Stygobromus floridanus Holsinger and Sawicki

Holsinger, John R. & Sawicki, Thomas R., 2016, A new species of the subterranean genus Stygobromus (Amphipoda: Crangonyctidae) from a cave spring in northern Florida, USA, Zootaxa 4067 (1) : -

Stygobromus floridanus Holsinger and Sawicki , sp. n.

Figures 2 , 3 , 4 , 5

Material examined. Holotype female 13.0 mm, 2 female paratypes (8.0 and 9.0 mm) collected by Tom Morris, 12 February 2003, and in addition, 1 juvenile paratype (6.0 mm) specimen collected by Tom Morris, 21 November 2011 from nearby Miller’s Crossing or Miller’s Ferry Spring. The holotype is deposited in the National Museum of Natural History, Smithsonian Institution ( NMNH 1222549); paratypes are in the research collection of J.R. Holsinger at Old Dominion University.

Diagnosis. Relatively large and rare species of troglomorphic facies distinguished by large and robust propodi of gnathopods 1 and 2, relatively long antennae, pereopods, and uropods 1 and 2 and long, narrow, tapered telson bearing 6 relatively robust, terminal spines and 2 tiny mid-lateral spines.

Description. Antenna 1 ( Fig. 2 a): approximately 60% length of body, approximately 65–70% longer than antenna 2; primary flagellum with 29 articles, 1st 10 or 11 bearing aesthetascs; accessory flagellum with 2 articles slightly shorter in length than first 2 flagellar articles. Antenna 2 ( Fig. 2 b): flagellum with 7 articles. Mandibles ( Figs. 2 c and 3d) generally similar but differing slightly in a number of important structural details as shown; molars differing slightly but both with heavily serrate cutting margins and 1 seta each; lower lip (inner margins vestigial ( Fig. 2 e); maxilla 1 ( Fig. 2 f); maxilla 2 ( Fig. 2 g); maxilliped ( Fig. 2 h) inner plate with 6 apical plumose setae, outer plate with 6 apical spines (all notched), palp with 7 apical spines. All mouthparts drawn to same scale; antennae to smaller scale.

Gnathopod 1( Fig. 3 a): propodus slightly larger than propodus of gnathopod 2, palm nearly straight and relatively smooth, much longer than posterior margin, bearing a complex, uneven double row of approximately 40 spines of highly variable length; dactyl nail much shorter than dactyl; posterior margin proportionately very short and lacking spines; coxa subovate, bearing few short setae. Gnathopod 2 ( Fig. 3 b): palm weakly convex, more than 2× length of posterior margin, bearing double row of approximately 40 spines of unequal length, in addition to 4 much longer spines near defining angle; posterior margin much shorter than palm, bearing several sets of setae of unequal length. Coxa subovate but larger than that of gnathopod 1, with 5 marginal setae of unequal length.

Pereopods 3 and 4 ( Figs. 4 a, 4b): subequal, shorter than pereopod 5, coxa of 3 smaller than that of 4 and bearing fewer marginal setae. Pereopods 5 and 6 ( Figs. 4 c, d) subequal in length and overall structure. Pereopod 7 ( Fig. 4 e) slightly shorter than pereopods 5 and 6, with shorter coxal plate, and lacking sternal gill and brood plate. Dactyls of pereopods relatively long, approximately 1/3 length of corresponding propodi. Stalked coxal gills present on pereopods 3 and 4; simple (unstalked) on pereopods 5 & 6; absent from 7.

Pleonal plates ( Fig. 5 a) generally similar: ventral margins weakly convex, each with 1 to 4 tiny marginal spines; posterior margins nearly straight, each with 1 tiny seta near corner. Pleopods biramous, normal for genus, not shown. Urosomites not fused. Uropod 1( Fig. 5 b2): peduncle robust, subequal in length to rami, with 5 spines on upper margin; rami sub equal in length, outer with 4 upper marginal spines and 5 shorter terminal spines. Uropod 2 ( Fig. 5 b1) approximately 75% length of uropod 1, peduncle with 3 spines on upper margin; rami sub equal in length, each bearing 4 upper marginal spines and 2 or 3 terminal spines. Uropod 3( Fig. 5 c) significantly shorter than uropod 1, bearing 3 short apical spines. Telson ( Fig. 5 d) relatively long, tapering, more than 2× longer than wide, apex bearing 6 relatively small spines.

Type locality. Skipper Spring, Washington County, Florida ( Fig. 1 ).

Etymology. The epithet floridanus is in recognition of its occurrence in the state of Florida. Distribution and Ecology. This species is known to date only from the Skipper Spring, and nearby Miller’s Crossing or Miller’s Ferry Spring in Washington County, Florida, USA.

Figures

FIGURE 1. Distribution of Stygobromus floridanus in the “ panhandle ” of northwestern Florida, USA.

FIGURE 2. Stygobromus floridanus, sp. n. Skippers Spring, Washington County, Florida. Paratype specimen (13 mm): (a, b) antenna 1, antenna 2; (c) right mandible; (d) left mandible in part (chewing structures enlarged); (e) lower lip); (f) maxilla 1; (g) maxilla 2; (h) maxilliped. All mouthparts except right mandible drawn to same scale. Antennae and right mandible drawn to smaller scale.

FIGURE 3. Stygobromus floridanus, sp. n. Skippers Spring, Washington County, Florida. Paratype specimen (13 mm): (a) gnathopod 1; (b) gnathopod 2.

FIGURE 4. Stygobromus floridanus, sp. n. Skippers Spring, Washington County, Florida. Paratype specimen (13 mm): (a) pereopod 3; (b) pereopod 4; (c) pereopod 5; (d) pereopod 6; (e) pereopod 7).

FIGURE 5. Stygobromus floridanus, sp. Skippers Spring, Washington County, Florida. Paratype specimen (13 mm): (a) pleonal plates; (b) uropod 1 and 2; (c) uropod 3; (d) telson. (pleonites not shown).