Hermesorchestia alastairi, Lowry, 2017

Lowry, James Kenneth, 2017, Hermesorchestia alastairi gen. et sp. nov. from Australia (Talitridae: Senticaudata: Amphipoda: Crustacea), Zootaxa 4311 (4), pp. 491-506 : 493-502

Hermesorchestia alastairi sp. nov.

( Figs 1–13 )

Talorchestia sp. 3 Richardson, Swain & Smith, 1991: 129, 130, tables 2, 5, 6.

Type material. Holotype hyperadult male, 16.5 mm, SEM pin and stubs, AM P.97207, Hibbs Lagoon, Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235). Paratypes: male, 15.8 mm, SEM pin and stub mounts, AM P.97208, Hibbs Lagoon, Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235); female, 13.6 mm, SEM pin and stub mounts, AM P.97209, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235); male, 15 mm, dissected, 1 slide, AM P.99116, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235); juvenile, 10.5 mm, dissected, AM P.99117, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235); female, 7 mm, dissected, AM P.99167, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235); 30+ specimens, AM P.96943, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), mid dune, pitfall 2:2 (A111), 10 January 1987, coll. S.J. Smith (TA235) ; 18 specimens (7 males including 2 with pleonite 3 projections, 11 females), AM P.96940, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), fore dune pitfall 1:2 (A110), 10 January 1987, coll. S.J. Smith (TA232) ; 21 specimens (12 males, including 6 with pleonite 3 projections, 9 females), AM P.96939, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), rear dune, pitfall 4 (A108), 10 January 1987, coll. S.J. Smith (TA231) ; 26 specimens (4 males, 22 females), AM P.96941, Hibbs Lagoon , Tasmania (42°34’26”S 145°18’05”E), top dune, pitfall 3 (A107), 10 January 1987, coll. S.J. Smith (TA233).

Additional material examined. Tasmania: 1 male specimen, AM P.96912, Cox Bight Beach, just west of Point Eric (43°29’33”S 146°14’26”E), sand burrows at extreme high water spring, 4 February 1990, coll. A. Richardson & S.M. Eberhard (TA145) ; 1 male hyperadult specimen, AM P.96923, South Cape Bay (43°36’07”S 146°47’04”E), sand at high water, 23 October 1988, coll. J. Jackson (TA179); many specimens, AM P.96927, South Cape Bay (43°36’04”S 146°47’04”E), from burrows in 1 m sand cliff at extreme high water spring, 22 August 1988, coll. R. Swain, J. Tupascz & A. Richardson (TA195) ; 10 males (incl. 3 with pl3 humps), AM P.96931, South Cape Bay (43°36’04”S 146°47’04”E), on vegetation at night (feeding), on ridge immediately above extreme high water spring, 21 August 1988, coll. A. Richardson & J. Tupascz (TA197) ; 24 specimens (23 males including 9 with pleonite 3 humps, 1 female), AM P.96932, South Cape Bay (43°36’04”S 146°47’04”E), on vegetation at night (feeding), on ridge immediately above extreme high water spring, 21 August 1988, coll. A. Richardson & J. Tupascz (TA197); 20+ specimens, AM P.96933, South Cape Bay , Tasmania (43°36’04”S 146°47’04”E), on vegetation at night (feeding), on ridge immediately above extreme high water spring, 21 August 1988, coll. A. Richardson & J. Tupascz (TA197) ; 2 specimens (1 male, 1 female), AM P.96947, Mulcahy Bay (43°07’11”S 145°44’02”E), Campsite, 13 January 1988, coll. J. Jackson (TA240, WHA177) ; 1 male with pl3 humps, AM P.96946, Mulcahy Bay (43°07’11”S 145°44’02”E), campsite under rock, 13 January 1988, coll. J. Jackson (TA238, WHA181) ; 7 specimens (3 males, 4 females /juveniles), AM P.97041, 1 km north of Rupert Point (41°38’10”S 144°54’05”E), in burrows under woody dune scrub, 4 December 2008, coll. A. Richardson (TA373) ; 12 specimens (5 males, including 1 with pleonite 3 projections; 7 non-gravid females), AM P.97023, Lighthouse Bay, Bruny Island (43°29’16”S 147°08’59”E), burrows in clay and wet sand, 1 m above beach flat, sedges, Correa sp., 16 November 1993, coll. A. Richardson, R. Swain, C. Shepherd & M. Nelson (TA341); many specimens, AM P.97026, Lighthouse Bay, Bruny Island (43°29’06”S 147°09’12”E), burrows in sand cliff in creek gully, 40 m from high water, bracken, sedges, 16 November 1993, coll. A. Richardson, R. Swain, C. Shepherd & M. Nelson (TA343) ; 1 female, AM P.99118, Lighthouse Bay, Bruny Island , 43°29′16″S, 147°08′59″E, burrows in clay and wet sand, 1 m above beach flat, sedges, Correa sp., 16 Nov 1993, coll. A. Richardson, R. Swain, C. Shepherd & M. Nelson (TA340) ; 4 females AM P.99119, Telegraph Bay, Three Hummocks Island , 40°24’55”S, 144°53’17”E, burrows in dunes less than 0.5 km in land, coll. A. Richardson, 8 September 2015 ; 5 specimens as genetic vouchers, AM P.99101–99105, Telegraph Bay, Three Hummocks Island , 40°24’55”S, 144°53’17”E, burrows in dunes less than 0.5 km in land, coll. A. Richardson, 8 September 2015.

