New Macrostylidae Hansen, 1916 (Crustacea: Isopoda) from the Gay Head-Bermuda transect with special consideration of sexual dimorphism Author Riehl, Torben Author Wilson, George D. F. Author Hessler, Robert R. text Zootaxa 2012 3277 1 26 journal article 10.5281/zenodo.209468 2c269ccb-4369-4adc-86f4-e5a5225fcc15 1175-5326 209468 Macrostylis dorsaetosa n. sp. ( Figs 1–7 ) Etymology. The species name 'dorsaetosa' is feminine and a shortened composition of three words: The first part is the prefix ‘dors-‘ derived from the Latin word 'dorsum'. The prefix is meant to provide position information regarding the second part, 'setae', owing to the presence of conspicuous setae dorsally on the posterior tergites. Finally, the greek suffix ‘-osis’ indicates the condition ‘dorsally setose’, which is the literal translation of the name. Type fixation. Holotype : adult female, 2.6 mm , AM P.86000, designated here. Type material examined. Holotype : non-ovigerous female, 2.6 mm , AM P.86000, used for the illustration of the habitus, WHOI 62. Paratypes : sub-adult male, 1.9 mm , AM P.86001, partly dissected for illustration of appendages, WHOI GH1; non-ovigerous female, 2.6 mm , AM P.86002, dissected for illustration of appendages and habitus, WHOI GH1; terminal male, 2.2 mm , AM P.86003, dissected for illustration of appendages, WHOI GH1; terminal male, 2.2 mm , AM P.86004, used for habitus illustration, WHOI 62; sub-adult male, 2.0 mm, AM P.86005, MI 633, gold-coated for SEM , WHOI 62; juvenile female, 1.9 mm , AM P.86006, MI 639, gold-coated for SEM , WHOI 62; 14 specimens , AM P.86021, male and female, WHOI 62; 4 specimens , AM P.86025, male and female, WHOI GH4. Type locality. Western North Atlantic off Long Island: 39°25.5'N ; 70°35.0'W ; 2500 m ( WHOI GH #1); 39°28.8'N , 70°34.2'W ; 2469 m ( WHOI GH#4); 39°26'N ; 70°33'W – 39°27.2'N ; 70°33.2'W ; 2496 m ( WHOI 62). Type material — Remarks. Collected on North American slope off Long Island during cruise R/V Atlantis- 273, stations WHOI GH1 (27. Septemember 1961) and WHOI GH4 ( 30. October 1961 ) and R/V Atlantis II-12 , station WHOI 62 ( 21 August 1964 ), about 3.4 km apart. Further records. WHOI G#1, 1 juvenile male (AM P86024); WHOI HH#3, 1 terminal male, AM P86026; WHOI 66, 1 non-ovigerous female, 1 manca, AM P98019; WHOI 128, 7 non-ovigerous females, AM P86007; WHOI 131, 12 specimen , male and female, AM P67257. Description, female. Body ( Figs 1 A, C, E, 6D, 7B). Length 2.6 mm , 6.5–6.9 width, subcylindrical, tergite surfaces with scattered setae. Ventral spines. Pereonite 1 spine acute, prominent. Pereonite 3–4 spine absent. Pereonite 5 spine acute, small, closer to posterior segment border. Pereonite 6 spine acute, prominent, closer to posterior segment border. Pereonite 7 spine small. Imbricate ornamentation (IO). Pereonite 4 IO in anterior region of tergite and sternite; pereonite 5–6 IO in anterior dorsal pereonal collum regions. Cephalothorax. Length 0.82–0.90 width, 0.10–0.11 body length; frons in dorsal view straight, frontal ridge present, straight. Posterolateral setae present. Posterolateral margins blunt. Fossosome. Length 1.1–1.2 width, 0.16–0.18 body length. Lateral tergite margins in dorsal view forming almost uninterrupted line, ventral surface with keel, sternite articulations present. Pereonite 1. Anterior margin straight; posterolateral setae simple. Pereonite 2. Posterolateral setae simple. Pereonite 3. Posterolateral setae simple, flexibly articulated. Pereonite 4. Width 0.96–1.0 pereonite 5 width, length 0.65–0.90 width; pereonal collum present. Lateral margins in dorsal view curved, narrow in pereonal collum, widest in middle and