Macrostylis matildae Riehl & Brandt, 2013, n. sp.

Macrostylis matildae n. sp.

(Figs 11–20)

urn:lsid:zoobank.org:act:CBDDFFA0-5539-4540-B04E-AA9CA1D695A5

Etymology. The name “ matildae ” is the latinized genitive case of “Matilda”, an Old German given name meaning “powerful battler”. It is derived from “Maud”, another variant of the same name, as in Maud Queen consort of Norway (1869–1938), spouse of King Haakon VII. This name is ment to reflect on the type locality seamount Maud Rise and the adjacent Norwegian claim of Antarctica, Queen Maud Land (Norwegian: Dronning Maud Land).

Type fixation. Holotype (Fig. 11): non-ovigerous female, 1.7 mm, ZMH K-43000, designated here.

Type material examined. Holotype: non-ovigerous female used for habitus illustrations, 1.7 mm, ZMH K- 43000. Paratypes (all from same sample as holotype): 1 ovigerous female with eggs used for habitus illustrations, 2.0 mm, ZMH K-43002; 1 non-ovigerous female dissected for illustrations, 1.9 mm, ZMH K-43003; 1 nonovigerous female used for SEM, ZMH K-43005; 1 adult male, dissected for illustrations, ZMH K-43004; 1 manca male, dissected for illustration ZMH K-43001; 29 specimens from the type locality: 6 ovigerous females with no eggs; 14 non-ovigerous females; 1 female manca ZMH; 1 manca male ZMH K-43006.

Type locality. Collected 04th January 2008 from the slope of the seamount Maud Rise. This is located off Queen Maud Land on the Antarctic continental slope. Samples were taken during the ANDEEP-SYSTCO project with R/V Polarstern, station ANTXXIV-2 039–17: start trawl at 64° 28.77’ S, 2° 52.69’ E; 2,152 m depth; end trawl at 64° 28.66’ S, 2° 53.14’ E; 2,153 m depth.

Diagnosis. Body and all external appendages covered with furry coat of cuticular setules. Pereonites 3–4 ventral spines present. Pereonite 4 posterolateral margins produced posteriorly, rounded. Female pereonite 6 length clearly larger pereonite 5 length. Pereonite 7 ventral spine small; posterolateral margins similar in female and male. Pleotelson shape similar in both sexes, narrowing evenly towards uropod insertions, lateral margins straight, waist present; posterior apex convex, apex length about 0.13 pleotelson length. Pereopod III ischium dorsal lobe triangular, apex with 1 prominent recurved seta. Operculum stout. Uropods and pleotelson respectively of similar length in adult male and female.

Description of non-ovigerous female. Body (Figs 11 A,B, 12A, 13A,B). Length 1.7–1.9 mm, 3.8–4.0 width, subcylindrical, tergite surfaces hirsute, densely covered with cuticular setules on all body parts, incl. pereopods and operculum. Ventral spines. All spines acute. Pereonite 1 spine prominent. Pereonite 3 spine prominent, closer to anterior segment border. Pereonite 4 spine directed posteriorly, small, closer to posterior segment border. Pereonite 5–6 spines prominent, closer to posterior segment border. Pereonite 7 spine small. Imbricate ornamentation (IO). Cephalothorax IO dorsally and laterally; pereonite 1–pleotelson IO on all tergites and sternites.

Cephalothorax. Length 0.73–0.84 width, 0.16–0.18 body length; frons convex, with wrinkles, frontal furrow present, slightly convex; dorsal surface with array of setae, in symmetrical arrangement: each side with 3 setae in a transversal row along frontal furrow, 1 seta posteromedially to antennal insertions, 2 setae along posterolateral ridge. Posterolateral setae present, robust, flexibly articulated. Posterolateral margins acute. Fossosome. Length 0.84–0.95 width, 0.22–0.24 body length. Lateral tergite margins confluent, ventral surface without keel; sternite articulations present, fully expressed, clearly reaching tergal margin. Pereonite 1. Anterior margin concave; posterolateral setae simple. Pereonite 2–3. Posterolateral setae simple, flexibly articulated. Pereonite 4. Width 1.1 pereonite 5 width, length 0.34–0.41 width; pereonal collum present. Lateral margins curved, narrow in pereonal collum, widest in the middle and slightly concave anterior of posterolateral angles. Posterior tergite margin with 4 simple, thin, flexibly articulated setae; setae extending beyond posterior margin. Posterolateral margins produced posteriorly, rounded. Posterolateral setae bifid, robust, spine-like.

