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The observation of pigmentation alteration in isopod crustaceans induced by acanthocephalans, known as pigmentation dystrophy, has been documented in North America in species of the aquatic genera Asellus Geoffroy, 1764, Lirceus Rafinesque-Schmaltz, 1820, and Caecidotea Packard, 1871, and in Europe, in Asellus. Recently, three depigmented specimens of Atlantoscia floridana (van Name, 1940), a terrestrial isopod, occurring from >Florida, USA to northern Argentina were found showing pigmentation dystrophy and harboring larval acanthocephalans. Photographic documentation of live and preserved, infected isopods is presented. Morphometric data and photomicrographs of the male, unencysted cystacanth specimen which allowed its placement in the genus Centrorhynchus Lühe, 1911 are presented. This is the first record of the phenomenon of pigmentation dystrophy in terrestrial isopod crustaceans, the first record of A. floridana infected by an acanthocephalan and the first record of a species of Centrorhynchus in a terrestrial isopod.

Nine species of asellid isopods are reported from groundwater habitats in Maryland. Three of these species are habitually found in springs: Lirceus brachyurus, Caecidotea kenki, and C. alleghenyensis, n. sp. The latter, described herein, is a member of the hobbsi group known only from the Allegheny Mountains in Garrett Co. Six species are obligate inhabitants of subterranean waters and are found primarily in Appalachian caves, although some have broad ranges that span noncavernous areas. The obligate subterranean species are Caecidotea pricei, C. franzi, C. holsingeri, C. mausi, C. vandeli and C. nordeni.

The quantitative significance of bacterial biomass in the nutrition of detritivores remains equivocal. We have used tritiated thymidine to specifically label stable macromolecules in natural assemblages of sediment-associated and detritus-associated bacteria. This material was presented to the isopod (Lirceus sp.) and incorporation of bacterial biomass measured. The isopod incorporated roughly 1 ng bacterial carbon (mg wet wt.)-1 h-1 from leaf discs and about 6 ng mg-1 h-1 from sediment. Calculation of grazing rate from changes in cell counts yields grazing rates from 2.3–17.9 ng C mg-1 h-1. Even the maximum grazing rate, which is an overestimate of C assimilated, represents only 14.7% of C respired by the isopod.

During the unusual molt sequence of the fresh-water isopod,Lirceus brachyrus (Harger), the posterior half of the exoskeleton is shed 24 hours before the anterior half. At the half-molt stage, occurs in the posterior part while the anterior portion is in a pre-molt condition. The percentage difference in calcium in the two halves at half-molt and full-molt is22 (p

We examined patterns of habitat use of an isopod, Lirceus fontinalis, that coexists with predatory fish in second and third order permanent streams in central Kentucky, USA. Isopods were significantly more dense in Cladophora, a filamentous green alga, than on bare substrates of silt, sand, and gravel, and in submerged leaf litter when predatory fish were present. The dense, entangled filaments of the algae precluded most fish from entering Cladophora mats and eating isopods. Nonetheless, fish predation significantly reduced total isopod densities in these habitats. In laboratory manipulations, emergences from and entrances into Cladophora along with overall movements by isopods in open sandy areas were significantly reduced when green sunfish (Lepomis cyanellus) were present. Lirceus responded similarly to only water conditioned with green sunfish, indicating isopods use chemical cues, in part, to detect predatory fish. Isopods predominantly ate decaying leaf tissue (i.e., coarse particulate organic matter [CPOM] > 0.5 mm in diameter), but amounts of CPOM were significantly lower in Cladophora than in sediments of bare substrates. Lirceus did not eat the algae. Over 80% of the organic particulates in algal mats were < 0.5 mm (fine POM). Isopods reared on FPOM grew significantly slower than those on CPOM. Long-term use of algal mats poor in forage by isopods may adversely affect relative fitness since egg production by females is dependent on body size.

The thermal tolerance of the aquatic isopod Lirceus brachyurus (Harger) was investigated. Survival, as measured by the time to 50% mortality (LT50), in- creased with increasing acclimation temperature. A tolerance polygon was constructed which defined the range of temperatures (0-23 C) tolerated by the isopods for 2 weeks. Upper lethal temperatures were lower than recorded for other isopod species. Lower lethal temperatures were related to those of other isopod species and to ice mineralization of creek water. The thermal tolerance of L. brachyurus did correspond to maximum and minimum water temperatures recorded in the study creek. The ecological significance with respect to the biology and habitat of L. brachyurus, and to power plant operation, is discussed.