slightly constricted anterior to posterolateral angles. Posterior tergite margin setae 8–9 altogether, bifid, robust, flexibly articulating, short, not extending beyond posterolateral margin. Posterolateral margins rounded. Posterolateral setae simple, not robust, flexibly articulated. Pereonite 5. Length 0.95–1.1 width. Posterior tergite margin setae 8 altogether, bifid, robust, flexibly articulating, long, extending beyond posterolateral margin. Posterolateral margins rounded. Tergite posterolateral setae bifid, robust. Pereonite 6. Length 0.90–0.97 width. Posterior tergite margin setae 8–9 altogether, bifid, robust, flexibly articulating, long, extending beyond posterolateral margin. Posterolateral margin produced posteriorly, rounded. Tergite posterolateral setae bifid, robust, flexibly articulated. Pereonite 7. Length 0.67–0.73 width. Posterior tergite margin setae 10–12 altogether, bifid, short, not extending beyond posterolateral margin. Posterolateral margin produced posteriorly. Tergite posterolateral setae bifid, robust, flexibly articulated. Pleonite 1. Sternal articulation with pleotelson absent. Pleotelson. Ovoid, length 0.21 body length, 1.6 width, narrower than pereonite 7; statocysts present, dorsal slot-like apertures absent. Posterior apex convex, bluntly rounded. Posterior apex setae 2 altogether, simple, positioned lateral to apex. Pleopodal cavity width 0.58 pleotelson width, preanal ridge width 0.42 pleotelson width. Anal opening subterminal, tilted posteriorly relative to frontal plane. Labrum. Anterior margin in dorsal view concave. Antennula ( Fig. 2 K–L). Length 0.41 head width, 0.25 antenna length, width 1.0 antenna width. Articles decreasing in size from proximal to distal. Article 1 distinctly longer than wide, longest and widest, with 2 simple setae. Article 2 distinctly longer than wide, tubular, with 2 simple setae. Article 3 squat, globular. Article 4 squat, globular. Article 5 minute, squat, globular, with 1 simple seta. Terminal article with 1 aesthetasc, penultimate article with 1 aesthetasc, aesthetascs simple, tubular. Antenna ( Fig. 2 M–N). Length 0.2 body length. Article 1 squat, globular. Article 2 elongate, longer than article 1. Article 3 elongate, longer than article 1. Article 4 longer than articles 1–3 together, distally with 1 simple seta. Article 5 shorter than article 4, distally with 6 simple setae, distally with 1 broom seta. Flagellum with 5 articles. Mandibles ( Fig. 2 A–D). In medial view strongly narrowing from proximal to distal, sub-triangular, with lateral setae; left mandible incisor process distal margin flattened and curved (shovel-like), with 3 cusps, lacinia mobilis grinding, with 4 cusps; right mandible incisior process with shovel-like appearance, with 3 cusps, lacinia mobilis grinding, clearly smaller than left lacinia, with 8 cusps. Maxillula ( Fig. 2 F). Lateral lobe with 14 robust setae. FIGURE 1. Macrostylis dorsaetosa n. sp. A–E, holotype Ψ (AM P86000). A, dorsal habitus, imbricate ornamentation and fine setation omitted. B, left pereopod III ischium, close-up. C, pleotelson, ventral. D, right uropod, close-up. E, lateral habitus. Scales: A, D–E = 1 mm, B–C = 0.5 mm. FIGURE 2. Macrostylis dorsaetosa n. sp. A–C, E, N, paratype adult (non-ovigerous) Ψ (AM P86002). M, paratype juvenile Ψ (AM P86006). D, F–G, K, paratype terminal ɗ (AM P86003). L, paratype juvenile ɗ (AM P86005). A, left mandible, medial view of incisor process and lacinia mobilis. B, left mandible, dorsal. C, right mandible, dorsal. D , right mandible, incisor process and lacinia mobilis, medial view. E, paragnaths, ventral view, ventral setae omitted in right