Microrchestia bousfieldi, Lowry & Peart, 2010

Lowry, J. K. & Peart, R., 2010, The genus Microrchestia (Amphipoda: Talitridae) in eastern Australia, Zootaxa 2349 (1), pp. 21-38 : 23-30

Microrchestia bousfieldi sp. nov.

( Figs 1–6 )

Type material. Holotype, male, 10 mm length, AM P80876, South West Rocks Creek , South West Rocks, New South Wales, Australia (30°53.50’S 153°01.78’E) in mangroves, under and in rotting logs, intertidal, Anna Murray, Rachael Evans & Penny Coleing, 30 April 1999 ( NSW 1560 ) . Paratypes: female, 9 mm length, AM P80877; 19 specimens, AM P80878, (same locality as holotype) .

Additional material examined. 6 specimens, AM P80879 , South West Rocks Creek , Trial Bay, New South Wales, Australia (30°53.24’S 153°02.09’E), under bark of dead Avicennia marina branches, P.B. Berents, K.B. Attwood and P. Coleing, 2 May 1999 ( NSW 1613 ) .

Type locality. South West Rocks Creek , South West Rocks, New South Wales, Australia (30°53.50’S 153°01.78’E) .

Etymology. Named for Ed Bousfield in recognition of his insightful work on talitrid amphipods.

Description. Based on holotype, male, 10 mm, AM P80876.

Head. Eye large (greater than 1/3 head length). Antenna 1 elongate (from midpoint to end of article 5 of antenna 2). Antenna 2 up to half body length; peduncular articles narrow; peduncular article 5 longer than article 4. Mandible left lacinia mobilis 4-dentate. Maxilliped palp article 2 with distomedial lobe; article 4 distinct, small.

Pereon. Gnathopod 1 not sexually dimorphic; subchelate; posterior margin of merus, carpus and propodus each with lobe covered in complex setae in both male and female; propodus subrectangular; palm transverse; dactylus subequal in length to palm. Gnathopod 2 sexually dimorphic; subchelate; coxal gill slightly lobate, smaller than gill 3; basis slightly expanded; posterior margin of merus, carpus and propodus each without lobe covered in complex setae; carpus triangular, reduced (enclosed by merus and propodus); carpus posterior lobe absent, not projecting between merus and propodus; palm acute; strongly toothed, incised or sinuous; with bimodal protuberance near dactylar hinge, protuberence with robust setae; without midpalmar sinus; posterodistal corner with socket; dactylus subequal in length to palm, not attenuated distally. Pereopods 2–4 coxae wider than deep. Pereopods 3–7 simplidactylate. Pereopod 3 coxal gill slightly lobate, smaller than gill 4. Pereopod 4 subequal or slightly shorter than pereopod 3; coxal gill slightly lobate, similar size to gill 5; carpus similar in length to pereopod 3 carpus, dactylus similar to pereopod 3 dactylus. Pereopod 5 coxal gill lobate, larger than gill 6; propodus distinctly longer than carpus. Pereopod 6 not sexually dimorphic; slightly shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner with small cusp, posterior margin (inner view) oblique to ventral margin, posterior lobe without ridge, with 1–2 marginal setae; coxal gill lobate. Pereopod 7 slightly sexually dimorphic; basis lateral sulcus absent, posterodistal lobe rounded, produced downwards almost to merus; distal articles (merus and carpus) slightly expanded; merus posterior margin evenly rounded; carpus subrectangular.

Pleon. Pleopods all well developed. Pleopods 1–3 peduncle not expanded. Pleopod 1 peduncle without marginal setae; biramous, outer ramus subequal in length to peduncle; inner ramus subequal in length to outer. Pleopod 2 biramous, outer ramus longer than peduncle. Pleopod 3 biramous, outer ramus longer than peduncle. Epimeron 2 subequal in length to epimeron 3. Epimeron 3 posterior margin smooth, without setae, posteroventral corner narrowly rounded; ventral margin robust setae absent. Uropod 1 not sexually dimorphic; peduncle with 7 robust setae on peduncle, distolateral robust seta present, small (less than 1/4 length of outer ramus), with simple tip; rami without ventral robust setae; inner ramus subequal in length to outer ramus, with 4–5 robust setae on the margins; outer ramus without marginal robust setae. Uropod 2 not sexually dimorphic; peduncle with 4 robust setae; inner ramus subequal in length to outer ramus, with 2 marginal robust setae; outer ramus without marginal robust setae. Uropod 3 peduncle with 2 robust setae; ramus shorter than peduncle, linear, narrowing, without marginal setae, with 4 to 5 apical robust setae. Telson as broad as long, entire, dorsal midline vestigial or absent, with 2 apical robust setae per lobe.

