Stygobromus felleri Holsinger

Holsinger, John R., Ansell, Lynnette Meador & Shafer, Justin, 2011, Four new species of the subterranean amphipod genus Stygobromus (Amphipoda: Crangonyctidae) from shallow groundwater habitats on the Coastal Plain and eastern margin of the Piedmont in Maryland and Virginia, USA, Zootaxa 2972, pp. 1-21 : 6-10

Stygobromus felleri Holsinger , sp. n.

Figures 5 , 6 , 7

Material examined. Holotype male (4.0 mm) and 3 paratypes (1 male, 1 female, 1 juvenile), from Funks Pond Spring, 1.7 km east-northeast of Kilby Corner, Cecil County, Maryland, collected by Daniel Feller, 25 March 2008; 3 paratypes (1 male, 2 juveniles) from same locality collected by Daniel Feller, 14 April 2010. The holotype is deposited in the National Museum of Natural History, Smithsonian Institution ( USNM 1154085); paratypes are in the research collection of J. R. Holsinger.

Diagnosis. Small species of troglomorphic facies, distinguished by robust accessory tripartite cutting plate of right mandible; relatively robust gnathopod propodi, with 1st propodus larger than 2nd; relatively broad bases of pereopods 5, 6 and 7; median and bifurcate lateral sternal gills (processes) present; and absence of peduncular process on uropod 1 of male. Largest males, 4.5 mm; largest females, 4.0 mm.

Description. Male (4.5 mm). Antenna 1 ( Fig. 5 a) 45 – 50% length of body, approximately 30% longer than antenna 2; primary flagellum with 12 articles, few with aesthetacs; accessory flagellum reaching to end of 2nd flagellar article. Antenna 2 ( Fig. 5 b): flagellum with 6 articles. Mandibles ( Figs. 5 c, d) differing in a few minor ways: spine rows of right and left with 3 lightly plumose spines; lacinia mobilis of left not apparent, that of right strong and tripartite; incisors 7 or 8 dentate; molar of left not protruding and bearing short seta, that of right prominent and cone-shaped, bearing long seta; article 2 of right palp with 2 setae, article 2 of left palp with 4 setae; article 3 of left palp with 2 E setae, 2 D setae and 1 A seta; segment 3 of right palp similar to left. Lower lip ( Fig. 5 e): inner lobes present. Maxilla 1 ( Fig. 5 f): inner plate with 3 plumose apical setae; outer plate with 5 notched apical spines; palp with 4 short apical spines. Maxilla 2 ( Fig. 5 g): inner plate with 2 lightly plumose setae subapically, and 6 short, naked spines apically; outer plate with 8 rather long spines apically. Maxilliped ( Fig. 5 h): inner plate with 3 apical spines; outer plate with row of 6 short spines or setae on inner margin and 2 similar ones apically; palp article 2 broader and longer than article 1, inner margin with 11 or 12 short setae; palp article 3 much shorter than 2 and bearing several apical setae; palp article 4 very short and bearing prominent terminal nail.

Gnathopod 1 ( Fig. 6 a): propodus approximately 25 to 30% larger than propodus of gnathopod 2, palm nearly straight, without serrations,nearly 2X length of posterior margin, bearing unequal row of 11 or 12 distally-notched spine teeth and 7 or 8 rather long setae; dactyl nail approximately 25% length of dactyl; posterior margin with several longish setae; carpus subtriangular, broader than deep, bearing several long setae; coxa subrounded, broader than deep, with 2 short, marginal setae. Gnathopod 2 ( Fig. 6 b): propodus smaller than that of gnathopod 1, palm straight, without serrations, approximately equal in length to posterior margin, bearing irregular double row of 12 distally bifid spines; nail of dactyl approximately 50% length of dactyl; posterior margin subequal in length to palm, bearing 4 sets of long setae. Posterior margin of carpus of gnathopod 2 convex, with 3 sets of longish setae and 1 prominent rasellate seta. Coxa of gnathopod 2 broadly rounded, bearing 3 long, ventral setae.

Pereopods 3 and 4 ( Figs. 7 a, b) subequal, approximately equal in length to pereopod 5; coxa of 3 broader than deep, with 4 short marginal setae; coxa of 4 subquadrate, posterior margin weakly convex, with 4 short setae. Pereopods 5, 6,7 ( Figs. 7 c,d,e): 7 slightly longer than 6 and much longer than 5; posterior margins convex; distoposterior lobes of 6 and 7 more prominent; dactyl of 5 about 45% length of corresponding propodus, those of 6 and 7 about 30% length of corresponding propodi. Median sternal gills ( Fig. 7 a) and 2 pairs bifurcate lateral sternal gills ( Figs. 7 f,g) present. Relatively large subovate coxal gills on pereopods 3 and 4 ( Fig. 7 b) and small coxal gill from pereopods 7 ( Fig. 7 e).

