Macrostylis papillata Riehl, Wilson & Hessler, 2012, n. sp.

Macrostylis papillata n. sp.

Etymology. The name 'papillata' is derived from the Latin word ‘papilla’, meaning 'wart' because this species is characterized by warty posterior margins of the cephalothorax' and the anterior four pereonites' tergites.

Type fixation. Holotype: ovigerous female, 1.5 mm, AM P.86009, designated here.

Type material examined. Holotype: ovigerous female, 1.5 mm, AM P.86009, used for habitus illustrations, WHOI 121. Paratypes: juvenile female, 1.3 mm, AM P86008, partly used for illustration of habitus and antennae, WHOI 121; non-ovigerous female, 1.5 mm, AM P86010, used for habitus illustrations and dissected for illustration of appendages, WHOI 121; terminal male, 1.3 mm, AM P86011, used for habitus illustrations and dissected for illustration of appendages, WHOI 121; ovigerous female, 1.5 mm, AM P86013, MI 638, gold-coated for SEM, WHOI 121; terminal male, AM P86014, MI 635–MI 637, dissected and gold-coated for SEM, WHOI 121; immature male, 1.3 mm, AM P86015, partly used for illustration of habitus and antennae, WHOI 121.

Type locality. Western North Atlantic abyssal plain between Long Island and Bermuda: 35°50.0'N; 65°11.0'W; 4800 m (WHOI 121), 35°51.0'N; 64°58.2'W; 4833 m (WHOI 122).

Type material – Remarks. Collected during cruise R/V Atlantis II-24 (21 August 1966).

Further records. 1 terminal male, AM P.86016, WHOI LL 1; 4 specimen, female and male, AM P.67254, WHOI 58; 1 terminal male, AM P.83030, WHOI 83; 1 non-ovigerous female, AM P.86028, WHOI 85; 8 specimen, female and male, AM P.86029, WHOI 95; 2 ovigerous female, AM P.86055, WHOI 120; 1 terminal male, AM P.86012, WHOI 125; terminal male, 1.3 mm, AM P.86012, MI 630, gold-coated for SEM, WHOI 125.

Description, female

Body (Figs 8 A–D, 15A–E). Length 1.5 mm, 4.5 width, subcylindrical, without setation. Ventral spines. Pereonite 1 spine acute, prominent. Pereonite 3 spine blunt, small, closer to anterior segment border. Pereonite 4 spine directed posteriorly, acute, small, closer to posterior segment border. Pereonite 5 spine blunt, closer to posterior segment border. Pereonite 6 spine acute, prominent, closer to posterior segment border. Pereonite 7 spine small. Imbricate ornamentation (IO). Pereonite 1 IO along anterior tergite margin and medially on tergite from anterior to posterior, covering whole sternite; pereonites 2 and 3 IO in an hourglass-shaped band medially on tergite, wider in pereonite 3 than in pereonite 2, covering whole sternite; pereonite 4–7 and pleotelson IO covering all tergites, sternites and operculum.

Cephalothorax. Length 0.82 width, 0.15 body length; frons in dorsal view convex, with wrinkles, frontal ridge absent; dorsal surface with array of setae, 1 pair on frons between anterior rims of antennulae articulations, 1 pair dorsally and 1 pair at back of cephalothorax. Posterolateral setae absent. Posterolateral corners acute. Posterior margin papillose. Fossosome. Length 0.85 width, 0.19 body length. Lateral tergite margins in dorsal view forming almost uninterrupted line, ventral surface without keel. Pereonite 1. Anterior margin concave; posterolateral setae simple, posterior tergite margin papillose. Pereonite 2. Posterolateral setae simple, posterior tergite margin papillose. Pereonite 3. Posterolateral setae simple, flexibly articulated, posterior tergite margin papillose. Pereonite 4. Width 1.2 pereonite 5 width, length 0.66 width; pereonal collum present. Lateral margins in dorsal view simple convex. Posterior tergite margin papillose. Posterolateral margin rounded. Posterolateral setae simple, not robust, flexibly articulated. Pereonite 5. Length 0.69 width. Posterolateral margin rounded. Tergite posterolateral setae bifid, robust. Pereonite 6. Length 0.72 width. Posterolateral margin produced posteriorly, rounded. Tergite posterolateral setae bifid, robust, flexibly articulated. Pereonite 7. Length 0.63 width. Posterolateral margin produced posteriorly, rounded. Tergite posterolateral setae bifid, robust, flexibly articulated.

