Stygobromus amicus Holsinger, sp. n.
Creators: name: Holsinger, John R.
name: Ansell, Lynnette
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Crangonyctidae
Stygobromus
Stygobromus amicus

description: Stygobromus amicus Holsinger, sp. n.
Figures 2, 3, 4, 5
Material examined. Holotype female 3.0 mm and 3 paratypes (2.5 – 3.0 mm), John Friend Cave, Garrett County, Maryland, 1.3 km WNW of Sang Run, Maryland, collected by Daniel Feller 28 Feb. 2009; additional 4 paratypes from same locality by Daniel Feller (29 Aug. 1992 and 11 Feb. 2006); 3 paratypes collected by Ben Hutchins, 12 July and 9 August 2007; and 6 paratypes collected by David C. Culver et al., January and May 2008. The holotype is deposited in the National Museum, Smithsonian Institution (USNM 2060768); paratypes are in the research collection of J.R. Holsinger at Old Dominion University. Additional material from Garrett County tentatively assigned to this species includes: 1 female collected from Crabtree Cave by Richard Franz, 22 Oct. 1966 and 1 juvenile collected from High Rock Wildland Spring by Daniel Feller, 19 December 1988.
Diagnosis. Tiny, presumably rare species of troglomorphic facies distinguished by long, needle-like terminal spines on uropods 1 and 2; ramus of uropod 3 reduced in size and bearing single short spine; and convex apical margin of telson bearing few short spines.
Description. Antenna 1 (Fig. 2 a): 0.45–0.50% length of body, approximately 2X longer than antenna 2; primary flagellum with 9 or 10 articles, lacking aesthetacs, accessory flagellum approximately equal in length to first flagellar article. Antenna 2 (Fig. 2 b): flagellum with 2 articles. Mandibles (Fig. 2 c, d) subequal, differing in few minor ways: spine row of right with 2 lightly plumose spines, that of left with 3 such spines; left and right lacinia mobili are forked spines of unequal lengths; incisors 4–5 dentate, more strongly developed on right mandible; articles 1 and 2 of palps naked; article 3 with 4 apical E setae, 4 much shorter D setae on inner margin and 1 B seta on outer margin. Lower lip (Fig. 2 e): inner lobes vestigial. Maxilla 1 (Fig. 2 f): inner plate with 2 apical plumose setae; outer plate with 5 apical spines (some notched); palp with 4 apical spines. Maxilla 2 (Fig. 2 g): inner plate with 6 naked spines apically; outer plate with 7 rather long spines apically. Maxilliped (Fig. 2 h): inner plate with 4 short apical spines; outer plate with long row of inner marginal spines; palp article 2 broader and longer than article 1, inner margin with row of relatively long setae/spines; palp articles 3 and 4 much shorter, with spines/ setae; article 4 (dactyl) with prominent nail and 3 or 4 short spines/setae.
Gnathopod 1 (Fig. 3 a): propodus approximately 30% larger than propodus of gnathopod 2, palm nearly straight and relatively smooth, approximately equal in length to posterior margin, bearing uneven row of 7 or 8 small spines; dactyl nail ca. 60% length of dactyl; posterior margin with 4 spines; carpus about 75% length of propodus, bearing 5 long setae on ventral margin; coxa oblong, longer than broad, with 2 long, marginal setae. Gnathopod 2 (Fig. 3 b): propodus smaller than that of gnathopod 1, palm slightly curved, smooth, approximately 50% length of posterior margin, bearing 6 small spines; nail of dactyl approximately 75% length of dactyl; posterior margin nearly 2X length of palm, bearing 5 sets of 2 long setae each. Posterior margin of carpus of gnathopod 2 slightly convex, with 7 setae of unequal length. Coxa of gnathopod 2 rounded, bearing 1 marginal seta.
Pereopods 3 and 4 (Figs. 4 a, b): subequal, approximately equal in length to pereopod 5; coxae subquadrate, approximately equal in size, anterior margins convex, posterior margins nearly straight or slightly concave and without marginal setae, ventral margins convex, with 4 or 5 setae of unequal length. Pereopods 5, 6 and 7 (Figs. 4 c, d, e): pereopod 5 slightly shorter, coxa 2-lobate; pereopods 6 and 7 subequal in length, coxae smaller and rounded ventrally); dactyls relatively long, approximately 50% length of corresponding propodi. Coxal gills present on pereopods 5 and 7 (and possibly 6) small and subovate. Paired median sternal gills or processes on pereonites 6 and 7 (Figs. 4 d, e).
Pleonal plates generally similar (Fig. 5 a): ventral margins weakly convex, lacking spines or setae; posterior margins slightly expanded, subrounded, each with single seta; ventral margins lacking setae or spines. Pleopods (Fig. 5 b) biramous, articles bearing long, plumose setae; tiny coupling spines on inner margin of peduncles not shown. Urosomites not fused. Uropod 1(Fig. 5 c): peduncle robust, longer than rami, with 3 short spines on upper margin; rami subequal in length, outer with 5 apical spines, one of which is much longer. Uropod 2 (Fig. 5 d): inner ramus longer and more robust than outer, approximately 75% length of peduncle, bearing 9 marginal spines; outer ramus bearing 5 apical spines of unequal length; peduncle with 3 short spines. Uropod 3 (Fig. 5 e): greatly reduced, only approximately 1/3 length of telson, outer ramus cap-like, bearing single short apical spine; telson (Fig. 5 f) relatively large, little longer than broad, apical margin convex and bearing 11 rather robust apical spines.
Type locality. John Friend Cave, 1.3 km WNW of Sang Run, Garrett County, Maryland (Fig. 1). See also Franz and Slifer (1971) for a detailed description and map of this cave.
Etymology. The epithet amicus is from the Latin meaning “friend” in recognition of “John Friend,” the longstanding name of the type-locality cave.
Distribution and ecology. This species is known to date primarily from drip pools in the type-locality John Friend Cave, and tentatively from a small stream in Crabtree Cave and High Rock Wildland Spring No 2, all three localities in Garrett Co., Maryland (Fig. 1).
description: Published as part of Holsinger, John R. & Ansell, Lynnette, 2014, A new species of the subterranean amphipod genus Stygobromus (Amphipoda: Crangonyctidae) from two caves and a spring in western Maryland, USA with additional records of undescribed species from groundwater habitats in central Maryland, pp. 386-394 in Zootaxa 3768 (3) on pages 387-392, DOI: 10.11646/zootaxa.3768.3.6, http://zenodo.org/record/230299