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

Abstract Descriptions of Macrostylis antennamagna sp. n. and Macrostylis uniformis sp. n. are presented with notes on intraspecific variability and sexual dimorphism. Macrostylis uniformis sp. n. showes differences to Macrostylis antennamagna sp. n. in the length of the antenna 2, the shape of the pleotelson and length of uropods. The genus Desmostylis Brandt, 1992 (formerly including the two species Desmostylis obscurus Brandt, 1992 and Desmostylis gerdesi Brandt, 2002) is synonymised with the genus Macrostylis. Based on type material additional remarks and additions to the original descriptions are provided for both species. Results lead to following nomenclatorial changes: Macrostylis obscurus (Brandt, 1992), comb. n. and Macrostylis gerdesi (Brandt, 2002), comb. n. A setal nomenclature is proposed and the diagnosis for the family is revised.


Introduction
During recent ANDEEP I-III cruises (ANtarctic benthic DEEP-sea biodiversity: colonization history and recent community patterns (Brandt et al. 2004a)), isopods have been found to be an important component of the Southern-Ocean deep sea (in terms of both richness and abundance). Most of the collected isopods belonged to the suborder Asellota Latreille, 1802(Brandt et al. 2004b, Brandt et al. 2007a). Among these, the family Macrostylidae Hansen, 1916 showed a remarkable species richness (Brandt et al. 2004, 2007, Kaiser et al. 2007.
To date, 78 valid macrostylid species are known worldwide of which ten occur in the Southern Ocean (Tab. 2). During the ANDEEP cruises at least 33 species of Macrostylidae have been collected, of which 23 where unlike any previously described species (Vey and Brix 2009). In the current paper, two of these previously unknown species, M. unifomis sp. n. and M. antennamagna sp. n. are described. Based on type material, additions to the original description of D. obscurus is presented and close examination of characters led to a rejection of the genus Desmostylis. It has been found synonymous with Macrostylis.

Material and methods
Specimens used for species descriptions were collected at four stations in the northern and south-eastern Weddell Sea during the ANDEEP II-III expeditions with RV Polarstern. Th ese cruises took part in Austral summer 2001/2002 and 2004/2005. An epibenthic sledge was used for sampling (Brenke 2005 and references therein). On board samples were immediately transferred into 96% pre-cooled ethanol and stored at -20° for at least 48 h. Samples were sorted into major groups on board. Sorting of isopods to family level has been continued in the laboratories of the Zoological Museum, Hamburg.
For habitus drawings and dissections of limbs, specimens were transferred into glycerine. Habitus were photographed in deionized water or glycerine. For identifi cations and pencil habitus sketches a Leica MZ12.5 with a camera lucida was used (max. 100 ×). Specimens were stained in high-concentration water solution of Figure 1. 1-13 Specialized setae, all articulating infracuticularly, except when mentioned otherwise; 1 Sensilla, pappose seta, shaft densely covered with fringe-like appearing setules; on pereopod 1-3 dactyli 2 broom seta, pedestal pappose seta 3 sensilla, distally pappose seta, densely covered with fringe-like appearing setules, showing a gradual transition from denticles to setules; on distal margins of maxilliped palp and on pereopods 4 tuft seta, a pedestal pappose seta, setule bases closely together, continuous transition to shaft cuticle; only known from distal articulation margin of 5. article in antenna 2 5, 7 simple setae, short 5 on general cuticle and pereopodal basis 6-8, 12 diff erent setal types, on lateral margin of pleopod cavity and operculum 6 plumose seta with few short setules on distal half 8 spine-like unequally bifi d seta 12 small pappose seta, with short setules 9 "feather-like" plumose seta like at pleopod 3 apex 10-11 pappose setae, on operculum distal apex and pleopod 2 distal apex 13 simple tubular seta with big apical pore and associated small simple seta, on antenna 1 articles and antenna 2 fl agellar articles.

Diagnosis.