Pereonites 5–7. Posterolateral margins produced posteriorly, rounded. Posterolateral setae bifid, robust, spinelike. Pereonite 5. Length 0.42–0.43 width, 0.86–0.94 pereonite 4 length. Posterior tergite margin with 6 simple, flexibly-articulated setae; setae not extending beyond posterolateral margin. Pereonite 6. Length 0.50–0.52 width, 1.1–1.2 pereonite 5 length. Posterior tergite margin with 10 simple, flexibly articulated setae; setae extending beyond posterolateral angles. Pereonite 7. Length 0.44–0.51 width. Posterior tergite margin with 11–15 simple, flexibly articulated setae; setae extending beyond posterolateral margin.

Pleonite 1. Sternal articulation with pleotelson absent.

Pleotelson (Figs 11 A,D, 13B). Narrowing evenly towards uropod insertions, lateral margins straight, waist present, setal ridges visible in dorsal view, dorsal length 0.22–0.23 body length, 1.4–1.6 width, narrower than pereonite 7; statocysts present, dorsal slot-like apertures present, diagonal across longitudinal axis, concave. Posterior apex slightly concave at uropod insertions, posteriorly convex, length 0.13 pleotelson length. Posterior apex with 10 pappose setae, positioned on and around apex. Pleopodal cavity width 0.75–0.78 pleotelson width, pre-anal trough width 0.38–0.42 pleotelson width. Anal opening terminally, parallel to frontal plane.

Labrum. Anterior margin convex. Antennula (Fig. 14 E). Length 0.38 head width, 0.22 antenna length, width 0.69 antenna width. Articles decreasing in width from proximal to distal. Articles 1–4 distinctly longer than wide, cylindrical. Article 1 with 1 broom seta. Article 2 longer than article 1, with 2 broom setae. Article 3 with 1 broom seta. Article 5 squat, with 2 setae: 1 simple, 1 aesthetasc with intermediate belt of constrictions.

Antenna (Fig. 14 E). Length 0.36 body length. Article 1 squat. Articles 2–3 elongate, longer than article 1. Article 4 longer than articles 1–3 together, distally with 1 simple seta. Article 5 length subequal article 4 length, distally with 3 broom setae. Flagellum with 7 articles.

Mandibles (Fig. 14 A–D). In medial view strongly narrowing from proximal to distal; left and right mandible incisor processes multidentate with dorsal and ventral subdistal teeth that partly enclose lacinia, left incisor with 4 cusps, lacinia mobilis grinding, with 4 cusps; right mandible incisior with 3 cusps, lacinia mobilis grinding, clearly smaller than left lacinia, with 4 cusps. Maxillula (Fig. 14 F). Lateral lobe with 12 robust setae. Maxilla (Fig. 14 H). Lateral lobe with 3 setae terminally; middle endite with 4 setae terminally; inner endite with 8 setae terminally. Maxilliped (Fig. 14 G). Basis length 3.3 width, medioventrally with seta present; epipod length 2.7 width, 0.99 basis-endite length; palp wider than endite, article 2 wider than articles 1 and 3, article 1 shorter than article 3.

Pereopod I (Fig. 15 A). Length 0.45 body length. Ischium dorsal margin with 5 setae: 1 small proximally, 4 long, thin submarginally. Merus dorsal margin with 4 submarginal setae: 3 long thin, 1 short, bifurcate; ventral margin with 2 medially serrate, distally f ringe-like sensillae. Carpus dorsally with 2 long, thin setae. Dactylus distally with 3 sensillae. Pereopod II (Fig. 15 B). Length 0.47 body length. Ischium dorsally with 3 submarginal setae: 1 small proximally, 2 long, thin distally. Merus dorsally with 4 submarginal setae: 3 long and thin, and 1 short, bifurcate; ventrally with 3 medially serrate, distally fringe-like sensillae. Carpus dorsally with 3 long, thin setae; ventrally with 5 setae: 4 medially serrate, distally fringe-like sensillae, 1 short bifurcate. Dactylus distally with 3 sensillae. Pereopod III (Figs 11 C, 12D, 15C). Length 0.47 body length. Ischium dorsal lobe triangular; proximally with 2–3 setae; apex with 1 prominent seta; apical seta robust, bifid, bent towards proximal, spine-like; distally with 1–2 setae. Merus dorsally with 4–6 setae: 1–2 long, thin and 2–4 long, bifurcate; ventrally with 3 medially serrate, distally fringe-like sensillae. Carpus dorsally with 5–6 setae: 4–5 long, bifurcate, 1 broom; ventrally with 4–5 setae: 3–4 medially serrate, distally fringe-like sensillae, 1 short bifurcate. Dactylus distally with 3 sensillae.