lateral lobe, all setae omitted in left medial lobe, dorsal setae omitted in left lateral lobe. F, right maxillula, dorsal. G, left maxilla, ventral. H, left maxilliped, endite setation, ventral. I, left maxilliped, ventral. J, right maxilliped, endite setation, dorsal. K right antennula, lateral. L left antennula and antenna, lateral. M, right antennula and antenna, lateral. N, right antennula and antenna, lateral. Scales: A–J = 0.05 mm, K–N = 0.1 mm. Maxilla ( Fig. 2 G). Lateral lobe with 4 setae terminally; middle endite with 3 setae terminally; inner endite with 8 setae terminally. Maxilliped ( Fig. 2 H–J). Basis endite length 4.2 width; epipod length 4 width, 1.0 basis-endite length; palp wider than endite, article 2 wider than articles 1 and 3, article 1 shorter than article 3. Pereopod I ( Fig. 3 A). Length 0.25 body length. Ischium dorsal margin with 5 setae, simple, in row, row of setae laterally to margin. Merus dorsal margin with 6 setae, 5 simple, 1 prominent, split, ventral margin with 4 setae, 3 biserrate, 1 split, with dorsal row of setae laterally to margin. Carpus dorsally with 3 setae, 2 simple, 1 prominent, split. Dactylus distally with 3 sensillae. FIGURE 3. Macrostylis dorsaetosa n. sp. A–C, paratype Ψ (AM P86002). A, pereopod I, lateral, close-up of split and monoserrate seta. B, pereopod II, lateral. C, pereopod III, lateral. Scale = 0.3 mm. Pereopod II ( Fig. 3 B). Longer than pereopod I, length 0.29 body length. Ischium dorsally with 6 setae, simple, with dorsal row of setae laterally to margin. Merus dorsally with 8 setae, 6 simple in row, 2 split disto-medially, with dorsal row of setae laterally to margin, ventrally with 4 setae, biserrate. Carpus dorsally with 5 setae, 3 simple, 1 broom, 1 prominent split, serrate, ventrally with 4 setae, 3 biserrate, 1 split. Dactylus distally with 3 sensillae. Pereopod III ( Fig. 3 C). Length 0.26 body length. Ischium dorsal lobe tapering; proximally with no setae; apex with 1 prominent seta; apical seta robust, robust sensillate, bent towards proximal, spine-like; distally with 2 simple setae. Merus dorsally with 11 setae, 6 simple, 5 split, serrate, ventrally with 3 setae, biserrate. Carpus dorsally with 7 setae, split, serrate, ventrally with 4 setae, 3 biserrate, 1 split. Dactylus with 3 sensillae. Pereopod IV ( Fig. 4 A). Length 0.15 body length, carpus laterally flattened. Pereopod V ( Fig. 4 B). Length 0.25 body length. Ischium mid-ventrally with 3 setae, simple, disto-ventrally with 3 setae, simple. Merus disto-dorsally with 4 setae, split, mid-ventrally with 3 setae, 1 split, 2 simple, distoventrally with 2 setae, 1 short, split, serrate, 1 long, simple. Carpus disto-dorsally with 3 setae, 1 split, 1 broom, 1 split, serrate, disto-ventrally with 3 setae, split. FIGURE 4. Macrostylis dorsaetosa n. sp. A–E, paratype Ψ (AM P86002). A, pereopod IV, posterior. B, pereopod V, lateral. C, pereopod VI, lateral. D, pereopod VII, lateral. E, operculum, ventral. Scales = 0.2 mm. Pereopod VI ( Fig. 4 C). Length 0.32 body length; ischium mid-ventrally with 3 setae, simple, disto-ventrally with 3 setae, all simple; merus disto-dorsally with 4 setae, 2 short, split, 1 simple, 1 long split, mid-ventrally with 4 setae, simple, disto-ventrally with 2 setae; carpus mid-dorsally with 2 setae, simple, disto-dorsally with 5 setae, 1 split, 2 broom, 1 split, serrate, 1 split, mid-ventrally with 2 setae, simple, disto-ventrally with 4 setae, 2 split, 2 prominent, split, serrate. Pereopod VII ( Fig. 5 D). Length less than pereopod VI length, 0.33 body length. Basis length 2.7 width; with row of elongate setae on posterior margin. Ischium length 3 