The Freshwater lsopods of the Genus Lirceus (Asellota, Asellidae) LESLIE HUBRICHT and J. G. MACKIN V Reprinted from "THE AMERICAN MIDLAND NATURALIST" Vol. 42, No. 2, pp. 334-349, September, 1949 Notre Dame, Ind. The Freshwater lsopods of the Genus Lirceus (Asellota, Asellidae) Leslie Hubricht 912 Main St., Danville, Virginia J. G. Mackin Texas A & M Research Foundation, Grande Isle, Louisiana 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 dif- ferences. 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 depau- perization is extreme the collection cannot be determined, but must be as- sumed to belong to the species in the range of which it was found. The isopods discussed herein have, in the past, been treated under the generic name Mancasellus Harger, rather than the prior Lirceus of Rafinesque. Rafmesque's description, though very poor, is sufficient to determine the genus. Since only one species of asellid occurs in the vicinity of Lexington, Kentucky, the type locality, there is no doubt as to the identity of Rafinesque's species. AN EVALUATION OF THE CHARACTERS USED TO DISTINGUISH SPECIES IN LIRCEUS Because appendages and other structures of taxonomic value are so much better developed in males than in the females, determinations can more advan- tageously be made from them. Therefore, in the following discussion and in the descriptions the females have been ignored, and of the males only those well developed are used as a basis for description. General body form.—Young specimens about 'A inch long are about 3.5 times as long as broad. In some species they become proportionately broader as they grow older until they may be a little less than twice as long as broad, so that this is a useful character in fully developed specimens but useless with depauperates. Whether or not the body is contracted or relaxed affects these 334 1949 HUBRICHT ET AL.: FRESHWATER ISOPODS 335 proportions and it was found that they could be expressed better by the pleo- telson alone. Color.—The basic color pattern is quite similar in all the species. There is a median zone which may or may not be mottled, on each side of this is a wide lateral zone which is mottled with yellowish and in some species has a dark border on both sides giving the animal the appearance of having four longitudinal bands, and there is a usually lighter marginal zone. Although some of the species are rather distinctly colored the differences are difficult to describe and must be seen to be really understood. Head.—In some species the head is incised but in others it is entire; in still others both conditions occur with occasional intermediates. Antennae.—The differences in the antennae between species are so slight and the age differences so great that they are useless as taxonomic characters and have not been used in this paper. Mouth Parts.—There are no specific peculiarities in the mouth parts other than those pertaining to the mandibulary palp. Most species are without a palp but some have a three-jointed palp and in others the structure has only one joint. In L. hoppinae the palp may consist of three joints, two, or only one, or the entire structure may be absent. Gnathopoda.—In the gnathopoda one finds the best characters for the dif- erentiation of species, but the study of immature or dwarfed specimens may be most confusing. The effects of depauperization are most noticeable in modification of the propodi and these structures are most subject to aberrations. In depauperate specimens the processes of the propodi do not develop fully, or in extreme cases not at all, on the other hand, in animals of normal size one or more processes may become over-developed. This is particularly true of the proximal process—when it becomes enlarged it usually produces a reduc- tion in the distal process. These aberrations are apparently of somatic origin as they rarely affect both gnathopoda. The palmar margin is usually armed with three processes, the proximal, median, and distal, and comparison of the relative development of these has proved most valuable in delimiting species. Pleopoda.—The first and second pleopoda of the male which have been found so useful in separation of species of Asellus are of doubtful, value in Lirceus. The tip of the endopodite of the second peopoda which in Asellus differs so completely from species to species, in Lirceus differs only by slight variations in a single basic pattern. The tip is usually bent forward but some- times it is twisted inwards which gives it a quite different aspect, but the differ- ence is more apparent than real. Uropoda.