Nedsia straskraba, Bradbury & Williams, 1996

Bradbury, J. H. & Williams, W. D., 1996, Freshwater amphipods from Barrow Island, Western Australia, Records of the Australian Museum 48 (1), pp. 33-74 : 37-43

Nedsia straskraba n.sp.

Figs 3-5

Etymology. Named for Milan Straskraba, noted limnologist and early contributor to our knowledge of the taxonomy of Australian freshwater amphipods.

Type locality. Barrow Island, Western Australia, Western Australian Museum sample BES531 .

Material examined. HOLOTYPE (Western Australian Museum WAM 1-96) male "a", 3 mm; male "b", 2.5 mm (collected at same site, at different date. Western Australian Museum sample BES539).

Diagnosis. Pleonite 6 without dorsal spines. First antenna: ratio of peduncular articles about 3:2:1. Second antenna: very short. Upper lip: margin not excavate; apically rounded and pilose. Mandibles: mandibular palp 2-articulate, article-2 cone like, setae 2E or 2D2E; interraker plumose setae absent; no additional serrations beyond rakers. Maxillae: moderately setose medially: first maxilla inner plate with 4 mediodistal setae; palps almost syrmnetric. Maxilliped: inner plate moderately long, no additional setae (plumose or naked) medially; outer plate with a blunt, naked tooth spine medially, the second pair of submarginal facial setae reduced to a single seta; palp article-3 lacking comb rows of setae near the base of the dactyl, facial comb row of setae from dactylar base to nail, nail of moderate length with similar length distal spine. Coxae: coxa 1 not expanded below; coxae 1-2 longer than broad with 1-3 posterior spines respectively; coxae 3-4 lacking posterior spines. First gnathopod: palmar spines evenly bifid; spines at corner of palm = lateral 2 long, medial 2 stout and bifid; setae along palm sparse; cutting edge of palm with many fine serrations. Second gnathopod: carpus only slightly lobate; defining corner of palm with 2 spines. Pereopods: posterior spine sets of article-6 of pereopods 3-4 reduced TODO TODO TODO TODO TODO TODO TODO TODO TODO TODO TODO to2spines on pereopod3. Gills: °coxal gills5 -6 slightly extending subequally; basomedial seta on inner rami not bifid; retinaculae 2 on each pleopod, accessory retinaculae 1,0,1. Uropods: apicolateral corner of peduncles of uropods 1-2 each with 1 spine; dorsal margins of uropod 2 naked; spine rows of rami of uropods 1-2 reduced to 1 (uropod 1) and 2 (uropod 2) medial spines. Telson : cleft 100%.