Cephalothorax free, about as broad as long. Body elongated. Eyes absent. Antenna 1 small, number of articles variable (1-9). Antenna 2 short or only moderately long, with articles 1-3 together about as long as articles 4 and 5 respectively, squama absent. Mandible with pars molaris reduced, subacute triangular and setiferous on apex; palp absent; lacinia mobilis ambilateral. Maxilliped with long and narrow basis; subtriangular epipod subequal in length to basis; palp articles 1-3 expanded and articles 4-5 minute.
Type species. Macrostylis spinifera Sars, 1864 Diagnosis. As of the family. Remarks. Some characters are absent or poorly illustrated in original descriptions and could not be analysed thoroughly during this study. Th erefore these have not been  (Brandt, 1992) and M. gerdesi (Brandt, 2002) are labelled as the genus Desmostylis.
included in the family diagnosis (e.g. presence of exopod of pleopod 5, setation patterns and setal substructures).
Following the original description (Brandt 1992), Desmostylis can be separated from Macrostylis by the following characters: absence of dorsal triangular expansion on the pereopod 3 ischium, lack of dactylus on pereopod 4 and of claws on pereopods 5-7. However, after comparisons of diff erent species of Macrostylis, and re-examination of the holotype of Desmostylis obscurus Brandt, 1992 these characters have been found not to be delimitating Desmostylis from Macrostylis. Shape and extension of pereopod 3 ischium varies greatly between species of Macrostylis. For example M. galatheae Wolff , 1956 (p. 101, Fig. 17) has a strong and acute extension and no extension is present in M. abyssalis Brandt, 2004 (p. 28, Fig. 15), very similar to D. obscurus. However, another described species of Desmostylis, D. gerdesi Brandt, 2002 shows a strongly fossorial pereopod 3 bearing a prominent dorsal extension on the ischium. Th us, the condition of this character in Desmostylis lies within the interspecifi c range of variation in Macrostylis. Th erefore, this character is not usable to maintain the genus Desmostylis.

Macrostylis uniformis
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 2 (Figs 3-5) basal fi ve articles reaching the posterior end of cephalothorax; fl agellum 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 fl agellar 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 diff erent lengths on lateral and medial margins, numerous setae of diff erent 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 diff erent 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 diff erent 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 fi ne 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 ven- trally, 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 diff erent 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 bifi d seta; carpus 2.8 times longer than wide, distodorsally with row of 5 long setae, fi rst 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 fl anks, with 3 serrate setae proximally and 2 distally of apex, on apex with 2 pronounced unequally bifi d 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.
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 diff erent 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 diff erent 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 diff erent lengths and 1 sensilla on apex.
Etymology. "Uniformis" is derived from the latin word for "uniform" as this species' female on the fi rst 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 diff erent station reveals little variation. Diff erences 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. Th e strong variation in pereopod 4 has to be treated carefully, as the articles are fl attened 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, M. zenkevitchi Birstein, 1963  . Th e 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 identifi ed and the male identity therefore remains unknown.  Table 1.
Antenna 1 (Figs 10, 11) with 5 articles, small, barely reaching halfway to posterior margin of cephalothorax when directed backwards; length 2.6 times article 1 width; all articles about as long as wide, gradually decreasing in size towards distally; fi fth article 0.1 times total length; at least 4 aesthetascs on each of articles 4 and 5, some broken off ; broom setae around distal margin of article 2; some distally fringed sensillae on distal margins of articles 1-3; with 1 seta distally on article 5, next to aesthetascs.
Antenna 2 (Figs 10, 11) relatively long and broad, peduncle reaching to the posterior end of pereonite 2 and fl agellum reaching to the posterior end of pereonite 3; each of articles 1-3 1.4 times longer than wide; article 4 longest, length 0.3 times total length, as wide as articles 1-3; article 5 0.8 times article 4 length, about 0.4 times article 4 width; fl agellum of 7 articles; all 5 basal articles with 1-several distal broom setae (not shown in illustration) and some simple setae; tubular setae with large apical pores distally on fl agellar articles 1-4 ans 7, articles 1-3 with 3 setae each, articles 4 and 7 with 2; article 7 with long simple distal setae, 3 times longer than article.
