The evolution of the eastern North American isopods of the genus Asellus (Crustacea: Asellidae) Part II

Abstract

This paper is the first in a three part series concerned with the evolution of North American isopods of the genus Aselllls. It contains the descriptions of four new species of isopods and a list of pertinent new range data of presently known species. Subsequent papers will deal with the generic status of Aselllls, recently discovered synonymies and a consideration of the evolution of the genus Aselllls. These three papers will constitute a thorough discussion of the genus Aselllls emphasizing the relationships between epigean and troglobitic species and the zoogeography of both. I am grateful to the following individuals for collecting this material and making it available to me: a.H. Tomson, R.S. Fox and L. Hubricht. I would like to thank Dr. Perry C. Holt for reviewing the manuscript. Asellus holti, sp. nov. (Figs. 1-5) Type-specimens.-Holotype, UNSM 79308; Allotype, UNSM 138241; 6 paratypes, UNSM 138242; taken from a small stream, 1.8 miles east of Casa, Perry County, Arkansas by Leslie Hubricht, May 4, 1940. Diagnosis.-Peduncle of male second pleopod 1.3 times longer than wide; exopod 0.55 times as long as peduncle; distal segment of exopod triangular; endopod terminating in 4 processes; lateral process, mesial process, cannula and accessory process; peduncle of first pleopod with 5 coupling hooks; palmar margin of propodus of gnathopod with 2 processes: medial and distal. Description.-A moderate sized, pigmented isopod with reduced eyes; holotype (largest male) 7.2 mm in length and 1.6 mm in width; allotype (ovigerous) 7.2 mm in length and 1.9 mm in width (at brood pouch); body slender, length (excluding uropods) 4.5 times width in ho10type and 3.7 times width in allotype. Palmar margin of propodus of male gnathopod (peraeopod 1) with 2 processes (Fig. 1): (l) large, subacute, medial process directed distally and (2) small distal process with flattened apex. Proximal end of palmar margin has 3 stout spines. A