Asellus intermedius Forbes

Asellus intermedius Forbes

Asellus intermedius Forbes, 1876, pp. 10–11.—Richardson, 1905, pp. 422–423, figs. 474–476.—Van Name, 1936, pp. 456–457, fig. 286.—Ellis, 1961, pp. 80–102, figs. 1–4.

Asellus militaris Hay, 1878, pp. 90–92.—Mackin, 1940, pp. 17–18.—Van Name, 1942, p. 317.

Although Forbes’ original description in 1876 of A. intermedius lacked drawings, it did give a rather complete description of the species except for critical details of the morphology of the tip of the endopodite of the second pleopod; about this Forbes wrote only (p. 11), “the outer terminal angle is prolonged into an incurved process, the inner provided with a movable (?) excurved claw.” Forbes did not mention deposition of types, but in the redescription by Richardson (1905), which included drawings of the first and second pleopoda, Richardson mentioned she had been sent “types” [sic] from the Museum of Comparative Zoology of Harvard University. Her redescription was based on this material, but unfortunately, like Forbes, she omitted details of the endopodite tip of the second pleopod. Inquiries directed to Dr. H. W. Levi of the Museum of Comparative Zoology revealed that this institution possessed no collection clearly labeled as the type of A. intermedius, but it did possess a collection consisting of three male specimens and one female specimen of Asellus labeled “Asellus intermedius Forbes S.A. Forbes Union Co. Ill.”

As the United States National Museum, with which institution Richardson was associated, also does not possess material labeled as the type of A. intermedius (T. E. Bowman, personal communication, 9 March 1967), we may reasonably assume that the collection examined by Richardson and referred to as type material was returned to the Museum of Comparative Zoology and is the same collection as that referred to above. Although no date of collection is given, the indication that the material had been collected by Forbes himself, and from an area within which he had collected specimens for the original description (“hill country of southern Illinois”), provides strong circumstantial evidence that the material is syntypic. This material, however, if it is syntypic, is not the only such material in existence. Inquiries to the Illinois Natural History Survey revealed the presence of two collections of Asellus, each one labeled “cotypes.” One was labeled, “Cotypes Asellus intermedius Forbes” and “Callahan Cr. Cobden. Ill. May 30, 1876 S. A. Forbes” and contained five males and six females. The other was labeled, “cotypes Asellus intermedius Forbes” and “Stoneft. Cr. Makanda Ill. Jy 30, 1876. S. A. Forbes,” and contained 13 males and 38 females; 2 of these males belonged to the taxon A. brevicauda brevicauda, whereas the other males belonged to a different taxon. The first of the two collections contained males belonging to a single species only, and since it predates the second collection, it is here regarded as consisting of syntype material and from it a lectotype and paralectotypes have been designated.

Asellus militaris was described without drawings by Hay in 1878. Shortly afterward (1882, p. 241) he commented that his taxon was the same as A. communis and this synonymy was accepted by Richardson (1905) and Van Name (1936). It was not accepted, however, by Mackin (1940) who regarded A. militaris as a valid species. Irrespective of the lengthy description given by Hay, his only comment on the morphology of the tip of the endopodite of the second pleopod was, “inner ramus navicular, notched at the distal extremity.” It is thus impossible to be certain about the identity of this taxon from the original description alone. No mention is made in Hay’s paper of type material, but there is in the collections of the Illinois Natural History Survey a collection of Asellus with the label, “Ill. State Lab. Nat. Hist. Abingdon Ill O.P. Hay 1878 S.A. Forbes.” Part of this label is in faded handwriting, namely “Abingdon Ill. O.P. Hay 1878”, while the rest is printed. These locality data correspond closely with the locality data given by Hay for his original material (1878, p. 92: “near Abingdon, Knox county, Illinois”), suggesting that the material was that used by Hay in the preparation of his description. Further evidence for this was kindly provided by Dr. J. D. Unzicker, taxonomist at the Illinois Natural History Survey, who wrote (personal communication, 5 June 1967):

I believe that the vial of A. militaris Hay, which I sent to you, is the type series for this species because (1) the collecting data correspond with that given in the original description, (2) the vial was in a rack labelled ‘check for type material,’ and (3) since Hay described this species in a paper published in our Bulletin series the type would ordinarily be deposited in our collection.

The material consisted of several detached peraeopoda and a detached pleon, two ovigerous females, the front half of a male specimen, one male specimen broken into two halves, and one almost complete male specimen. The last specimen was fully dissected and examined by the present author; only the genital pleopoda of the other damaged male were examined. The examinations revealed that the material was conspecific with lectotype material of A. intermedius and accordingly A. militaris may now be synonymized with this species. The first and second pleopod of the least damaged male are illustrated in Figure 16. The material remains in the collections of the Illinois Natural History Survey where it has no number and is referred to as “INHS (uncataloged)” (J. D. Unzicker, personal communication, 10 August 1967).

