Caecidotea forbesi (Williams 1970)

Asellus forbesi

ETYMOLOGY.—Named for S. A. Forbes.

TYPE MATERIAL AND TYPE LOCALITY.—Holotype: adult , USNM 122052. Allotype: adult nonovigerous , USNM 122053. Paratypes: 5 , 5 nonovigerous and 9 ovigerous , USNM 122054. Type locality: flood pool of Rappahannock River, Culpeper County, Virginia. The type collection was made 28 March 1967 by Dr. A. Weaver.

[males only]

DESCRIPTION OF HOLOTYPE.—Body: Length, 12.5 mm.

Head: Eyes large and distinct.

First antenna: Flagellum 14-merous and tip reaching to point about two-thirds along last segment of peduncle of second antenna; penultimate 3 segments bearing aesthetascs. Second segment of peduncle longest; first, three-quarters length of second; third, two-thirds length of second. First peduncle segment about 1.5 times as long as wide; second and third respectively 4 and 3 times as long as wide.

Second antenna: Length (8.5 mm) about two-thirds (0.68) body length. Flagellum 66-merous.

First peraeopod (Figure 37A): Dactylus distinctly longer than palm of propodus. Propodus 1.2 times as long as wide, subovate; palm with a single large triangular projection near midpoint, a smaller blunt projection between larger projection and point of attachment of dactylus, a single toothlike spine on a low proximal projection with 3 stout spines proximal to this, and a submarginal row of spines on inner and outer surfaces.

First pleopod (Figure 37B): Total length subequal (1.06) to that of second pleopod. Sympod subrectangular, about 1.33 times as long as wide; inner margin with one hooklike protuberance for coupling. Distal segment subovate, widest about one-third towards distal margin; maximum width just over half (0.59) maximum length; several simple short spines occur on the distal margin.

Second pleopod (Figures 37C–E): Sympod subquadrate, maximum length only slightly greater (1.17) than maximum width; medial and lateral margins very slightly convex. Proximal segment of exopod irregularly subtriangular, with 3 short and simple spines on outer margin. Distal segment of exopod ovate, almost twice (1.87) as long as wide, with 13 long plumose spines on margin of distal half of segment, and a row of very fine short spines on inner proximal margin. Endopod two-thirds total length of exopod, and about three-quarters (0.77) length of distal segment of exopod; endopod slightly less (1.86) than twice as long as maximum width (regarded in all specimens of A. forbesi as the distance between the outer margin of the outer basal apophysis and the inner proximal angle of endopod). Outer basal apophysis not well developed, rounded in outline; inner basal apophysis scarcely present. Cannula short and wide. Ventral groove prominent. Mesial process sclerotized, large, wide, hooklike, and as long as cannula. Lateral process not prominent. Caudal process wide, margin broadly rounded and sclerotized, without associated hooks or spines, and not protruding far beyond cannula and mesial process.

Uropod (Figures 37F, G): 1.33 times as long as telson. Peduncle about twice as long as maximum width. Exopod two-thirds length of peduncle, endopod as long as peduncle; both rami have several moderately long and fine spines distally, and numerous stronger ones laterally.

[males only]

PARTIAL DESCRIPTION OF ALLOTYPE ().—First peraeopod (FIGURES 38A, B): Relatively slender, but dactylus and propodus arranged in a subchelate manner. Dactylus distinctly longer than palm of propodus and with 8 teethlike spines on inner margin and a long terminal claw. Propodus subtriangular, about 1.5 times as long as maximum width; palm with a low triangular projection near midpoint, and at proximal end 2 long teethlike spines. Otherwise as described for a female paralectotype of A. attenuatus.

“First” pleopod (Figure 38C): Almost subrectangular in shape. Distal margin with 14 long finely plumose spines.

MATERIAL EXAMINED.—GREAT LAKES: Lake Huron: Sta. 13, 15 meters, 1 , coll. Great Lakes Institute, 6.xi.1963 (GLI).

