Caecidotea brevicauda bivittatus (Walker 1961)

Asellus brevicauda bivittatus Walker

Asellus bivittatus Walker, 1961, pp. 385–390, figs. 1–5.

TYPE MATERIAL.—Walker (1961) gives the following information concerning the deposition and collection of the types of her taxon: Holotype: adult cf 4.3 mm in length, USNM 107465. Paratypes: a series of 100 specimens, USNM 107466. Type locality: Doe Run, Meade County, Kentucky, approximately 3 miles east and 0.4 miles north of Ekron. The type material was collected 24 October 1959

PARTIAL REDESCRIPTION OF HOLOTYPE.—As previously indicated, Walker’s description of her taxon is detailed, the only significant omission being information upon the morphology of the tip of the endopodite of the male second pleopod (her omission of a description of the mouthparts is not significant). A reexamination of the holotype enables the description now to be completed.

Second pleopod (Figure 15): Sympod subrectangular, maximum length 1.34 times maximum width. Endopod rather wide, about half as wide as long. Dorsal surface of endopod near distal margin lacking minute spines, but otherwise morphology of tip of endopodite closely similar to that of A. brevicauda brevicauda (see Figures 12C, D).

MATERIAL EXAMINED.—KENTUCKY: Doe Run, Meade County, ∞ , coll. W. L. Minckley, 4.viii.1962; Doe Run, Meade County, 10 , coll. L. A. Krumholz, 22.viii.1967.

GEOGRAPHICAL DISTRIBUTION AND ECOLOGY.—The only locality from which A. brevicauda bivittatus is known is the type locality (Figure 13). This lies in the southern part of the range of the nominate subspecies. According to Minckley (1961), Doe Run is a large spring-fed creek with an average flow of 50 cubic feet per second. Only the upper 3 miles of the creek are inhabited by A. brevicauda bivittatus. Minckley (1963) provides a detailed description of the locality.

SEPARATION OF A. brevicauda bivittatus FROM THE NOMINATE SUBSPECIES ( only).—Comparison of Walker’s description of A. brevicauda bivittatus with the description of A. brevicauda brevicauda given in this paper indicates that the principal differences between the two taxa are that A. brevicauda bivittatus is shorter in total length, has fewer segments in the flagella of its first and second antennae and fewer teethlike spines on the dactylus of its gnathopod, lacks a triangular process near the midpoint on the palm of the propodus of the gnathopod, has a propodus which is only half as wide as long, bears fewer spines on the distal segment of the first pleopod and on the exopod of the second pleopod, and has a slightly shorter uropod. A consideration of topotypic material of A. brevicauda bivittatus negates one of these differences but supports the remainder. The one it negates is that relating to the width/length ratio of the propodus of the gnathopod; this ratio in A. brevicauda bivittatus (0.61 to 0.68) is similar to that displayed by A. brevicauda brevicauda. The principal differences between the two subspecies, as indicated by the material at my disposal, are shown in Table 3, which includes a further difference not apparent from the comparison of Walker’s paper, namely that the distal segment of the first pleopod of A. brevicauda bivittatus is broader relative to length than it is in the nominate subspecies. Also the spines on the uropoda of A. brevicauda bivittatus are longer relative to the length of the rami than they are in A. brevicauda brevicauda.

[Males only]