Notorchestia lobata, Serejo & Lowry, 2008

Serejo, C. S. & Lowry, J. K., 2008, The Coastal Talitridae (Amphipoda: Talitroidea) of Southern and Western Australia, with Comments on Platorchestia platensis (Krøyer, 1845), Records of the Australian Museum 60 (2), pp. 161-206 : 180-185

Notorchestia lobata n.sp.

Figs 13–16

Type material. HOLOTYPE: male, 10.8 mm, AM P69051 (slide, stubs J085–J087, J091–J094) . PARATYPES: male, 10.8 mm, AM P69055 (stub J084) ; 1 female, 11 mm, AM P69052 (slide, stubs J088, J090 [part, G1–2]) ; 2 juvenile males, 10 mm and 7.9 mm, AM P69053 (mixed on stub J089, SEM micrographs) ; male, 12.5 mm, AM P69054 ; female, 9.1 mm, AM P60956 (stub J090 [part, G1]) ; 51 specimens, AM 69057 , all from Goolwa Beach, Encounter Bay , South Australia (35°31.47'S 138°48.51'E), wide beach with a lot of dead seagrass and seaweed over hard grey sand, C. Serejo, J.K. Lowry & J. Bradbury, 15 Oct. 2003, SA 144 .

Type locality. Goolwa Beach , Encounter Bay (35°31.47'S 138°48.51'E), SA .

Additional material examined. Victoria: 42 specimens, AM P69015, supra-littoral zone on exposed ocean beach, Point Ricardo (37°48.39'S 148°38'E), beach-hoppers under dead Sargassum on exposed ocean beach, C. Serejo & J.K. Lowry, 8 Oct.2003,VIC 120; 20 specimens, AM P69016, Woodside Beach (between Sale and Yarram) (38°33.29'S 146°58.47'E), beach-hoppers under dead Sargassum , exposed windswept beach with little seaweed, C. Serejo & J.K. Lowry, 9 Oct. 2003, VIC 123; AM P69017, 85 specimens, Lorne Beach near mouth of Erskine River, Lorne (38°32.1'S 143°58.59'E), broad ocean beach with dead seaweed in supra-littoral, C. Serejo & J.K. Lowry, 12 Oct. 2003, VIC 128; 72 specimens, AM P69018, Ocean beach, Separation Creek (38°37.96'S 143°53.78'E), ocean beach with rock reefs immediately offshore, C. Serejo & J.K. Lowry, 12 Oct. 2003, VIC 130; 22 specimens, AM P69019, Peterborough Beach, Peterborough (38°36.6'S 142°52.67'E), ocean beach with beach-hoppers under seaweed, C. Serejo & J.K. Lowry, 12 Oct. 2003, VIC 132; 130 specimens, AM P69020, Sandy beach, The Craigs (38°22.36'S 142°6.59'E), narrow sandy beach with vertical cliffs directly behind and rock platform in front with Ulva , Sargassum and Cystophora, C. Serejo & J.K. Lowry , 13 Oct. 2003, VIC 134; 76 specimens, AM P69021, Shelly Beach, Bridgewater Bay (38°21.65'S 141°26.14'E). Sandy beach with accumulations of small gastropod shells, C. Serejo & J.K. Lowry, 13 Oct. 2003, VIC 136; 47 specimens, AM P69033, Sandy Point (38°50'S 146°08'E), under dry kelp, A. Murray, 29 Dec. 2003, VIC 137.

South Australia: 12 specimens, AM P69022 , Beachport Beach, Rivoli Bay (37°29.01'S 140°3.39'E), sheltered beach, dunes behind beach, C. Serejo & J.K. Lowry, 14 Oct. 2003, SA 140 ; 35 specimens, AM P69023 , Victor Harbour, Encounter Bay (35°33.07'S 138°37.44'E), sheltered harbour beach, C. Serejo, J.K. Lowry & J. Bradbury, 15 Oct. 2003, SA 146 ; 89 specimens, AM P69024 , beach in Yankalilla Bay, Fleurieu Peninsula (35°28.73'S 138°46.75'E), sandy, rocky beach, C. Serejo, J.K. Lowry & J. Bradbury, 15 Oct. 2003, SA 148 .

