Mallacoota chiltoni, Kilgallen, Niamh M. & Ahyong, Shane T., 2011

Kilgallen, Niamh M. & Ahyong, Shane T., 2011, The genus Mallacoota (Crustacea, Amphipoda, Maeridae) in New Zealand, Zootaxa 2929, pp. 22-36 : 23-28

Mallacoota chiltoni sp. nov.

( Figs 1–3 )

Moera petriei . — Chilton 1883: 82, pl. 2 fig. 4. [Not M. petriei Thomson, 1882 ]. Moera subcarinata . — Chilton 1884: 230; 1885b: 369 [Lyttelton specimens]. Elasmopus subcarinatus . — Chilton 1915: 321, figs 5–6 [“form 2”].

Maera subcarinata . — Hurley 1954: 603 (list, in part).

Mallacoota subcarinata . — Barnard 1972b: 114, figs 59, 60.

Mallacoota nananui . — Webber et al. 2010: 220 [not M. nananui Myers, 1985 ].

Type material. Holotype: male (15.0 mm), NIWA 69797, Port Waitangi Wharf, Chatham Islands, 43°56.736’S, 176°33.570’E, pile scraping at 0.5 m depth, bottom depth 5 m, site 24, CHT 288, 0 8 Feb 2007. Allotype: female (12.5 mm), NIWA 69788, same collection data as holotype. Other paratypes: 1 male (16.0 mm), 3 females (11.5– 15.0 mm), NIWA 69789, Port Waitangi Wharf, Chatham Islands, 43°56.758’S, 176°33.602’E, pile scraping at 3.0 m depth, bottom depth 5 m, site 25, CHT 310, 0 8 Feb 2007; 1 female (12.0 mm), NIWA 68790, Point Weeding Bay, Chatham Islands, 43°57.677’S, 176°34.937’E, 6 m, site 28, CHT 352, 0 9 Feb 2007.

Other material examined. Golden Bay: 1 male (15.0 mm), MITS 29464, Separation Point, 40°40.967’S, 173°00.196’E, site 18, GLD372, 0 6 Nov 2007. Kaikoura: 1 female (15.0 mm), MITS 25456, 42°26.448’S, 173°41.962’E, 11.9 m, KBZ216, 18 May 2007. Dunedin: 1 male (10.0 mm), 2 females (8.5–10.0 mm), MITS 34459, 45°48.839’S, 170°37.723’E, 11 m, 2DUD245, 28 Feb 2006; 3 males (8.0–12.0 mm), 2 females (9.0– 10.5 mm), MITS 4975, 45°48.839’S, 170°37.723’E, 10 m, 2DUD253, 28 Feb 2006; 1 male (12.0 mm), 2 females (6.0– 7.0 mm), MITS 4747, 45°48.839’S, 170°37.723’E, 9 m, 2DUD260, 28 Feb 2006; 1 female (11.0 mm), MITS 4973, 45°48.839’S, 170°37.723’E, 9 m, 2DUD261, 28 Feb 2006; 18 males (7.5–14.0 mm), 17 females (8.0– 15.5 mm), MITS 4748, 45°48.839’S, 170°37.723’E, 9 m, 2DUD263, 0 2 Mar 2006. Bluff: 1 female (10.5 mm), MITS 3823, 46°35.796’S, 168°20.561’E, 7 m, 2BLU040, 14 Feb 2006; 1 female (12.0 mm), MITS 3832, 46°35.484’S, 168°20.976’E, 7 m, 2BLU093, 13 Feb 2006; 1 male (12.0 mm), 2 females (9.5–13.0 mm), 46°35.656’S, 168°20.377’E, MITS 3818, 7 m, 2BLU071, 14 Feb 2006; 5 males (8.0– 14.5 mm), 4 females (9.5–15.0 mm), MITS 33452, 46°35.656’S, 168°20.377’E, 3 m, 2BLU067, 14 Feb 2006; 1 male (14.0 mm), 5 females (6.5–11.0 mm), MITS 3829, 46°35.656’S, 168°20.377’E, 7 m, 2BLU063, 14 Feb 2006; 1 male (8.0 mm), 4 females (6.0–13.0 mm), MITS 3817, 46°35.656’S, 168°20.377’E, 7 m, 2BLU062, 14 Feb 2006; 1 male (9.0 mm), 1 female (10.0 mm), MITS 4020, 46°35.709’S, 168°20.002’E, 7.5 m, 2BLU149, 16 Feb 2006; 1 female (12.5 mm), MITS 3803, 46°35.656’S, 168°20.377’E, 3 m, 2BLU072, 14 Feb 2006; 1 male (8.0 mm), MITS 33450, 46°35.619’S, 168°20.340’E, 13.1 m, 2BLU022, 13 Feb 2006. Stewart Island: 3 females (8.0–13.0 mm), MITS 17450, Horseshoe Bay jetty, 46°52.512’S, 168°07.887’E, site 10, quadrat scraping at 0.5 m, STW181, 27 Sep 2006.

