Macrostylis scotti Riehl & Brandt, 2013, n. sp.
Creators: name: Riehl, Torben
name: Brandt, Angelika
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Macrostylidae
Macrostylis
Macrostylis scotti

description: Macrostylis scotti n. sp.
(Figs 2–10)
urn:lsid:zoobank.org:act:8EBFDE96-E5CB-4D62-A56D-8E23B910EDC7
Etymology. The name “s cotti” is dedicated to the British explorer Robert Falcon Scott CVO, in order to mark the 100th anniversary of his heroic trial to be the first person to reach the geographic South Pole. He reached the pole second, after Roald Amundsen, and died on this ill-fated Terra Nova Expedition around the 29th March 1912.
Type fixation. Holotype (Figs 2, 3): adult male, 5.4 mm, ZMH K-42990, designated here.
Type material examined. Holotype: adult male, 5.4 mm, ZMH K-42990, used for the illustration of the habitus and DNA studies. Paratypes: adult male, 5.1 mm, ZMH K-42991, dissected for illustrations of appendages and habitus as well as DNA studies; non-ovigerous female, 5.3 mm, ZMH K-42992, dissected for illustration of appendages and DNA studies.
Type material - Remarks. The holotype is comlplete except for posterior pereopods that have been removed from one side for DNA studies; complete holotype and carcasses of paratype are conserved in 96% EtOH, dissected parts are mounted on slides using Euparal.
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 heavily calcified, cuticular setules absent. Tergal plates laterally projecting below coxae, coxal articulations ventrally or medioventrally. Ventral spines keeled. Pereonites 1–5 in male with rows of long simple setae along posterolateral margins. Pereonite 3 posterolateral margin not produced posteriorly. Pereonites 3 and 4 ventral spines absent. Pereonite 4 width exceeding pereonite 5 width. Pereonite 6 posterolateral margin rounded. Pereonite 7 ventral spine present, small. Female pleotelson ovoid; waist present, posterior apex length about 0.20 pleotelson length. Antenna article 2 squat. Mandibular incisors not cuspidate, bluntly rounded. Pereopod III ischium dorsal lobe tapering, with 2 prominent apical setae. Pereopod V ischium distodorsally with setae present. Operculum elongate, ovoid, lateral fringe of setae with fluent transition to apical row of pappose setae. Uropod protopod distal margin tapering laterally, endopod articulation subterminally.
Description of non-ovigerous female. Body (Fig. 4 A,D). Length 5.3 mm, 4.0 width, subcylindrical, tergite surfaces with very long, simple ventrolateral setae anteriorly of pereopod insertions. Tergal plates laterally projecting below coxae. Ventral spines. Pereonite 1 spine acute, prominent. Pereonites 3–4 spines absent. Pereonite 5 spine acute, small, placed medially. Pereonite 6 spine acute, prominent, closer to anterior segment border. Pereonite 7 spine small. Imbricate ornamentation (IO). Pereonite 4 IO on tergite in a thin irregular anterior transversal band along the collum margin and on bottom of collum; pereonite 5 IO on tergite in a broad transversal band covering anterior half of segment; and on bottom of collum. Oval areas free from IO probably represent muscular attachments; pereonites 6–7 IO on tergite in a broad transversal band covering more than anterior half of segment; and on bottom of collum. With oval areas free from IO; pleotelson IO covering whole tergite except posterior margin.
Cephalothorax. Length 0.68 width, 0.15 body length; frons straight, frontal furrow and posterolateral setae present. Posterolateral margins blunt. Fossosome. Length 0.76 width, 0.19 body length. Lateral tergite margins confluent, ventral surface keeled; sternite articulations present. Pereonite 1. Anterior margin concave; posterolateral setae simple. Pereonites 2–3. Posterolateral setae simple, flexibly articulated. Pereonite 4. Width 1.1 pereonite 5 width, length 0.46 width; pereonal collum present. Lateral margins convex. Posterior tergite margin with 2 simple, asetulate, flexibly articulated setae; setae not extending beyond posterolateral margin. Posterolateral margins rounded; posterolateral setae simple, asetulate, flexibly articulated.
