Eurycope denticollis, Mursch, Andre, Brenke, Nils & Wägele, Johann Wolfgang, 2008

Mursch, Andre, Brenke, Nils & Wägele, Johann Wolfgang, 2008, Results of the DIVA­ 1 Expedition of RV “ Meteor ” (Cruise M 48: 1): Three new species of Munnopsidae Sars, 1864 from abyssal depths of the Angola Basin (Crustacea: Isopoda: Asellota) *, Zootaxa 1866, pp. 493-539 : 509-526

Eurycope denticollis sp. nov.

Material examined

Holotype ( ZMH K­ 41797), male (3.23 mm), Angola Basin, 16 14.3’ S, 5 26.8’ E to 16 14.9’ S, 5 26.7’ E, 5389 m, Station No. 350, expedition M48:1 RV “ Meteor ”. Paratype ( ZMH K­ 41798), female (4.71 mm), same locality.

Additional material: 10 males, 10 females ( ZMH K­ 41799 ­ K­ 41802)

Diagnosis

As Eurycope monodon , but rostrum with 2 to 7 spine­like setae, the medial pair longest and always present. Anterior margin of pereonite 1 with cone­shaped spine­like setae. Distolateral lobes of male pleopod 1 with caudally pointing cusp.

Description of male holotype

Body ( Fig. 11 a, b) length 3.23 mm, length: width = 2.58, longishly oval, dorsoventrally slightly flattened. Only slightly widening from head to pereonite 5. Caudally tapering to roundly triangular pleotelson. Natasome about two thirds of total length. Body height at head and ambulosoma 0.22 times body length, at posterior half of pereomer 5 increasing to 0.25 times body length, caudally evenly decreasing in height.

Head ( Fig. 11 a–c; Fig. 12 a) length = 0.18 times body length, width = 0.71 times maximum body width, length: width = 0.66, wider than pereonite 1, anteriorly slightly tapering, as wide as pereomer 1. Lateral side with 3 cone­shaped spine­like setae in a nearly horizontal row. Anterolateral margin with shallow curvature on a level with insertion of antenna 2. Rostrum width 0.15 times cephalic width, length: width = 0.75, overhanging, tapering anteriorly and with rounded tip. Anterolateral margin in apical half with cuticular keel. Distally 5 short spine­like setae pointing anteriorly, median pair about twice as long as outer ( Fig. 11 c). Rostral spine­like setae anteriorly reaching insertion of antenna 1 article 2. Frons clearly concave due to overhanging rostrum. Clypeus swollen dorsomedially, length: labrum length = 0.69. Labrum and clypeus only separated by a fold. Anterior margin of labrum with sparse setation.

Ambulosome ( Fig. 11 a, b): Pereonites increasing in width from 1 to 4: 0.69, 0.73, 0.74, 0.79 times maximum body width. Medial length 0.9 to 0.1 times its width. Pereonites dorsally overlapping preceding segment. Anterior margins of pereonite 1 and 2 only slightly curved caudally, of pereonite 3 and 4 curved cranially. Each anterolateral corner with 1 short seta. Coxal lobes prominent and triangular, projecting anteriorly, with stout spine­like seta and 1 to 6 short lateral setae. Sternites less sclerotized with shallow cuticular grooves. Anterior margin of pereonite 1 with 10 cone­shaped spine­like setae of 0.02 mm length ( Fig. 12 b, c).