Etymology. Named for Charles Chilton who was the first to report this species from New Zealand, albeit misidentified as Moera petriei Thomson.

Diagnosis. Coxae 1–3 lacking posteroventral notch. Gnathopod 2 (male) propodus massive, not hirsute, slightly concave anterodistally, straight posteriorly; posterior margin of palm irregularly toothed for full length of occlusal surface; dactylus distally spatulate. Pereopod 5 basis posterior margin straight to slightly rounded; pereopod 6 basis posterior margin slightly concave; pereopod 7 basis posterior margin rounded posteriorly.

Description of holotype. Body laterally compressed. Head with notch below lateral cephalic lobe, rostrum absent. Eyes oval. Antenna 1 longer than antenna 2; peduncle article 1 broader than and subequal in length to article 2, with 3 robust setae along distal half of ventral margin; article 2 slender, much longer than article 3; primary flagellum>40-articulate, article 1 slightly longer than following articles; accessory flagellum with 5 articles, article 5 minute. Antenna 2 peduncle article 4 longer than article 5; flagellum article 1 slightly longer than following articles.

Upper lip broader than long, entire. Mandibles with weakly triturative molar; palp small, slender, 3-articulate, article 3 with 2 or 3 medial and 2 apical slender setae; right incisor irregular, lacinia mobilis 8-dentate; left incisor smooth, lacinia mobilis 4-dentate (based on 14.5 mm male, MITS 33452). Lower lip with inner lobes well developed; 2 robust setae on apex of outer lobes. Maxilla 1 with 2-articulate palp; inner plate with 2 terminal spine-like processes, apparently with distal pore. Maxilla 2 inner and outer plates slender, with terminal slender setae. Maxilliped palp 4-articulate; outer plate not reaching distal end of palp article 2, with numerous robust setae along inner and distal margins; inner plate shorter than outer plate with plumose setae along inner margin and simple setae along distal margin.

Gnathopod 1 subchelate; coxa anterior margin slightly concave, rounded distally, posteroventral corner lacking notch; carpus subequal in length to propodus; palm acute, slightly convex, defined by 2 robust setae posteriorly; dactyl fitting palm.

Gnathopod 2 massive, subchelate; basis with anterodistal lobe; carpus compressed, propodus enlarged, anterodistal margin slightly concave, posteroventral margin straight; posterior margin of palm irregularly toothed for full length of occlusal surface; dactylus spatulate.

Pereopods 3–7 dactyli with unguis tapering to acute apex. Pereopod 5 moderately armed with long robust setae; basis longer than broad, slightly rounded posteriorly; merus expanded posteriorly; carpus much shorter than propodus. Pereopod 6 strongly armed with long robust setae; basis longer than broad, slightly concave posteriorly; merus widely expanded posteriorly; carpus much shorter than propodus, widened distally. Pereopod 7 strongly armed with long robust setae; basis longer than broad, rounded posteriorly; merus widely expanded posteriorly; carpus slightly shorter than propodus, widened distally. Gills present on gnathopod 2 to pereopod 6.

