Caecidotea brevicauda brevicauda (Forbes 1876)

Asellus brevicauda brevicauda Forbes

Asellus brevicauda Forbes, 1876, pp. 8–10.

Asellus brevicaudus Mackin and Hubricht, 1938, pp. 631–632.

TYPE MATERIAL.—Lectotype, adult , deposited in the Museum of Comparative Zoology; the reference is the specific name (catalog number 6800): Labels read: “MCZ Illinois: Union Co., July 30, 1876; S. A. Forbes coll. Asellus brevicauda Forbes” and “hololectotype.”

DESCRIPTION OF LECTOTYPE.—Body: Length, 13.0 mm.

Head (Figure 11A): Eyes large and distinct; posterolateral lobes large, prominent and rounded, and with numerous strong spines.

First antenna (Figure 11B): Flagellum 12-merous and tip reaching to point about two-thirds distally along last segment of peduncle of second antenna; penultimate 2 segments bearing aesthetascs. Flagellum about two-thirds length of peduncle. First segment of peduncle slightly shorter than second; third segment about half length of second. First segment of peduncle about twice as long as wide and bearing distally a circlet of short strong spines; second and third segments respectively about 3 and 2.5 times as long as wide.

Second antenna: Length (8.0 mm) about three-fifths (0.62) that of body. Flagellum 80-merous. Fourth and fifth segments of peduncle respectively about 2.5 and 4.5 times as long as wide, but peduncle otherwise similar to A. communis.

First peraeopod (Figure 11C): Dactylus slightly longer than palm with 8 teethlike spines on inner margin and ending in a long terminal claw. Propodus about three-fifths (0.61) as wide as long, and subtra- pezoidal in shape; palm with a small, low, conical projection near midpoint, a very large toothlike spine proximally, and a submarginal row of spines on inner and outer surfaces.

Second to seventh peraeopoda: Similar in construction to A. communis; most noticeable minor difference is occurrence of fewer teethlike spines on inner margin of each dactylus.

First pleopod (Figure 12A): Total length of appendage slightly greater (1.15) than that of second pleopod. Sympod subrectangular, about three-fifths as wide as long; inner margin with 7 hooklike protuberances for coupling. Distal segment also subrectangular, but distinctly curved outward so that the outer lateral margin is deeply concave and the inner lateral margin is convex; proximal width slightly greater than distal width; maximum width slightly less (0.47) than half maximum length; distal margin bearing 11 long plumose spines and 9 shorter simple spines somewhat irregularly arranged; lateral distal angle with a row of short strong spines arranged regularly; inner proximal angle with 2 short simple spines.

Second pleopod (Figures 12B–D): Sympod subrectangular, maximum length over one and a half (1.65) times maximum width; medial and lateral margins more or less straight, and medial margin bearing 4 simple spines beneath attachment of endopodite. Proximal segment of exopod with 7 simple spines on outer margin, inner margin conspicuously sclerotized. Distal segment of exopod subtriangular with 17 long plumose spines marginally and conspicuously sclerotized near inner proximal angle. Endopod narrow and gently curved outward in long axis, total length subequal to that of exopod; a prominent inner basal apophysis and a less prominent outer basal apophysis are present. Cannula short and wide and completely overlapped ventrally by a flattened, expanded, and rounded lateral process. Ventral groove prominent, moderately long and wide. Mesial process large, sclerotized, and expanded so that it wholly occupies the inner lateral margin of the endopod tip; distally its outer face is concave. Caudal process not developed, but dorsal surface of distal tip of endopod with several minute, short spinules.

Uropod (Figure 11D): About half as long (0.48) as telson. Peduncle about as wide as long and bearing distally numerous short to moderately long spines; subtriangular in shape. Exopod as long as peduncle and about twice as long as greatest width; endopod slightly longer than peduncle (1.13) and also about twice as long as greatest width; both exopod and endopod bear numerous strong and relatively short spines.

Telson (Figure 11E): Subcircular, as long as wide; uropodal sinuses prominent.

