Stygobromus stellmacki (Holsinger 1967)

Stygobromus stellmacki (Holsinger)

Stygonectes stellmacki Holsinger, 1967:33–36, fig. 6 [type-locality: Millers Cave, near Rockspring, Centre Co., Pennsylvania]; Holsinger, 1969a:32–33; Holsinger, 1972:60; 1976:76.

Stygobromus stellmacki (Holsinger).—Karaman, 1974:119.—Holsinger, 1977:262.

MATERIAL EXAMINED.—PENNSYLVANIA. Centre Co.: Millers Cave, 2 topotypes, J. A. Stellmack, 4 Sep 1966.

DIAGNOSIS.—A relatively large cavernicolous species corresponding to the diagnosis and description by Holsinger (1967). Largest male, 14.2 mm; largest female, 16.5 mm.

FEMALE.—Since the original description, which was based on a single male, the following characters have been noted for the female: Antenna 1, 55–62 percent length of body, 50–55 percent longer than antenna 2; primary flagellum with 25–26 segments. Flagellum of antenna 2 with 8–10 segments. Gnathopod 1: propod a little larger than 2nd propod; segment 5 with 2 rastellate setae. Gnathopod 2: propod with 3 or 4 sets setae on posterior margin; segment 5 with 2–5 rastellate setae. Coxal gill on pereopod 7. Three, rather small median sternal gills on pereonites 2–4; 2 pairs bifurcate lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Ramus of uropod 3 with 4 apical spines. Apical margin of telson with or without small notch, armed with 16 spines.

DISTRIBUTION AND ECOLOGY.—This rare species is known only from its type-locality, where three specimens (one male and two females) have been collected from a wide, shallow mud-bottom pool on an upper level of the cave. A small stream in the lower level is inhabited by S. allegheniensis (Holsinger, 1967:36). The two females in the September 1966 collection did not have setose brood plates but otherwise appeared mature.

Stygobromus stellmacki, commonly called Stellmack's cave amphipod is a troglomorphic species of amphipod in family Crangonyctidae. It is endemic to Pennsylvania in the United States.