Pereonites 5–7. Posterolateral margins produced posteriorly, rounded, with bifid, robust, flexibly articulated posterolateral setae. Pereonite 5. Length 0.39 width, 0.81 pereonite 4 length. Pereonite 6. Length 0.58 width, 1.5 pereonite 5 length. Posterior tergite margin with 2 simple, asetulate, flexibly articulated setae; setae not extending beyond posterolateral margin. Pereonite 7. Length 0.46 width. Posterior tergite margin with 4 simple, asetulate, flexibly articulated setae; setae not extending beyond posterolateral margin.
Pleotelson (Fig. 4 A,C). Ovoid, waist present, setal ridges not visible in dorsal view, length 0.24 body length, 1.2 width, narrower than pereonite 7; statocysts and dorsal slot-like apertures not visible or absent. Posterior apex convex, smoothly curving medially, slightly concave at uropodal insertions; setae absent. Pleopodal cavity width 0.50 pleotelson width, pre-anal trough width 0.19 pleotelson width. Anal opening subterminally, parallel to frontal plane.
Antennula (Fig. 4 B). Length 0.24 head width, 0.27 antenna length, width 1.3 antenna width. Articles decreasing in size from proximal to distal, L/W ratios of articles 1.2, 1.3, 1.3, 1.0, 0.5. Article 1 longest and widest, with 1 broom seta. Articles 2–4 cylindrical. Article 2 with 3 setae: 1 simple, 2 broom. Article 4 with 1 aesthetasc. Article 5 minute, squat, with 2 setae: 1 simple, 1 aesthetasc. Aesthetascs with intermediate belt of constrictions. Antenna (Fig. 4 B). Length 0.19 body length. Article 1 squat. Article 2 squat, longer than article 1. Article 3 longer than article 1. Article 4 about as long as articles 1–3 together, distally with 1 broom seta. Article 5 longer than article 4, distally with 5 broom setae. Flagellum with 7 articles. Mouthparts. See description of adult male.
Pereopod I. Broken, missing. Pereopod II (Fig. 5 A). Length 0.42 body length; article L/W ratios 3.7, 3.1, 1.6, 2.8, 3.4, 7.3; relative article length ratios 1.0, 0.65, 0.39, 0.52, 0.24, 0.31. Ischium dorsally with 7 simple setae submarginally. Merus dorsally with 4 simple setae; ventrally with 4 medially biserrate, distally fringe-like sensillae. Carpus dorsally with 4 simple setae; ventrally with 5 setae: 4 medially biserrate, distally fringe-like sensillae, 1 bifurcate distally. Dactylus distally with 2 sensillae. Pereopod III (Fig. 5 C). Length 0.44 body length; article L/W ratios 3.0, 1.6, 1.7, 2.9, 4.2, 5.5; relative article length ratios 1.0, 0.72, 0.60, 0.66, 0.32, 0.34. Ischium dorsal lobe tapering; proximally with 3 simple setae; apex with 2 prominent, robust, bifid setae; apical seta bent towards proximal, spine-like; subapical seta flexibly articulated; distally with 3 simple setae. Merus dorsally with 7 setae: 6 simple, 1 bifurcate; ventrally with 5 setae: 4 medially biserrate, distally fringe-like sensillae in row, 1 small simple distally. Carpus dorsally with 6 setae: 5 simple, in row, 1 broom; ventrally with 3 setae: 2 medially biserrate, distally fringe-like sensillae, 1 bifurcate distally. Dactylus with 3 sensillae. Pereopod IV (Fig. 5 B). Length 0.25 body length; article L/W ratios 3.2, 1.9, 1.3, 1.9, 2.0, 1.7; relative article length ratios 1.0, 0.44, 0.30, 0.30, 0.18, 0.09; carpus laterally flattened.
