Macrostylis uniformis, Riehl, Torben & Brandt, Angelika, 2010

Riehl, Torben & Brandt, Angelika, 2010, Descriptions of two new species in the genus Macrostylis Sars, 1864 (Isopoda, Asellota, Macrostylidae) from the Weddell Sea (Southern Ocean), with a synonymisation of the genus Desmostylis Brandt, 1992 with Macrostylis, ZooKeys 57, pp. 9-49 : 14-23

Macrostylis uniformis sp. n. Figs 38

Material examined.

Holotype. Preparatory female, 4.6 mm long, ZMH (K-42172). South-eastern Weddell Sea southwest of Maud Rise; station ANTXXII-3 59-5 (ANDEEP III; 67°29.81'S; 000°00.23'W); 4651 m depth. Paratypes. 1 paratype, ovigerous female, damaged, ZMH (K-42173) from type locality; 1 paratype female without oostegites fixed for SEM, 3.5 mm, ZMH (K-32174) northern Weddell Sea, station 137 (ANDEEP II; 63°45.00'S; 033°47.81'W), 4975 m depth. For further material examined for comparison see: Table 1.

Diagnosis.

Cephalothorax almost semicircular, little longer than wide with no transverse ridge on frons; antenna 1 minute, incl. aesthetascs not reaching article 4 of antenna 2; mandible with blunt pars incisiva, left lacinia mobilis spiniform, integrated into spine row; dorsal extension of ischium of pereopod 3 positioned much more distally, on apex with 2 conspicious setae, 1 bent robust and spiniform unequally bifid seta proximally, and another more straight and less robust unequally bifid seta distally; posterolateral corners of posterior pereonites rounded; pleotelson compact, not constricted anteriorly of uropod articulations; uropod endopod of half the length of protopod.

Description of holotype female.

Body (Figs 3-4) elongate, 5.3 times longer than wide; maximal body width in pereonite 3 1.2 times maximal width of pleotelson; pereonites 1-5 about the same width, gradually narrowing from pereonite 6 towards pleotelson. Surface of tergites, sternites and operculum bearing comb-like structures, which can be worn off due to abrasion to a smooth surface in exposed areas (e.g. cephalothorax, pereonite 3); posterolateral setae only in pereonite 7, otherwise lacking or broken off; no sockets found in SEM (probably due to dirt on cuticle). Cephalothorax free, almost semicircular with maximal width at posterolateral margin, length 1.1 times maximal width and 0.2 times total body length; 0.9 times width of pereonite 1; no transverse ridge on frons.

Fossosome 1.1 times longer than wide, laterally slightly convex, median length: pereonite 1 about 1.4 times longer than pereonite 2, as long as pereonite 3; lateral length: pereonite 1 1.3 times as long as pereonite 2 and 0.5 times as long as pereonite 3; pereonite with prominent anteroventral spine and pereonite 3 with very small posteroventral spine. Pereonites 4-5 of same length and width, 1.6 times wider than long; pereonite 4 laterally convex, maximal width amid segment. Pereonites 5-7 posterolateral corners tapering, with tiny simple apical setae; pereonites with short posterior ventral spines. Pereonite 6 0.8 times pereonite 4 length, 1.7 times wider than long. Pereonite 7 0.7 pereonite 4 length, 1.9 times wider than long; Pleotelson 1.5 times longer than wide, length about 0.2 times total body length, as long as fossosome and as long as pereonites 5 and 6 together; laterally convex, slightly narrowing towards uropodal articulations with no constriction; apex bluntly rounded with several long setae; compared to rest of body with strongest sculpturation of cuticle; cuticle not translucent, dorsal organ not visible; slot-like apertures in dorsal cuticle not present; pleopodal chamber maximal opening width 0.6 times maximal pleotelson width; longitudinal excavation minimal width about 0.3 times max pleotelson width.

Antenna 1 (Figs 3-5) of 5 articles, 0.25 times fossosome median length; 2,6 times longer than wide; articles gradually decreasing in size and length-width ratio towards distal end, relative length ratios: 1:0.5:0.3:0.2:0.1; article 1 length 1.4 times of width, 50% of total antenna 1 length, article 5 as long as wide, less than 0.1 times total antenna 1 length; articles 4 and 5 with 1 aesthetasc each; articles 1 and 2 with distal broom setae; simple setae on distal margins of articles 2 and 3, 1 seta on article 5.