Mandible (Fig. 11) fl at, dorsoventrally constricted proximally to lacinia; pars incisiva without teeth, but bump-like structures, left mandible with 1 terminal, 1 ventral and 2 dorsal cusps, right mandible with a centered lobe-like cusp; left lacinia mobilis longer and more robust than right lacinia mobilis, with 4 strong blunt teeth, 1.5 times longer than following spines of spine row; right lacinia mobilis twice as long as following spines of spine row, with 6 teeth, more acute than in left lacinia mobilis, dorsoventrally arranged, with ventral teeth projecting most distally; spine row of about 8 spines with multiple cusps, partially serrated; Maxilla 1 and 2: see description of female paratype.
Maxilliped (Fig. 11) epipod oblong-subtriangular, distally narrowing to multiple small tips, distolaterally concave, without any setae or setules, reaching distal end of palp article 2; endite with 2 coupling hooks, densely covered with fi ne but rather long simple setae, medially broadening, more proximally and dorsally forming lobe-like protrusion with 4 setae on lateral blunt apex, together constituting a sheath in which the epipod rests; lateral margins of basis, and palp articles 1-2 with row of small setae, basis and epipod subequal in length; palp article 2 3 times longer than article 1, articles 2-4 distomedially and distolaterally with medially scaled and distally pappose (fringed) sensillae, article 5 with the same setae terminally and subterminally.
Pereopod 3, relative length ratios: 1:0.6:0.8:0.7:0.3:0.3, basis 2.9 times longer than wide with at least 3 broom setae, row of short setae on ventral side; ischium 1.8 times longer than wide, dorsal extension strongly expanded, sub-triangular, with 7 robust setae, apical 2 setae bifurcate, about as long as maximum ischium width, proximal 2 and distal 3 setae simple, but slightly increasing towards apex, proximodorsally 1 short seta, bent and directed towards proximal hollow of ischium articulation; merus twice as long as wide with weak distoventral extension and strong distodorsal extension bearing 6 bifurcate setae of similar length, 1.4 times maximal merus width, furcation not observed in most proximal seta of row, 4 simple setae ventrally; carpus 2.8 times longer than wide, distodorsally with 5 bifurcate setae and 1 broom seta, with 4 simple setae ventrally; propodus of 0.4 times carpus length, 3.6 times longer than wide, distoventrally with 1 simple and 1 broom seta, distodorsally with sensilla; dactylus 5.5 times longer than wide, 1.1 times carpus length, with 4 sensillae of diff erent lengths arranged in 2 pairs on opposite sides.
Posterior pereopods (Fig. 13) length ratios: 1:1.7:2.3:1.9. Pereopod 4 0.6 times pereopod 2 length, relative length ratios: 1:0.4:0.3:0.3:0.2:0.1, basis 3.9 times longer than wide, with at least 4 broom setae; ischium twice as long as wide, with 2 short and 2 long setae; merus about 1.8 times longer than wide, row of 3 setae of same length as merus, most distal seta bifurcate, with 1 simple seta distally on opposite side of the article; carpus 3 times longer than wide, 1.3 times longer than merus, setation similar to merus but most proximal seta of row with bifurcation, and 1 very long bifurcate seta, almost reaching distal tip of propodus; with 1 very long bifurcate seta reaching the tip of the most distally reaching seta of propodus, projecting beyond all setae of dactylus; propodus distally projecting into a subtriangular lobe, 2.3 times longer than wide, distally with 1 long simple seta and 1 robust and acute seta; dactylus very small, twice as long as wide, about 0.4 times propodus length, with 1 terminal bifurcate claw of 1.3 times dactylus length and 1 subterminal claw of 0.5 times dactylus length, with 1 thin terminal seta of intermediate length.