Pleonal plates 1–3 ( Fig. 7 h): posterior margins weakly convex; plates 1 and 2 with 2 setae each, plate 3 with single seta; posterior corners distinct; ventral margins of 1 and 3 with 2 tiny spines, 2 lacking setae or spines. Pleopods ( Fig. 7 i) biramous, segments bearing long plumose setae, peduncles with 1 or 2 coupling spines each. Uropod 1 ( Fig. 7 j): inner ramus slightly longer than outer ramus, about 75% length of peduncle, armed with 7 spines, outer ramus with 5 apical spines; peduncle with 3 spines. Uropod 2 ( Fig. 7 k): inner ramus longer and broader than outer ramus, subequal in length to peduncle, armed with 5 apical and 3 lateral spines; outer ramus with 3 apical and 1 upper marginal spines; peduncle with 1 spine. Uropod 3 ( Fig. 7 l): ramus approximately 50% length of peduncle, armed with 3 apical spines. Telson ( Fig. 7 m) approximately 40 % longer than broad, not tapered distally, apical margin uneven and bearing 10 spines of unequal length.

Type locality. Funks Pond Spring, 1.7 km ENE of Kilby Corner, Cecil County, Maryland ( Fig. 1 ).

Etymology. It is a pleasure to name this new species in honor of its discoverer, Daniel Feller of the Maryland Natural Heritage Program, who has made many important collections of amphipods and other invertebrates from groundwater habitats and other substantial contributions to our knowledge of the natural history of Maryland.

Distribution and ecology. This species is known only from its type locality, Funks Pond Spring in Cecil County, Maryland ( Fig.1 ). In addition to S. felleri , a large specimen of the relatively widespread, troglomorphic amphipod Stygobromus pizzinii (Shoemaker) (see Holsinger 1978) and several specimens of the widespread troglomorphic isopod crustacean Caecidotea pricei Levi were collected from this locality by Daniel Feller on 14 April 2010. Funks Pond spring is apparently developed in Paleozoic igneous rocks just west of the eastern margin of the Piedmont Province.The exact source of the spring water is undetermined.

Figures

FIGURE 1. Distribution of four new species of Stygobromus from the Coastal Plain and eastern Piedmont in Maryland and Virginia, United States. The restricted distributions of S. caecilius, S. felleri and S. paxillus. are indicated by single symbols. Stygobromus foliatus is more widely distributed and recorded from multiple locations on opposite sides of the Potomac River in Charles and S. Mary’s counties in Maryland, and Caroline, Westmoreland and King & Queen counties in Virginia. Several closely spaced localities in Caroline County are indicated by a single symbol. The curved line through MD and VA marks the approximate boundary between the Coastal Plain to the east and the Piedmont to the west.

FIGURE 5. Stygobromus felleri, sp. n. Funks Pond Spring, Cecil County, Maryland. Paratype male (4.0 – 4.5 mm): (a, b) antenna 1, antenna 2 (accessory flagellum and aesthetacs of antenna 1 enlarged); (c) left mandible (inner face enlarged); (d) right mandible in part (inner face enlarged); (e) lower lip; (f) maxilla 1; (g) maxilla 2; (h) maxilliped. Antennae drawn to same scale; maxillae 1 & 2 to same scale; maxilliped and lower lip to smaller scale.

FIGURE 6. Stygobromus felleri, sp. n. Funks Pond Spring, Cecil County, Maryland. Paratype male (4.0 – 4.5 mm): (a, b) gnathopods 1, 2 (palmar margins enlarged). Gnathopods drawn to larger scale than antennae.

FIGURE 7. Stygobromus felleri, sp. n. Funks Pond Spring, Cecil County, Maryland. Paratype male (4.0 – 4.5 mm): (a, b, c, d, e) pereopods 3, 4, 5, 6, 7; (f) lateral sternal gill from pereopod 7; (g) lateral sternal gill from pereopod 6; (h) pleonal plates; (i) pleopod; (j, k, l) uropods 1, 2, 3; (m) telson. Antennae, pereopods 3, 4, 5, 6, 7 and pleonal plates drawn to same scale; gnathopods 1 & 2, pleopod, uropods and telson to larger scale. Maxillae 1 & 2 drawn to larger scale than other mouthparts. Inner faces of molars and palms of gnathopods greatly enlarged.