Antenna 2 (Figs 3-5) basal five articles reaching the posterior end of cephalothorax; flagellum reaching the anterior margin of pereopod 2 basis when directed posteriorly; article 1 broadest, 1.4 times wider than long, article 2 1.2 times longer than wide and article 3 1.4 times longer than wide, article 4 little narrower than articles 1-3, 4 times longer than wide, article 5 longest 1.1 times article 4, 4.5 times longer than wide; several broom setae distally on basal articles, most on article 5; seven flagellar articles, width about 0.5 times article 5 width.

Mandible (Fig. 5) gradually narrowing towards pars incisiva; pars incisiva blunt and rounded, without teeth; left lacinia mobilis spine-like, with subtriangular basis in dorsal and medial view and 1 small spine on apex, little shorter than adjacent spine row; right lacinia mobilis tiny with several short spine-like projections; spine row of 5-7 fanned spines, more in left mandible, partially serrated at tips and along proximal margin, especially more proximal ones; pars molaris shorter than adjacent spines of spine row, apex oriented proximally.

Maxilla 1 (Fig. 5) inner endite shorter and more slender than outer one, terminally spatulate; dense accumulation of simple setae around distal apex, along a dorsal ridge as well as along medial and lateral margins with setae; outer endite broad, narrowing in the most distal quarter, with numerous setae of different lengths on lateral and medial margins, numerous setae of different lengths around distomedial corner 12 robust setae, some two-sided serrate, on distal margin.

Maxilla 2 (Fig. 5) inner and outer endites of similar width, equally projecting distally; medial endite thinner and shorter; along proximedial margin of inner endite more than 15 long simple setae of less than half the length of inner endite, an accumulation of about 10 small and intermediate simple setae distolaterally, on distal margin 7 strong setae, some heavily denticulate, medial endite with few simple setae along lateral and medial margins, distally with 3 simple setae of different lengths, longest seta less than half as long as the medial endite; outer endite with simple setae around lateral margin, distally with four robust setae of different lengths the most lateral one longest and one-sided denticulate.

Maxilliped (Fig. 6) epipod 3.6 times longer than wide, distally narrowing to multiple small tips, with tiny setae or setules, laterally concave, reaching midlength of palp article 3; endite medially thickening, proximomedially with two coupling hooks, distally with heavily sclerotized and denticulate tooth-like setae and fine dense setae; row of setae along rounded distolateral margin, lateral margins of basis and palp articles 1-3 with rows of thin setae; article 2 largest and longest, 3.5 times longer than article 1 and 2.3 times longer than article 3; articles 4 and 5 distomedially and distolaterally with medially scaled and distally pappose sensillae: 3 medially and 1 laterally on article 2, 5 medially and 2 laterally on article 3, 3 medially and 1 laterally on article 4, article 5 with 6 such setae terminally and subterminally; basis including endite 0.9 times epipod length.

Anterior pereopods (Fig. 6) slightly increasing in length, pereopod 1 0.9 times length of pereopods 2 and 3 respectively; all articles covered with tiny setules of varying density of coverage.

Pereopod 1 relative length ratios: 1:0.6:0.4:0.4:0.3:0.2, basis with at least 3 broom setae and 1 short simple seta dorsally and 2 broom setae and row of 5 short setae ventrally, 3.6 times longer than wide; ischium 2.4 times longer than wide, with row of 4 long and slender setae distally, 1 seta on the opposite side, 1 short distally pappose sensilla ventrally, 1 short seta proximodorsally; merus compact, 1.4 times longer than wide, posteriorly on dorsal extension with row of 4 simple setae of different length and 1 bifurcate setae, along ventral margin 4 distally pappose setae and on distoventral extension 1 stout bifurcate seta; carpus 2.3 times longer than wide, distodorsally with row of 2 simple setae and 1 bifurcate seta most distally, 1 broom seta on distoventral margin, ventral margin with four distally fringed setae; propodus 3.4 times longer than wide, dorsally with 1 short setae, ventral side with 3 short sensillae, caudally with 1 long and slender seta; dactylus 3 times longer than wide, about 0.7 times carpus length, with 1 sensilla on dorsal and ventral side respectively.