width, mid-dorsally with 2 setae, simple, mid-ventrally with 1 seta, simple, disto-ventrally with 1 seta, simple. Merus length 2.2 width, disto-dorsally with 3 setae, 1 split, 2 simple, mid-ventrally with 2 setae, simple, disto-ventrally with 2, 1 simple, long, 1 split, short. Carpus length 5.5 width, mid-dorsally with 2 setae, simple, disto-dorsally with 5 setae, all split, possibly all serrate or biserrate, midventrally with 2 setae, simple, disto-ventrally with 4 setae, 1 long, split, serrate, 1 simple, 2 split. Propodus length 4.3 width. Dactylus length 2.5 width. FIGURE 5. Macrostylis dorsaetosa n. sp. A–B, paratype terminal ɗ (P86004). C–F, paratype terminal ɗ (AM P86003). A, close-up of pleopods I, ventral. B, pleotelson, ventral. C, left pleopod II, ventral. D–F, right pleopods III – V, d o r s a l. Scales: A, C–F = 0.1 mm, B = 0.5 mm. Operculum (female pleopod II; Fig. 4 E). Elongate, length 1.6 width, 0.60 pleotelson length, distally tapering, without keel, with 14 pappose setae on apex, completely covering anal opening. Pleopod III ( Fig. 5 D). Length 2.5 width, protopod length 1.6 width, 0.46 pleopod III length; exopod with fringe of fine setae, about as long as pleopod III exopod width, with simple seta subterminally, exopod length 0.77 pleopod III length. Pleopod V ( Fig. 5 F). Present. Uropod ( Figs 1 A, D, 7B). Length 0.79–0.82 pleotelson length; protopod length 0.55–0.56 pleotelson length, inserting on pleotelson ventrally on posterior margin. Protopod distal margin blunt, endopod insertion terminal, length 7.5–8.1 width; endopod length 4.7–6.1 width, 0.46–0.47 protopod length, endopod width subequal protopod width. Description, terminal male. Body. Length 2.2 mm , 6.6 width. Cephalothorax. Frons smooth, frontal ridge present, straight; length/width ratio greater than in female, length 0.96 width, 0.12 body length; with conspicious dorsal array of setae, posterolateral corners rounded, posterolateral setae absent. Fossosome. Length/width ratio greater than in female, length 1.4 width, length/body-length ratio greater than in female, length 0.21 body length. Pereonite 4. Lateral margins in dorsal view convex; posterolateral margin not produced posteriorly. Pereonal collum present, medially convex. Pleonite 1. Sternal articulation with pleotelson present. Pleotelson. In dorsal view approximately rectangular, length/width ratio in male greater than in female, length 1.8–2.1 width, 0.23 body length, width less than pereonite 7 width. Pleopodal cavity width 0.69 pleotelson width, preanal ridge width 0.37 pleotelson width. Antennula ( Figs 2 K–L, 6A–B, E). Length 0.52 head width, 0.33 antenna length, width 2.0 antenna width, articles 1, 2 and 5 elongate, tubular; articles 3–4 squat or noticeably shorter; terminal article with 3 aesthetascs, penultimate article with 4 aesthetascs, aesthetascs simple, tubular. Article 1 elongate, subequal in width and length compared to more distal articles, with 1 simple seta and 1 broom seta. Article 2 squat, globular, shorter than article 1, with 1 simple seta and 2 broom setae. Article 3 squat, globular, shorter than article 1, article 4 squat, globular, shorter than article 1. Article 5 elongate, longer than article 1, with 2 simple setae. Antenna ( Figs 2 L, 6A, E). Length 0.2 body length, flagellum of 4 articles. Article 1 squat, globular. Article 2 elongate, longer than article 1. Article 3 elongate, longer than article 1. Article 4 shorter than articles 1–3 together, distally with 1 simple seta. Article 5 longer than article 4, with 3 broom setae. Pereopod I ( Fig. 6 F). Ischium dorsally with 4 setae, all simple, with dorsal row of setae shifted