Henry Co., Mo. (ANSP).

Marais des Cygnes River Drainage: Marais des Cygnes River, 3 mi (4.8 km) E of Ottawa, Franklin Co., Kan.

Osage River Drainage: Osage River 5 mi (8.0 km) N of Schell City, Bates/Vernon Co., Mo. (1964, C. B. Stein! (OSUM).

Meramec River Drainage: Meramec River, 2.7 mi (4.3 km) SSE of Fenton, St. Louis/Jefferson Co., Mo. (OSUM).

LOWER MISSISSIPPI RIVER SYSTEM.—St. Francis River Drainage: St. Francis River, Poinsett Co., Ark. (OSUM).

Reelfoot Lake Drainage: Reelfoot Lake, Obion Co., Tenn. (ANSP).

Black River Drainage: Black River, W of Hendrickson, Butler Co., Mo. (1964, C. B. Stein! (OSUM)); Pocahontas, Randolph Co., Ark. (1964, C. B. Stein!); Kincaid Bar, Randolph Co., Ark.; Black Rock, Lawrence Co., Ark. (both USNM).

Red River Drainage, Louisiana: Frierson Mill, De Soto Parish (USNM). Saline Bayou, 7 mi (11.6 km) E of Natchitoches, Natchitoches Parish (1964, J. E. Allen! (OSUM)).

Atchafalaya River Drainage, Louisiana: Bayou des Glaises, NE of Opelousac, St. Landry Parish (1964, C. B. Stein, et al! (OSUM)). Bayou Waukasha, 3 mi (4.8 km) SW of Lebeau, St. Landry Parish (1953, H. D. Athearn! (MCZ, NMC)). Arm of Atchafalaya River, 10 mi (16.0 km) SE of Lebeau (1964, R. I. Johnson and C. B. Stein! (MCZ)).

Gulf of Mexico River Systems

CHOCTAWATCHEE RIVER SYSTEM.—Double Bridge Creek, Enterprise, Coffee Co., Ala. (USNM).

MOBILE RIVER SYSTEM.—Tombigbee River Drainage: East Fork, Tombigbee River, 11.3 mi (18.1 km) S of Fulton, Itawamba Co., Miss. (1974, J. D. Williams, et al! (OSUM)). Tombigbee River, 9.6 mi (15.4 km) NW of Columbus, Lowndes Co., Miss. and 4 mi (6.4 km) S of Pickensville, Pickens Co., Ala. (both 1974–1975, J. D. Williams, et al! (OSUM)). Black Warrior River, 5.8 mi (9.3 km) SE of Eutaw, Greene Co., Ala. (1975, J. D. Williams, et al! (OSUM)).

Main Mobile River Drainage: Bayou Mache, Mobile River, 30 mi (48.0 km) N of Mobile, Mobile Co., Ala. (MCZ).

PEARL RIVER SYSTEM, MISSISSIPPI.—Pearl River, Jackson, Hinds Co. (ANSP, MCZ, USNM).

SABINE RIVER SYSTEM.—Sabine River, 13.5 mi (21.6 km) W and 10.0 mi (16.0 km) SW of Marshall, Harrison Co., Tex. (1964, C. B. Stein! (OSUM)); Logansport, DeSoto Parish, La. (MCZ and 1964, C. B. Stein! (OSUM)); 10.5 mi (16.8 km) W of Zwolle, Sabine Parish, La. (1964, C. B. Stein, et al! (OSUM)).

NECHES RIVER SYSTEM, TEXAS.—Angelina River Drainage: Angelina River, Angelina Co. (1972, H. Kemper, et al! (OSUM)).

Main Neches River Drainage: Neches River, 18 mi (28.8 km) E of Woodville, Tyler Co. (1964, R. Long! (OSUM)).

TRINITY RIVER SYSTEM, TEXAS.—Trinity River, Dallas, Dallas Co. (MCZ).

SAN JACINTO RIVER SYSTEM, TEXAS.—Main San Jacinto River Drainage: West Fork San Jacinto River, 4.5 mi (7.2 km) S of Conroe, Montgomery Co. (1960, D. H. Stansbery! (OSUM)).

Buffalo Bayou Drainage: Buffalo Bayou, Houston, Harris Co. (USNM); near Eureka, Harris Co. (MCZ).

BRAZOS RIVER SYSTEM, TEXAS.—Brazos River Drainage: Brazos River, Cameron, Milam Co. (USNM).

Navesota River Drainage: Navesota River, 2.3 mi (3.7 km) NW of Navesota, Grimes Co. (1968, C. Boone! (OSUM)).

COLORADO RIVER SYSTEM, TEXAS.—Colorado River (USNM). Skull Creek, Colorado Co. (USNM).

* * *

*Except for the Tar River specimens collected by me, most of the records from the Potomac drfainage south to and including the Ogeechee drainage are also cited by Johnson (1970:150–152) under A. undulata and A. triangulata. Unless otherwise stated, the museum specimens and literature records listed here have also been examined by me and the original sources are therefore cited.

Arcidens confragosus is a species of freshwater mussels in the family Unionidae, the river mussels. It is commonly known as the rock pocketbook, but also has many other common names: bastard, black pocketbook, grandmaw, queen, and rockshell.