Natasome ( Fig. 11 a, b): Entire natasome stiffened by fusion of sternites. Posterior margin of pereonite 5 and 6 overlapped by anterior margin of the following tergite. Anterior margins slightly bent dorsally, especially on pereonite 5. Lateral margins in anterior half with up to 6 setae. Posterolateral angles covered by anterior margin of following pereonite. Pereonite 5 widest, length: width = 0.34, length: body length = 0.13, with nearly straight anterior and concave posterior margin, anterolateral angles rounded, posterior margin with 2 inconspicuous bulges, forming a pair of small cavities. Pereonite 6 shortest, length = 0.93 times pereonite 5 length, width = 0.96 times pereonite 5 width, length: width = 0.33, caudally narrowing, anterior and posterior margin curved anteriorly. Anterolateral angle acute, with short apical seta. Pereonite 7 length = 1.14 times pereonite 5 length, width = 0.87 times pereonite 5 width, length: width = 0.45. Anterior margin convex, posterior margin almost straight. Acute anteriolateral angle with short apical spine­like seta. Coxae and sternites less sclerotized, with weakly developed cuticular grooves. Coxae inserting on posterolateral margin of sternites. Posterior margin of sternite of pereonite 7 with a pair of triangular penes, fitting into basal cavities of pleopod 1.

Pleotelson ( Fig. 11 a, b; Fig. 17 a) length = 0.30 times body length, width = 0.84 times maximum body width, length: width = 0.92, width: depth = 2.69, dorsoventrally flattened, resembling caudally rounded triangle. Anterior margin separated from pereonite 7 by intersegmental membrane of 0.49 times pleotelson width, nearly straight, seemingly concave when pleotelson is bent ventrally. Anterolateral angles with short setae, slightly overlapping pereonite 7. Dorsolaterally in anterior third a pair of inconspicuous tubercles of 0.04 times pleotelson width with central broom seta ( Fig. 11 d). Lateral margin of each side with 17 short setae, in lateral view nearly straight, without angle near insertion of uropods. Dorsum smooth, lateroventral surface with cuticular grooves.

Antenna 1 ( Fig. 12 d, e) length: body length 0.31. Peduncular article 1 appearing dorsoventrally flattened due to lateral extension, length: width = 1.16, slightly wider than a quarter of cephalic width. Small dorsomedial broom seta, another and a short spine­like seta close to insertion of second article, 2 dorsolateral simple setae. Distally differentiated into shorter, anterolateral outer lobe and longer, acute, anteromedial inner lobe. Inner lobe distally with 3 long spine­like setae. Outer lobe with 1 broom seta, 3 small simple setae and a spine­like seta. Article 2 slightly more than half as long as article 1, 2.5 times as long as wide, widening to distal margin, distally 2 simple setae, 2 broom setae and 3 short spine­like setae. Article 3 cylindrical, two thirds of length and width of preceding article. 2 short distodorsal setae. Flagellum 17­jointed. First flagellar article as wide as peduncular article 3 but only a third as long. Following articles slightly narrower. Articles 1, 3, 11 and 12 each with 1 short distal seta, article 13 with 1 short and 1 longer seta, article 9 dorsally with 1 short, article 10 lateral with 2 longer setae. Articles 4, 5 and 7 to 16 each with 1 distoventral aesthetasc, article 17 with subapical long seta and apical broom seta.

Antenna 2 ( Fig. 12 f, g): 1.12 times body length. 6 peduncular articles and 43­jointed flagellum. Proximalmost 4 peduncular articles short but widest, 0.24 times cephalic width. Article 5 and 6 longest. Article 1 short, extending into rounded lateral lobe, 1 spine­like seta. Article 2 as long as first, evenly cylindrical, with 3 long lateral spine­like setae. Article 3 about as long as 1 and 2 together, distal margin sloping. Distomedial row of 5 spine­like setae. Lateral side with subdistal, acute, triangular scale reaching insertion of article 5, lateral side with 2 small, 1 larger, and 1 broom seta. Article 4 half as long and 0.75 times as wide as preceding article, distal margin extended to a dorsomedial and ventromedial lobe. Article 5 length 0.24 times total length of antenna 2, with numerous stout spine­like setae. 8 stronger distal spine­like setae, distomedially with 1 simple seta and 1 broom seta. Article 6 length 0.24 times antenna 2 length, numerous spine­like setae as on the preceding article, distally with 3 stronger spine­like setae and 3 broom setae. Length of flagellum 0.38 times length of antenna 2, evenly tapering over entire length, terminal article only about a ninth the diameter of first article of flagellum. Article 1 longest. Article 2 nearly half as long. Following articles evenly increasing in length, only 0.2 to 0.3 times as long as first article. Articles 1, 3, 4, 6 and 23 each with 1 short seta, article 2 with 2 setae, articles 22 and 24 with a longer seta. Distal margin with a row of 3 to 7 long and slender setae on articles 19, 25, 27 and 29 to 43.