Western Australia: 2 males and 3 females, AM P69025, Ocean beach, Eucla (31°43.29'S 129°53.31'E), broad white sand beach with clumps of seagrass and seaweed, with dunes behind, C. Serejo & J.K. Lowry, 20 Oct. 2003, WA 753 ; 40 specimens, AM P69026, Fourth Beach, Esperance (33°53.29'S 121°50.7'E), exposed white sand beach with small amounts of seaweed, C. Serejo & J.K. Lowry, 21 Oct. 2003,WA 754 ; 10 males and 19 females, AM P69027, West Beach, Hopetoun (33°52'S 121°52'E), on seaweed at enclosed sheltered white sand beach, C. Serejo & J.K. Lowry, 21 Oct.2003, WA 755 ; 2 males and 3 females, AM P69028, Slippery Rock, Cape Leuwin (34°21.44'S 115°7.64'E), mixed and dead seaweed lodged between large boulders at the end of a steeply sloping white sand beach, C. Serejo & J.K. Lowry, 23 Oct. 2003, WA 759 ; 48 specimens, AM P69029, Binningup Beach, Bunbury (33°9.02'S 115°41.08'E), exposed sandy beach, C. Serejo & J.K. Lowry, 24 Oct.2003, WA 761 ; 33 specimens, AM P69030, South Cottesloe Beach, Perth (32°0.28'S 115°45.03'E), sandy beach with a lot of dead seagrasses and seaweed, C. Serejo, J.K. Lowry & D. Jones, 26 Oct. 2003, WA 762 ; 140 specimens, AM P69031, Jurien Beach, Jurien (30°18.38'S 115°1.99'E), sandy beach with a lot of dead seagrasses and seaweed, C. Serejo & J.K. Lowry, 28 Oct. 2003, WA 765 ; 1 female, AM P69032, Disappointment Loop, Henri Freycinet Harbour, Shark Bay (26°40.21'S 113°40.31'E), low rock platform moving into clayey mudflats with small banks covered in holes with small smooth clay channels between, C. Serejo & J.K. Lowry, 4 Nov. 2003, WA 775 .

Etymology. This species is named for the lobate structure on the posterodistal margin of the merus of gnathopod 2.

Diagnosis. Mandible left lacinia mobilis 4-dentate. Dactylus of gnathopod 1 with row of ventral short setae. Gnathopod 2 male, propodus subquadrate; palm slightly acute to transverse, with large midpalmar concavity. Female and male juvenile gnathopod 2 merus with distally rounded posterodistal medial lobe. Coxa 6 posterior lobe posteroventral margins with 13–15 robust setae. Basis of pereopod 7 with lateral sulcus. Telson cleft to half length.

Description

Holotype male, 10.8 mm. Eye medium, 1⁄5–1/3 head length. Antenna 1 short, rarely longer than peduncle article 4 of antenna 2. Antenna 2 shorter than head and first 3 pereonites; peduncular articles narrow; with many robust setae; article 5 longer than article 4. Epistome of upper lip without robust setae. Lower lip distolateral setal tuft absent. Mandible left lacinia mobilis 4-dentate. Maxilliped palp article 2 with distomedial lobe, article 4 present, reduced.

Gnathopod 1 sexually dimorphic; subchelate; posterior margin of carpus and propodus with rugose lobe; propodus sub-triangular; palm transverse; dactylus subequal in length to palm, with ventral setal row, simplidactylate. Gnathopod 2 sexually dimorphic; sub-chelate; basis anteriorly smooth; merus without posterodistal medial lobe; propodus subquadrate; palm slightly acute to transverse, with large midpalmar concavity; dactylus longer than palm, concave and not attenuated distally. Coxae 2–4 deeper than wide. Pereopods 3–7 cuspidactylate; dactylus with row or patch of dorsal short setae. Pereopod 4 significantly shorter than pereopod 3. Pereopod 4 dactylus thickened and pinched posteriorly, different to pereopod 3 dactylus. Pereopod 5 propodus distinctly longer than carpus. Pereopod 6 not sexually dimorphic; shorter than pereopod 7; coxa posterior lobe anterodistal corner rounded, posteroventral margins with 13–15 robust setae, posterior margin perpendicular to ventral margin, outer surface with ridge; carpus slender. Pereopod 7 sexually dimorphic; basis with lateral sulcus well developed, posterodistal lobe present; distal articles slender. Coxal gills convoluted, processiferous or simple. Pereopods 3–5 gills smaller than gills 2 and 6.

Pleopods 1–3 well developed, biramous. Peduncles of pleopods 1–2 with 10 robust setae, 8 on outer margin and 1–2 facial. Peduncle of pleopod 3 with 14 setae, 7 on outer margin and 7 facial. Epimeron 2 longer than epimeron 3. Epimeron 3 posterior margin minutely serrate, with setae, posteroventral corner with small subacute spine, ventral margin without robust setae. Uropod 1 peduncle with 16 robust setae in two rows; distolateral robust seta absent; inner ramus shorter than outer ramus, with 6 marginal robust setae; outer ramus with 5 marginal robust setae. Uropod 2 peduncle with 10 robust setae in two rows; inner ramus longer than outer ramus, with 3 marginal robust setae; outer ramus with 3–4 marginal robust setae. Uropod 3 peduncle with 5 robust setae; ramus shorter than peduncle; triangular, narrowing distally; with 5 marginal setae and 4–5 apical setae. Telson longer than broad; incised to half length; with marginal and apical robust setae; about 3 to 5 robust setae per lobe.