Genback accession. COI sequence KX812494 -812498 from AM P.99101–99105.

Type locality. Hibbs Lagoon , Tasmania, Australia (42°34’26”S 145°18’05”E).

Etymology. Named in honour of Associate Professor Alastair Richardson. His extensive reference collection and published ecology of Tasmanian Talitridae was the catalyst for this taxonomic research.

Description. Head. Eye medium size (greater than 1/5 to 1/3 head length). Antenna 1 long, reaching from midpoint to end of peduncular article 5 of antenna 2. Antenna 2 slightly less than half body length (0.45 × length); peduncular articles slender, with many large robust setae; article 5 longer than article 4; flagellar articles final article large, cone-shaped forming a virgula divina. Labrum with apical setal patch; epistome with many robust setae. Mandible left lacinia mobilis with 4 cusps. Labium distolateral setal tuft present, distomedial setal tuft present; without inner plates. Mandible left lacinia mobilis 4-cuspidate. Maxilla 1 with 1-articulate small palp. Maxilliped palp article 2 distomedial lobe well developed; article 4 fused with article 3.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; coxa smaller than coxa 2; carpus longer than propodus, 1.5 as long as propodus, posterior margin with palmate lobe; propodus subrectangular, twice as long as broad, anterior margin with 6 groups of robust setae, posterior margin with palmate lobe, palm transverse; dactylus simplidactylate, subequal in length to palm, without anterodistal denticular patch. Gnathopod 2 sexually dimorphic; subchelate; basis slender; ischium anterior margin with lateral and medial rounded lobe, lobes dissimilar in size; carpus triangular, reduced, enclosed by merus and propodus; propodus 1.8 × as long as wide, palm subacute, 55% along posterior margin, evenly rounded, lined with robust setae, posteroproximal corner with groove, without cuticular patch at corner of palm; dactylus curved, subequal in length to palm, without anteroproximal bump, apically acute. Pereopods 2–4 coxae deeper than wide. Pereopods 3–7 tricuspidactylate laterally, dactylus without anterodistal denticular patch. Pereopod 3 carpus length twice width. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3, length 1.8 × width; dactylus without anterodistal denticular patch, posterior margin thickened proximally with 1 proximal and 1 distal projections. Pereopod 5 merus length 1.5 × width; carpus length 2.1 × width; propodus distinctly longer than carpus, length 5 × width; dactylus long, slender, length 6 x width. Pereopods 6–7 sexually dimorphic, basis, merus and carpus broadly incrassate; lined with many robust setae. Pereopod 6 subequal in length to pereopod 7; coxa posterior lobe posteroventral corner rounded, posterior margin perpendicular to ventral margin; merus broad, length 1.6 × width; carpus expanded, length 1.7 × width; propodus distinctly longer than carpus, length 6 × width. Pereopod 7 basis expanded, produced posteriorly, ventrally incised, posterior margin convex, lined with small robust setae, lateral sulcus, strongly pronounced; merus developed as 3-dimensional complex article (see SEM image), length 1.7 × width; carpus subovate, length 1.1 × width; propodus distinctly longer than carpus, length 8 × width.

