Caecidotea brevicauda (Forbes 1876)

Asellus brevicauda Forbes

Asellus brevicauda Forbes, 1876, pp. 8–10.—Richardson, 1905, pp. 423–425, figs. 477–479.—Van Name, 1936, pp. 462–463, fig. 290.

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

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

Asellus brevicauda was described by Forbes in 1876, but the description though rather lengthy did not include details of those parts of the body of most taxonomic significance; it did not, moreover, include drawings despite Richardson’s indication (1905, fig. 477) that it did, and it was obviously a composite description based on several specimens. A later description by Richardson (1905) seems to be original in that it was not based entirely on Forbes’ description and contained additional (but relatively unimportant) descriptive material. It was based upon a single specimen, but Richardson made no comment as to where this came from, and neither her description nor the original one of Forbes’ mentions deposition of type material. In Richardson’s redescription of A. intermedius in the same paper (pp. 422–423), however, she mentions that she had been sent “types” [sic] of A. intermedius from the Museum of Comparative Zoology of Harvard University, and since this species was described by Forbes at the same time he described A. brevicauda, it seems possible that Richardson was sent similar material for A. brevicauda, although she does not say so. At all events, inquiries to the curator at the Museum of Comparative Zoology, Dr. H. W. Levi, revealed the presence in the collections of that institution of a single male specimen of Asellus in a tube with the label: “MCZ Illinois; Union Co., July 30, 1876; S. A. Forbes coll. Asellus brevicauda Forbes.” Bearing in mind Forbes’ only statement (1876, p. 10) about the distribution of the species, namely that it is found in Jackson and Union counties in southern Illinois, and the fact that other crustaceans collected on 30 July (Gammarus fasciatus Say, p. 6) and in 1876 (Eubranchipus serratus Forbes, pp. 13–14) were referred to in the same paper, the circumstantial evidence is very strong that this specimen is a syntype.

According to Dr. H. W. Levi (personal communication, 13 September 1967), the specimen was originally deposited in the Peabody Academy of Science and later transferred. It could have been so deposited by Forbes as a result of his contact with S. I. Smith of Yale College (cf. Forbes, 1876, p. 3), although in view of Forbes’ position as curator of the Illinois Museum of Natural History deposition in his own institution would have been normal. The Illinois Natural History Survey, although possessing syntype material of A. intermedius, did not possess syntype material for A. brevicauda (Dr. J. D. Unzicker, personal communication, 5 June 1967). The specimen from the Museum of Comparative Zoology is accordingly now designated as the lectotype of A. brevicauda. It is not certain that this is the actual specimen examined in 1905 by Richardson, but because its dimensions correspond to those given by Richardson this seems likely.

Apparently under the impression that the specific name brevicauda was adjectival, Mackin and Hubricht (1938) altered it to brevicaudus to seem to agree in gender with the genus name. It is, however, a noun, and the original spelling is correct.

Asellus bivittatus was described by Walker (1961) from a stream, Doe Run, in Meade County, Kentucky. Unfortunately, although her description was very detailed in most respects, she omitted critical details concerning the morphology of the tip of the endopodite of the male second pleopod, stating only (p. 388), “pore at distal end giving appearance of bifurcation.” She provided a figure of the second pleopod of the male, but it was at too small a scale to provide clarification. Her type material is deposited in the United States National Museum, and reexamination of the sexual pleopods of the holotype as well as male topotypic material kindly given me by Prof. H. B. N. Hynes and Dr. L. A. Krumholz revealed that the morphology of the tip of the endopodite of the second pleopod was almost identical with that of the lectotype of A. brevicauda. Her taxon is therefore regarded as conspecific with A. brevicauda. There seem to be, nevertheless, differences between other parts of the morphology of her taxon and the lectotype of A. brevicauda, and these are such that it is appropriate at present to accord her taxon subspecific status.

It should be noted that both Walker’s taxon and what she regarded as “somewhat differentiated” A. brevicauda occur in the same stream, although spatially separated (see also Minckley, 1963, who regarded such material as aberrant A. bivittatus). It is perhaps possible that the differences displayed by her taxon are no more than phenotypic variations of typical A. brevicauda brought about by the physical nature of the environment (upper reaches of Doe Run, associated with the moss Fissidens). Some of the significant distinguishing criteria of Walker’s taxon, according to Walker, are small size and body color pattern. The present author has been unable to examine a collection of small males of A. brevicauda brevicada and unable to compare the color patterns of live specimens from the upper reaches of Doe Run and A. brevicauda brevicauda. Until such examination and comparison have been made, preferably on material gathered entirely from Doe Run, subspecific status for Walker’s taxon is appropriate. It may be added that through the courtesy of Dr. L. A. Krumholz, University of Louisville, an attempt to examine live material from Doe Run was made, but unfortunately the material did not survive the postal journey.