Search

Troglobitic isopods of the family Asellidae, comprising about 42 species (Fleming, 1973), are widespread in the eastern United States, mostly in non-glaciated areas, but extending into some glaciated parts of Illinois and Indiana. To the west, troglobitic asellids range to central Kansas, Oklahoma and Texas. West of this area, if we exclude the 4 Mexican species of Mexistenasellus (Cole and Minckley, 1972; Magniez, 1972; Argano, 1973) which belong to a separate family, Stenasellidae (Henry and Magniez, 1968, 1970), only 2 troglobitic asellids are known from North America: Asellus californicus Miller (1933) from northern California and Conasellus pasquinii Argano (1972) from Veracruz state, Mexico. The 3 new species of western troglobitic asellids described herein extend the records of blind asellids in North America south to Chiapas state, Mexico, and north to central Alberta, Canada (ca. 53''N), and add a second species from California. The new species from Chiapas is very similar to Conasellus pasquinii Argano (1972); the new asellids from Alberta and California show no close affinities with known species. The generic status of North American species of Asellus is still unsettled. Henry and Magniez (1970) divided tlie species between Conasellus Stammer (1932) and ,Pseudobaicalasellus Henry and Magniez (1968) except A. tomalensis Harford and ... A. californicus Miller, which they believed to be closely related to far-eastern forms belonging to Aseltus (Asellus) and Nipponasellus Matsumoto (1962). I have indi" cated that this is unlikely for A. tomalensis (see Bowman, 1974); the case oi A. californicus will be discussed later in this paper. ' '""'*

A curious abnormality of the pereon segmentation in a fresh-water isopod of the family Asellidae, not so far encountered, is described. It affects the last thoracic segment of a male specimen of the cavernicolous species, Asellus cavaticus Leydig. The right half of this segment is atrophied in such a way as to cause a dextrogyrous deviation of the pleotelson; moreover, the right seventh pereiopod and the penis are absent. As this anomaly is certainly of embryonic origin, there is no doubt about its teratological nature. The specimen behaves quite normally and no change in its appearance followed either of the two moults that it underwent since it was discovered.

In the genus Asellus we have, in the first and second pleopoda of the male, characters which can be relied upon to distinguish the species, but in Lirceus these appendages are so similar in different species that they are, with one exception, useless as a means of separation. This is not because the species of Lirceus are less distinct than Asellus, but requires that the animal as a whole be studied rather than a single appendage. To an experienced observer the various species are easily distinguished in the field by those subtile differences in form and color which are almost impossible to describe. Difficulties begin when one brings specimens into the laboratory and attempts to define the differences. The commonest cause of difficulty is depauperate specimens. Under adverse conditions the animals are stunted, the gnathopoda do not develop their processes, and the uropoda remain in juvenile form. When this depauperization is extreme the collection cannot be determined, but must be assumed to belong to the species in the range of which it was found.

In an effort to furnish data bearing on the problems of geographic distribution of the Isopoda, the following records are published. It seems highly desirable that more locality records be made available, since in this manner only may exact extent of distribution be ascertained. It should be pointed out that specific determinations of some forms in the genera Asellus and Mancasellus are attended with much difficulty. This is due to the fact that in most descriptions up to date stress has been laid on certain characters which are so broad that they are generic in value rather than specific, and conversely, on characters so variable that at most only local races may be defined by them, or only growth stages. As an example of the former, we cite the descriptions of mouth parts, and of the latter, number of segments in the antennae, and relative length of uropods. In a group in which the studies have been so scattered and uncorrelated, it is inevitable that there should be wide discrepancies of opinion as to what constitute characters of family, generic and specific rank, and value of various specific characters in separation of species. There are certain principles which should be considered carefully when describing species belongintg to the genera Asellus and Mancasellus. These are, first, determination of, and deletion of, generic characters and those of greater rank, second, specific characters should be used in such a manner as to utilize variational data rather than allow them to be confusing factors. In the specific descriptions in this paper certain customary "specific" characters have been intentionally omitted, such as proportions of the peduncular segments of the antennae. Such characters have been found to be more confusing than helpful, for variations of interspecific nature are slight, while growth variations are greater.