Pereopod V (Fig. 6 A). Length 0.32 body length; article L/W ratios 2.9, 2.3, 1.4, 3.2, 4.4, 2.7; relative article length ratios 1.0, 0.60, 0.42, 0.60, 0.42, 0.15. Ischium middorsally with 2 long, pappose setae; distodorsally without seta; midventrally with 2 long, pappose setae; distoventrally with 3 setae: 1 simple, small, 2 long, pappose. Merus distodorsally with 5 setae: 3 bifurcate, pappose, 2 simple; midventrally with 3 long, pappose setae; distoventrally with 2 setae: 1 short, bifurcate, pappose, 1 long, pappose. Carpus distodorsally with 2 setae: 1 broom, 1 broken, missing; distoventrally with 4 setae: 3 bifurcate, pappose, 1 long, simple. Pereopod VI (Fig. 6 B). Length 0.46 body length; article L/W ratios 3.9, 3.2, 1.8, 4.1, 6.3, 3.5; relative article length ratios 1.0, 0.64, 0.41, 0.74, 0.67, 0.21. Ischium dorsally with 5 long setae; midventrally without seta; distoventrally with 5 setae. Merus middorsally without seta; distodorsally with 4 setae: 1 minute, simple, 1 pappose, 1 bifurcate, 1 broken; midventrally without seta; distoventrally with 2 setae. Carpus middorsally with 1 seta; distodorsally with 3 bifurcate, pappose setae; midventrally with 3 setae: 1 bifurcate, pappose, laterally, 2 simple, medially; distoventrally with 5 setae: 3 bifurcate, pappose, 2 long, broken medially. Pereopod VII (Fig. 6 C). Length 0.42 body length, relative article length ratios 1.0, 0.61, 0.36, 0.80, 0.67, 0.21. Basis length 4.4 width; dorsal margin row of 17 elongate setae present, exceeding beyond proximal half of article, setae longer basis width; ventral margin with row of 4 elongate setae, setae longer basis width. Ischium length 3.1 width, middorsally with 9 long, pappose setae; midventrally with 4 long, pappose setae in row; distoventrally with 3 long, pappose setae. Merus length 1.7 width; distodorsally with 6, midventrally with 4, distoventrally with 2 long, pappose setae respectively. Carpus length 4.5 width; middorsally with 1 pappose seta; distodorsally with 3 setae: 1 broom, 2 bifurcate, pappose; midventrally with 2 setae: 1 bifurcate, pappose, 1 pappose; distoventrally with 4 setae: 2 bifurcate, short, pappose, 2 bifurcate, long, pappose. Propodus length 6.8 width. Dactylus length 3.3 width.
Operculum (Fig. 4 C,H). Elongate, length 1.9 width, 0.70 pleotelson dorsal length; apical width 0.87 operculum width; distally not reaching anus, ovoid, ventrally keeled; with lateral fringe consisting of 14–16 pappose setae, with fluent transition to apical row of setae; with 30–33 pappose setae on apex, completely covering anal opening. Pleopod III (Fig. 4 G). Length 3.5 width, protopod length 2.5 width, 0.47 pleopod III length. Exopod length 0.64 pleopod III length; with fringe of fine setae, setae shorter exopod width; subterminal seta present. Pleopod IV (Fig.
4F). Length 2.4 width, endopod length 1.5 width; exopod length 6.0 width, 0.65 endopod length, exopod leteral fringe of setae absent. Pleopod V (Fig. 4 E). Present.
Uropod (Fig. 4 A). Inserting on pleotelson posterior margin; length 0.83 pleotelson length; protopod length 5.9 width, 0.66 pleotelson length, protopod distal margin tapering laterally, endopod articulation subterminally; endopod length 7.3 width, 0.27 protopod length, endopod width at articulation noticeably narrower than protopod.