Female (sexually dimorphic characters). Based on paratype, female, 11 mm, AM P80877. Eye medium (1/ 5–1/3 head length). Gnathopod 1 propodus subrectangular. Gnathopod 2 mitten-shaped; basis slender; posterior margin of merus, carpus and propodus each with lobe covered in complex setae; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; palm obtuse, smooth, posterodistal corner without spine; dactylus shorter than palm. Pereopod 7 basis posterodistal lobe absent; distal articles (merus and carpus) slender. Oostegites longer than wide, weakly setose, setae with multifurcated tips. Uropod 1 peduncle with 8 robust setae; with 3 robust setae on the margins. Telson with 3–6 robust setae per lobe.

Habitat. Intertidal in mangroves, under and in rotting logs.

Remarks. Microrchestia bousfieldi appears to be most similar to M. macrochela ( Bousfield, 1971) , based on the shape of the palm of male gnathopod 2, but whereas M. bousfieldi has two distinct humps along the palm, M. macrochela has only one. In addition Microrchestia bousfieldi lacks robust setae on the posterior lobe of coxa 6 (present in M. macrochela ); it has more setae on the peduncles and rami of uropods 1 and 3 than does M. macrochela ; and it has only apical robust setae on the telson (apical and marginal in M. macrochela ).

Microrchestia bousfieldi differs significantly from M. watsonae in the shape of male gnathopod 2 which is strongly sculptured with few marginal robust setae on the palm (palm with a shallow distal plate and the main palmar area is lined with robust setae in M. watsonae ). In addition, M. bousfieldi has no setae on the posteroventral margin of coxa 6 and the corner forms a small cusp (with marginal setae and rounded corner in M. watsonae ); the posteroventral corner of epimeron 3 is narrowly rounded (forming a small subacute tooth in M. watsonae ); the ramus of uropod 3 has more robust setae than that of M. watsonae and the telson is as long as broad (longer than broad in M. watsonae ).

No male of M. similis has been reported, but the females differs in the posterior margin of pereopod coxa 6 which is has no marginal setae in M. bousfieldi (setae present in M. similis ); in the posterior margin of epimeron 3 which lacks setae and the posteroventral corner which is narrowly rounded (setae present and posteroventral corner with a small subacute spine in M. similis ); uropod 3 peduncle and ramus slightly more setose in M. bousfieldi .

Distribution. Australia. Southwest Rocks, northern New South Wales.

Figures

FIGURE 1. Microrchestia bousfieldi sp. nov., holotype, male, AM P80876, 10 mm length; paratype female, 9 mm length, AM P80877, South West Rocks Creek, South West Rocks, NSW, Australia.

FIGURE 2. Microrchestia bousfieldi sp. nov., holotype, male, 10 mm length, AM P80876; paratype female, 9 mm length, AM P80877, South West Rocks Creek, South West Rocks, NSW, Australia. Scales represent 0.2 mm.

FIGURE 3. Microrchestia bousfieldi sp. nov., holotype, male, 10 mm length, AM P80876; paratype, female, 9 mm length, AM P80877, South West Rocks Creek, South West Rocks, NSW, Australia. Scales represent 0.5 mm.

FIGURE 4. Microrchestia bousfieldi sp. nov., holotype, male, 10 mm length, AM P80876, South West Rocks Creek, South West Rocks, NSW, Australia. Scales represent 0.5 mm.

FIGURE 5. Microrchestia bousfieldi sp. nov., holotype, male, 10 mm length, AM P80876; paratype female, 9 mm length, AM P80877, South West Rocks Creek, South West Rocks, NSW, Australia. Scales represent 0.1 mm for female U3 and T. Scales represent 0.2 mm for female U1–2, pleopods and male U1–3 and T. Scales represent 0.5 mm for the gills.

FIGURE 6. Microrchestia bousfieldi sp. nov., paratype female, 9 mm length, AM P80877, South West Rocks Creek, South West Rocks, NSW, Australia. Scales represent 0.2 mm for the oostegites and 0.5 mm for P6–P7.