Mandibles ( Fig. 13 a—k): Left mandible 0.16 times body length, length: width = 2.04. Right mandible 0.15 times body length, length: width = 1.96. Dorsal surface between condyle and insertion of palp with few scale setae, more dense on left mandible. Palp length 0.75 times mandible length. Proximal 2 articles flattened. Article 1 basally tapering, distally with a long seta on both sides. Article 2 about 0.5 times as long and as wide as first. Distal half densely covered with scale setae consisting of 3 to 13 setulae, distally with 3 large stout setae, the largest one­sidedly serrated. Third article strongly flattened, apical half twisted clockwise in right, counter­clockwise in left mandible. Medial surface with numerous scale setae. Ventral margin with a row of 12 cleaning setae, 2 strong apical stout setae, the larger one one­sidedly serrated. Incisor process on each mandible with 3 sclerotized and wrinkled cusps, the middle cusp largest. Lacinia mobilis sclerotized, 0.12 times as long as mandible, length: width = 2. Sloping distal edge with a row of 7 cusps, from dorsal to ventral evenly increasing in size, most dorsal much smaller than the following. 3 ventrolateral setae pointing ventrally. Spine row of left mandible with 4 one­sidedly serrated stout setae, from distally to proximally evenly longer and more slender, right mandible with 5 stout setae, distalmost strongest and with 6 teeth ( Fig. 13 h, i). Second stout seta one­sidedly serrated, third longest, fifth broken off. Molar process with oval chewing areas about equal size on both mandibles, anterior margin with row of 6 shallow tubercles on left and 5 on right mandible. Posterior margin with elevated cusp row, right mandible with 9, left mandible with 6 cusps. Cusp row of each mandible with 3 strong setae. Right chewing area with 5 sensory cavities. Condylus elevated, about as long as molar process.

Paragnath: Lost during dissection and therefore unknown.

Maxilla 1 ( Fig. 14 a—c): Slightly curved medially, larger outer endite inserted dorsally, length: body length = 0.09, length: width = 4. Numerous fine setae in dorsomedial rows. Dorsolateral row of 14 long setae. Apex diagonally truncate with 12 strong stout setae, 3 one­sidedly dentated. Proximomedially to stout seta bases 1, proximoventrally 4 simple setae. Inner endite length: outer endite length = 0.64, width: outer endite width = 0.57, ventrolateral longitudinal row of 8 setae. Medial margin in distal third and lateral margin in distal fifth each with 5 setae. Apex bluntly cone­shaped, with 2 long stout setae, medial one longer and stronger than the other, further dorsally 2 shorter stout setae.

Maxilla 2 ( Fig. 14 d—g): Inner endite 0.07 times as long as body, length: width = 4.6. Medial half along entire length with numerous setae. Apex rounded, 14 long stout setae, most caudomedial stout seta longest. 7 distomedial setae. Inner part of outer endite ending on a level with inner endite, width: inner endite width = 0.6. Apex dorsally with rounded lobe and 2 long stout setae, hemiplumose in middle third. Further proximoventrally a one­sidedly serrated stout seta. Outer part of outer endite surpassing inner part, lateral margin with 24, medial margin in distal half with 5 setae in a row. Apex truncate, with rounded lobe and 3 long stout setae and 1 seta. Subapical stout seta on medial margin.

