On the morphological differentiation between Libinia spinosa and L . ferreirae ( Crustacea : Brachyura : Majoidea : Epialtidae )

Libinia spinosa H. Milne Edwards in Guérin, 1832 and L. ferreirae Brito Capello, 1871, inhabit very similar environments, and their geographic and bathymetric distributions overlap for about 3000 km along the southwestern Atlantic. Both species are commonly caught in the same haul and differentiating between them can often be difficult. Traditionally, morphological differentiation between L. spinosa and L. ferreirae has been based exclusively on the number of spines along the median, longitudinal line of the carapace and the development of a process at the anterolateral angle of the basal segment of the antenna. Because Libinia spinosa and L. ferreirae share similar numbers of median spines (7 and 6, respectively), and the number of median spines of the carapace and the process at the anterolateral angle of the basal antennal segment are variable, they are of little value in separating these species. It is shown herein that unequivocal identification can be easily achieved based on features of the male and female thoracic sternum, pereiopod dactyli, and infraorbital notch. A lectotype is designated for L. spinosa and its authorship and date are corrected. Libinia gibbosa A. Milne-Edwards, 1878, is demonstrated to be a junior synonym of L. ferreirae. The holotype of L. gibbosa is figured for the first time.

The spider crabs Libinia spinosa H. Milne Edwards in Guérin, 1832, and L. ferreirae Brito Capello, 1871, are two major components of the soft-bottom, invertebrate megafauna in the southwestern Atlantic (BOSCHI 1964, PIRES 1992, NEGREIROS-FRANSOZO & NAKAGAKI 1998, BERTINI & FRANSOZO 2004, BERTINI et al. 2004, BRAGA et al. 2005, DE LEO & PIRES-VANIN 2006, AMARAL et al. 2011).Libinia spinosa and L. ferreirae are commonly found in mud and sand bottoms at depths between the intertidal zone and 170 m (MELO 1996), and in some seasons, these species are locally abundant in fishermen's nets.Adults can reach a carapace length of about 89 mm with a leg span of about 568 mm (authors' personal observations), and their color in life ranges from whitish to dark yellow.Libinia spinosa is a generalist species feeding on algae, poriferans, cnidarians, mollusks, polychaetes, other crustaceans and small fishes (BARROS et al. 2008), and the same probably holds true for L. ferreirae.Libinia spinosa is restricted to the southwestern Atlantic, from Espírito Santo (Brazil) south to Uruguay and Argentina, whilst L. ferreirae has a much broader geographical range occurring along the Central and South American coast from Costa Rica to Uruguay (RATHBUN 1925, HOLTHUIS 1959, GUINOT-DUMORTIER 1960, RODRIGUEZ 1980, LEMAITRE 1981, TAKEDA 1983, MELO 1996, 2008).
Historically, the morphological differentiation between Libinia spinosa and L. ferreirae has been based exclusively on the number of spines along the median longitudinal line of the carapace and the development of a process at the anterolateral angle of the basal segment of the antenna (H.MILNE EDWARDS 1834: 301, BRITO CAPELLO 1871: 262, RATHBUN 1925: 310, GUINOT-DUMORTIER 1960: 178, MELO 1996: 258, TAKEDA 1983: 137).However, both characters vary frequently, and reliable identification is, therefore, not always possible.Ongoing studies on the taxonomy of the genus Libinia prompted us to further explore the morphological differences between L. spinosa and L.
ZOOLOGIA 29 (6): 577-588, December, 2012 ferreirae.We show herein that unequivocal identification can be easily achieved based on features of the male and female thoracic sternum, pereiopod dactyli, and infraorbital notch.
We follow NG et al. (2008) in the citation of the name of the French author Félix Édouard Guérin: simply Guérin for the works published before 1836; Guérin-Méneville for the ones published after 1836 (for the rationale see EVENHUIS 2003: 16).Abbreviations are: cl, carapace length (from the rostral notch to the posterior margin of the carapace, unless otherwise noted); cw, carapace width (branchiostegal spines not included, unless otherwise noted); P1, cheliped; P2-P5, walking legs or pereiopod 2 to pereiopod 5.; stn, station.The material herein studied belongs to the collections of the Muséum national d'Histoire naturelle, Paris (MNHN), Museu de Zoologia, Universidade de São Paulo (MZUSP), and the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM).
