Nedsia fragilis, 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 : 57-59

Nedsia fragilis n.sp.

Figs 14, 15

Etymology. Named for the fragile nature of the appendages.

Type locality. Barrow Island, Western Australia., Western Australian Museum sampling site BES738 .

Material examined. HOLOTYPE (Western Australian Museum WAM 5-96), male 2.4 mm.

Diagnosis. First antenna (broken in type specimen): ratio of peduncular articles = 82:23:-. Upper lip: symmetrical, not excavate below. Right mandible: bearing inter-raker plumose setae, left mandible without; palp 2-articulate, article-l reduced, subtruncate; article-2 Iinear, subtruncate, setae = 2E. Maxillae: inner plate of both maxillae without pubescence of medial or lateral margins; outer plate of first maxilla bearing 5 denticulate and 2 naked terminal spines. Coxae: coxa 1 longer than broad, slightly expanded below, coxa 2 lacking posterior marginal spines, coxae 3-4 with posterior spines. Maxilliped: inner plate with distal row of 4 plumose setae, lacking medial plumose setae; outer plate medial margin barely sinuous, paired submarginal setae curved and blunt, reduced in number; apex of palp article-3 not produced, setae not organised into combs; dactyl bearing a row of comb setae, single dorsal spine seta, moderate nail and equally long accessory spine. First gnathopod: palmar spines curved, not bifid except at palmar corner where spines = 3 lateral, 2 medial. Second gnathopod: defining corner of palm bearing I long lateral seta and 1 slender medial trigger spine. Epimera: posteroventral tooth present on epimera 2-3, epimeron 3 with small ventromarginal spine at MO.6. Pleopods: peduncles without setae, basomedial setae of inner rami not bifid, 2 retinaculae on each peduncle, without accessory retinaculum. Uropods: dorsal margins of peduncles of uropod 2 not spinous, spine rows of rami reduced to o or 1 spine each. Telson : cleft 100%; single distolateral spine at MO.8; single lateral penicillate setule at MO.7 on either lobe.