Maxilliped ( Fig. 15 a—e): 0.24 times as long as body. Coxa 0.3 times as long as basis. Basis length: maxilliped length = 0.44, length: width = 1.55, with lateral seam of fine setae, beginning after proximal third, distally reaching insertion of palp. Medial margin bent dorsally. 3 distal retinacula on each side, surrounded by 6 short setae. Retinacula club­shaped, distodorsally with 2 pairs of elongated tubercles. Endite spatulate, length: basis length = 0.53, length: width = 2, medial margin bent dorsally. Apex truncate, sloping at an angle of approximately 120 ° to medial margin, 4 ventrally and 1 dorsally inserting fan setae. Lateral margin slightly rounded, with 14 setae. Dorsal surface with area of 48 long setae, subapically as wide as endite, proximally narrower and reaching level of retinacula. Palp 5­jointed. Article 1 shortest, slightly wider than proximal end of basis. Lateral setae continued here. Article 2 largest, length: basis length = 0.56, length: width = 1.06, 3 times as long as article 1, distally increasing in width, distal margin oblique. Lateral setae continued in first 2 thirds of its length, distally followed by 3 larger setae. 1 distolateral and 1 ventrolateral large seta. Medial margin with 5 distomedially pointing pappose setae with bald proximal third, demarcated by an annulus. Article 3 subtrapezoidal, slightly shorter than preceding, lateral margin much shorter than medial, with large distolateral seta. Medial margin up to distally rounded tip with 16 pappose setae shaped as on article 2, and half as long. Ventral surface with 5 short setae. Article 4 nearly y­shaped due to distomedial lobe and broadened insertion of article 5, inserting distolaterally on article 3, proximally tapering to a third of maximum width of article 3. 3 lateral, at distomedial lobe 7 setae, lobe with 2 pappose setae. Article 5 cylindrical, seemingly moved laterally due to distolateral lobe of article 4, setose apices of both lying parallel to each other. Distally and subdistally 10 setae, the 4 distalmost longest. Epipodite length: basis length = 1.56, length: width = 1.66, broadly y­shaped to triangular due to lateral lobe. Apex acute, with 3 short setae, another short seta further subapically. Lateral lobe rounded and slightly bent dorsally, in situ covering insertion of mandible.

Pereopods 1—4 ( Fig. 16 a, b): Only pereopod 1 preserved distally of basis, length: body length = 0.66. Basis cylindrical, elongate, length: pereopod 1 length = 0.28, length: width = 6, sparsely setose, proximodorsally 1 broom seta and 1 ventrodistal spine­like seta. Ischium proximally slightly tapering, length: pereopod 1 length = 0.1, length: width = 2.75, with 6 setae. Merus proximally tapering, length: pereopod 1 length = 0.06, length: width = 1.86. 4 short and 2 long distal setae. Carpus longest, length: pereopod 1 length = 0.34, length: width = 12, slender and cylindrical, sparsely setose, ventral setae longest. Propodus cylindrical, length: pereopod 1 length = 0.16, length: width = 8.5, with 5 setae, distal end with 8 setae. Dactylus scythe­shaped, length: pereopod 1 length = 0.06, laterally flattened, evenly tapering and ventrally curved with blunt apex. Medially at middle of length with 1 long and 3 short setae.