Epimeron 1 anterodistal corner narrowly rounded. Epimeron 2 posterodistal corner produced to a small spine. Epimeron 3 posterodistal corner producing spine.

Urosomite 1 dorsally bicarinate. Uropods prominently armed with robust setae. Uropod 1 peduncle with a basofacial seta, peduncle slightly longer than rami; rami subequal in length. Uropod 2 peduncle subequal in length to rami; rami subequal in length. Uropod 3 peduncle much shorter than rami; rami subequal in length. Telson about as long as broad; deeply cleft (>66%); apices acutely bifid, with longer outer and shorter inner apical conical extensions and with long robust setae.

Description of female allotype (sexually dimorphic characters). Gnathopod 2 subchelate, not enlarged; basis lacking anterodistal lobe; merus acutely produced posterodistally; carpus short, shorter than propodus; propodus palm acute, dactylus fitting palm. Oostegites slender from gnathopod 2 to pereopod 5.

Variation. Gnathopod 2 of juvenile males differing slightly from adult males in having a narrower dactylus, slightly sharpened apically, and a more weakly sculptured palm.

Habitat. Intertidal to at least 13.1 m, amongst algal fouling, primarily rhodophytes. Algal species from which M. chiltoni was collected are as follows:

Chlorophyta— Cladophora sp., Ulva sp.

Ochrophyta— Carpophyllum sp., Dictyota kunthii , Halopteris paniculata , Lessonia tholiformis , Macrocystis pyrifera , Marginariella sp., Undaria pinnatifida, Zonaria sp.

Rhodophyta— Adamsiella chauvinii , Anotrichium crinitum , Asparagopsis armata , Brongniartella australis , Callophyllis atrosanguinea , Callophyllis variegata , Ceramium apiculatum , Ceramium flaccidum , Ceramium rubrum , Ceramium vestitum , Chondria sp., Delesseria sp., Dipterosiphonia heteroclada , Griffithsia crassiuscula , Griffithsia traversii, Gloiderma saccatum, Haraldiophyllum crispatum , Heterosiphonia concinna , Hymenena variolosa , Laingia hookeri , Medeiothamnion lyallii , Phycodrys quercifolia , Plocamium angustum , Plocamium cartilagineum , Plocamium cirrhosum , Plocamium microcladioides , Pugettia delicatissima , Rhodymenia obtusa , Rhodophyllis acanthocarpa , Schizoseris dichotoma .

Distribution. New Zealand, from the Chatham Islands (type locality) and localities around the South Island including Bluff, Kaikoura, Golden Bay, Dunedin and Stewart Island.

Remarks. Mallacoota chiltoni sp. nov. is common and widespread in South Island, New Zealand. Chilton (1883) first recorded it from Lyttelton Harbour as Moera petriei , a different species originally described by Thomson (1882) from Port Pegasus, Stewart Island. The following year Chilton (1884) placed Moera petriei in the synonymy of Megamoera subcarinata Haswell, 1879 , and from then the species underwent a series of name changes until placed in Mallacoota ( Barnard 1972a) . Barnard (1972b) reported New Zealand material of the species as Mallacoota subcarinata and noted that all belonged to ‘form 2’ as described by Chilton (1915). Lowry & Springthorpe (2005) clarified the identity of M. subcarinata , which is clearly separated from M. chiltoni by the acute rather than rounded apex of the male gnathopod 2 dactylus.

Mallacoota chiltoni has a southerly distribution in New Zealand. All known localities are south of the Subtropical Convergence, a general marine biogeographic ‘barrier’ recognised for many benthic (albeit usually deepwater) species ( Nodder et al. 2003).