Pleon. Pleonites 1–2 without dorsal spines. Pleonite 3 with or without pair of well developed projections. Pleopods 1–3 reduced, rami unsegmented. Epimera 1– 2 posterior margin straight, smooth to weakly serrate. Epimeron 3 posteroventral corner produced, ventral margin without robust setae, posterior margin concave, smooth to weakly serrate, lined with robust setae. Uropod 1 not sexually dimorphic; peduncle with 10 robust setae along margins, with apical spear-shaped setae; rami positioned directly on top of each other; inner ramus subequal in length to outer ramus, with 19 marginal robust setae in 2 rows; outer ramus with 3 marginal robust setae 1 row. Uropod 2 peduncle with 12 robust setae; inner ramus subequal in length to outer ramus, with 17 marginal robust setae in 2 rows; outer ramus with marginal robust setae in 1 row. Urosomite 3 subrectangular, dorsally expanded, engulfing telson, deeper than broad, 1.2 x as deep as broad. Uropod 3 vestigial; peduncle dorsally concave, margin accommodating telson, depth greater than length, 0.9 x depth, with 6 robust setae; ramus linear, not fused to peduncle, shorter than peduncle, 1.2 × as long as broad, with 5 marginal setae. Telson subovate, broader than long, lateral and apical margins convex, weakly incised apically, dorsal midline entire, with around 20 dorsal, marginal and apical robust setae per lobe; length extending beyond uropod 3 peduncle.

Female (sexually dimorphic characters). Gnathopod 1 simple; carpus and propodus posterior margin without palmate lobe; propodus palm near transverse; dactylus overreaching palm. Gnathopod 2 mitten-shaped; basis not expanded anteromedially; ischium without lobe; carpus well developed (not enclosed by merus and propodus), length 2.5 × width, posterior lobe absent; propodus twice width, palm obtuse; dactylus shorter than palm, posterior margin smooth. Pereopods 6–7 not enlarge. Pereopod 6 merus rectilinear, length 1.9 × width; carpus rectilinear, length 3 × width; propodus slightly longer than carpus. Pereopod 7 basis weakly expanded, posterior margin convex, lined with small robust setae, lateral sulcus absent; merus subquadrate, length twice width; carpus rectilinear, length 3.5 × width; propodus longer than carpus, length 7 × width.

Variation. Sexually dimorphic characters on pereopods 6 and 7 begin to develop in males at ~ 10.5 mm. There is little to no change in the male gnathopod 2 propodus palm structure between growth stages observed (10.5 – 16.5 mm). Pleonite 3 projections may be present or absent in males and when present become increasingly more pronounced with growth stage. Males without projections were 10.5 to 17 mm in length (n=5). Weak projections development was observed in males 15.5 to16.5 mm (n=2), large projections in males 12 to 15.9 mm (n=5) and very large projections in male 12 to 15 mm (n=4). Juvenile males without sexually dimorphic pereopods 6 to 7 were 9 to 11 mm (n=2). Non-gravid females 8.9 to 15 mm (n=8) and gravid females 12 to 13.5 mm (n=2).

Remarks. Hermesorchestia alastairi gen. et sp. nov. can be distinguished from Australian talitrids by the dense covering of robust setae on the dorsal, lateral and apical margins of the telson. In males, the posterior margin of the pereopod 7 basis is greatly expanded, with the merus a complex 3-dimensional structure and the carpus also expanded. The presence of projections on pleonite 3 in only some male specimens of H. alastairi gen. et sp. nov. is difficult to resolve. This character was not related to allometric growth. Multiple specimens (n=28) from a single collection event contained examples of both male forms (body size 10.5 to 17 mm without projections; 12 to 16.6 mm with projections). No other character variation was observed between males. Assessment of individuals with pleonite 3 projections revealed the size of projections increases with growth stage but this was not a linear association, as some smaller specimens had better developed projections than larger individuals (15.5 to 16.6 mm weak projections; 12 to 15.9 mm large projections, fig. 9; very large projections 12 to 15 mm, fig. 5). Therefore males with projections on pleonite 3 are considered as a morphotype within the species. The possibility that males with and without projections are separate species is ruled out as all other characters including the gnathopod 2 propodus palm, pereopod 7 basis posterior expansion and telson setation are consistent. These characters are well documented as species level characters elsewhere in the Talitridae .

Feeding studies on Hyalella S.I. Smith, 1874 , a genus also within the Talitroidea Rafinesque, 1815, show diet quality influence the development of male secondary sexual characters ( Cothran, et al., 2014). Within the Talitridae , food resources have been shown to effect survivorship, with algal diet choice influencing longevity ( Poore & Gallagher, 2013). Manipulative studies using both morphotypes of H. alastairi gen. et sp. nov. are needed to further understand the expression of sexually dimorpic characters.