Pereopods 5—7 ( Fig. 16 c—g): Basis cylindrical, stouter and shorter than on ambulatory pereopods. Pereopod 5 with 4 simple, 2 broom setae and 1 spine­like seta. Pereopod 6 with 5 short, 1 long distal seta and 1 broom seta. Pereopod 7 with 3 short setae. Ischium cylindrical, laterally flattened dorsal lobe along entire length, in situ pointing caudally, especially distinct on pereopod 6 and 7, with insertions of long swimming setae. On pereopod 5 7 short, simple setae and row of 8 long swimming setae. On pereopod 6 3 short, simple and 1 larger seta, distal margin with 3 bluntly cone­shaped spine­like setae, row of 8 long swimming setae. On pereopod 7 3 simple setae and 2 bluntly cone­shaped spine­like setae, a row of 5 swimming setae. Merus cylindrical, half as long as ischium, distal at insertion of carpus with membranous seam and swimming seta, in situ pointing dorsally. Pereopod 5 longest. On pereopod 6 3 simple setae. Pereopod 7 shortest, with 3 simple setae. Carpus on each limb of same length, length: width from pereopod 5 to 7 = 1.13, 1.18, 1.29. Laterally strongly flattened, dorsal margin convexly enlarged to semi­circular shape, widest in basal half. Ventrally less enlarged to almost straight margin, with membranous seam on nearly entire length; on each limb with 3 distodorsal, bluntly cone­shaped spine­like setae. Swimming setae inserting on outer side of dorsal and ventral margin, dorsal at least twice as long as ventral. On pereopod 5 23 dorsal and 15 ventral, on pereopod 6 22 + 16, on pereopod 7 25 + 14 swimming setae. Propodus inserting slightly shifted to outer side of carpus, about two thirds as long and half as wide as carpus, laterally flattened, dorsal margin slightly and ventral margin more strongly convex. On pereopod 5 unknown. Pereopod 6 0.82 times as long as carpus, length: width = 1.76, 17 dorsal and 11 ventral swimming setae. Pereopod 7 0.78 times as long as carpus, length: width = 1.84, 17 + 10 swimming setae, ventral ones more robust and only in distal half, 0.3 times as long as dorsal. Pereopod 6 and 7 with short distoventral seta and long distodorsal broom seta. Dactylus lancet­shaped, laterally flattened, about a third as long as propodus, pereopod 6 0.41 times as long as propodus, length: width = 3.75, pereopod 7 0.34 times as long as propodus, length: width = 4. Insertion slightly shifted to outer side of propodus. Apex with 1 short seta and 1 spine­like seta. Pereopod 6 distal third with short dorsal seta.

Pleopods ( Fig. 17 b—e; Fig. 18 a—c): Pleopods 1 and 2 inserting on a level with coxae of pereopod 7. Fused pleopods 1 0.27 times as long as body, length: width = 3.83, apical quarter unfused. Suture visible on whole length, dorsal side of each half with elevated cuticular ledge, hanging over in distal third, with fine, short setation. Area between ledges with numerous scale setae in distal half. Further distally on each half a pair of similar, shorter ledges on a level with inner lobe, enclosing deepened groove, the lateral one with medially overhanging edge. Ventral side of distal third on left half with 10, on right with 9 setae. Distal fifth differentiated into distomedial and a narrower, less distinct distolateral lobe. Distomedial lobe half as wide as proximal end of sympodite, with rounded triangular tip and inconspicuous, distoventral ridge, apices of both sides separate from each other, margin with 12 setae, medially to cusp of distolateral lobe 2 setae. Distolateral lobes shorter than distomedial lobes, narrow, pointed, ending in protopodite of pleopod 2 almost semicircular, 0.91 times pleopod 1 length, length: width = 2.35, with slender and acute tip, proximolaterally 2 long, distolaterally with 7 short hemiplumose setae and 5 simple setae. Exopod short, rounded and lobiform, inserting dorsally in distal quarter of protopodite. Proximal half on caudal side with fine, dense setation. Endopod inserting from distal third of protopodite, bent between basal article and caudally pointing stylet. Stylet 0.57 times as long as protopodite, acute, strongly curved after proximal third, sperm duct opening after basal fourth of stylet. Pleopod 3 length: pleopod 1 length = 0.64, length: width = 2, with large lobiform endopod, distally with 3 long plumose setae. Exopod 2­jointed, a fifth as wide as endopod, slightly surpassing it in length. First article twice as long as second, the latter lancet­shaped, flattened, with a stronger apical seta. Both articles framed by seam of fine setae, longer on the lateral margin. Pleopod 4 length: pleopod 1 length = 0.6, length: width = 1.71, with large lobiform endopod, without setation, exopod consisting of a single article. Basal width a third of width of endopod, evenly tapering to apex, lateral and distomedial margin with seam of fine setae. Apex with 1 long plumose seta. Pleopod 5 length: pleopod 1 length = 0.66, length: width = 1.71, lobiform, delicate and membranous. Lateral margin convex, medial straight, surface bald.

