Stygobromus fecundus Holsinger 1978

Stygobromus fecundus

Stygobromus exilis Hubricht, 1943:697–699, pl. 4 [in part].—Barr, 1961:32 [in part].

Stygobromus sp. K.—Holsinger, 1969a:31.

MATERIAL EXAMINED.—TENNESSEE. Blount Co.: Gregorys Cave, holotype (USNM 168814), 10 and 4 paratypes (JRH), J. R. Holsinger, S. B. Peck, and R. M. Norton, 16 Mar 1964. Additional paratypes from Gregorys Cave as follows: 25 , 4 (USNM 79326), 63 , 12 (USNM), L. Hubricht, 9 Aug 1939; 6 (JRH), S. B. Peck, 5 Aug 1965; 1 , 1 (JRH), L. M. and B. L. Ferguson, 12 Jun 1972.

DIAGNOSIS.—A moderately small cavernicolous species distinguished by relatively long posterior margins of gnathopod propods, 2-spined ramus of uropod 3, and slightly notched apical margin of telson. Largest males, 3.5 mm; largest females, 4.0 mm.

FEMALE.—Antenna 1, 45 percent length of body, 50–55 percent longer than antenna 2; primary flagellum with 12 segments. Antenna 2, flagellum with 3 segments. Mandibles subequal; spin row with 2 or 3 spines; segment 2 of palp with 1 long seta on inner margin, segment 3 with 1 long seta on outer margin, row of short setae on distal half of inner margin and 3 long setae on apex. Maxilla 1: inner plate with 6 apical, plumose setae; palp with 4 stiff setae apically. Maxilla 2, inner plate with oblique row of 6 plumose setae on inner margin. Maxilliped: inner plate with 3 bladelike spines and 1 naked seta apically, 1 bladelike spine and 1 plumose seta subapically; outer plate with naked setae on inner margin and apex and 1 lightly plumose seta apically. Inner lobes of lower lip absent.

Propod of gnathopod 1 a little smaller than 2nd propod; palm relatively short, slightly convex, armed with double row of about 5 spine teeth; defining angle with 2 long spine teeth on outside, 2 shorter ones on inside; posterior margin rather long, nearly as long as palm, with 5 singly inserted setae; medial setae singly inserted. Dactyl nail of gnathopod 1 moderately long. Segment 5 of gnathopod 1 without rastellate setae. Coxal plate of gnathopod 1 longer than broad, margin with 1 seta. Gnathopod propod 2: palm rather short, slightly convex, armed with 6 spine teeth on outside, 3 on inside; defining angle with 2 long spine teeth on outside, 2 shorter ones on inside; posterior margin rather long, nearly as long as palm, with 4 or 5 sets setae; medial setae singly inserted. Dactyl nail of gnathopod 2 moderately long. Segment 5 of gnathopod 2 without rastellate setae. Coxal plates of gnathopod 2 and pereopod 3 longer than broad, margins with 2 setae each. Coxal plate of pereopod 4 about as broad as long, reaching about 45 percent length of basis, margin with 3 setae. Pereopod 6 a little longer than pereopod 7, 45 percent length of body, 15–20 percent longer than pereopod 5. Pereopods 5–7: distoposterior lobes of bases well developed, broadly rounded; dactyl of 5 about 40 percent length of corresponding propod, dactyls of 6 and 7 about 33 percent length of corresponding propods. Coxal gill absent from pereopod 7. Two or 3 median sternal gills on pereonites 2–4; 2 pairs simple lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Brood plates narrow, not expanded distally.

Pleonal plates: posterior margins of 1 and 3 slightly convex, that of 2 nearly straight, margins with 1 seta each; posterior corner of plate 1 distinct, bluntly rounded, those of plates 2 and 3 indistinct, broadly rounded; ventral margin of plate 2 with 2 spines, that of plate 3 with 3 spines. Uronites free. Uropod 1: inner ramus subequal in length to outer ramus, about 55 percent length of peduncle, armed with 9 spines; outer ramus with 7 spines; peduncle with 7 or 8 spines. Uropod 2: inner ramus longer than outer ramus, a little shorter than peduncle, armed with 11 spines; outer ramus with 6 or 7 spines; peduncle with 5 spines. Uropod 3: ramus about 30 percent length of peduncle, armed with 2 apical spines. Telson a little longer than broad, slightly broader proximally than distally; apical margin with small notch, armed with 12–14 spines.

MALE.—Differing slightly from female as follows: Gnathopod propods proportionately a little broader, armed with 2 or 3 more spine teeth; posterior margin of gnathopod propod 2 with few less setae. Peduncular process of uropod 1 about 25 percent length of outer ramus, apex serrate.

TYPE-LOCALITY.—Gregorys Cave, located in Great Smoky Mountain National Park in Blount Co., Tennessee, is also the type-locality for S. sparsus (see p. 82 for further descriptive details on the type-locality).

DISTRIBUTION AND ECOLOGY.—This species is known only from its type-locality, where it is common is a series of rimstone pools fed by ceiling drips. Collections have been made during March, June, and August and those from March and August contained females (3.5–4.0 mm in length) with setose brood plates. The August 1939 collection had three ovigerous females (3.5–4.0 mm), two brooding one egg each and one brooding two eggs.

Both S. sparsus and S. fecundus have been collected from pools in Gregorys Cave, but only the latter has been found with regularity (on four separate visits to the cave over the last 33 years) and is by far the most abundant of the two species (127 out of 130 specimens collected to date) in the cave.