Pereopod IV (Figs 12 C, 15D). Length 0.25 body length, carpus cylindrical.

Pereopod V (Fig. 16 A). Length 0.40 body length. Ischium middorsally with 2 setae; distodorsally without seta; midventrally with 1 seta; distoventrally with 3 setae. Merus distodorsally with 4 setae: 2 bifurcate, 2 simple; midventrally with 1 seta; distoventrally with 2 setae: 1 simple, 1 bifurcate. Carpus distodorsally with 1 seta; distoventrally with 3 bifurcate setae. Pereopod VI (Fig. 16 B). Length 0.51 body length. Ischium dorsally with 2 setae; midventrally with 4 setae, arranged in bundle; distoventrally with 2 setae. Merus middorsally without seta; distodorsally with 6 setae; midventrally with 2 bifurcate setae, arranged in bundle; distoventrally with 2 setae: 1 long, 1 bifurcate. Distodorsally with 3 setae: 1 broom, and 2 bifurcate; midventrally with 2 bifurcate setae; distoventrally with 4 bifurcate setae. Pereopod VII (Fig. 16 C). Length 0.35 body length; basis length 3.8 width, dorsal margin with row of 14 elongate setae, exceeding beyond proximal half of article; setae longer basis width; ventral margin with 2 setae; setae shorter basis width. Ischium length 2.3 width, middorsally with 2 setae, midventrally and distoventrally with 1 seta respectively. Merus length 2.3 width; distodorsally with 3 setae; midventrally and distoventrally with 1 seta respectively. Carpus length 4.7 width, distodorsally with 4, midventrally with 1, distoventrally with 3 bifurcate setae respectively. Propodus length 5.5 width. Dactylus length 4 width.

Operculum (Figs 11 D, 13C). Elongate, length 1.6 width, 0.83 pleotelson dorsal length; apical width 0.52 operculum width; distally tapering, not reaching anus; without keel. With lateral fringes of 7–10 setae, distinctly separate from apical row of setae. With 10 pappose setae on apex, completely covering anal opening. Pleopod III (Fig. 13 D). Length 2.8 width; protopod length 2.3 width, 0.56 pleopod III length; exopod with fringe of fine setae; setae longer than pleopod III exopod width, length 0.64 pleopod III length, seta subterminally present. Pleopod V (Fig. 13 F). Present.

Uropod (Figs 11 A, 12A, 13B). Inserting on pleotelson posterior margin; length 1.0–1.1 pleotelson length; protopod length 8.8–10.0 width, 0.77–0.88 pleotelson length, protopod distal margin blunt, endopod insertion terminal; endopod length 4.5 width, 0.26–0.30 protopod length, width at articulation narrower than protopod.

Description of adult male. Body (Fig. 17 A,B). Length 2.6 mm, 4.2 width. Cephalothorax. Length 0.77 width, 0.14 body length. Fossosome. Not keeled. Pereonites 1-3. With 2, 3, 6–7 long, thin posterolateral setae respectively. Pereonite 4. Length 0.52 width. Pereonal collum present, medially convex. Posterolateral margins produced posteriorly. Pereonite 5. Length 0.59 width.

Pereonite 6. Length 0.55 width, 0.90 pereonite 5 length. Pereonite 7. Posterior tergite margin with 15 simple, asetulate, flexibly articulated setae; setae not extending beyond posterolateral margin.

Pleonite 1. Sternal articulation with pleotelson present.

Pleotelson (Fig. 17 B,C). Similar to female. Posterior apex length 0.10 pleotelson length, pleopodal cavity width 0.67 pleotelson width, pre-anal trough width 0.33 pleotelson width.

Antennula (Fig. 17 D). Length 0.39 head width, width 1.3 antenna width. Article 1 elongate, longest and widest, with 1 broom seta. Article 2 elongate, with 3 distally fringe-like sensillae. Article 3 squat, with 2 simple setae. Article 4 squat, with 6 aesthetascs. Article 5 squat, with 6 setae: 1 simple, 5 aesthetascs. Aesthetascs with intermediate belt of constrictions. Antenna (Fig. 17 D). Damaged. Article 1 squat. Article 2 squat, longer than article 1. Article 3 elongate, longer than article 1.