Pleonite 1. Tergal articulation with pleotelson present.

Pleotelson (Figs 8 D, G, 15C). Ovoid, constricted anteriorly to uropod articulations, length 0.22 body length, 1.8 width, narrower than pereonite 7; statocysts present, dorsal slot-like apertures absent. Posterior apex convex, bluntly rounded. Posterior apex setae absent. Pleopodal cavity width 0.72 pleotelson width, preanal ridge width 0.44 pleotelson width. Anal opening terminal, tilted posteriorly relative to frontal plane.

Labrum (Fig. 14 F). Anterior margin in dorsal view concave.

Antennula (Fig. 8 E–F). Length 0.25 head width, 0.25 antenna length, width 1.5 antenna width. Articles decreasing in size from proximal to distal. Article 1 squat, globular, widest but not longest, with 1 broom seta. Article 2 distinctly longer than wide, tubular, subequal article 1 length, with 1 broom seta. Article 3 distinctly longer than wide, tubular, length subequal article 1 length, with 1 simple seta. Article 4 squat, globular. Article 5 minute, squat, globular, with 1 simple seta. Terminal article with 1 aesthetasc, aesthetasc with intermediate belt of constrictions.

Antenna (Fig. 8 E–F). Length 0.18 body length. Article 1 squat, globular. Article 2 squat, globular, longer than article 1. Article 3 elongate, longer than article 1. Article 4 shorter than articles 1–3 together, distally with 1 broom seta. Article 5 longer than article 4, distally with 4 broom setae. Flagellum with 4 articles.

Mandibles (Fig. 11 A–D). In medial view dorsoventrally flattened, with lateral setae; left mandible incisor process distal margin flattened and curved (shovel-like), with 4 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 6 cusps.

Maxillula (Fig. 11 E). Lateral lobe with 13 robust setae.

Maxilla (Fig. 11 H, 15F–G). Lateral lobe with 4 setae terminally, simple; middle endite with 5 setae terminally, simple; inner endite with 9 setae terminally, 4 monoserrate, 5 slim, simple.

Maxilliped (Figs 11 F–G, 15F). Basis endite length 3.5 width; epipod length 3.5 width, 1.2 basis-endite length; palp width subequal endite width, article 2 wider than article 1, article 2 wider than article 3, article 1 shorter than article 3.

Pereopod I (Fig. 9 A). Length 0.33 body length. Ischium dorsal margin with 1 seta, split, bisetulate, latero-distally. Merus dorsal margin with 3 setae, bisetulate, distally, ventral margin with 2 setae, bisetulate, placed distally. Carpus dorsally with 1 seta, bisetulate, placed distally. Dactylus distally with 2 sensillae.

Pereopod II (Fig. 9 B–C). Longer than pereopod I, length 0.39 body length. Ischium dorsally with 3 setae, bisetulate, placed distally. Merus dorsally with 3 setae, bisetulate, placed distally. Carpus dorsally with 3 setae, 1 bisetulate and 1 broom medially, 1 split distally, ventrally with 2 setae, 1 medially, 1 distally. Dactylus distally with 2 sensillae.

Pereopod III (Fig. 9 D). Length 0.41 body length. Ischium with no seta proximo-dorsally, dorsal lobe tapering; proximally with 1 bisetulate seta; apex with 1 prominent seta; apical seta robust, bifid, bent towards proximal, spine-like; distally with 1 bisetulate seta. Merus dorsally with 4 setae, 2 bisetulate, 2 split, bisetulate, ventrally with 2 setae, simple. Carpus dorsally with 5 setae, 1 bisetulate, 2 split, bisetulate, 1 broom, 1 split, bisetulate, ventrally with 3 setae, simple. Dactylus with 2 sensillae.