Pereopod 2 1.1 times longer than pereopod 1; setation comparable to pereopod 1 with slight variations in length and numbers; relative length ratios: 1:0.7:0.5:0.6:0.4:0.3, basis 3.1 times longer than wide; ischium 2.6 times longer than wide; merus 1.8 times longer than wide, with row of 5 distally serrate setae; on the anterior side of distodorsal extension with 1 robust unequally bifid seta; carpus 2.8 times longer than wide, distodorsally with row of 5 long setae, first 4 of this setae distally serrate, most distal one bifurcate, 1 broom seta; propodus 4.5 times longer than wide, 1 broom seta and terminally expanded to subtriangular lobe dorsally with two notches at apex; dactylus 5 times longer than wide, anterior and posterior claw of about the same length, slender posterior extension clasping, reaching beyond claws.

Pereopod 3 1.1 times longer than pereopod 2, with bigger dorsal and ventral extensions and generally longer and more robust setae, relative length ratios: 1:0.7:0.7:0.8:0.3:0.3, basis damaged in holotype, 3.3 times longer than wide in paratype, with at least 2 broom setae and 3 short setae on ventral side, with 2 small setae on dorsal margin; ischium 1.8 times longer than wide, dorsal extension with concave flanks, with 3 serrate setae proximally and 2 distally of apex, on apex with 2 pronounced unequally bifid setae; proximal seta very robust and bent proximally; 1 seta bent towards proximal hollow of ischium articulation; merus about 2 times longer than wide with distodorsal and distoventral extensions, with row of 7 serrate setae dorsally, the most distal seta bifurcate and robust, along ventral margin with 7 distally pappose, fringed setae; carpus 3 times longer than wide, distodorsally with row of 7 serrate setae, most distal seta bifurcate, with 1 broom seta and 6 distally pappose, fringed setae ventrally; propodus 4.3 times longer than wide, distodorsally with 2 sensillae and 1 broom seta ventrally; dactylus long and slender, 6 times longer than wide, as long as carpus, with 1 proximal, 2 medial and 3 subterminal sensillae, claws as in pereopod 2.

Posterior pereopods (Fig. 7; pereopods 6-7 of paratype missing) length ratios: 1:1.4:1.9:1.7.

Pereopod 4 about 0.6 times the length of pereopod 1, relative length ratios: 1:0.5:0.4:0.3:0.2:0.1, basis 3.7 times longer than wide with at least 4 broom and 2 short simple setae; ischium 2.9 times longer than wide, distodorsally with row of 3 setae and 1 tiny seta distoventrally; merus 1.9 times longer than wide, distodorsally expanded and with 4 setae of very different lengths, first 3 longer than carpus, serrate, the most distal one smaller, 2 distally pappose, fringed setae on ventral margin; carpus 2.2 times longer than wide, anterior-posteriorly flattened, and 3 times broader than propodus, dorsally extended with row of 4 long serrated, bifurcate setae reaching beyond dactylus tip, distodorsally with broom seta, on ventral margin with 4 distally pappose, fringed setae; propodus distally projecting into a subtriangular lobe, 3.5 times longer than wide, distoventrally with 1 long bifurcate and terminally fringed seta projecting beyond dactylus tip, 1 broom seta distally on dorsal side; dactylus of half propodus length, twice as long as wide, 1 short terminal claw, 1 subterminal claw of 0.5 times dactylus length, with 1 long thin seta subterminally and 2 sensillae.