Pereopod 7 1.1 times longer than pereopod 2, relative length ratios and setation similar to pereopod 6 except basis without broom setae, but dorsally with row of more than 25 simple setae of twice the length of basis width and a ventral row of at least 5 simple setae.
Antenna 1 (Fig. 16) of 5 articles, 3.4 times longer than article 1 width; articles 1 and 5 as long as wide, fi fth article 0.1 times total length, articles 2-4 2 times longer than wide, gradually decreasing in size; 1 aesthetasc on article 5, 0.6 times the length of antenna 1.
Antenna 2 (Fig. 16) relatively slender compared to male antenna 2; articles 1-3 as long as wide; article 4 half as wide as articles 1-3; article 5 0.6 times article 4 length and of same width.
Maxilla 1 (Fig. 16) inner endite shorter and more slender than outer endite, terminally narrowing, around distal apex, dorsally and along lateral margin with numerous long and some very small simple setae; outer endite 1.4 times longer than inner one, narrowing distolaterally, with at least 11 simple setae on lateral margin, with 4 combs of 2-4 simple setae on medial margin, numerous simple setae of different lengths distomedially and 12 robust distal setae, some two-sided denticulate on distal margin.
Maxilla 2 (Fig. 16) inner endite broadest, outer endite of intermediate width, medial endite longest, outer endite 0.8 times middle-endite length, inner endite 0.9 times middle-endite length; margin of inner endite with 12 long simple basomedial setae of more than half the length of endite, numerous small simple setae ventrally and laterally, distal margin with 8 robust setae: 5 simple and 3 denticulate; medial endite with 1 lateral row of simple setae, distally with 4 long simple setae; outer endite with small simple setae along both margins, distally with 4 stiff simple setae of diff erent lengths, the longest of which is of more than half the length of the outer endite. Measurements of article lengths ratios and length-width ratios of articles are listed in Table 3.
Anterior pereopods (Fig. 17) increasing in length, relative length ratios, omitting basis: 1:1.2:1.3, with basis longest article. Shapes and setation as in holotype. Pereopod 2 basis damaged. Except: pereopod 3 relative length ratios and setation diff erent from holotype: basis relatively elongated; ischium only 2.2 times longer than wide, dorsal expansion less prominent than in holotype; propodus 0.5 times the length of carpus; dactylus long and slender, 0.9 times carpus length; lengths and robustness of setae as well as the number of setae per row increased in merus and carpus.
Sexual dimorphism. Th e male specimen is more slender than the female, its pleotelson is less narrowing posteriorly. Th e antenna 1 is relatively smaller but wider than in female and with more aesthetascs. Th e antenna 2 is little larger in the male, almost 0.4 times the length of the total body, 0.3 in female. Pereopods are dimorphic by means of article length ratios while pereopod length in relation to body length and setation are identical in both sexes.
Etymology. "Antennamagna" is derived from the Latin word for "big antenna" as the second antennae are conspicuously large in both sexes.
Remarks. Macrostylis antennamagna sp. n. can be delimited from all other species by the large antenna 2, the three-lobed pars incisiva, the roundish appearance of the cephalothorax without a transverse ridge on frons and the shape of male pleopod 1. M. antennamagna sp. n. is most similar to M. urceolata Mezhov, 1989 which is the only known species of this genus with comparably prominent antenna 2. Both species also share the general appearance in dorsal view and have high similarities in following characters: mandibles, male pleopod 1 and ventral spines. M. antennamagna sp. n. can be distinguished from M. urceolata by the transverse ridge on frons lacking, antenna 1 being stouter, lacinia mobilis being smaller, the male pleopod 1 being wider and stouter, the smaller relative length of the pleotelson, and the "bifurcate" caudal tip of the pleotelson. M. gerdesi (Brandt, 2002), M. carinifera Mezhov, 1988, M. grandis Birstein, 1970, M. hirsuticaudis Menzies, 1962, M. longiremis (Meinert, 1890, M. minuscularia Mezhov, 2003, M. sarsi Brandt, 1992, M. sensitiva Birstein, 1970, M. ovata Birstein, 1970, and M. vinogradovae Mezhov, 1992 have a comparably long antenna 2. However, these species show distinct characters clearly delimitating them from M. antennamagna sp. n. of which only the most obvious are listed below: antenna 1 of M. gerdesi has nine articles, M. carinifera bears a posterior ventral spine on pereonite 4 and a much more stout pleopod 2, M. grandis and M. ovata have a much wider habitus in dorsal view, M. hirsuticaudis has an uniquely shaped pleotelson with an almost straight posterior end, the habitus of M. longiremis is constantly narrowing towards posteriorly and the cephalothorax bears spines in posterolateral corners, M. minuscularia has a comparably long but thinner antenna 2 and antenna 1 diff ers in article length ratios and size, M. sarsi shows a stouter habitus and more slender antenna 2, the latter is also true for M. sensitiva and M. vinogradovae.
