Macrostylis dorsaetosa, Riehl, Torben, Wilson, George D. F. & Hessler, Robert R., 2012

Riehl, Torben, Wilson, George D. F. & Hessler, Robert R., 2012, New Macrostylidae Hansen, 1916 (Crustacea: Isopoda) from the Gay Head-Bermuda transect with special consideration of sexual dimorphism, Zootaxa 3277, pp. 1-26 : 4-12

publication ID	https://doi.org/ 10.5281/zenodo.209468
DOI	https://doi.org/10.5281/zenodo.6176728
persistent identifier	https://treatment.plazi.org/id/D602547E-FFED-5F0D-12C7-F9BCFC38FCC9
treatment provided by	Plazi
scientific name	Macrostylis dorsaetosa
status	sp. nov.

Treatment

Macrostylis dorsaetosa View in CoL n. sp.

( Figs 1–7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 2 F). Lateral lobe with 14 robust setae.

Maxilla ( Fig. 2 View FIGURE 2 G). Lateral lobe with 4 setae terminally; middle endite with 3 setae terminally; inner endite with 8 setae terminally.

Maxilliped ( Fig. 2 View FIGURE 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 View FIGURE 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.

Pereopod II ( Fig. 3 View FIGURE 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 View FIGURE 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 View FIGURE 4 A). Length 0.15 body length, carpus laterally flattened.

Pereopod V ( Fig. 4 View FIGURE 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.

Pereopod VI ( Fig. 4 View FIGURE 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 View FIGURE 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.

Operculum (female pleopod II; Fig. 4 View FIGURE 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 View FIGURE 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 View FIGURE 5 F). Present.

Uropod ( Figs 1 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 5 A–B). Length 0.64 pleotelson length, with simple setae ventrally.

Pleopod II ( Fig. 5 View FIGURE 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 View FIGURE 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.

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 View FIGURE 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 View FIGURE 3 C, 6G, 7A).