—The uropoda vary considerably with age, also they are easily lost and the regenerated ones are never as large as the originals, and in some species dimorphism occurs. However, the uropoda of mature specimens con- tribute important characters for delimiting species. 336 THE AMERICAN MIDLAND NATURALIST 42 (2) Genus LIRCEUS Rafinesque 1820. Lirceus Rafinesque, Annals of Nature, 1: 7. 1874. Asellopsis Harger, Amer. Jour. Sci. & Arts, III, 7: 601-602. (non) Asellopsis Brady at Robertson, Ann. & Mag. Nat. Hist., IV, 12: 137-138. 1873. 1876. Mancasellus Harger, Amer. Jour. Sci. & Arts, III, 11: 304-305. Description.—With the characters of the family Asellidae. Head laterally expanded and flattened and with a well-defined median anterior keel projecting forward between the antennae. Epimera broad, coalesced with their segments. Mandible without a palp, with a three-jointed palp, or of various intermediate conditions. Peni set close together. Suture between the basal and distal seg- ments of the exopodite of the third pleopod very oblique, the distal segment triangular or half-moon shaped. Type species.—Lirceus fontinalis Rafinesque. Distribution.—Southern Canada and eastern United States west to the Great Plains. Remarks.—The genus Lirceus probably consisted originally of a single entity which under the influence of geographical and ecological isolation has evolved into a number of distinct species which, with a few exceptions, replace each other geographically. This divergence is without pattern or geographical trends. Species inhabiting adjacent areas are apt to differ most. Unlike Asellus, in which the majority of the species are subterranean, Lirceus has produced no true cave forms. It is rarely found in caves, and in only one instance is it known to have become modified by cave life. KEY TO THE SPECIES I. Mandible with a palp 2 Mandible without a palp 7 2. Mandibular palp of a stub or one or two joints 3 Mandibular palp with three joints 5 3. Pleotelson distinctly broader than long L. hoppinae ozarkensis Pleotelson only very slightly wider than long 4 4. Median propodal process acutely pointed, distinctly longer and more strongly developed than the proximal process; distal process present, small L. fontinalit Median process blunt, and little, if any longer than the proximal process; distal process absent L. bidentatus 5. Both median and distal propodal processes bicuspid_ L. bicuspidatus Neither median nor distal propodal processes bicuspid 6 6. Pleotelson wider than long L. hoppinae hoppinae Pleotelson longer than broad L. alabamae 7. Median and distal propodal processes absent L. brachyurus Median process and usually also the distal process of the propodi present 8 8. Uropodal sinuses of the pleotelson acutely incised L. trilobus Uropodal sinuses of the pleotelson not acutely incised, represented by rounded con- cavities or absent 9 9. Endopodite of the uropoda equal to or longer than the basal segment 10 Endopodite distinctly shorter than the basal segment 15 10. Proximal process of the propodi as large as or larger than the median process 11 Proximal process distinctly smaller than the median process 12 1949 HUBRICHT ET AL.: FRESHWATER ISOPODS 337 11. Proximal and median processes of the propodi crowded close together, the distance between them being little if any greater than the width of the proximal process L. garmani Proximal and median processes widely separated, the distance between them being sensibly greater than the width of the proximal process L. hargeri 12. Uropoda flattened 13 Uropoda cylindric in form 1,. lineatus 13. Median process of the propodi bicuspid or squarely truncate terminally L. richardsonae Median process either rounded terminally or acutely pointed 14 14. Uropodal sinuses of the pleotelson weakly developed; tip of the median propodal process acutely pointed; pleotelson only slightly broader than long L. fontinalis Uropodal sinuses of the pleotelson moderately well developed, the pleotelson dis- tinctly broader than long; median process of the propodi rounded truncate ter- minally L. hoppinae ouachitaensis 15. Pleotelson longer than broad 16 Pleotelson as broad as long or very distinctly broader 17 16. Proximal process of the propodi large, well developed, larger than the median process L. megapodus Proximal process absent, represented by a blunt spine at the angle of the palm L louisianae 17. Uropoda flattened L. fontinalis Uropoda cylindric L. lineatus As a further aid in the determination of specimens the species are arranged geographically from east to west and from north to south.