Pereopod I (Fig. 18 A,B). Length 0.36 body length. Ischium dorsally with 4 setae. Carpus dorsally with 2 setae: 1 broom, 1 simple; ventrally with 3 setae: 2 medially serrate, distally fringe-like sensillae, 1 small simple. Pereopod II (Fig. 18 C). Length/body-length ratio smaller than in female: length 0.41 body length. Ischium dorsally with 5 long, thin setae. Merus dorsally with 3 setae; ventrally with 3 medially serrate, distally fringe-like sensillae. Carpus dorsally with 3 setae: 2 long, thin, 1 broom; ventrally with 5 setae: 4 medially serrate, distally fringe-like sensillae, 1 small, simple. Pereopod III (Fig. 18 D,E). Length 0.44 body length. Ischium dorsal lobe triangular, proximally with 3 simple setae; apex with 1 prominent, robust, spine-like, bifid seta; distally with 3 simple setae. Merus dorsally with 7 setae: 1 long, thin, simple, 6 bifurcate; ventrally with 3 medially serrate, distally fringe-like sensillae. Carpus dorsally with 5 setae: 4 bifurcate, 1 broom; ventrally with 4 setae: 3 medially serrate, distally fringe-like sensillae, 1 short bifurcate.

Pereopod IV (Fig. 18 F,G). Length 0.23 body length. Pereopod V (Fig. 19 A,B). Ischium middorsally with 1 seta, distodorsally with 2 bifurcate setae; midventrally with 3 setae in bundle; distoventrally with 2 setae. Merus distodorsally with 3 setae: 1 long, slim, 2 short, bifurcate; midventrally with 1 bifurcate seta; distoventrally with 3 setae: 1 bifurcate, 1 simple. Carpus distodorsally with 2 setae: 1 broom, 1 simple; distoventrally with 4 short, bifurcate setae. Pereopod VI (Fig. 19 C). Length 0.36 body length. Ischium setation as in female: dorsally with 2 setae; midventrally with 4 setae in bundle; distoventrally with 3 setae. Merus distodorsally with 4 setae: 1 short, bifurcate, 3 simple; midventrally with 1 bifurcate seta; distoventrally with 2 setae: 1 bifurcate, 1 long, simple. Carpus middorsally with 1 bifurcate seta; distodorsally with 4 setae: 1 broom, 3 bifurcate; midventrally with 2 bifurcate setae; distoventrally with 3 bifurcate setae. Pereopod VII (Fig. 19 D). Shorter pereopod VI; basis length 3.0 width; dorsal margin with row of 19 elongate setae exceeding proximal half of article; setae longer basis width; ventral margin with 3 setae; setae shorter basis width; ischium length 3.0 width; middorsally with 2 setae; midventrally with 3 setae; distoventrally with 3 setae. Merus length 2.8 width, setation as in female; carpus length 9.0 width; distodorsally with 4 setae: 1 broom, 3 bifurcate; midventrally with 3 bifurcate setae; distoventrally with 2 bifurcate setae. Propodus length 8.5 width. Dactylus length 5.0 width.

Pleopod I (Fig. 17 E). Length 0.66 pleotelson length, lateral horns not extending distally beyond medial lobes; distally with 8–9 sensillae, ventral setae present. Pleopod II (Fig. 17 F). Protopod apex rounded, with 15 setae on proximolateral margin; with 7 pappose setae distally. Endopod distance of insertion from protopod distal margin 0.37 protopod length. Stylet weakly curved, not extending to distal margin of protopod, length 0.40 protopod length. Uropod (Fig. 17 B). Length 0.97 pleotelson length; protopod length 9.2 width; endopod length 0.22 protopod length, less than in female, length 5.0 width.

Remarks. The pleotelson of the best intact adult male specimen available is strongly damaged. This might have affected the measurements related to the pleotelson width.

The most distinct character state of this species is the dense coat of cuticular setules covering all body parts and external appendages. Different from other species of which both adult sexes have been described, no dimorphism can be found in the shape and size ratios of the pleotelson and uropods. Setal microstructures might have been overlooked in several instances due to the small size of the specimens. There are some indications for several pereopodal setae for which not further attributes were described to be mono- or bisetulate.

Macrostylis matildae n. sp. can be regarded closely related to several species from the Southern and Indian Oceans: M. expolita Mezhov, 2003 b, M. latiuscula Mezhov, 2003 b, M. medioxima Mezhov, 2003 a, M. sarsi Brandt, 1992, M. setulosa Mezhov, 1992, and M. vinogradovae Mezhov, 1992. This is due to the similar body shape and ventral spination; body covered with cuticular setules; pereonite 3 posterolateral spine-like setae absent (not in M. setulosa); pereonite 4 posterolateral spine-like setae present; operculum distally narrowing with lateral fringe of setae distinctly separate from apical row of setae.