Pereopod IV (Fig. 10 A). Length 0.24 body length.

Pereopod V (Fig. 10 B). Length 0.33 body length. Ischium mid-ventrally with 1 seta, bisetulate, disto-ventrally with 2 setae, bisetulate. Merus disto-dorsally with 2 setae, 1 short, bisetulate, 1 long, bisetulate, disto-ventrally with 2 setae, 1 long, bisetulate, 1 short, bisetulate. Carpus disto-dorsally with 1 seta, bisetulate, disto-ventrally with 2 setae, bisetulate.

Pereopod VI (Fig. 10 C). Length 0.41 body length; ischium mid-ventrally with 2 setae, bisetulate, disto-ventrally with 2 setae, bisetulate; merus disto-dorsally with 2 setae, bisetulate, disto-ventrally with 2 setae, bisetulate; disto-dorsally with 3 setae, 1 broom, 1 prominent, split, bisetulate, 1 small, bisetulate, mid-ventrally with 1 seta, bisetulate, disto-ventrally with 2 setae, 1 short, bisetulate, 1 long, bisetulate.

Pereopod VII (Fig. 10 D). Length less than pereopod VI length, 0.33 body length. Basis length 4.3 width; with no elongate setae. Ischium length 3.5 width, disto-ventrally with 1 seta, bisetulate. Merus length 3.0 width, distodorsally with 1 seta, bisetulate, disto-ventrally with 1 seta, short, bisetulate. Carpus length 6.0 width, disto-dorsally with 2 setae, 1 broom, 1 split, bisetulate, disto-ventrally with 2 setae, 1 short, bisetulate, 1 long bisetulate. Propodus length 4.0 width. Dactylus length 4.0 width.

Operculum (female pleopod II; Figs 8 G, 11J). Stout, length 1.5 width, 0.48 pleotelson length, ovoid, without keel, with 10 pappose setae on apex, extending to anal opening.

Pleopod III (Fig. 11 I). Length 2.2 width, protopod length 2.0 width, 0.55 pleopod III length; exopod with fringe of fine setae, about as long as pleopod III exopod width, with simple seta subterminally, exopod length 0.73 pleopod III length.

Uropod (Fig. 8 D, H). Protopod length 1.3 pleotelson length; inserting on pleotelson on posterior margin. Protopod distal margin blunt, endopod insertion terminal, length 24.0 width.

Description, terminal male

Body (Figs 12 A–B, E, 14A–B, D). Length 1.3 mm, 5.0 width. Ventral spines. Pereonite 3 spine acute, prominent, located closer to anterior segment border. Pereonite 4 spine directed ventrally and posteriorly, blunt, prominent, located closer to posterior segment boder.

Cephalothorax. Frons with wrinkles, frontal ridge present, as cluster of slight transversal scratches between antennulae articulations; length/width ratio subequal to female, 0.16 body length; with conspicious array of setae, posterolateral corners acute, posterolateral setae absent, posterior margins papillose. Fossosome. Length/width ratio greater than in female, length 0.94 width, length/body-length ratio subequal to female; keeled. Pereonite 4. Narrower than pereonite 5, length/width ratio subequal to female; pereonal collum present. Lateral margins in dorsal view medially convex. Posterolateral margin not produced posteriorly.

Pleonite 1 (Fig. 14 B). Tergal and sternal articulations with pleotelson present.

Pleotelson (Figs 12 B, D–F, 14A–B). In dorsal view, approximately rectangular, length/width ratio in male subequal to female, 0.23 body length, width subequal pereonite 7 width. Posterior apex convex, more obtusely-angled compared to female, without setae on margin, pleopodal cavity width 0.75 pleotelson width, preanal ridge width 0.43 pleotelson width.