Remarks.The name Libinia spinosa appeared for first time in a plate from Guérin's Iconographie du Règne Animal in association with the following illustrations: habitus, female abdomen, and ventral view of the cephalothorax (GUÉRIN 1832: pl. 9, figs 3, 3a, 3b).Guérin's Iconographie was issued in parts, the plates appeared in 1832, whereas the text was published in only 1844 (see COWAN 1971 for the dates of publication of Guérin's Iconographie).The publication of the name Libinia spinosa in Guérin's Iconographie meets the requirements of availability of the ICZN (1999: Art.11, Art.12.1 and Art.12.2.7)and therefore the name was made available at this occasion and not in H. Milne Edwards' Histoire Naturelle des Crustacés as traditionally accepted (H.MILNE EDWARDS 1834).GUÉRIN (1832) clearly attributed the name L. spinosa to H. Milne Edwards, "Libinia spinosa.M. Edw.", and according to the provisions of the ICZN (1999: Art.50.1.1)this name should be attributed to him and not to Guérin, namely Libinia spinosa H. Milne Edwards in Guérin, 1832.
The morphology of Libinia spinosa was first described by H. MILNE EDWARDS (1834: 301) and from his text it is clear (as it is from GUÉRIN's 1832 figures, see below) that at least one male and female were examined: "Une épine médiane sur les deux premiers segments de l'abdomen du mâle; pates [sic] de la seconde paire ayant une fois et quart la longueur de la carapace, et notablement plus longues que celles de la première paire, même chez le mâle."H. Milne Edwards did not provide illustrations of the male of L. spinosa he described, but instead referred to Guérin's fig.3, therefore suggesting that a male was depicted there: "L.spinosa.Edwards, Guérin, Icon.Cr.Pl. 9, fig.3." GUÉRIN-MÉNEVILLE's (1844: 9, 10) explanations for the figures published in GUÉRIN (1832: pl. 9, figs 3, 3a, 3b) made no references to the female: "3.Libinia spinosa.Edwards.";2.a.[sic] La bouche et l'épistome; 3.b.Queue du mâle."[male abdomen].However, GUÉRIN'S (1832: fig.3b) illustration shows a female abdomen instead.Clearly, at least one male and one female were illustrated by GUÉRIN (1832), namely the male figured in Guérin's figure 3 (as stated by H. MILNE EDWARDS 1834: 301) and the female illustrated in Guérin's figure 3b.In accordance with the provisions of the ICZN (1999: Art.73.2) the male and female specimens illustrated by GUÉRIN (1832: pl. 9, figs 3, 3a, 3b) are syntypes of Libinia spinosa H. Milne Edwards.The individual illustrated in GUÉRIN's Iconographie (1832: fig. 3) is herein fixed as the lectotype.Whether or not this specimen subsists or can be traced does not of itself have any bearing on this designation (ICNZ, 1999: Art. 74.4).The remaining type specimens are the paralectotypes.In the collections of the Muséum national d'Histoire naturelle, there is one dry male and female (MNHN-B4453) labeled "Libinia spinosa M. Edw., M. Freycinet, Brésil" .Although neither of which served as the basis for GUÉRIN's (1832: figs 3, 3b) illustrations, they most certainly belong in the type series of L. spinosa and are herein regarded as paralectotypes.Indeed, the dry male has one double and one single spine on the left and right sides of the carapace, respectively (Fig. 22) and the abdomen of the dry female is wide and rounded (Fig. 25).Neither of GUÉRIN's (1832: figs 3, 3b) illustrations show these characteristics.The dry specimens from the MNHN labeled "Libinia spinosa M. Edw., M. Freycinet, Brésil" were actually obtained in Rio de Janeiro.In 1817, the French government launched an expedition of circumnavigation and appointed Louis Claude de Saulses de Freycinet as Commander of the corvette "L'Uranie".Charles Gaudichaud-Beaupré, Jean René Constantin Quoy and Joseph Paul Gaimard embarked as naturalists and ship surgeons, respectively."L'Uranie" departed from Toulon in 1817 arriving in Rio de Janeiro on 6 December 1817.The expedition stayed in Rio de Janeiro for two months, where Gaudichaud-Beaupré, Quoy and Gaimard gathered large collections.From Rio de Janeiro, they crossed back the Atlantic towards the Cape of Good Hope and then headed to Mauritius and New Zealand.The expedition lasted 3 years and two months, and on its way back to France, stayed in Rio de Janeiro again (the only port visited in Brazil).From there it sailed to Le Havre, where it arrived on 13 November 1820 (PAPAVERO 1971: 124, 125).No specimens that can be attributed as the ones used in GUÉRIN's (1832) in his illustrations subsist in the collections of the MNHN, and thus the dry male and female (MNHN-B4453) might well be the only specimens left from an originally larger type series.