Antenna 2 can be found even bigger in M. spinifera Sars, 1864, M. polaris Malyutina & Kussakin, 1996and M. porrecta Mezhov, 1988. However, in M. spinifera shape and size ratios of male and female pleopods 1 and 2 diff er from M. antennamagna sp. n. and in the other two species antenna 2 has more slender peducular articles and antenna 1 is bigger compared to M. antennamagna sp. n.
Th e slender habitus with almost parallel sides in dorsal view shown by M. antennamagna sp. n. is common in Macrostylidae. Th e "bifurcated" caudal end is also present in M. bifurcatus Menzies, 1962, although much stronger developed there. Th e pleopods 5 have not been found in both sexes. It is unclear, though, whether these have been broken off during dissection or if they are generally reduced in this species. Th e analysis of fi ve specimens from two stations has revealed little individual variation. Variations in setal counts are probably allometric (compare Hessler 1970 for Desmosomatidae). (Brandt, 1992), comb. n. Fig. 19 Desmostylis obscurus Brandt, 1992, p. 69-74, Fig. 11-13 Additions to original description. Pereopod 4 relative article length ratios: 1:0.5:0.5:0.4:0.3:0.1, basis 2.3 times longer than wide, with at least 5 broom setae, 1 short simple seta distodorsally; ischium 1.8 times longer than wide, with 1 short simple seta distodorsally; merus almost 1.8 times longer than wide, distodorsally with 1 stout bifurcate seta, distoventrally 2 acute simple setae, 1 reaching beyond propodal articulation; carpus 1.6 times longer than wide, distodorsally with 1 bifurcate seta, 1 broom seta distoventrally next to 1 long simple seta exceeding dactylus in length; propodus twice as long as wide, dorsally expanding into a distal lobe, with 1 long bifurcate seta distoventrally, exceeding dactylar claw, and 1 short and simple seta ventrally; dactylus small, twice as long as wide, about half propodus length and width, with 1 terminal stout and acute claw, 1.5 times article length, and 1 subterminal bifurcate claw, shorter than article, 2 setae terminally and 1 thin and long simple seta subterminally, twice as long as article.

Macrostylis obscurus
Pereopod 5 propodus 3.3 times longer than wide, with 2 long simple setae distoventrally, thinner seta more than twice as long as dactylus, the stouter one almost reaching the tip of dactylus, 1 simple seta ventrally; dactylus 5 times longer than wide, half propodus length, with 3 simple, acute claws, terminal claw longer than dactylus, subterminal claw stout, robust and shorter than dactylus, second subterminal claw slender and more than twice as long as dactylus.

Macrostylis gerdesi
Remarks. Re-examination revealed spines on all sternites not illustrated before, except from pereonite 4. In the latter a ventral constriction is present close to the posterior margin. In M. gerdesi comb. n. long sensory terminal setae on dactyli and additionally long sensory setae on propodi of posterior pereopods are considered to be apomorphies for Desmostylis. Th e value of these characters to discriminate between genera is discussed above. However, a dactylus is present in pereopod 4 and in contrast to the M. obscurus comb. n. holotype, pereopod 3 ischium is triangularly expanded in M. gerdesi comb. n. As a consequence of the character discussion listed above this species is transferred the genus Macrostylis.