Antennula (Figs 12 C, G, 14C). Length 0.35 head width, 0.27 antenna length, width 1.2 antenna width; terminal article with 2 aesthetascs, penultimate article with 2 aesthetascs, aesthetascs with intermediate belt of constrictions; article 1 squat, globular, longest and widest, 1 broom seta, article 2 squat, globular, shorter than article 1, 2 broom setae, article 3 squat, globular, shorter than article 1, 1 broom seta, article 4 squat, globular, minute, article 5 squat, globular, minute, with 1 simple seta.

Antenna (Figs 12 C, G, 14C). Length 0.22 body length, flagellum of 4 articles, article 1 elongate, article 2 elongate, longer than article 1, article 3 elongate, longer than article 1, article 4 shorter than articles 1–3 together, 1 broom seta, article 5 longer than article 4, distally with 1 simple seta, 4 broom setae.

Pereopod I. Length 0.37 body length. Merus setation as in female. Carpus dorsally with 2 setae, 1 broom, 1 bisetulate, carpus ventrally with 3 setae, 1 simple, 2 split.

Pereopod II. Ischium setation as in female. Merus dorsally with 4 setae, dorso-distally, bisetulate, ventrally with 2 setae, along margin, distally, bisetulate. Carpus dorsally with 4 setae, 2 bisetulate along margin, 2 split distally, bisetulate, ventrally with 3 setae, 1 bisetulate, 1 broom, 1 split, bisetulate.

Pereopod III. Length 0.44 body length.

Pereopod V. Length 0.35 body length. Merus disto-dorsally with 2 setae; 1 short, bisetulate, 1 long, bisetulate; mid-ventrally with 1 seta; bisetulate; disto-ventrally with 2 setae; 1 short, bisetulate, 1 long, bisetulate. Carpus disto-ventrally with 2 setae, 1 short, bisetulate, 1 long, bisetulate.

Pereopod VI. Length 0.51 body length; ischium, merus and carpus setation as in female.

Pereopod VII. Length 0.35 body length, less than pereopod VI length, segment L/W ratios sexually dimorphic; basis length 4.3 width; ischium length 2.8 width, setation as in female; merus length 1.7 width, disto-dorsally with 1 seta, bisetulate, disto-ventrally with 2 setae, 1 short, bisetulate, 1 long, bisetulate; carpus length 5 width, carpus setation as in female; propodus length 4.0 width; dactylus length 3.0 width.

Pleopod I (Fig. 13 A). Length 0.58 pleotelson length, distally with fringe-like sensillae. Pleopod II (Fig. 13 B). Protopod apex tapering, with setae on proximal lateral margin, 3 pappose setae altogether, with 5 pappose setae distally. Endopod distance of insertion from protopod distal margin 0.38 protopod length. Stylet weakly curved, not extending to distal margin of protopod, length 0.52 protopod length.

Uropod (Fig. 12 F). Length 2.0 pleotelson length; protopod length/width ratio greater than in female, length1.5 width, with endopod inserting terminally; endopod length 0.31 protopod length, 11.5 width, width less than protopod.

other authors, M. reticulata Birstein, 1963 has strongly developed imbricate ornamentation and could thus potentially show marginal wartyness as well. This latter species is substantially different from M. papillata n. sp. because it has the ornamentation on all somites. Both species differ in the shape of their pereopod III ischium, in that M. papillata has an narrow dorsal projection bearing a robust proximally curved seta with two flanking bisetulate setae, whereas M. reticulata has a more rounded projection with only 3 straight non-robust setae.

Remarks. M. papillata differs from any previously described macrostylid owing to the presence of a tergal pleonite 1 articulation with the pleotelson. Furthermore, the ridges that create the imbricate ornamentation in this species overlap posteriorly with the margin of the pereonites 1–4 and head. As a result, the margins of these somites have a warty appearance that is most evident in the SEM images (Figs 14–15), but can be seen in the light microscope (Fig. 12 B). Although this subtlety of the imbricate ornamentation may not have been fully noted by