Uropods ( Fig. 18 d): Inserting ventrolaterally in shallow cavities in posterior quarter of pleotelson, length: body length = 0.07. Protopodite rectangular, laterally slightly flattened, length: width = 1.57. Distally with 8 spine­like setae, 3 of which at insertion of endopod and 1 at insertion of exopod. Further proximally 1 simple seta. Rami cylindrical with rounded apex, inserting distally on protopodite. Endopod length: protopodite length = 1.18, length: width = 3.25. At half of its length 1 simple seta, apex with 7 broom setae, 3 longer and 4 shorter setae and 3 spine­like setae. Exopod length: endopod length = 0.46, length: width = 3. Apex with 6 simple setae, 1 slightly longer than endopod.

Description of female paratype ( Fig. 17 e ; Fig. 19 c)

Length 4.71 mm, body as in male, rostrum with 7 spine­like setae, lateralmost shorter than central. Pleotelson as in male, with dorsal tubercles of 0.07 mm diameter. Sexual dimorphism only in antenna 1 and pleopods. Antenna 1: Flagellum 8­jointed, 1 aesthetasc on article 8 of flagellum. Pleopods: Operculum length 0.3 times body length, length: width = 1.64, boat­shaped with sharp anteromedian keel, apex shifted far cranially, overlapping posterior margin of sternite of pereomer 7. Outline of operculum therefore an angulate ellipsoid. Posterior half rounded, decreasing in height, medial keel diminishing. Proximolateral margin on each side with 2 hemiplumose setae. Caudal margin bulged on a level with insertion of uropods, basis of uropod remaining uncovered. Cuticular grooves limited to area around bulges and medial keel.

Remarks

To decide whether anterior and posterior margins of a pereonite are straight, convex or concave, the angle of view is to be considered, as a truly vertical view is hard to achieve as long as the long pereopods are still present. The articulation between segments can obviously lead to different angles of view as well. Therefore, anterior margins of pereomer V and pleotelson in dorsal views of Eurycope monodon and E. denticollis seem to differ a lot from each other without actually doing so. This circumstance makes additional lateral views inalienable.

The two species described here can be easily distinguished from most of the described species by some conspicuous differences. Many species of Eurycope have a medially depressed rostrum without overhang, as for example E. cornuta Sars, 1864 ( Wilson and Hessler 1980) . Furthermore, all species with a pleotelson not dorsoventrally flattened and with a caudal end distinctly bent ventrally on a level with the insertion of uropods can be excluded, this is the case for all species belonging to the Eurycope complanata complex ( Wilson 1983), as well as for E. tumidicarpus Schmid Brenke and Wägele, 2002 which has also been collected in the Angola Basin.

The remarkable female operculum of E. monodon and E. denticollis with an apex shifted far frontally was only known from E. glabra Kensley, 1978 (“Operculum of female with strong median crest, forming spinelike process”). It is not figured in that publication, but comparisons with the paratype of E. glabra confirm the similarities. Wilson and Hessler (1981) and more recently Malyutina and Brandt (2006) doubt that E. glabra belongs to Eurycope at all and consider it as incertae sedis. Thus, all three species are only provisionally classified as Eurycope . Furthermore, the diagnosis of Eurycope by Malyutina and Brandt (2006) was not modified here, even though in contrast to them, E. monodon and E. denticollis have a third article of antenna 1 that is distinctly shorter than the second article.