TYPE MATERIAL.—Lectotype, adult . Paralectotypes, 4 and 6 . All material is deposited in the Illinois Natural History Survey, Urbana; the material is not numbered, the reference is “INHS (uncataloged).” Data on original label reads: “Callahan Cr. Cobden. Ill. May 30, 1876 S.A. Forbes” and “Cotypes Asellus intermedius Forbes.”

DESCRIPTION OF LECTOTYPE.—Body: Length, 4.5 mm.

Head: Eyes large and distinct. Anterolateral lobes not prominent.

First antenna: Tip of flagellum broken off, flagellum at least 5-merous and reaching to point one-third distally along last segment of peduncle of second antenna. All segments of peduncle about twice as long as wide; first segment longest, second about three-quarters length of first, and third about three-quarters length of second.

Second antenna: Tip of flagellum broken off, but length of antenna (2.5 mm) at least half (0.55) body length. Flagellum at least 31-merous.

First peraeopod (Figure 17A): Dactylus slightly longer than palm of propodus and with 6 teethlike spines on palmar edge and a long terminal claw. Propodus about 1.5 times as long as wide, almost subtriangular; palm with a large obtuse triangular projection about half width of opposing dactylus situated near midpoint, 1 large toothlike spine at proximal end, and a submarginal row of spines on inner and outer surfaces.

First pleopod (Figure 17B): Total length of appendage 1.10 times as long as second pleopod. Sympod subcircular, about as wide as long; inner margin with 3 hooklike protuberances for coupling. Distal segment subovate but distal margin somewhat truncate and distal part of segment distinctly narrower than proximal part; maximum width slightly greater (0.57) than half maximum length; distal margin and adjacent part of outer lateral margin with 9 simple spines of moderate length.

Second pleopod (Figures 17C–E): Sympod subsquare, maximum length equal to maximum width. Proximal segment of exopod with a single spine on outer margin. Distal segment of exopod ovate with 2 short and 11 long setose spines. Endopod subrectangular, rather wide (maximum width about half maximum length), and total length subequal to that of exopod; conspicuous basal apophyses not present. Cannula prominent, wide, as long as wide, and subequal in length to caudal process. Caudal process prominent, sclerotized, and terminated by a sharp point. Mesial process not developed.

Uropod (Figures 18A, B): Slightly shorter (0.77) than telson. Peduncle about twice as long as greatest width. Exopod as long as peduncle, endopod rather longer (1.3); both rami have a number of long fine spines distally, and numerous shorter and stronger spines laterally.

PARTIAL DESCRIPTION OF FEMALE PARALECTOTYPE.—“First” pleopod (Figure 18C): Approximately trapezoidal in shape, almost (2.3) two and a half times as long as maximum width. Distal margin and distal half of outer margin with 7 long and 3 shorter finely plumose spines; a short simple spine occurs near inner proximal angle.

MATERIAL EXAMINED.—ONTARIO: Humber River,* York County, 4 , coll. Ontario P. & D., 12.vi.1946 (NMC); Underwood Creek, Collingwood, 7 , coll. J. B. Sprague, 2.iv.1955 (ROM); Rideau River, 4 , coll. Macoun Field Club, 30.iv.1955 (NMC); Rideau River, 2 , coll. E. L. Bousfield, 7.V.1955 (NMC); stream east of Houghton, 2 , coll. Ontario P. & D., 7.vi.1955 (NMC); Little Otter Creek, 2 , coll. Ontario P. & D., 9.vii.1955 (NMC); Rideau River, 1 , coll. Macoun Field Club, 12.V.1956 (NMC); Underwood Creek, Collingwood, 5 , coll. J. B. Sprague, 11.viii. 1956 (NMC); Frazer Dontile Quarry Pond, Ottawa, 8 , coll. E. L. Bousfield, 29.ix.1956 (NMC); Taylor’s Hill Quarry, Ottawa, 4 , coll. E. L. Bousfield, 13.iv.1957 (NMC); Taylor’s Hill Quarry, Ottawa, 3 , coll. E. L. Bousfield, 4.v.1957 (NMC); Cooksville, 5 , coll. D. Barr, 5.iv.1962 (ROM); Cooksville, 14 , 5.iv.1962 (ROM); Ottawa, 5 , coll. E. L. Bousfield, 21.v.1962 (NMC); Cooksville, 14 , coll. D. Barr, 14.vii.1962 (ROM).

ILLINOIS: Golconda, 3 , coll. B. D. Burks, 12.iii.1940 (INHS); Palas Hills, Cook County, ∞ , coll. L. Hubricht, 2.v. 1941 (USNM); Lemont, Cook County, ∞ , coll. L. Hubricht, 3.v.1941 (USNM); Galesburg, Knox County, ∞ , coll. L. Hubricht, 4.v.1941 (USNM); Glendale, , coll. Messrs. Ross and Burks, 18.iv.1942 (INHS); Carbondale, 4 , coll. R. L. Lippson, 6.iv.1967; Hutchin’s Creek, Union County, 4 , coll. R. L. Lippson, 7.iv.1965.