Pereopod 5 0.9 times pereopod 1 length, relative length ratios: 1:0.6:0.5:0.5:0.4:0.2, basis broad, 2.9 times longer than wide with at least 3 broom setae dorsally, 2 broom setae and 3 small setae ventrally, 1 large simple seta distoventrally; ischium 2.3 times longer than wide, on dorsal and ventral side with 2 simple setae respectively; merus about 1.8 times longer than wide, distodorsally extending with 1 bifurcate and 1 long seta, with 2 tiny and 2 long setae on ventral side, longer seta longer than merus; carpus 2.6 times longer than wide, wide, ventrally with 1 stout bifurcate seta, articulation to propodus surrounded by 5 bifurcate setae, 1 broom seta and ventrally with 3 long and slender simple setae, longest seta exceeding propodus in length; propodus 5 times longer than wide, with 1 short bifurcate seta ventrally, distally with 2 setae on ventral side, the longest more than 2 times dactylus length, 1 broom seta dorsally; dactylus 2 times longer than wide, half propodus length, with 2 setae ventrally of more than 2 times dactylus length, with 2 short claws, 0.7 times dactylus length; at least 2 thin subterminal sensillae.

Pereopod 6 1.2 times pereopod 1 length, relative length ratios: 1:0.6:0.4:0.7:0.7:0.4, basis 4.3 times longer than wide, dorsally with 3 short setae and 3 broom setae, ventrally with 4 broom setae and 4 short setae; ischium 2.7 times longer than wide, dorsally slightly projecting with row of 7 long setae, ventrally with 2 setae and distoventrally with a group of 3 simple setae of different lengths; merus short and broad, 1.8 times longer than wide, distodorsally extending with 6 setae, the longest exceeding carpus, some denticulate or bifurcate, with row of 6 setae on ventral side; carpus slender, 4.4 times longer than wide, dorsally with row of 3 short setae and 1 broom seta, 2 simple setae ventrally, distally 4 robust, bifurcate and one-sided serrate setae and 2 slender setae, longer than propodus; propodus 7.6 times longer than wide, along ventral margin with 2 groups of 1 short bifurcate and 1 slender seta each; dactylus 6 times longer than wide, with 2 small sensillae on anterior side, with 2 very long simple setae along ventral margin, with terminal claw as long as dactylus and 1 subterminal claw, 1.7 times longer than dactylus.

Pereopod 7 1.1 times longer than pereopod 1, relative length ratios: 1:0.6:0.4:0.8:0.9:0.4, basis 4.1 times longer than wide, dorsally with 9 simple setae as well as 2 broom setae, ventrally with 4 broom setae and 6 simple setae of different lengths as well as 1 broom seta; ischium 3.2 times longer than wide, dorsally with row of 6 long simple setae, ventrally with 5 simple setae; merus 2 times longer than wide, distodorsally extending with 6 long setae, on the ventral margin with 1 simple and 1 serrate seta; carpus slender, 5.7 times longer than wide, dorsally with 2 bifurcate setae and a broom seta distally, a group of serrate setae on ventral margin, mero-carpal articulation surrounded by 6 short, robust, bifurcate and one-sided serrate setae; propodus slender, 9 times longer than wide, 4 setae ventrally, the two proximal ones serrate and very long; dactylus 3.8 times longer than wide, with 1 intermediate and 1 long seta of 2 times dactylus length on ventral side, with 2 claws of different lengths and 1 sensilla on apex.

Pleopods 2-4 (Fig. 8). Presence of pleopod 5 could not be clarified for both specimens. Relative length ratios: 1:0.8:0.6; operculum (Figs 5, 9) 0.7 times pleotelson length. Operculum covered ventrally with small setules and setae, along proximolateral margins with plumose setae with few short setules, distally with at least 8 pappose setae, several setae broken off and substructures not reconstructable. Pleopod 3 protopod constituting half of total length, rhomboid shape, endopod as wide as protopod, not considerably narrowing distally, with 3 distally plumose setae of 0.4 times pleopod 3 length, exopod 0.7 times total length, proximally about 0.7 times maximal width of endopod, distally narrowing, with 1 pronounced seta subterminally, row of numerous simple setae laterally. Pleopod 4 endopod long oval, 0.8 times total length; protopod as long as wide; exopod thin and long, 0.6 times total length and 7.7 times longer than wide, distal seta broken off and missing.

Uropod (Figs 3, 4, 8) of 2 articles, about half pleotelson length, protopod 5.5 times longer than wide, endopod 0.5 times protopod length, protopod with at least 1 broom seta distally, and endopod with at least 4 broom setae distally next to 3 very long and 3 short simple setae.