Most species of Eurycope do not show any subapical lateral cusps on the distolateral lobes of the male pleopod 1. The only exceptions are E. baea Wilson, 1983 and E. glabra with similarly developed apices of pleopod 1. However, a classification as E. baea is not accepted due to the completely different shape of the operculum with caudally shifted apex.

Among all previously described species of Eurycope , E. glabra shares the most similarities with both new species discussed here, especially E. denticollis . Besides the general appearance inclusive of length and width ratios of the pereonites, the rostrum of E. glabra has spine­like setae in a pair­wise arrangement, decreasing in length from median to lateral like the one of E. denticollis . The general shape of the male pleopod 1 with a laterocaudally pointing cusp is similar to that of E. denticollis as well. Essential differences are the larger and stronger rounded lateral lobe of the first basal article of antenna 1, the narrower endite of the maxilliped with only one retinaculum, pleopod 2 without proximolateral hemiplumose seta and uropod with an exopod distinctly reduced to less than a quarter of the length of the endopod in E. glabra . The pair of tubercles on the pleotelson described for E. monodon and E. denticollis are absent in the type material of E. glabra .

Eurycope monodon and E. denticollis have more taxonomic features in common with each other than with any previously described species. These include a similar rostrum, the lateral row of 3 spine­like setae on either side of the head, the dorsal pair of tubercles on the pleotelson, similar pleopods 1 and 2 of the male and the characteristic operculum with an acute apex shifted far anteriorly. Apart from that, there are significant differences remaining which are compared in table 1. One of the most striking characters to distinguish both species is the rostral setation. To exclude the possibility of high intraspecific variability, the rostra of several specimens of each species are compared ( Fig. 19 ). It shows that individuals of Eurycope monodon always show the single long anteromedian seta. E. denticollis shows shorter setae in pairs already in manca stages ( Fig. 19 e ); older individuals apparently develop successively additional lateral spine­like setae up to a total of 7. No intermediate conditions were found between both versions. In addition, the anterodorsal elements of the head (compare Fig. 2 a and Fig. 12 a) are shaped differently, with a particularly expanded clypeus in E. denticollis . Further differences are the grade of extension of the medial lobe on the first peduncular article of antenna 1and the subapical lateral dentation of the male pleopod 1.

TABLE 1: Morphological differences between E. monodon sp. nov. and E. denticollis sp. nov.

The head is relatively broader in examined species of E. denticollis than in E. monodon with a cephalic width: pereonite 1 width ratio> 1 (<1 in E. monodon ). As intraspecific variance is to be expected, the diagnostic value of this character is limited. Yet it can help for an initial separation of both species.

However, both species can only be determined with certainty when highly magnified. The conformity of both species even within the scarcely variable genus Eurycope may suggest a sister­group relationship. At present neither if this is due to two phylogenetically young taxa shortly after speciation, nor what ecological differences separate both sympatric species, can be answered.

In the regenerated right pereopod 7 of the E. monodon holotype ( Fig. 7 e ), the new cuticle lying under the preceding was drawn to show its relatively larger propodus. The lack of a dactylus is apparently an anamorphic development in contrast to the epimorphic ontogenesis of the pereopod 7 during the post­embryonic stages as described for the genus by Wilson (1981). The naming spine­like setae on the anterior margin of the first pereonite as described for E. denticollis are not present on the holotype of E. monodon , but were found on a specimen photographed with the scanning electron microscope ( Fig. 10 d, f), this feature is therefore unsuitable for separating both species from each other. The distalmost stout seta in the spine row on the right mandible’s incisor process of E. denticollis is stronger than the others and has 6 cusps. It resembles in shape the 7­ cusped lacinia mobilis of the left mandible. The similarities between both parts may possibly be explained by their homology as postulated by Richter et al. (2002).