ONTARIO: Go Home Bay, 1 , Coll. W. A. Clemens, August 1912 (ROM); New Durham, Brant County, 4 , coll. R. F. Cain, 24.v.1929 (ROM); Lake Nipissing, 1 , coll. J. Oughton, 8.vii.L929 (ROM); L. Nipissing, 1 , coll. J. Oughton, 8.viii.L930 (ROM); Laird, ∞ , coll. unmarked, June 1931 (ROM); Beattie Point, Ottawa R., 5 , coll. Macoun Field Club, 28.iv.1955 (NMC); Spider Ck., Holbrook, 3 , coll. Ont. P. & D., 1.vi.1955 NMC); Tillsonburg, 18 . coll. E. L. Bousfield, 30.viii.1956 (NMC); Metcalfe, 3 , coll. W. Sinclair, 4.v.1957 (NMC); Spitler Cr., Norwich, 9 , coll. E. L. Bousfield, 29.v.1957 (NMC); Long Point, 5 , coll. D. Barr, 26.v.1963 (ROM); Rondeau Province Pk., Kent Co., 4 , coll. I. M. Smith, 2.vi.1965 (ROM); Chalk River, 8 , coll. H. B. N. Hynes, 27.v.1966; Perch Creek, 8 , coll. J. Bishop, 2.v.1967; Pond near Laurel Creek Reservoir, ∞ , coll. C. Patterson, 16.v.1967.

DISTRICT OF COLUMBIA: Carberry Meadows, 8 , coll. W. P. Hay, 10.xii.1892 (USNM); Piney Branch, 3 , coll. W.H. Ball, 7.iv.1930 (USNM); Piney Branch, ∞ , coll. W. H. Ball, l.v.1930 (USNM); Georgetown, ∞ , coll. L. Hubricht, date unmarked (USNM).

INDIANA: Hammond, 4 , coll. V. E. Shelford, 25.iv.1908 (USNM); La Porte, La Porte County, ∞ , coll. L. Hubricht, 2.v.1941 (USNM).

IOWA: Riverside, Washington County, ∞ , coll. L. Hubricht, 24.iv.1942 (USNM).

KENTUCKY: Bullitt County, 2 , coll. G. A. Cole, 7.iii.1954; Caperton Swamp, 4 , coll. G. A. Cole, 26.iii.1954; Jefferson County, 1 , coll. G. A. Cole, 2.v.1954; Louisville, 9 , coll. G. A. Cole, 26.xii.1954; Jefferson County, 7 , coll. G. A. Cole, 24.iii.1956 (NMC).

MARYLAND: Great Falls, 7 , coll. W. D. Appel, 9.xi.1912 (USNM); Linden, ∞ , coll. J. E. Benedict, 28.ii.1926 (USNM); Hyattsville, ∞ , coll. R. Greenfield, 18.ii.1928 (USNM); Hyattsville, ∞ , coll. R. Greenfield, 10-ii. 1929 (USNM); Ridge, St. Mary’s County, 11 , coll. W. H. Ball, 26.iv.1930 (USNM); Point No Point, 1 , coll. W. H. Ball, 27.iv.1930 (USNM); near Plummer’s Island, ∞ , coll. W. D. Appel, 5.v.1935 (USNM); near Plummer’s Island, 5 , coll. W. D. Appel, 19.v.1935 (USNM).

MICHIGAN: Ann Arbor, ∞ , coll. L. Hubricht, 30.iv.1941 (USNM); Fenton, ∞ , coll. L. Hubricht, 19.iv.1942 (USNM); Kalamazoo County, 2 , coll. R. L. Lippson, 12.iv.1967.

MISSOURI: Benbush, St. Louis County, ∞ , coll. L. Hubricht, 8.iii.1936 (USNM); St. Charles, 11 , coll. L. Hubricht, 24.iv.1937 (USNM); River Kirkwood, St. Louis County, ∞ , coll. L. Hubricht, 10.iv.1938 (USNM); Grimsby, ∞ , coll. L. Hubricht, 25.iv.1938 (USNM).

NORTH CAROLINA: Chapel Hill, Durham County, 6 , coll. A. Weaver, 4.xii.1966; Chapel Hill, Durham County, 2 , coll. A. Weaver, 27.iii.1967.

OHIO: Shreve, Wayne County, 2 , coll. W. A. Shear, 23.iii.1967.

SOUTH CAROLINA: Anderson County, 4 , coll. R. Prinz, 6.i.1966.

