Actaea grimaldii, a new species of reef crab from Papua New Guinea (Crustacea, Brachyura, Xanthidae)

A new species of xanthid crab, Actaea grimaldii, is described from the coral reefs of Papua New Guinea. This species has a distinctive red and white coloration and is closest to Actaea spinosissima Borradaile, 1902, from the Indian Ocean. However, the new species can be distinguished by the arrangement of spines on the carapace, chelipeds and ambulatory legs, and the structure of the male gonopods. Actaea grimaldii sp. nov. has also been confused with A. polyacantha (Heller, 1861), but differs markedly in the carapace armature.


Introduction
In the 1970-1990s, extensive marine biology field work was carried out on the north coast of Papua New Guinea: at Laing Island, in Hansa Bay, at King Leopold III Biological Station, and in the Madang Lagoon, at a facility run by the Christensen Foundation. Several authors (e.g., Gosliner 1992;Thomas 1996) highlighted the exceptionally high species richness of Madang Lagoon, which became a famous place in marine biodiversity lore. Both King Leopold III Biological Station and the Christensen Foundation facility ceased operations in the mid-1990s, and, as a result, marine biologists essentially stopped research activities on the north coast of Papua New Guinea. However, in 2012 a large expedition, under the "Our Planet Reviewed" programme, was hosted on the campus of the Divine Word University in Madang. A new wave of novel marine species descriptions (e.g., Fricke 2014; Rubio & Rolán 2014;Summers et al. 2014;Ng & Anker 2014;Meyer-Wachsmuth et al. 2014;Macpherson & Robainas-Barcia 2015) was generated by this multinational expedition which lasted two months and involved 110 participants. Many more reports await publication. Between November 30 and December 2, 2012, the expedition was visited by Prince Albert II of Monaco, whose Foundation had made the expedition possible. During his visit, the Prince was presented with a species of xanthid crab that, pending confirmation then, appeared new to science. Its colour pattern was similar to the colours of the armorial of the Grimaldi family and, with the Prince's approval, we offered to name the species after his family if it was confirmed to be new. The purpose of the present paper is to describe this new species of Actaea De Haan, 1833.
Actaea (type species Cancer granulatus Audouin, 1826; see Guinot & Cleva 2009) is a xanthid genus typically associated with tropical coral reefs and currently containing 31 species (updated from Ng et al. 2008). The genus has been studied by Odhner (1925), Guinot (1968Guinot ( , 1969Guinot ( , 1976 and Serène (1984) (see also Guinot & Low 2010). However, many Actaea species are not well known, and a revision of Actaea s. str. is needed. One poorly known species is Actaea spinosissima Borradaile, 1902, originally described from the Indian Ocean. This species has also been reported from Australia and the Moluccas in eastern Indonesia by Odhner (1925) and Serène (1984), respectively. Examination of the type of A. spinosissima shows that a series of specimens from Papua New Guinea, as well as Serène's (1984) specimen, should be referred to a new species, here named A. grimaldii.

Remarks
Although the subfamily Actaeinae has been well studied by many authors, one name that was missed by most revisors is Actaeodius Klunzinger, 1913. For instance, the name is not listed in the revisionary studies and compilations by Serène (1984) and Ng et al. (2008). Klunzinger (1913: 231) established Actaeodius (as "Actäodius") when discussing the taxonomy of Actaea fragifera (White, 1848) and A. polyacantha (Heller, 1861). He decided that these names were synonyms and described and illustrated the species as "Actäodius fragifer". Guinot (1976: 236-237) followed and treated Klunzinger's "Actäodius fragifer" as a synonym of Actaea polyacantha. The status of the genus, however, has not been discussed. Although Klunzinger (1913) did not specifically state which was the type species of Actaeodius, his synonymy of the two treated species means that Chlorodius fragifer White, 1848 is the type species of the genus by monotypy. Currently, the two species are regarded as distinct species of Actaea s. str. (see Odhner 1925;Guinot 1976;Ng et al. 2008).  Borradaile, 1902).

Diagnosis
Anterior surfaces of carapace regions (1M, 2M, 3M, 2L, 5L) covered with numerous short sharp spines and sharp tubercles of varying sizes, 2M and 2L surface gently convex, not distinctly inflated in frontal view, 2M separated by median longitudinal groove anteriorly, 4M lunate, with sharp granules; 1P flattened, divided into many smaller regions by shallow grooves, with distinct transverse groove on anterior third, confluent with series of flattened granules on 3R, 2R and 1R (

Etymology
The species name is in honour of His Serene Highness Albert II, Prince of Monaco, patron of the PAPUA NIUGINI Expedition and several other biodiversity expeditions of the "Our Planet Reviewed" programme conducted by MNHN and Pro-Natura International. The red and white colour pattern of the new species also alludes to the colours associated with the House of Grimaldi.    (ZRC 1969.12.27.3-4).