Description of adult male. Body (Figs 2, 3 A,B, 7A,B). Length 5.1–5.4 mm, 4.5 width. Cephalothorax. Frontal furrow present, straight; L/W ratio larger than in female, length 0.92–0.93 width, 0.16 body length; posterolateral corners rounded, posterolateral setae present, posterior margins papillose and setose. Fossosome. L/ W ratio greater than in female, length 0.88–0.94 width, length/body-length ratio subequal to female; ventrally keeled (Fig. 2 B). Pereonites 1–3. With 4–5, 2 and 5 long, simple, asetulate setae respectively in rows along posterolateral margins.
Pereonite 4 (Fig. 2 A,E). Pereonal collum present, medially convex. Posterolateral margins not produced posteriorly. Posterior tergite margin with 6 simple, asetulate setae. Pereonite 5. Length 0.50–0.53 width, 1.1 pereonite 4 length. Pereonite 6. Length 0.60 width. Pereonite 7. Posterior tergite margin with 4 simple, asetulate, flexibly articulated setae; setae posteriorly not extending beyond posterolateral margin.
Pleonite 1 (Fig.2 C). Sternal articulation with pleotelson present.
Pleotelson (Figs 2 A,C, 3B,E, 7A,D). L/W ratio in male greater than in female, length 1.4–1.5 width, 0.23–0.26 body length, width subequal pereonite 7 width; rectangular, waist present, setal ridges in dorsal view not visible. Posterior apex convex, almost straight with a narrow, rounded tip; without setae on margin; pleopodal cavity width 0.51–0.54 pleotelson width, pre-anal trough width 0.14–0.17 pleotelson width.
Antennula (Fig. 7 C). Length 0.29 head width, 0.26 antenna length, width 1.5 antenna width; article L/W ratios 0.83, 0.78, 0.57, 0.60, 1.0; relative article length ratios 1.0, 0.70, 0.40, 0.30, 0.30. Articles 1–5 squat. Article 1 longest and widest, with 1 broom seta and 2 distally fringe-like sensillae. Article 2 with 2 setae: 1 simple, 1 distally fringe-like sensilla. Article 3 with 1 broom seta. Article 4 with 4 aesthetascs. Article 5 with 6 setae: 2 simple, 4 aesthetascs; aesthetascs with intermediate belt of constrictions. Antenna (Fig. 7 C). Article 1 squat. Article 2 elongate, longer than article 1. Article 3 squat, longer than article 1. Article 4 longer than articles 1–3 together, distally with 2 setae: 1 simple, 1 broom. Article 5 longer than article 4, distally with 8 setae: 1 simple, 7 broom.
Mandibles (Fig. 8 A,B,D,E). In medial view strongly narrowing from proximal to distal, subtriangular, with lateral setae; left mandible incisor process simplified, bluntly rounded, with 1 cusp, lacinia mobilis spine-like, adjacent to spine row without separating gap; right mandible incisior process simplified, bluntly rounded, with 3 minute cusps, lacinia mobilis spine-like, subsimilar in size to left lacinia, adjacent to spine row without gap. Maxillula (Fig. 8 F). Lateral lobe with 12 robust setae. Maxilla (Fig. 8 J). Lateral lobe with 4 partly serrate setae terminally; middle endite with 3 partly serrate setae terminally; inner endite with 6 partly serrate setae terminally. Maxilliped (Fig. 8 G–I). Basis length 4.0 width, medioventrally with seta present. Epipod length 3.6 width, 1.1 basis length; palp wider than endite, article 2 wider than articles 1 and 3, article 1 shorter than article 3.