Within H. alastairi gen. et. sp. nov. the lack of sculpturing in the male gnathopod 2 propodus palm across growth stages is remarkable, given the significant tooth and sinus structures in other species which are known to become exaggerated with increasing size. The potential that a further male adult growth stage remains unobserved seems plausible given the modest size of male specimens at hand (9 to 16.6 mm). Other Australian species can reach more than 20 mm, Bellorchestia pravidactyla ( Haswell, 1879) and the New Zealand species Orchestia aucklandiae Spence Bate, 1862 , can reach ~ 40 mm (LEH pers. obs.). The expansion of the pereopods 6 to 7 indicate the males observed are developing sexually dimorphic characters. The male pereopod 7 posterior lobe couples neatly with the expanded carpus, and several specimens were preserved with their pereopods folded into this position ( Fig. 1 ). The dorsal projections, where present, rest upon the ground when the urosome is folded under the body. This contact point may provide stability and leverage for saltation. Locomotion documented for several species of talitrid show that the flicking action of the urosome is used for propulsion ( Sudo & Amano 2014; Amano & Sudo 2013; Vogel 1985; Bracht 1980).

Ecology. Burrowing in sand cliffs, clay, wet sand and under woody dune scrub (current study). Identified as ‘ Talorchestia sp. 3’ sand-hopper in Richardson et al. (1991), occurring at the interface between bare sand and vegetated areas, not extending into vegetated dunes. See Richardson et al. (1991) for in-depth seasonal information across sites.

Distribution. Tasmania: Cox Bight Beach, South Cape Bay, Hibbs Lagoon, Mulcahy Bay, Rupert Point, Bruny Island, Three Hummocks Island (current study).

Figures

FIGURE 1. Hermesorchestia alastairi gen. et sp. nov., from top to bottom, paratype, male 15 mm, AM P. 99116, paratype, juvenile, 10.5 mm, AM P. 99117, Hibbs Lagoon, Tasmania. Scale 2 mm.

FIGURE 2. Hermesorchestia alastairi gen. et sp. nov., paratype, juvenile, 10.5 mm, AM P. 99117, paratype, male *, 15 mm, AM P. 99116, Hibbs Lagoon, Tasmania. Scale 2 mm.

FIGURE 3. Hermesorchestia alastairi gen. et sp. nov., paratype, juvenile, 10.5 mm, AM P. 99117, paratype, male *, 15 mm, AM P. 99116, Hibbs Lagoon, Tasmania. Scale 2 mm.

FIGURE 4. Hermesorchestia alastairi gen. et sp. nov., paratype, female, 7 mm, AM P. 99167, Hibbs Lagoon, Tasmania. Scale 2 mm.

FIGURE 5. Hermesorchestia alastairi gen. et sp. nov., holotype, hyperadult male, 16.5 mm, SEM image, AM P. 97207, Hibbs Lagoon, Tasmania. Scales H, A 2 = 200 µm, all other parts = 100 µm.

FIGURE 6. Hermesorchestia alastairi gen. et sp. nov., holotype, hyperadult male, 16.5 mm, SEM image, AM P. 97207, Hibbs Lagoon, Tasmania. Scales G 1 = 100 µm G 2, Ur = 200 µm.

FIGURE 7. Hermesorchestia alastairi gen. et sp. nov., holotype, hyperadult male, 16.5 mm, SEM image, AM P. 97207, Hibbs Lagoon, Tasmania. Scales P 3, 4 = 200 µm, P 4 dactylus = 20 µm, P 3 dactylus = 10 µm.

FIGURE 8. Hermesorchestia alastairi gen. et sp. nov., holotype, hyperadult male, 16.5 mm, SEM image, AM P. 97207, Hibbs Lagoon, Tasmania. Scales P 5 = 200 µm, all other parts = 1 mm.

FIGURE 9. Hermesorchestia alastairi gen. et sp. nov., paratype, male, 15.8 mm, SEM image, AM P. 97208, Hibbs Lagoon, Tasmania. Scales = 100 µm.

FIGURE 10. Hermesorchestia alastairi gen. et sp. nov. paratype, male, 15.8 mm, SEM image, AM P. 97208, Hibbs Lagoon, Tasmania. Scales = 100 µm.

FIGURE 11. Hermesorchestia alastairi gen. et sp. nov. paratype, male, 15.8 mm, SEM image, AM P. 97208, Hibbs Lagoon, Tasmania. Scales P 5 – P 7 = 100 µm, P 3, Ep = 200 µm.

FIGURE 12. Hermesorchestia alastairi gen. et sp. nov. paratype female, 13.6 mm, SEM image, AM P. 97209, Hibbs Lagoon, Tasmania. Scales Md = 10 µm, G 1 = 100 µm, G 2 = 200 µm.

FIGURE 13. Hermesorchestia alastairi gen. et sp. nov. paratype, female, 13.6 mm, SEM image, AM P. 97209, Hibbs Lagoon, Tasmania. Scales Ur = 100 µm, ep = 200 µm.