Aotearorchestia chathamensis Hughes & Lowry 2023, comb. nov.
Creators: name: Hughes, Lauren E.
name: Lowry, James K.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Talitridae
Aotearorchestia
Aotearorchestia chathamensis

description: Aotearorchestia chathamensis (Hurley, 1956) comb. nov.
(Figs. 1–10, 66–67)
Talorchestia telluris.— Chilton, 1917: 299 (in part), figs. 17, 18.
Talorchestia chathamensis Hurley, 1956: 379, figs. 108–131.— Serejo, 2004: 19 table 2.— Hughes & Lindsay, 2021: 86, 87.
Bellorchestia chathamensis.— Serejo & Lowry, 2008: 169.— Lowry, 2012: 2.
Material examined. A, male, 8.3 mm, dissected; C, male, 9 mm, dissected; F, male, 11.8 mm, dissected; I, male, 13 mm, dissected; B, male, 10 mm SEM whole animal pin mount, part on stubs; G, male, 13.1 mm, SEM whole animal pin mount, part on stubs; H, male, 13.2 mm, SEM whole animal pin mount, part on stubs; z female, 14 mm, x female, 7.5 mm, whole animal pin mount, part on stubs; 100+ specimens, NIWA 8387, Waitangi, Chatham Island (43°57′0′′S 176°33′42′′), formalin traps in sand above high tide mark, 30 January 1954 (Station Z6041). 7 male specimens, AM P.105568, Dunedin, New Zealand, (45°52′S 170°30′ E). [NB. Originally Registered as Orchestia telluris].
Type locality. Chatham Islands, New Zealand.
Diagnosis (male). Gnathopod 2 with proximal spine defining palm, palm with large projections near dactylar hinge. Pereopod 7 carpus greatly enlarged, circular.
Description. (based on A, male, 8.3 mm; C, male, 9 mm; F, male, 11.8 mm; I, male, 13 mm; B, male, 10 mm; G, male, 13.1 mm; H, male, 13.2 mm; z female, 14 mm, x female, 7.5 mm NIWA 8387). Head. Eye large (greater than 1/3 head length). Antenna 1 short. Antenna 2 unknown. Upper lip with apical setal patch; epistome without robust setae. Lower lip 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, 1.8 × as long as propodus, posterior margin with palmate lobe; propodus distally expanded, twice as long as broad, anterior margin with 5–6 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 1.3–1.5 × as long as wide, palm subacute, 55% along posterior margin, evenly rounded, with subacute distomedial tooth, lined with robust setae, posteroproximal corner with shelf and groove, without cuticular patch at corner of palm; dactylus curved, subequal in length to palm, without anteroproximal bump, apically acute. Pereopods 3–4 coxae deeper than wide. Pereopods 3–7 asymmetrically, 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 × width; propodus distinctly longer than carpus, length 4 × width; dactylus long, slender, length 6 × width. Pereopod 6 subequal in length to pereopod 7; coxa posterior lobe posteroventral corner rounded, posterior margin rounded or crenulate; merus broad, length twice width; carpus length 3 × width; propodus longer than carpus, length 6 × width. Pereopod 7 sexually dimorphic; basis expanded, produced posteriorly, posterior margin convex, serrate, lined with small robust setae, lateral sulcus, strongly pronounced; merus developed as a 3-dimensional complex article (see SEM image, Fig. 8), length subequal to width; carpus posterior margin greatly expanded, developed as 3-dimensional subovate convex article (see SEM image, Fig. 8), length subequal to width; propodus distinctly shorter than carpus, length 8 × width.
Pleon. Pleonites 1–3 without dorsal spines. 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 straight, smooth to weakly serrate, lined with robust setae. Uropod 1 not sexually dimorphic; peduncle with 26 robust setae, with apical spear-shaped setae; rami positioned directly on top of each other; endopod subequal in length to exopod, with 4 marginal robust setae in 2 rows; exopod with 19 marginal robust setae. Uropod 2 peduncle with 5 robust setae; endopod subequal in length to exopod, with 10 marginal robust setae in 2 rows; exopod with 7 marginal robust setae in 2 rows. Urosomite 3 subrectangular, dorsally expanded, almost engulfing telson, deeper than broad, 1.2 × as deep as broad. Uropod 3 reduced; peduncle dorsally weakly concave, margin accommodating telson, longer than deep, 1.5 × depth, with 6 robust setae; ramus linear, not fused to peduncle, longer than peduncle, 4 × as long as broad, with row of 11 marginal setae. Telson proximally broad distally tapering, lobes with 5–8 marginal and apical robust setae per lobe; length not extending beyond uropod 3 peduncle.
Female (sexually dimorphic characters). Gnathopod 1 simple; carpus and propodus posterior margin without palmate lobe; propodus palm nearly 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 × width, posterior lobe absent; propodus twice width, palm obtuse; dactylus shorter than palm, posterior margin smooth.
Variation. The large growth series available for male specimens of A. chathamensis shows that the palmate lobe on the gnathopod 1 merus becoming more pronounced in larger specimens. The male gnathopod 2 propodus transitions from a smooth palm in smaller specimens (7.6 mm), to a sculptured palm margin with tooth and sinus structures which become increasingly exaggerated. The plate-like pereopod 7 merus begins to develop in 9 mm length specimens, however, some intraspecific variation was observed indicating that the development may be a function of diet/fitness in conjunction with the growth stage, as some relatively smaller males had a more developed merus structure than a specimen of slightly larger body size.
Size. 7.6 to 18 mm.
Remarks. Aotearorchestia chathamensis comb. nov. and A. telluris comb. nov. are morphologically similar enough to be considered originally as one species by Chilton (1917). The large mature males, of greater than 11 mm, are readily distinguishable by the sculpturing of the male gnathopod 2 propodus palm, while smaller males of both species are more difficult to identify using this character alone (Hurley 1956) (Figs. 2, 13). The difference in the pereopod 7 carpus shape, being more rounded in A. chathamensis comb. nov. and more ovate in A. telluris comb. nov., is more consistent regardless of the male growth stage. There is also considerable variation in the form of the pereopods 7 merus between the two species, however being developed as a complex three dimensional structure, makes it difficult to compare and contrast the shapes in the written text (see Figs. 8, 18). Although immature males are difficult to distinguish, these two species are highly isolated from each other geographically, with A. chathamensis currently endemic to the New Zealand offshore Chatham Islands and A. telluris known from the New Zealand mainland.
Habitat. Supralittoral, burrowing in sand (Hurley 1956).
Distribution. New Zealand. Chatham Islands (Hurley 1956).
description: Published as part of Hughes, Lauren E. & Lowry, James K., 2023, Review of New Zealand Coastal Talitroids with description of three new genera (Crustacea, Amphipoda, Senticaudata), pp. 1-81 in Zootaxa 5268 (1) on pages 7-18, DOI: 10.11646/zootaxa.5268.1.1, http://zenodo.org/record/7840854