Pereopod I (Fig. 9 A). Length 0.33 body length; article L/W ratios 4.0, 3.2, 1.5, 2.1, 2.8, 4.3; relative article length ratios 1.0, 0.55, 0.30, 0.36, 0.22, 0.20. Ischium dorsally with 6 setae: 1 small, simple proximally, 4 long, distally pappose in submarginal row, 1 small, simple. Merus dorsally with 3 long, distally pappose setae; ventrally with 5 setae: 4 medially serrate, distally fringe-like sensillae, 1 simple, small. Carpus dorsally with 4 setae: 3 long, distally pappose in row and 1 broom seta; ventrally with 4 setae: 3 medially serrate, distally fringe-like sensillae and 1 simple, small mediodistally. Pereopod II (Fig. 9 B). Length/body-length ratio sexually dimorphic; length 0.40 body length; article L/W ratios 4.0, 3.3, 1.7, 3.0, 3.4, 6.0; relative article length ratios 1.0, 0.63, 0.38, 0.56, 0.27, 0.28. Ischium dorsally with 9 setae: 1 small, simple proximally, 7 long, distally pappose in submarginal row, 1 short, simple mediodistally. Merus dorsally with 4 long, distally pappose setae; ventrally with 5 medially serrate, distally fringe-like sensillae. Carpus dorsally with 3 long, distally pappose setae; ventrally with 6 setae: 5 medially serrate, distally fringe-like sensillae and 1 bifurcate, distally fringe-like sensilla. Pereopod III (Fig. 9 C). Length 0.43 body length; article L/W ratios 3.2, 1.8, 1.6, 3.0, 4.2, 5.7; relative article length ratios 1.0, 0.72, 0.57, 0.70, 0.35, 0.28. Ischium sexually dimorphic, triangular, dorsal lobe proximally with 3 distally pappose setae, apex with 2 prominent, robust, spine-like, straight, bifid setae; distally with 4 distally pappose setae. Merus dorsally with 8 setae: 7 distally pappose, 1 robust, bifurcate fringe-like sensilla; ventrally with 6 medially serrate, distally fringelike sensillae. Carpus dorsally with 6 setae: 5 distally pappose, 1 broom; ventrally with 4 setae: 3 medially serrate, distally fringe-like sensillae and 1 robust, bifurcate, fringe-like sensilla.
Pereopod IV (Fig. 10 A). Length 0.22 body length; article L/W ratios 2.9, 2.0, 1.3, 2.1, 2.0, 2.5; relative article length ratios 1.0, 0.51, 0.37, 0.44, 0.19, 0.12.
Pereopod V (Fig. 10 B). 0.34 body length; article L/W ratios 3.4, 2.4, 1.6, 4.5, 6.5, 4.0; relative article length ratios 1.0, 0.61, 0.43, 0.71, 0.51, 0.16. Ischium middorsally with 2 setae; distodorsally with 1 short seta; midventrally with 2 distally pappose setae; distoventrally with 5 distally pappose setae. Merus distodorsally with 6 setae: 2 robust, short, bifurcate, fringe-like sensillae and 4 distally pappose; midventrally with 3 setae: 1 short, robust, bifurcate, fringe-like sensilla and 2 long, thin distally pappose; distoventrally with 3 setae: 2 damaged, 1 long distally pappose. Carpus distodorsally with 1 broom seta; distoventrally with 5 setae: 3 robust, bifurcate, fringe-like sensillae and 2 long, thin, distally pappose. Pereopod VI (Fig. 10 C). Article L/W ratios 3.6, 2.6, 2.2, 5.7, 10.8, 5.0; relative article length ratios 1.0, 0.60, 0.54, 0.89, 0.75, 0.26. Ischium dorsally with 9 simple setae; midventrally with 4 distally pappose setae; distoventrally with 6 distally pappose setae. Merus distodorsally with 8 setae: 2 bifurcate, fringe-like sensillae, 2 bifurcate, biserrate, 4 distally pappose; midventrally with 3 distally pappose setae; distoventrally with 2 setae: 1 bifurcate, biserrate, 1 distally pappose. Carpus middorsally with 3 distally pappose setae; distodorsally with 5 setae: 1 broom, 4 robust, bifurcate, fringe-like sensillae; midventrally with 2 setae: 1 robust, bifurcate, fringe-like sensilla, 1 thin, long, distally pappose; distoventrally with 5 bifurcate, fringe-like sensillae: 3 short, robust, 2 long, bifurcate.