Male unknown.

Intraspecific variations in pereopods.

(Numerals in brackets and italics are variations in the ovigerous female, paratype).Pereopod 1 ischium 2.4 (3.2) times longer than wide, with row of 4 (3) setae distally. propodus 3.4 (2.8) times longer than wide; dactylus 3 (3.7) times longer than wide. Pereopod 2 basis 3.1 (3.7) times longer than wide; ischium 2.6 (3.2) times longer than wide; merus with row of 5 (6) setae; carpus distodorsally with row of 5 (6) long setae; propodus 4.5 (4) times longer than wide; dactylus 5 (5.5) times longer than wide.

Pereopod 3 ischium with 3 (4) setae proximally; merus with row of 7 (9) setae dorsally, along ventral margin with 7 (8) setae; carpus distodorsally with row of 7 (8) serrate setae, with 6 (7) setae ventrally. Pereopod 4 basis 3.7 (4.3) times longer than wide; ischium 2.9 (2.4) times longer than wide; merus 1.9 (2.4) times longer than wide; carpus 2.2 (2.8) times longer than wide; propodus 3.5 (3) times longer than wide. Pereopod 5 basis 2.9 (5) times longer than wide; ischium 2.3 (3) times longer than wide; carpus 2.6 (3.1) times longer than wide, propodus 5 (4.4) times longer than wide.

Etymology.

“Uniformis” is derived from the latin word for “uniform” as this species’ female on the first view resembles a most common macrostylid appearance and is hard to distinguish from other species.

Distribution.

Only known from the type locations: Southern Ocean, northern and south-eastern Weddell Sea, 4651-4975m depth.

Remarks.

Analysis of two specimens from different station reveals little variation. Differences in body shape and limb segments are usually too subtle to be detected in visual inspection. Variation in setal count tends to be allometric in the pereopods (compare Hessler 1970 for Desmosomatidae ). Variation was observed in pereopod 3 in setal counts on ischium, merus and carpus, but none in length-width ratios. Setal variation also occurs in pereopod 1 ischium as well as pereopod 2 merus and carpus. In all cases, the number of setae is increased by one or two per row in the female paratype. In pereopods 1, 2 and 5 length-width ratios of all articles are increased or identical in the ovigerous female except for the propodus. The strong variation in pereopod 4 has to be treated carefully, as the articles are flattened and in the appendage contortions along the proximo-distal axis limit comparability between both specimens.

In the shape of the cephalothorax and lateral pleonite borders as well as the pleotelson apex Macrostylis uniformis sp. n. closely resembles that of Macrostylis hadalis Wolff, 1956, Macrostylis zenkevitchi Birstein, 1963 and Macrostylis longifera Menzies & George, 1972. Macrostylis uniformis sp. n. also shares the small subtriangular lacinia mobilis and the minute pars molaris with Macrostylis hadalis . They can be separated by bicusp and acute pars incisiva in Macrostylis hadalis (blunt and rounded in Macrostylis uniformis sp. n.) and the smaller relative length of the antenna 2 compared to the antenna 1 in Macrostylis hadalis . Macrostylis zenkevitchi has more acute posterolateral corners of the posterior pereonites than found in Macrostylis uniformis sp. n. The mandible of Macrostylis zenkenvitchi has incisors with 3 blunt teeth and a strong lacinia mobilis (incisor without teeth, blunt and rounded, lacinia mobilis spine like and integrated into spine row in Macrostylis uniformis sp. n.). From Macrostylis longifera it can be distinguished by the pronounced posterolateral setae in pereonites 3-7 (no or tiny posterolateral setae in Macrostylis uniformis sp. n.) and in the stretched posterolateral protrusions of the posterior pereonites in Macrostylis longifera (protrusions subtle in Macrostylis uniformis sp. n.). The paratype female has damage on the pereon and exact measurements could not be taken. Nevertheless, length and width data from the anterior subsection indicate a high similarity in length and the ovigerous female being less wide in these pereonites.

No male specimen of this species could be identified and the male identity therefore remains unknown.