VIRGINIA: Driver, ∞ , coll. L. Hubricht, 26.iii.1944 (USNM); South Gap, Bland County, 6 , coll. A. Weaver, 21.iii.1967; Prince William County, 14 , coll. A. Weaver, 28.iii.1967; Keysville, 4 , coll. A. Weaver, 28.iii.1967; Culpepper County, 7 , coll. A. Weaver, 28.iii.1967.

WEST VIRGINIA: Mercer County, 3 , coll. W. A. Shear, 16.iv.1966; Mercer County, 1 , coll. A. Weaver, 1.xii.1966.

GEOGRAPHICAL DISTRIBUTION AND ECOLOGY.—The localities listed above, together with the type locality, are plotted in Figure 39. This indicates that A. forbesi is found over a very large area of east-central United States and in southern Ontario. It is clearly one of the most widespread species occurring in North America.

The most frequently mentioned sort of locality from which collections have been made are temporary ponds, flood pools, and sloughs. However, the species has also been collected from marshes, small creeks, and at least on a few occasions from lakes also. One of the lakes from which it has been collected is Lake Huron where the species was obtained from a depth of 15 m. Like several other geographically widespread species of Asellus in North America, A. forbesi is clearly able to live in a variety of macrohabitats.

FURTHER DESCRIPTION ().—Body: The largest examined was 18.5 mm long, and the smallest 6.0 mm.

First antenna: Flagellum 10- to 17-merous; flagellum tip reaching to midpoint or to distal end of the last segment of the peduncle of the second antenna; penultimate 3 segments bear aesthetascs.

Second antenna: Length 0.5 to 1.0 times that of body, but usual length between one-half and two-thirds body length. Flagellum 40- to 87-merous depending upon size.

Mouthparts: See Table 1.

First peraeopod: Spine on proximal projection of palm usually toothlike but sometimes relatively slender; proximal projection itself prominent to scarcely developed, and with 1 to 5 relatively long spines on proximal margin. Some variation occurs in the shape of the palm (cf. Figure 40).

First pleopod: Total length of appendage 0.84 to 1.19 times as long as second pleopod. Inner margin of sympod with 0 to 4 (usually 2 or 3) coupling hooks. Maximum width of distal segment 0.48 to 0.69 times maximum length. Distal spines few to numerous, but always simple and of moderate length. The typical shape of the distal segment is subovate, but a little variation occurs.

Second pleopod: Maximum length of sympod from 1.10 to 1.60 (usually 1.2 to 1.4) times maximum width. Proximal segment of exopod with 0 to 4 short and simple spines on outer margin; distal segment with 10 to 20 marginal spines. The shape of the distal segment of the exopod varies from almost subcircular to elongate oval, the maximum length ranging from 1.48 to 2.54 times the maximum width; the usual shape, however, is ovate, and the maximum length is usually about twice the maximum width. Endopod shape is also rather variable, particularly concerning the extent of development of the basal apophyses; an indication of the range of variation is given in Figure 41. Considerable variation in endopod shape may occur even within a single population, but the typical shape is that shown for the holotype (Figure 37G). The maximum length of the endopod is from 1.65 to 2.64 (usually 1.9 to 2.3) times the maximum width; the length in proportion to the length of the distal segment of the exopod ranges from 0.60 to 1.04. The morphology of the tip of the endopodite, while constant in fundamental characters, is subject to some variation particularly in the nature of the cannula and the mesial process and the relationship these have to each other. Figure 42 has been compiled to illustrate the range of this variation. As may be seen, the mesial process may appear to be much shorter than the cannula in some specimens, subequal in length in others, and even in some slightly longer; its shape, moreover, is rather variable and its tip may be blunt and rounded or acute and narrow.

Depending to at least some extent it seems upon the state and nature of preservation of the specimen involved and the position of mounting of the pleopod for examination, the cannula may appear as a prominent semitubular structure or as a scarcely visible and almost flattened structure; it is always membranous. The caudal process is always rounded, sometimes irregularly so, sclerotized, and lacks associated protuberances. With regard to the morphology of the tip of the endopodite, A. forbesi appears to be one of the more variable of North American epigean species of Asellus, and the same can also be applied with respect to the overall shape of the endopod. A study of the available material did not indicate that any of this variation had an obvious geographical basis, although this is not to say of course that the variability is not correlated with the very wide geographical distribution of the species (the wide geographical distribution may be a consequence of the variability).

Uropoda: See Table 2.