Pereopod VII (Fig. 10 D). Length/body-length ratio as in female, length 0.41 body length; relative article length ratios 1.0, 0.61, 0.39, 0.88, 0.71, 0.25; segment L/W ratios sexually dimorphic. Basis length 5.1 width, posterior margin with row of 17 setae, not exceeding beyond proximal half of article, setae longer basis width; ventral margin sexually dimorphic, with row of 8 elongate setae; setae longer basis width. Ischium length 2.8 width; middorsally with 8, midventrally with 5, distoventrally with 4 distally pappose setae respectively. Merus length 2.2 width; distodorsally with 7, midventrally with 2 distoventrally with 2 distally pappose setae respectively. Carpus length 7.0 width; distodorsally with 1 broom seta; midventrally with 1 robust, bifurcate, fringe-like sensilla; distoventrally with 2 setae: 1 robust, bifurcate, fringe-like, 1 long, bifurcate, biserrate. Propodus length 10.0 width. Dactylus length 4.7 width.
Pleopod I (Figs 2 C, 7G). Length 0.56 pleotelson length, lateral horns not extending distally beyond medial lobes, distally with 6–8 sensillae, ventrally with setae present. Pleopod II (Fig. 7 I). Protopod apex tapering, with row of 13–15 setae along entire lateral margin; with 12 pappose setae distally. Endopod distance of insertion from protopod distal margin 0.32 protopod length. Stylet weakly curved, not extending to distal margin of protopod, length 0.48 protopod length.
Uropod (Fig. 7 A). Length 0.99–1.0 pleotelson length; protopod L/W ratio greater than in female, length 6.3– 7.5 width; distally narrowing, tapering laterally, endopod inserting subterminally; endopod/protopod length ratio 0.19–0.24, smaller than in female; endopod length 8.0–10.5 width, width narrower than protopod.
Remarks. Macrostylis scotti n. sp. is among the largest species of Macrostylidae currently described with only M. galatheae Wolff, 1956 and M. magnifica Wolff, 1962 of similar size or larger than M. scotti. This species appears closely related to M. uniformis Riehl & Brandt, 2010. The character states shared by both species are e.g. a heavily calcified cuticle of the body and appendages, strong and simple, unidentate mandibular incisors, an oval, elongate operculum with continuous transition between lateral setal fringe and terminal row of setae. Furthermore, both terminal and subterminal articles of the female antennulae bear one aesthetasc respectively and the pereopod III ischium dorsal lobe features two prominent setae.
A group of species potentially closely related consists of M. abyssicola Hansen, 1969, M. minuta Menzies, 1962, M. robusta Brandt, 2004. Similar to M. scotti, these have tergal plates laterally projecting below coxal articulations. In combination with keeled sternites, this allows the pereopods to be positioned close to the sternites. This might have important implications for a burrowing lifestyle. Further, they share the body free from dense cover with setules, and a subterminally articulating uropod endopod with M. scotti and M. uniformis. On the other hand, in this group, one can identify a tendency to reduce the antennula as well as the seventh pereopods, which is not the case in M. scotti.
Among the characters unique for M. scotti are the very long setae that can be found laterally on the tergites.
description: Published as part of Riehl, Torben & Brandt, Angelika, 2013, Southern Ocean Macrostylidae reviewed with a key to the species and new descriptions from Maud Rise, pp. 160-203 in Zootaxa 3692 (1) on pages 166-178, DOI: 10.11646/zootaxa.3692.1.10, http://zenodo.org/record/220612