Distribution

South­eastern Atlantic: Angola Basin at a depth of 5125–5410 m (22 20.0’ S, 3 18.3’ E to 22 20.2’ S, 3 18.4’ E, 5125­5144 m, station 318; 18 19.4’ S, 4 39.7’ E to 18 20.8’ S, 4 38.6’ E, 5397­5398 m, station 338; 18 18.3’ S, 4 41.3’ E to 18 19.4’ S, 4 41,9’ E, 5395 m, station 340; 17 06.2’ S, 4 41.7’ E to 17 07.5’ S, 4 42.3’ E, 5415 m, station 344; 16 18.1’ S, 5 27.2’ E to 16 19.3’ S, 5 27.2’ E, 5387­5390 m, station 348; 16 14.3’ S, 5 26.8’ E to 16 14.9’ S, 5 26.7’ E, 5389 m, station 350 of expedition M48:1 RV “ Meteor ”).

Figures

FIGURE 11. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) dorsal view; b) lateral view; c) rostrum, dorsal view; d) broom seta on tubercle of pleotelson.

FIGURE 12. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) head, lateral view; b) pereonite 1, dorsal view; c) seta on pereonite 1; d) right antenna 1, dorsal view; e) distal articles of flagellum; f) right antenna, dorsal view; g) detail of basal articles of antenna.

FIGURE 17. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) pleotelson, ventral view; b) pleopod 1, ventral view; c) dorsal view; d) apex, ventral view; e) right pleopod 2, ventral view

FIGURE 13. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) left mandible, dorsal view; b) medial view; c) left incisor process and lacinia mobilis, medial view; d) dorsal view; e) left molar process, dorsal view; f) right mandible, dorsal view; g) medial view; h) right incisor process, dorsal view; i) medial view; k) right molar process, medial view.

FIGURE 14. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) left maxilla 1, dorsal view; b) distal part of outer endite; c) distal part of inner endite; d) left maxilla 2, dorsal view; e) distal part of outer endite; f) middle endite; g) inner endite.

FIGURE 15. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) right maxilliped, ventral view; b) endite, dorsal view; c) fan seta on endite of maxilliped; d) pappose seta on medial margin of third article of palp; e) retinacula, dorsal view.

FIGURE 16. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) left pereopod 1, medial view; b) dactylus; c) right pereopod 5, lateral view; d) right pereopod 6, lateral view; e) left pereopod 7, lateral view; f) swimming seta on propodus of pereopod 7; g) distodorsal seta on carpus of pereopod 7

FIGURE 18. E. denticollis sp. nov., male holotype ZMH K­ 41797. a) pleopod 3; b) pleopod 4; c) pleopod 5; d) uropod. E. denticollis sp. nov., female paratype ZMH K­ 41798. e) pleotelson, ventral view

FIGURE 19. E. denticollis sp. nov. (a – e) and E. monodon sp. nov. (f – i) comparison of rostral setation on different stages. a) male; b) paratype, female; c) male; d) female; e) manca; f) male; g) female; h) paratype, female; i) female

FIGURE 2. E. monodon sp. nov., male holotype ZMH K­ 41791. a) head, lateral view; b) right antenna 1, dorsal view; c) right antenna, basal articles, dorsal view; d) left uropod, dorsal view.

FIGURE 7. E. monodon sp. nov., male holotype ZMH K­ 41791. a) left pereopod 5, medial view; b) left pereopod 6, medial view; c) left pereopod 7, lateral view; d) dactylus; e) right pereopod 7 (regenerated), lateral view

FIGURE 10. E. monodon sp. nov., scanning electron microscope photographs. a) stage IV male, ventral view; b) stage IV male pleotelson, ventral view; c) stage IV male, apex of operculum, ventral view; d) male, head and pereonites 1 to 4, dorsal view; e) male, rostrum, dorsal view; f) male, seta on pereonite 1, dorsal view.