Discussion
Pereopodal measures are variable within a species. Not only can diff erences be found between the sexes (see below) but also within a sex. Certain variability does not necessarily occur in all pereopods at the same time and to the same extend. In Macrostylis uniformis sp. n., for example, we have found the pereopod 3 to be almost similar with regard to length-width ratios in an ovigerous and a non-ovigerous female specimen. Here, only the number of setae per row was slightly diff erent. Contrastingly, pereopod 5 shows rather strong variation. While the pereopod 5 in general and most of its articles were longer in the ovigerous female, ischium and merus had the same length compared to the preparatory female. Besides propodus and dactylus, all articles had the same width or were narrower in the ovigerous female compared to the preparatory one. Th ese measures could be interpreted as allometry but may also be variable within a stage.
In M. antennamagna sp. n. we observed diff erences in posterolateral setation of cephalon and pereomeres with regard to robustness, length and substructures. Th ese diff erences occurred between male and female as well as between left and right side of the same pereomere of one specimen. Th is indicates that such setal features are intraspecifi cally variable. To clarify if this is general variability or sexual dimorphism, higher numbers of specimens need to be analysed.
Sexual dimorphisms have been reported for a wide range of taxa. Not much is known about dimorphism in Macrostylidae. Here, species have been described based on one sex only. Sexual dimorphism is probably the reason why correct allocation of a complementary male or female is often impossible based solely on morphological characters. Th is is the case for example in M. uniformis sp. n. Knowledge about general patterns of dimorphism in closely related species could provide an aid for allocation in new species. However, we found distinct diff erences between males and females in macrostylids. A general pattern of sexual dimorphism can be found in the copulatory organs and a few additional characters: the male antenna 1 bears more aesthetascs and is sometimes broader than in the female (Hansen 1916, Menzies andGeorge 1972). Furthermore, in the antenna 2 articles are sometimes broader in males than in females (Mezhov 2003a, b).
To date no cases of more extreme sexual dimorphism, as for example reported for the paramunnid genus Abyssaranea Wilson & Hessler, 1974, have been described in Macrostylidae. It is possible that no example has been discovered so far but it also may be that in strongly dimorphic species males and females have been defi ned as distinct species. Wilson and Hessler (1974) mentioned the possible value of the dimorphic degree as being a signifi cant character on generic level. A comprehensive comparison of gender diff erences has been reported for M. dellacrocei Aydogan, Wägele & Park, 2000. In the original description a juvenile male was compared to the preparatory female holotype. Diff erences found exceed the above mentioned general pattern for Macrostylidae by far. Th e diff erences that occurred between sexes (i.e. lack of sternal projection in pereonite 1, the relatively smaller pereonite 7, the smaller aesthetasc and terminal article in the antenna 1, the reduced sizes of pars molaris and spine row in the mandible, the reduced sizes in right and left lacinia mobilis, reduced number of setae on pereopod 7), though, are most likely allometric characters at an early ontogenetic stage in the juvenile male specimen. Th erefore, these characters cannot be used to infer sexual dimorphism in this species or to gain insights into general patterns of sexual dimorphism in Macrostylidae.
On this background we assume sexual dimorphism likely to be common in Macrostylidae and to vary from species to species. Both sexes have so far only been described in species with low degree of sexual dimorphism, where allocation was straight forward. It is likely that in some cases only one gender per species has been collected, particularly where sample size is low. It may also be likely that strong sexual dimorphism leads to allocation of male and female specimens into separate species. Th is could e.g. be the case in M. uniformis sp. n. To allocate specimens safely it is necessary to know characters that are less aff ected by sexual dimorphism. For the identifi cation of such characters, analyses of higher numbers of specimens from one sampling site are needed. Patterns could be not only generalized to allocate species where lower numbers of specimens are available but probably also be used to infer subtaxa (i.e. genera) within Macrostylidae.