Description of holotype (male). Body 2.4 mm. Urosome: poorly armed dorsally. Head ( Fig. 14 ): rostrum obsolescent; eyes absent. First antenna ( Fig. 14 ): ratio of peduncle articles = 82:23:-. Setae of peduncular article-l limited to single dorsal and ventral sub marginal setae, one submarginal ventral and one long mediodistal setae; article two naked. Second antenna ( Fig. 14 ): length 0.3x body, peduncle longer than flagellum, article-4 longer than article-5 (63:52), articles 3-4-5 with weak ventral setation, article-3 with 1 dorsomedial spine, flagellum of 4 articles, without ca1ceoli. Upper lip ( Fig. 14 ): apical margin rounded, not excavate, connection to epistome symmetrical. Mandibles ( Fig. 14 ): left mandibular palp of 2 articles (broken), incisor 5 toothed, lacinia mobilis 5 toothed, 6 barely setose accessory blades, no inter-raker plumose setae; molar triturative, lacking distal plumose seta, slight pubescence around base of accessory blades; right mandible incisor 5 toothed, lacinia mobilis denticulate, accessory blades of 6 plumose spines; molar triturative, with distal plumose seta; palp 2-articulate, reduced, ratio of articles 2:16, articles truncate, naked, terminal article with 2 Esetae only. Maxillae ( Fig. 14 ): first maxilla palp article- 2 bearing (5 spines), outer plate with 7 spines; 2 naked, 5 denticulate, inner plate (bearing fine medial setae); second maxilla outer plate, outer apical margin lacking pubescence with few fine setae; inner plate lacking pubescence; terminal spines of both plates half rastellate, half finely setulate. Maxilliped ( Fig. 14 ): palp article- 3 with a pair of long subterminal setae medially, diagonal distal row of 3 facial setae, apex with subterminal transverse row of unorganised comb setae; nail of moderate length with an accessory spinule of equal length; palp article-2 bearing mid-medial serrations; inner plate with a pair of plumose facial spines and two distal submarginal medial spines, one small and sharp the other moderate, stout and blunt. First gnathopod ( Fig. 15 ): coxal plate with 1 moderate apical seta, several (3) anterior and posterior (2) facial setae, without a posteroventral spine; article-4 posteriorly bulbous and pubescent; carpus not lobate; propodus trapezoidal, slightly expanded apically, longer than wide; posterior edge naked except for an apical pair of long setae basal to the dactyl; palmar corner rounded, marked by 3 naked lateral spines and 2 stout bifid medial spines; palm convex, finely serrated, dactylus reaching the end of the palm. Second gnathopod ( Fig. 15 ): palm with 4 setae; 2 lateral, 2 medial, the fourth marking the corner medially, along with a strong elongate lateral spine; palm finely serrate along most of its length; dactyl bearing a single dorsal spinule at MO.3, and small bent spinule laterofacial at MO.6; coxal plate 2 broader than coxa 1, poorly setose with 1 posteroventral marginal spine and a ventrofacial spine both at MO.6, as well as a single anteroventral spine at MO.l. Pereopods ( Fig. 15 ): coxa 3 with 1 anteroventral spine, 1 posteroventral submarginal seta-spine; coxa 4 similar; pereopods (3)- 4 longer than gnathopod 2, pereopod (3) equal to pereopod 4; pereopod 4 articles 4-5 sparsely setose posteriorly, (pereopods 5-7 similar, consecutively elongate, with 2 locking spines, pereopod 7 article-6 anterior spines displaced by an anterior keel); coxae 5-7 bearing no setae on ventral margins of the posterior lobes, article-2 weakly expanded, (not lobate but extended posteriorly, with thin, short posterior setae); coxae 3- 7 dactyls simple, with no accessory spinules. Gills: coxal gills of limbs 2-6 flask shaped, simple, gill 6 not reduced, gill coxa 2 largest, gill coxae 5-6 smallest but not significantly reduced. Pleopods ( Fig. 15 ): two retinaculae per pleopod, with no accessory retinaculae; peduncle 2 only with apicolateral seta; rami extend subequally, outer rami with 5 articles each, the inner with 5-4-4; setae of the basal articles = 1-1-1-1-, none are bifid. Epimera ( Fig. 15 ): each posteroventrally quadrate, though epimeron 2 barely so; posterior margins scarcely convex, smooth, and barely setulose; epimeron 3 with 1 ventrofacial spine, lacking lateral oblique ridge. Pleon ( Fig. 15 ): pleonite 2 only without dorsal or dorsolateral posterior setae; pleonite 6, no dorsolateral or distoventral spines. Uropods ( Fig. 15 ): lengths relative to uropod l-uropod 2 = 0.5, uropod 3 absent; uropod 1 peduncle length 1.3x medial ramus, outer margin with a row of 5 small submarginal spines and 1 moderate laterofacial spine at MO.6, single apicomedial and apicolateral trigger spines, basofacial spine weak, the medial ramus longer than the lateral; both rami with sparse setation, terminating in 4 spines; peduncle of second uropod 0.6x length of inner ramus, single apicomedial and apicolateral spines; medial margin of both rami pubescent; outer ramus shorter than inner (62:81), both bearing few marginal spines and 4 terminal spines; uropod 3 absent. Telson ( Fig. 15 ): length 1.6x width, as long as urosomite 3, cleft 100%; apices notched, subapices with 2 long plumose setae; 1 marginal seta at MO.8, each lobe bearing a single penicillate setule marginal at MO.7.

Relationship. Nedsia fragilis varies from N. douglasi in the relative length of the second antenna, the greater length of the second peduncular article, the presence on the third article of a dorsomedial spine, a round and symmetrical upper lip, mandible bearing additional accessory blades, the molar bearing a distal plumose seta, palp of right mandible with elongate first article, second maxilla lacking pubescence, terminal spines of both plates either rastellate or terminally setulate, first gnathopod palmar corner rounded not square, with fewer medial spines, palm of second gnathopod with fewer spines, retinaculae of pleopods not associated with an accessory, rami of pleopods with fewer articles, epimera 2-3 without ventrofacial spines, pleonite 6 without dorsolateral or distoventral spinules or spines, basofacial spine weak, peduncle of the second uropod short and less spinous, rami marginally pubescent with fewer terminal spines, telson more slender. Nedsia fragilis differs from others of the genus in lacking marginal pubescence on both plates of the second maxilla, except for N. straskraba , from which it differs in possessing dorsal pleonal spines, and from N. humphreysi in lacking distolateral spines on the first epimeron, possessing a row of facial spines on the peduncle of the first uropod, the outer plate of the maxilliped tapers apically and is weakly cuspidate, and the palmar corner of the first gnathopod is rounded.

Distribution. Barrow Island, Western Australia.

Figures

Fig. 14. Nedsia Jragilis holotype male 2.4 mm. Body, antenna, mouthparts.

Fig. 15. Nedsia fragilis ho1otype male 2.4 mm. Legs, p1eopods, uropods, te1son, abdomen.