Female (sexually dimorphic characters), 11 mm. Gnathopod 1 parachelate; posterior margin of merus, carpus and propodus without rugose lobe; propodus ovoid; palm very short, acute; dactylus longer than palm, with ventral row of setae. Gnathopod 2 mitten-shaped; basis slightly expanded; about 1.5× longer than wide; merus with distally rounded posterodistal lobe on medial surface; palm obtuse; dactylus shorter than palm. Pereopod 7 basis with lateral sulcus slightly pronounced. Oostegites setae with simple and multi-furcate tips. Oostegites 2–4 moderately setose (around 24 setae).

Variation. Juvenile males observed (7.9–10 mm) presented the gnathopod 2 with a distinct medial lobe on merus as seen in females, a lobe that reduces gradually in each moult, until disappearing completely in adult forms. The medial palm concavity of the gnathopod 2 is very shallow or imperceptible.

Habitat. Supra-littoral zone mainly on exposed ocean beaches, but also occurring in sheltered areas.

Remarks. Notorchestia lobata n.sp. is similar to Orchestia quadrimana ( Dana, 1852) , originally described from Illawarra, New South Wales. Both species have the shape of propodus of male gnathopod 2 subquadrate with palm excavate. However, N. lobata has the outer ramus of uropod 1 with 5 robust setae, while O. quadrimana lacks marginal setae on outer ramus of uropod 1. Dana’s (1852; 1853) description of O. quadrimana is poorly detailed and the species needs to be redescribed. Unfortunately, the type material appears to be lost (Ardis Jonston, in litt, from the Museum of Comparative Zoology, Harvard) and our attempts to recollect this species from the type locality were unsuccessful.

Notorchestia lobata ( Stebbing, 1899) is also close to N. novaehollandiae ( Stebbing, 1899) , originally described from Manly, New South Wales. Both species have setose antenna 2, subquadrate shape of propodus of male gnathopod 2, basis of pereopod 7 with lateral sulcus and a cleft telson. Distinct differences are noticed on the male palm of gnathopod 2, which in N. lobata is strongly excavate (10.8 mm), not slightly excavate (10 mm); female palm of gnathopod 1 is parachelate, not simple; and the presence of the conspicuous lobe on the merus of female gnathopod 2, not described for N. novaehollandiae . The excavation on the palm of gnathopod 2 varies with the stage of development as noticed in N. lobata . Thus, the 10 mm male herein observed had a less excavate palm, but also had the medial lobe on the merus ( Fig. 15 ), a character also not described for the N. novaehollandiae males.

Distribution. Victoria: Point Ricardo; Woodside Beach (between Sale and Yarram); Lorne Beach near mouth of Erskine River; Ocean Beach, Separation Creek; Peterborough Beach, Peterborough; Sandy Beach, The Craigs; Shelly Beach, Bridgewater Bay; Sandy Point. South Australia: Beachport Beach, Rivoli Bay; Goolwa Beach and Victor Harbour, Encounter Bay; Yankalilla Bay, Fleurieu Peninsula. Western Australia: Ocean Beach, Eucla; Fourth Beach, Esperance; West Beach, Hopetoun; Slippery Rock, Cape Leuwin; Binningup Beach, Bunbury; South Cottesloe Beach; Jurien Beach, Jurien; Disappointment Loop, Henri Freycinet Harbour, Shark Bay.

Serejo & Lowry: Coastal talitrid amphipods 185

Figures

Fig. 13. Notorchestia lobata n.sp., paratype male, 10.8 mm, habitus, AM P69055; holotype male, 10.8 mm, other parts, AM P69051, Goolwa Beach, Encounter Bay, South Australia. Scales for habitus: 1 mm; remainder: 0.5 mm.

Fig. 14. Notorchestia lobata n.sp., holotype male, 10.8 mm, AM P69051, Goolwa Beach, Encounter Bay, South Australia. Scales represent 0.5 mm.

Fig. 15. Notorchestia lobata n.sp., holotype male, 10.8 mm, U3 and T, AM P69051; female, 9.1 mm, G1, AM P60956; female 11 mm, G2 and P7, AM P69052, juvenile male, 10 mm, G2, AM P69053, Goolwa Beach, Encounter Bay, South Australia. Scales for G1, G2, P7, U1–3: 0.3 mm; EP1–3: 1 mm; merus (juvenile) and T: 0.2 mm.

Fig.16. Notorchestia lobata n.sp., paratype female, 11.0 mm, O2–5, AM P69052; holotype male, 10.8 mm, PL1–3 and BR2–6, AM P69051. Scales represent 0.5 mm.