laterally. Merus dorsally with 5 setae, 4 simple in row, 1 split distally, ventrally with 3 setae, 2 biserrate, 1 split seta distally. Carpus dorsally with 2 setae, 1 simple, 1 split distally, ventrally with 2 setae, biserrate. Pereopod II. Ischium dorsally with 5 setae, all simple, with dorsal row of setae shifted laterally. Merus dorsally with 8 setae, 6 simple in row, 2 split disto-medially, ventrally with 3 setae, all two-sided serrate. Carpus setation as in female. Pereopod V. Merus disto-dorsally with 3 setae, split, mid-ventrally with 2 setae, simple; disto-ventrally with 2 setae. Carpus disto-dorsally with 4 setae, 1 small, split, 1 broom, 2 serrate, split. Pereopod VI. Ischium setation as in female. Merus disto-dorsally with 4 setae, 2 short, split, 1 simple, 1 long split, mid-ventrally with 2 setae, simple, disto-ventrally with 1 seta, split. Carpus mid-dorsally with 2 setae, simple, disto-dorsally with 3 setae, 1 split, serrate, 1 broom, 1 split; mid-ventrally with 2 setae, simple, disto-ventrally with 4 setae, 3 split, 1 long, split, serrate. Pereopod VII. Length/body-length ratio as in female, segment L/W ratios sexually dimorphic; basis length 2.6–2.8 width; ischium length 2.6 width, mid-dorsally with 2 setae, simple, mid-ventrally with 1 seta, simple, distoventrally with 2 setae, simple; merus length 2.2–2.8 width, merus setation as in female; carpus length 4.8–5 width, carpus mid-dorsally with 2 setae, simple, disto-dorsally with 5 setae, split, mid-ventrally with 2 setae, simple, disto-ventrally with 3 setae, split; propodus length 7 width; dactylus length 4 width. Pleopod I ( Fig. 5 A–B). Length 0.64 pleotelson length, with simple setae ventrally. Pleopod II ( Fig. 5 C). Protopod apex rounded, with setae on proximal lateral margin, 3 pappose setae altogether, with 6 pappose setae distally. Endopod distance of insertion from protopod distal margin 0.54 protopod length. Stylet sinuous, extending near to distal margin of protopod, length 0.84 protopod length. Uropod ( Figs 5 B, 6H). Length 0.88–1.1 pleotelson length; protopod length/width ratio greater than in female, 9.6–10.3 width, with endopod inserting terminally; endopod/protopod length ratio less than in female, endopod length 0.29–0.3 protopod length, length 5.4–6 width, width less than protopod. FIGURE 6. Macrostylis dorsaetosa n. sp. A–H, paratype juvenile ɗ (AM P86005). A, cephalothorax, dorsal. B, antennula close-up, dorsal. C, pereonites 5 – 6, dorsal. D, habitus, lateral. E, cephalothorax close-up, lateral. F, pereopod I, lateral. G, pereopod III, lateral. H, posterior apex of pleotelson and uropods, dorsal. Scales: A–B, F–H = 0.1 mm, D = 1 mm. Remarks. Macrostylis dorsaetosa n.sp. is unlike any other species in the genus owing to the row of bifid setae on the posterior margins of pereonites 5–6 ( Figs 1 A, E, 6C). M. strigosa Mezhov, 1999 shows remarkable similarity in important characters such as the ischium setation of pereopod III, a character often applied for differentiation of macrostylid species, and body shape. This latter species could therefore be regarded as closely related to M. dorsaetosa n. sp. However, the above mentioned dorso-marginal setae are missing in M. strigosa . M. grandis Birstein, 1970 has smaller marginal setae on pereonites 4–6 and the pleotelson, but this latter species is also unusual in having pereonite 6 laterally overlapping pereonite 7. The chaetotaxy of the pereopod III ischium is substantially different in the two species as well, with M. dorsaetosa having one robust proximally curving seta on the apex and 2 simple setae on the distal slope of the dorsal projection ( Figs 3 C, 6G, 7A).