Description of holotype (male "a"). Body (Fig. 3) 2.7 mm Urosome: poorly armed dorsally. Head: rostrum obsolescent; eyes absent. First antenna (Fig. 3): length 0.9x body, 3.2x antenna-2; flagellum longer than peduncle (470:188); peduncular article-3 shortest, article-1 longest, ratio of lengths = 88:68:32; setae sparse; aesthetascs present on articles 8, 9, 11, 12, 14; calceoli absent; flagellum of 18 articles; accessory flagellum 2-articulate, reaching MO.7 of article-1 of primary flagellum, article- 2 tiny; articles of primary flagellum not uniform, sparsely setulate. Second antenna (Fig. 3): length 0.28x body (206:745); peduncle much longer than flagellum, articles 4-5 equally long, 3-5 with weak ventral setation, article-3 with 1 dorsomedial spine; flagellum 4-articulate, no calceoli. Upper lip: margin not excavate. Mandibles (Fig. 3): left mandibular palp 2-articulate, articles unequal in length (17:10), article-2 with 2 long apical setae (2E) and 2 short setae (2D); incisor 5 toothed; lacinia mobilis with 4 denticles; 5 setose accessory blades; molar without distal plumose seta (probably lost by damage to specimen), triturative; no other pubescence; right mandibular incisor 4 toothed; lacinia mobilis bifid, broad, finely denticulate; accessory blades of 5 plumose spines; palp 2-articulate, length ratio of articles 17:10. First maxilla (Fig. 3): palp article-2 with 5 thin apical spines, all naked on R, one plumose on left side; outer plate of left with 7 denticulate spines, of right with 6; inner plate bearing 4 terminal plumose setae medially, medial margin pubescent. Second maxilla (Fig. 3): outer plate devoid of pubescence; inner plate pubescent on basomedial margin. Maxilliped (Fig. 3): nail of palp short (11:32 of dactyl), article-3 with few thin setae at inner edge, none proximal; inner plate with single ventrofacial spine and short spur at MO.5 and 0.6, and a single submarginal medial naked spine at MO.8. First gnathopod ( Fig. 4 ): coxal plate with several short setae apically and one posteroventrally; article-4 slightly bulbous posteriorly, carpus not lobate; propodus trapezoidal, expanding slightly apically, longer than wide, the posterior edge naked, corner of palm rounded, 2 long, naked lateral spines, 2 stout bifid spines medially, palm slightly convex, dactyl reaching beyond the palm. Second gnathopod ( Fig. 4 ): palm with 2 medial and 2 lateral spines, all but the corner spines being bifid, and 2 long and 1 medium setae; spines at palmar corner = 1 medial and 1 lateral (naked); coxal plate similar to first with 1 anterior and 3 posterior setae. Pereopods ( Fig. 4 ): coxa 3 with setae similar to coxa 1, arranged 1 anterior, 1 posterior; coxa 4 similar, both setae anterior; pereopods 3-(4) longer than gnathopod 2; pereopods 3-5 approximately equal, articles 4,5 sparsely setose posteriorly, the posterior margin of article-6 (pereopod 3 only) with armament formula = ---1--1, thus with only one locking spine; pereopods 5- 7 similar but consecutively elongate, with 1,2,1 locking spines; pereopod 7 anterior spines of articles 5 and 6 displaced inward by keel-like expansion of the segment; coxae 5-7 bearing 0,0,1 setae on posterior lobes, article- 2 weakly expanded progressively from pereopods 5-7, not lobate, but extended posteriorly and bearing few setae on pereopod5, becoming increasingly robust in pereopods 6 and 7; dactyls of pereopods 3-7 simple, naked except for an anterior basal penicillate setule, with the addition of an outer terminal setule on pereopod 7. Gills: coxae 2-6 with flask shaped gills, gill of coxa 3 largest, of coxae 5-6 slightly reduced. Pleopods (Fig. 5): retinaculae 2 per pleopod, one accessory each; peduncles 1 and 3 with an apicolateral seta, 2 without; rami extending subequally, the inner with 5:5:5 articles, the outer with 6:6:5; no bifid setae on basal articles. Epimera (Fig. 5): epimera posteroventrally quadrate; posterior margins scarcely convex on 1-2, concave on epimeron 3, all smooth, with few or no setae; epimera 2-3 with 2 and 1 weak ventral spines, lacking lateral oblique ridge. Pleon (Fig. 5): pleonites 1-4 with dorsolateral posterior setae; pleonite 6 with 1 dorsolateral and 1 distoventral spinule. Uropods (Fig. 5): uropod lengths relative to uropod 1 are uropod 2 = 0.6x, uropod 3 = 1.5x; uropod 1 peduncle length 1.3x inner ramus, the outer margin bearing a single apicodistal spine and reduced row of 2 mid-dorsal spines, the medial apex bearing 2 spines; rami of subequal length (inner outer = 62:54), both naked except for a single mid-dorsal spine on the inner ramus; both rami with 5 terminal spines; uropod 2 peduncle length 0.9x inner ramus, bearing a single apicolateral spine only; inner ramus length lAx outer, the medial margin bearing 2 spines only, 5 terminal spines; outer ramus shorter, devoid of any but 5 terminal spines; uropod 3 strongly extended beyond uropods 1-2 in entire animal; peduncle length 0.14x outer ramus, shorter than urosomite 3 (25:50), bearing single mid-dorsal and laterodistal marginal setae, 1 subapical lateral seta, and 1 small mid-medial submarginal, facial seta; outer ramus proximal article with few marginal setae, 2 apicomedial setae, 3 apicolateral setae and I subapical submarginal lateral seta, article-2 shorter (80:100), similarly armed, terminating in a cluster of 5 spines; inner ramus scale like, subquadrate, length O.13x outer, bearing a single apicomedial spine. Telson (Fig. 5): length 1.5x width, widest at base, subequal in length to urosomite 3 (45:50), cleft 100%; apices slightly notched laterally female), apex of right lobe notched minutely medially; subapices with 2 long plumose setae, 1 submarginal medial seta and 1 lateral seta at MO.8, no other dorsal setae except for single penicillate setules on both lobes laterally at MO.7.

Description of other material. Specimen "b", male, length 2.5 mm. Pleonite 6 with a single dorsolateral spine. First antenna: flagellum of 20 articles, aesthetascs present on articles 8,9,10,12,13,14,16. Mandibles: 牾瑩漠 of length of palp articles 1-2 = 15:12; setae of termmal article = 2E; interraker plumose setae present between accessory blades. Left mandible: palp article-2 shorter than in type; 15:12, setae = 2E; distal plumose seta present on both molars. Maxillae: spines of pal~ of left first maxilla not plumose Maxilliped: palp artlcle- 3 with rows of setae basal to dactyl; nail of dactyl short. First gnathopod: coxal plate without posteroventral seta. Pleopods: accessory spines adjacent to retinaculae = 1,0,0. accessory spine present adjacent retinacula of pleopod 1 only. Uropod: lengths relative to uropod 1; uropod 2 0.7x, uropod 3 2x; peduncle of uropod 1 1.9x length of inner ramus, of uropod 2 equal to ramus; uropod 2 inner ramus 1.3x outer; peduncle of uropod 3 0.27x length of outer ramus (longer than in type; 0.14x), second article of outer ramus relatively longer than in type (90:102).

Relationship. Nedsia straskraba varies from N. douglasi in that pleonites lack dorsal spines, the second peduncular article of the first antenna is relatively shorter, the maIldibular palp is similar being 2-articulate, with reduced terminal setation, the inner plate of the second maxilla has fewer medial setae, coxae 1-2 are longer than broad versus broader than long, the palmar spines of the first gnathopod are apically dentate, not asymmetrically bifid, there are no setae along the palm and the inner edge is finely serrate, the second gnathopod is weakly enlarged, melitid, the carpus less lobate, the palm more strongly oblique with few spines or setae and palmar corner poorly defined, the fifth and sixth coxal gills are reduced slightly compared with N. douglasi . The principle feature separating this species from all but N. fragilis and N. humphreysi is the absence of marginal pubescence on both plates of the second maxilla, and from N. macrosculptilis , N. sculptilis , N. fragilis and N. humphreysi the absence of dorsal spines or sculpturing of the pleon and of facial spines on the epimera. Nedsia straskraba is unlike N. fragilis in that the palmar corner of the gnathopod 1 is subquadrate and unlike N. hurlberti in lacking a spine-like extension of the first urosomite.

Distribution. Barrow Island, Western Australia.

Figures

Fig. 4. Nedsia straskraba ho!otype male "a" 2.7 mm. Legs.