Myers (1985) described Mallacoota nananui from Fiji, and the following year recorded it again from Niue Island ( Myers 1986). In those studies, Myers considered M. subcarinata ‘form 2’ reported from New Zealand ( Chilton 1915; Barnard 1972b) to be identifiable with M. nananui . However, as Lowry & Hughes (2009) observed, the New Zealand specimens differ from M. nananui in the dentition of the male gnathopod 2 propodus palm and shape of the posterior margin (straight versus concave). These authors also mentioned the lack of a basofacial seta on New Zealand specimens as figured by Barnard (1972b: fig. 60h), but all material examined in this study have such a seta present. In addition, the anterodistal (extensor) margin of the male gnathopod 2 propodus is concave in M. chiltoni , whereas that of adult M. nananui is straight to slightly convex. Care should be taken, however, in separating small M. nananui from M. chiltoni . The degree of concavity of the posterior (flexor) margin of the male gnathopod 2 propodal palm in M. nananui appears to increase allometrically, and in small specimens, the concavity is slight ( Fig. 4 A). Nevertheless, the extent of the palmar dentition appears to differ between M. nananui and M. chiltoni at all sizes, distinctly falling short of the dactyl tip (when occluded) in the former and extending the full length of the occlusal surface in the latter; and the ventral margin of the.

Specimens from Sandal Bay, Lifou (AM P48000: 7 males, 3.6–5.2 mm; 7 females, 2.4–4.5 mm), closely resemble M. chiltoni in the slightly concave distodorsal margin and straight (or nearly straight) posterior margin of the of the gnathopod 2 propodus ( Fig. 4 B). The Lifou specimens might represent M. chiltoni , with the differences in mature male body size between Lifou and New Zealand specimens (5.2 mm versus 15.0 mm) reflecting Bergmann’s Rule. The Lifou specimens, however, also differ from M. chiltoni in having only a single ventrodistal robust seta on article 1 of the antennular peduncle (versus a row of 3 robust setae along the distal half of the ventral margin in M. chiltoni ) and in the extent of the palmar dentition of gnathopod 2, which, as in M. nananui , falls short of the dactyl tip (when occluded) (versus extending the full length of the occlusal surface in M. chiltoni ). The Lifou specimens probably represent an undescribed species. Mallacoota latidactylus Ledoyer, 1982 [type locality: Madagascar], and M. worimi Hughes, 2011 [type locality: Boondelbah Island, New South Wales] also exhibit the blunt, spatula-like male gnathopod 2 dactylus of M. Chiltoni . Mallacoota latidactylus can be distinguished by the posteroventral notches on coxae 1–3, the straight anterior margin of the male gnathopod 2 propodus, and the wellrounded posterior margin of the pereopod 7 basis. Mallacoota worimi is perhaps the most similar species to M. chiltoni but differs in the straight rather than concave anterior margin on the male gnathopod 2 propodus, with a proportionally much longer palm, and a convex posterior margin on the basis of pereopod 6.

Figures

FIGURE 1. Mallacoota chiltoni sp. nov. Holotype male, 15.0 mm, NIWA 69787, from Chatham Islands, CHT 288, 0 8 Feb 2007. Scale bars: a, 2.0 mm (habitus); b, 0.2 mm (mouthparts).

FIGURE 2. Mallacoota chiltoni sp. nov. Holotype male, 15.0 mm, NIWA 69787, from Chatham Islands, CHT 288, 0 8 Feb 2007. Allotype female ‘ f’, 12.5 mm, NIWA 69788. Scale 0.4 mm.

FIGURE 3. Mallacoota chiltoni sp. nov. Holotype male, 15.0 mm, NIWA 69787, from Chatham Islands, CHT 288, 0 8 Feb 2007. Scale: a, 0.4 mm (pereopods); b, 0.4 mm (uropods, antennae, telson).

FIGURE 4. Male gnathopod 2 dactylus and propodus. A, Mallacoota nananui Myers, 1985, 6.3 mm, between Ilot des Goelands and Grand Recif Abore, New Caledonia, AM P 47502; Mallacoota sp., B, 5.2 mm, Sandal Bay, Lifou, Loyalty Islands, AM P 48000. Scale 0.2 mm.