Libinia gibbosa A. Milne-Edwards, 1878, was very briefly described in a footnote based on a single young specimen from Desterro, Brazil (currently Florianópolis) (A.MILNE-EDWARDS 1878: 131).According to the provisions of the ICZN (1999: Art.73.1.2) that single specimen upon which A. MILNE-EDWARDS (1878) based his description is the holotype fixed by monotypy.In the collections of the MNHN, there is one young, dry female (MNHN-B385) labeled "M.F. Müller, Desterro (Brésil).Décrit dans une note de l'ouvrage du Mexique" (Figs 26, 27), which, therefore, is the holotype of L. gibbosa A. Milne-Edwards.No illustration of L. gibbosa has been published, nor has any additional description been made subsequent to A. MILNE-EDWARDS' (1878) footnote.RATHBUN (1925) synonymized L. gibbosa with L. ferreirae.She offered no reason for this synonymy probably because A. MILNE-EDWARDS (1878) compared L. gibbosa with L. spinosa only and made no references to L. ferreirae.Though RATHBUN (1925) mentioned that the type of L. gibbosa was in the MNHN, judging from her list of material examined she never saw it.Subsequent authors followed Rathbun in listing L. gibbosa under the synonymy of L. ferreirae.In the absence of illustrations of the only known specimen of L. gibbosa and from A. Milne Edwards' extremely brief notes alone, it is not possible to separate L. gibbosa from L. ferreirae or L. spinosa.Nevertheless, upon the examination of the illustrations of the holotype of L. gibbosa (Figs 26,27), it is clear that the posterolateral margins of the thoracic episternites IV-VII are rounded and unarmed, leaving no doubt that L. gibbosa is indeed conspecific with L. ferreirae.Both specimens also are similar in regards the carapace and orbital ornamentation.Adult and young individuals of L. ferrairae look somewhat different from each other.In larger individuals the carapace is more globose (Figs 6, 10), whereas in young individuals it looks more pear shape (Fig. 26), the same applying to L. spinosa.

Morphological differentiation between Libinia spinosa and L. ferreirae
Libinia spinosa and L. ferreirae inhabit very similar environments, and their geographic and bathymetric distributions overlap for about 3000 km along the southwestern Atlantic coast (from Espírito Santo, Brazil to Uruguay).Both species are commonly caught in the same haul and differentiating between them can often be difficult.H. MILNE EDWARDS (1834: 300, 301) proposed to separate the species of Libinia known to him into two groups according to the development of a process projecting from the anterolateral angle of the basal segment of the antenna.According to him, L. spinosa falls into the group with the angle of the basal segment of the antenna spiniform (Fig. 1).However, in L. spinosa the anterolateral angle of the basal antennal segment is actually variable, being either spiny or toothed (e.g., RATHBUN 1925: 310, MELO 1996).BRITO CAPELO (1871: 262, fig. 1, 1a) never described the antenna in L. ferreirae, but from his illustration of the holotype, partially redrawn here, it is clear that the anterolateral angle of the basal antennal segment is furnished with a prominent tooth (Fig. 2).In some individuals of L. ferreirae, however, the anterolateral angle of the basal antennal segment is very poorly projected (Fig. 3).The spinulation of the basal antennal segment led HELLER (1865) astray in describing a new species, Libidoclaea brasiliensis Heller, 1865, as previously mentioned, a junior synonym of Libinia spinosa H. Milne Edwards in Guérin, 1832.Heller's species was based upon the existence of an additional spine posterior to the outward projection of the anterolateral angle of the antennal basal segment (HELLER 1865: 1, table 1, fig. 1a).He was led amiss by GUÉRIN's (1832: plate 9, fig.3a) poor illustration of the anterior ventral region of the female holotype of L. spinosa, in which the posterolateral basal antennal spine is lacking.And yet, Guérin's illustration clearly shows that the anterolateral angle of the basal antennal segment is toothed on one side and spiny on the other side.The number of spines along the median, longitudinal line of the carapace has historically been used as well to differentiate between Libinia spinosa, with 7 median spines (Figs 4,8,22,24) RATHBUN 1925, TAKEDA 1983: 137, MELO 1996).Nevertheless, the number of median spines of the carapace can vary and it is not uncommon to encounter either males or females of L. spinosa with 5, 8 or 10 median spines (e.g., MZUSP 7375, 12091 and 14197, and 20271, respectively).Also, in some specimens of L. ferreirae there is a tubercle between the two anterior most median spines (RODRIGUEZ 1980: 282).Because Libinia spinosa and L. ferreirae can have similar numbers of median spines (7 and 6, respectively) and the number of median spines of the carapace and the process at the anterolateral angle of the basal antennal segment are variable, they are both of little value in separating L. spinosa from L. ferreirae.
Libinia spinosa can, however, be easily separated from L. ferreirae in having: (i) male and female thoracic episternites IV-VII armed with strong, posterolateral-projecting, broad teeth,    Garth & Méndez, 1983;L. rhomboidea Streets, 1870;L. setosa Lockington, 1877;and L. spinosa H. Milne Edwards in Guérin, 1832, all from either the Atlantic or Pacific coasts of the Americas.The taxonomy of L. spinosa and L. ferreirae is fully resolved herein, but further studies are necessary to elaborate on the taxonomy of the remaining eight species of the genus, with special reference to L. dubia, L. emarginata and L. erinacea.