INDIANA: Wabash River, New Harmony, l, coll. U.S. Dept. Interior, 29.ix.1965; Wabash River, New Harmony, 1 , coll. U.S. Dept. Interior, 20.xii.1965.

IOWA: Swedesburg, Henry County, ∞ , coll. L. Hubricht, 24.iv.1942 (USNM).

KENTUCKY: Fish Pond Creek, Jefferson County, 3 , coll. G. A. Cole, 21.iii.1954; Pennsylvania Creek, Jefferson County, 7 , coll. G. A. Cole, 21.iii.1954; Cedar Creek, Jefferson County, 1 , coll. G. A. Cole, 28.iii.1954; Fern Creek, Jefferson County, 7 , coll. G. A. Cole, 4.iv.1954; Beargrass Creek, Jefferson County, 2 , coll. G. A. Cole, 25.iv.1954; Pennsylvania Run, Jefferson County, 1 , coll. G. A. Cole, 23.v.1954; Spring, Oldham County, 3 , coll. G. A. Cole, 17.iv.1955 (NMC); Goose Creek,* Jefferson County, 4 , coll. G. A. Cole, 4.v.1955; Acc. 59–173, Jefferson County, l, coll. G. A. Cole, 1957 (NMC).

MICHIGAN: Wolf Lake Hatchery, Van Buren County, 1 , coll. R. L. Lippson, 25.xi.1965.

MISSOURI: Meramec State Park, Franklin County, ∞ , coll. L. Hubricht, 25.vii.1937 (USNM).

WISCONSIN: Lake Mendota, 32 , coll. H. W. Levi, September 1948 (CMZ); Lake Superior, Ashland, 6 , coll. E. L. Bousfield, 26.vi.1957 (NMC); Lake Mendota, ∞ , coll. H. B. N. Hynes, 15.viii. 1962; Milwaukee River, l, coll. U.S. Dept. Interior, 23.viii.1962.

GEOGRAPHICAL DISTRIBUTION AND ECOLOGY.—The localities listed above, together with the type locality, are plotted in Figure 19. From this it can be seen that A. intermedius occurs within a large area of east-central United States and southern Ontario. Over a part of its range it is sympatric with A. brevicauda brevicauda, but its range is more extensive than that of this species and it extends farther northward.

Most of the collections examined, as indicated by the data on labels, had been obtained from creeks, streams, or rivers, so that we may assume that A. intermedius is characteristically associated with running waters. Some of the collections, however, were from springs, lakes, ditches, or ponds, and it is clear that A. intermedius is by no means restricted to running waters. The ecology of this species has been intensively studied by Ellis (1961); certainly for his correct identification of the species is provided by his drawings of the male genital pleopods (1961, figs. 2–4), which are undoubtedly those of A. intermedius.

FURTHER DESCRIPTION ().—Body: The largest examined was 16.0 mm long, and the smallest 4.0 mm.

First antenna: Flagellum 7- to 17-merous; flagellum tip reaching to one-third along or to distal end of the last segment of the peduncle of the second antenna; penultimate 2 to 4 (unusually 3) segments bear aesthetascs.

Second antenna: Length 0.48 to 0.79 times that of body. Flagellum 32- to 93-merous, depending upon size.

Mouthparts: See Table 1.

First peraeopod: Dactylus with 4 to 14 teethlike spines on palmar margin; in general, these spines are large and few in small specimens, and small and many in large ones. The shape of the palm shown in Figure 17A (lectotype) occurs only in young specimens, and the shapes typically encountered in large adult males are more like those illustrated in Figures 18D–K, which indicate the range of variation that occurs. Thus, the large triangular structure near the midpoint of the palm is always large and quite prominent (often sharply pointed and occasionally toothlike), and the proximal end of the palm is also usually produced outward, this projection bearing a blunt wide tooth (very occasionally 2 such teeth) and beyond this 1 to 4 but usually 2 stout spines.

First pleopod: Total length of appendage 0.88 to 1.22 times as long as second pleopod. Inner margin of sympod with 3 to 5 (usually 3 or 4) coupling hooks. Maximum width of distal segment 0.36 to 0.71 times maximum length; marginal spines few to numerous, but always simple and of moderate length. The typical shape of the distal segment is subovate; only a little variation occurs.

Second pleopod: Maximum length of sympod from 1.0 to 1.2 times maximum width. Proximal segment of exopod with 1 to 6 spines on outer margin; distal segment with 7 to 23 plumose spines on margin. Inner basal angle of endopod obtuse, sharply angled, or produced into a small acutely pointed apophysis. The main features of the morphology of the tip of the endopod are constant, the principal variation occurring only in the shape and extent of development of the caudal process; this may be rounded, pointed, or have a terminal claw; it is frequently produced at approximately right angles to the main body of the endopod, and may in some cases have pointed basal protuberances, although this is not usually so and is found only in very large specimens. Figure 20 indicates the range of variation in the morphology of the endopod tip. The typical morphology is as illustrated for the lectotype (Figures 17D, E).

Uropod: See Table 2.