Females and variation
The females agree with the males in almost all non-sexual characters. A female measuring 6.7 × 4.9 mm (MNHN IU 2013-759) is still immature, with the abdomen triangular in shape. An adult female, 10.2 × 7.8 mm (pleopods fully setose, ZRC, ex MNHN IU 2013-1245), has an ovate abdomen that covers about half the surface of the thoracic sternum. The vulvae are small, positioned on the anterior half of sternite 6 submedially and each has a distinct opercular cover in the form of a narrow plate (Fig. 4B). There is hardly any variation in the diagnostic characters, although some of the specimens (e.g., ZRC, ex MNHN IU 2013-1245) are twice the size of the smaller crabs (e.g., ZRC, ex MNHN IU 2013-920).
The long, simple setae on the ambulatory legs are easily broken, and while obvious in fresh specimens (Fig. 1), they are often lost in preserved material. The holotype male has a developed G1 (Fig. 5D-F) but does not appear to be fully mature. While the setae on the subdistal part of the G1 are long (Fig. 5E-F), they are simple and not plumose as is typical for actaeine gonopods (cf. Guinot 1976).

Colour
In life (Fig. 1), the colour is a striking bright orange to red across the median part of the carapace, with the lateral regions white. There may be patches of white on the gastric and adjacent regions in smaller specimens. The legs are banded red and white, and the chelipeds are red and white, with parts yellowishwhite in colour. The fingers of the chela are reddish-orange basally and white at the tips. The ventral surfaces are white, but abdominal somites 1 and 2 may have large patches of red.

Distribution
This species is known for certain from the Moluccas and Papua New Guinea, and is probably also present in Australia.
The identity of A. spinosissima Borradaile, 1902 is more problematic and its G1 structure has not been figured before. Actaea spinosissima s. str. is now known for certain only from the western Indian  Ocean. Described from the Maldives by Borradaile (1902: 256, fig. 55), it was recorded again shortly after that by Rathbun (1902: 128) who also found two juveniles from these islands. Rathbun (1911) subseqently recorded another juvenile female from Cargados Carajos islands in Mauritius in the western Indian Ocean, but provided no figures. Serène (1984: 114) noted that the record of a male specimen of "A. spinosissima" from St. Brandon in Mauritius by Ward (1942: 87) is A. polyacantha instead. Whether this also includes Rathbun's (1911) specimens cannot be ascertained. The other records of Fig. 9. Actaea spinosissima Borradaile, 1902, ♂, 8.9 × 6.6 mm (ZRC), Chagos Islands A. Dorsal view of carapace. B. Thoracic sternum showing vulvae. C. Right fourth ambulatory leg. this species by Odhner (1925: 59, pl. 4, fig. 4), Serène (1961Serène ( : 206, 1968, Guinot ( : 559, 1969Guinot ( : 238, 1971Guinot ( : 1071Guinot ( , 1976 fig. 3) and Ng et al. (2008: 195) merely list or discuss the species and do not record fresh material. Fortunately, among recent material examined from the Chagos Islands in the western Indian Ocean is an adult male (Figs 8-9) that agrees well with the holotype male of A. spinosissima; its G1 is figured here (Fig. 10). Although the specimen is slightly faded, the remaining colour and pattern suggest they are similar to those of A. grimaldii sp. nov.
The specimen figured as "A. spinosissima" by Serène (1984: 115, pl. 14F) (a male 6.0 × 4.6 mm from Moluccas) agrees well, even in the colour and pattern (cf. Fig. 1), with what is described as A. grimaldii sp. nov. and they appear to be conspecific. Calman (1900: 10) recorded a male specimen measuring 14.0 by 10.0 mm that he provisionally attributed to "Actaea peronii var. squamosa" and noted as differing from A. peronii by its sharp and spiniform anterolateral teeth. Odhner (1925: 59) and Serène (1984: 114) suggested that his record was probably A. spinosissima, but could not be sure as he did not have the specimen and Calman did not figure the species. Davie (2002: 511) accepted Serène's identification and listed this species from Australia. On the basis of geography, it seems Calman's specimen is more likely to belong to A. grimaldii sp. nov. than to A. spinosissima s. str. Actaea grimaldii sp. nov. differs from the type of A. spinosissima s. str. in several key characters: the granules on 1M, 2M, 3M, 2L and 5L are conical and sharp (Figs 1, 2A, 3A, 4A) (vs granules raised but tips broad and rounded in A. spinosissima, Fig. 6); the 1P and tranverse granules adjacent to it are raised and rounded (Figs 1, 2A, 3A, 4A) (vs area and granules distinctly flattened in A. spinosissima, Fig. 6); 2P is raised and rounded (Figs 1, 2A A. spinosissima, Fig. 7C); the ambulatory merus is proportionately longer (Figs 2A, 3B, 4C) (vs distinctly shorter in A. spinosissima, Figs 6, 8A, 9C); and the G1 is proportionately stouter (Fig. 5D) (vs more slender in A. spinosissima, Fig. 10A).