Nectocarcinus antarcticus (Hombron & Jacquinot, 1846)

Published, First, 2009, New records of crabs (Decapoda: Brachyura) from the New Zealand region, including a new species of Rochinia A. Milne-Edwards, 1875 (Majidae), and a revision of the genus Dromia Weber, 1795 (Dromiidae), Zootaxa 2111, pp. 1-66 : 46-49

Nectocarcinus antarcticus (Hombron & Jacquinot, 1846)

Figs 23a, b, 24a, b

Portunus antarcticus Jacquinot, 1853: 51 , figs 1–5, pl. 5.

Nectocarcinus antarcticus — Milne-Edwards 1860: 220. — Miers 1874: 2, fig. 2, pl. 1; 1876: 30. — Hutton 1879: 340. — Filhol 1886: 383. — Wilson 1907: 65. — Chilton 1909: 608; 1911: 291. — Thomson 1913: 237. — Rathbun 1918: 3. — Thomson & Anderton 1921: 98, 2 figs. — Chilton & Bennett 1929: 754. — Young 1929: 151. — Powell 1937: 375, 377, 387. — Richardson 1949a: 31, fig. 1. — Ralph & Yaldwyn 1956: 74, fig. 42. — Yaldwyn 1958: 125. — Dell 1960: 5: 1963a: 44; 1963b:253; 1968: 227. — Stephenson 1962: 315; 1972: 21. — Bennett 1964: 65, fig. 130. — Inoue et al. 1968: 135, 137. — Takeda & Miyake 1969: 165, figs 4c, d. — Dell et al. 1970: 54, figs. 1b, 2b, e, 3c, d, pl. 2. — Dawson & Yaldwyn 1974: 47. — Fenwick 1978: 207. — Probert et al. 1979: 381. — Willan 1981: 230. — Rainer 1981: 37. — Probert & Wilson 1984: 390. — Wear & Fielder 1985: 49, figs 126–129. — McLay 1988: 220, fig. 49a–d. — Takeda 1990: 372, colour photograph. — Ahyong et al. 2007: 170, colour photograph.

Material Examined. Wellington Harbour 41°17’S, 174°46’E: WT046 CB, 1 female, 5.5 mm x 4.7 mm

( NIWA 48737); WLG604 CB, 1 male , 10.9 mm x 8.6 mm ( NIWA 48738 ); WLG612 CB, 1 female , 7.9 mm x 6.7 mm ( NIWA 48739 ) .

Tauranga Harbour 37°39’S, 176°10’E: 1 female, 11.6 mm x 9.3 mm, TRG800 CB, 23 Feb. 2004 ; 1 female, 7.4 mm x 6.3 mm, TRG801 CB, 24 Feb. 2004 ( NIWA 48740 ) ; 1 female, 15.1 mm x 12.2 mm, TRG838 CB, 25 Feb. 2004 ; 1 female, 18.9 mm x 15.3 mm, 37°39’S, 176°10’E, 2TRG050 CB, 5 Apr. 2005 .

Nelson Harbour 41°15’S, 173°18’E: 1 male, 8.9 mm x 7.6 mm, 2NSN167 CB, 17 Dec. 2004 ( NIWA 48742 ) .

Lyttelton Harbour 43°37’S, 172°44’E: 1 female, 28 mm x 21.9 mm, 3 m, personal collection.

Dunedin Harbour 45°53’S, 170°31’E: 1 male, 53.8 mm x 40.7 mm, 14 m, DUD035 CB, 26 Feb. 2003 .

Remarks. Initially the small specimens shown in Fig. 22a, b were considered to possibly be a new species of Nectocarcinus , but after examining a whole range of sizes it became apparent that these were juvenile stages of N. antarcticus because there were no adult stages that matched the juvenile features. The most parsimonious hypothesis is that they all belong to the same species.

The most detailed description of N. antarcticus is to be found in Dell et al. (1970), but this is based on male and female crabs with CW> 70 mm and so does not encompass juvenile differences. The main changes to morphology as size increases are: 1) in small crabs the anterolateral teeth (and post-orbital tooth) are prominent, acute, with last tooth directed laterally whereas in large crabs the anterolateral teeth are relatively inconspicuous and are directed anteriorly; 2) curvature of the anterolateral margin becomes much stronger with increasing size; 3) while the pereopods of all specimens are fringed with long setae, body tomentum only becomes evident with increasing size and maturation.

Figs 22, 23 are a series of specimens increasing in size to show changes in the proportions of the carapace. In both males and females the ratio of CW/CL increases from around 1.17 (CW = 5.5mm) to 1.32 (72.7 mm). In females the ratio suddenly changes to around 1.27 upon reaching sexual maturity. Dell et al. (1970) noted that N. antarcticus females achieve maturity over a range of sizes that seem to decrease northwards. Conversely maximum size attained by both sexes seems to increase southwards to the southern off-shore islands. Ontogenetic changes in morphology are also seen in the two Australian species N. integrifrons ( Latreille, 1825) and N. tuberculosus A. Milne-Edwards, 1860 (see Dell et al. 1970).

Dell et al. (1970) provide a key to the six species of Nectocarcinus , but the two New Zealand species are easily distinguished because N. bennetti Takeda & Miyake, 1969 is dark red-purple and iridescent, lacks body tomentum and the male G1 is strongly curved, while N. antarcticus is red, non-iridescent, tomentose and the male G1 is not curved.

Distribution. Endemic to New Zealand. The specific name “ antarcticus ” is probably based on the fact that the type locality was the Auckland Is, a remote locality south of New Zealand. However, the name is not a good indicator of the distribution of this species which occurs along the whole length of New Zealand between 34°S – 51°S, and a lot further north than N. bennetti which is restricted to 44°S – 53°S. The northern limit of the N. bennetti is Stewart I. and the two species overlap from 44°S – 51°S. Depth range 0– 550 m.