MATERIAL EXAMINED.—ILLINOIS: Fountain Gap, Monroe County, ∞ , coll. L. Hubricht, 26.V.1937 (USNM); Burkesville, Monroe County, ∞ , coll. L. Hubricht, 6.xi.1937 (USNM); Bluffside, St. Clair County, ∞ , coll. L. Hubricht, 16.i.1938 (USNM); Burkesville, ∞ , coll. Burk et al., 24.i.1947 (INHS); Shawnee National Forest, Union County, 1 , coll. R. L. Lippson, 7.iv.1967.

KENTUCKY: Goose Creek,* Jefferson County, 1 , coll. G. A. Cole, 4.V.1955.

MISSOURI: Glencoe Creek, St. Louis County, ∞ , coll. L. Hubricht, 1.iii.1936 (USNM); Harine, Jefferson County, ∞ , coll. L. Hubricht, 21.V.1936 (USNM); Gray Summit, Franklin County, ∞ , coll. L. Hubricht, 29.V.1937 (USNM); Antonia, Jefferson County; ∞ , coll. L. Hubricht, 6. vi.1937 (USNM); St. Louis, ∞ , coll. L. Hubricht, 25.xi.1937 (USNM); Cave brook, Boone County, ∞ , coll. C. Boll, 6.X.1956 (NMC).

GEOGRAPHICAL DISTRIBUTION AND ECOLOGY.—The localities detailed above, together with the type locality, are plotted in Figure 13. From some of the localities, A. brevicauda has been recorded by Mackin and Hubricht (1938); none of their additional records are plotted. This procedure gives greater certainty to and does not detract substantially from the conclusions that may be drawn from Figure 13, since they recorded A. brevicauda from only one additional State, Arkansas (1 locality). From Figure 13 it is clear that A. brevicauda brevicauda occurs in a large but relatively restricted area of east-central United States, south of Lake Michigan.

According to the data on labels in the collections examined, A. brevicauda brevicauda is typically a species associated with springs or spring-fed streams. It has also been collected on a few occasions, however, from cave streams, from which macrohabitat A. brevicauda was recorded also by Mackin and Hubricht (1938).

FURTHER DESCRIPTION ().—Body: The largest male examined was 17.0 mm long, and the smallest 8.5 mm.

First antenna: Flagellum 11- to 17-merous; flagellum tip reaching to midpoint or slightly beyond the distal margin of the last segment of the peduncle of the second antenna; penultimate 2 or 3 segments bear aesthetascs.

Second antenna: Length 0.53 to 0.76 times that of body. Flagellum 60- to 124-merous.

Mouthparts: See Table 1.

First peraeopod: Nearly always only one thick toothlike spine is present at proximal end of palm, but occasionally a smaller similar spine is also present. The small, low conical process near the midpoint of the palm, likewise, is almost invariably present; it was absent, however, in one male specimen examined. Dactylus with 8 to 14 teethlike spines on inner margin. Propodus 0.5 to 0.72 times as wide as long, but about two-thirds is the usual value. Figures 12E–I illustrate the range of variation which may occur in the shape of the palm. The typical shape is as shown by the lectotype (Figure 11c).

First pleopod: Total length of appendage 1.03 to 1.24 times as long as second pleopod. Inner margin of sympod with 4 to 7 (usually 6 or 7) coupling hooks. Maximum width of distal segment 0.43 to 0.52 times maximum length; distal margin bearing 5 to 11 long setose spines and 6 to 9 shorter simple spines somewhat irregularly arranged; lateral distal angle with a row of 7 to 11 short strong spines arranged more or less regularly.

Second pleopod: Maximum length of sympod from 1.37 to 2.00 times maximum width; medial and lateral margins of sympod more or less straight to slightly convex. Proximal segment of exopod with 3 to 7 simple spines on outer margin; distal segment with 12 to 17 long setose spines marginally, and subovate to elongate triangular in shape. The morphology of the tip of the endopodite displays very little variation. The greatest variation that occurs in the second pleopod involves the length /width ratio of the sympod, the shape of the distal segment of the exopod, and the relative positions of the distal tips of the exopod and endopod. Figure 14 illustrates the nature of this variation.

Uropod: See Table 2.