PLAGUSIIDAE Dana, 1851

Guinot, Danièle, Ng, Ngan Kee & Rodríguez Moreno, Paula A., 2018, Review of grapsoid families for the establishment of a new family for Leptograpsodes Montgomery, 1931, and a new genus of Gecarcinidae H. Milne Edwards, 1837 (Crustacea, Decapoda, Brachyura, Grapsoidea MacLeay, 1838), Zoosystema 40 (26), pp. 547-604 : 576-578

Family PLAGUSIIDAE Dana, 1851

INCLUDED GENERA. — Plagusia Latreille, 1804 ; Davusia Guinot, 2007 ; Guinusia Schubart & Cuesta, 2010 ; Euchirograpsus H. Milne Edwards, 1853 ; Miersograpsus Türkay, 1978.

REMARKS

The Plagusiidae , traditionally treated as a subfamily of Grapsidae and comprising five genera ( Euchirograpsus and Miersograpsus are not studied here), was raised to full family status by Sternberg & Cumberlidge (1998), Schubart & Ng (2000) (see also Cuesta & Schubart 1998; Davie 2002; Schubart et al. 2000b, 2002; Guinot 2007; N. K. Ng et al. 2007; Schubart & Cuesta 2010; Davie et al. 2015c). The genus Percnon was removed from the Plagusiidae and finally recognised as a separate family, Percnidae , by Schubart & Cuesta (2010). Species of Plagusiidae , from rocky shores or on exposed reefs ( Alcock 1900; Rathbun 1918; Dawson 1987; Emmerson 2016), are able to extensively swim (sideways swimming) thanks to specialised modifications: on the postero-dorsal regions of carpi, propodi and dactyli of P2-P5, dense fringes of long pinnate setae can stand erect for the propulsive stroke or lie flat for the forward recovery stroke; their swimming method gave them the name of “rafting crabs” ( Hartnoll 1971: 44, figs 6b, 9A-C).

ADDITIONAL STERNAL AND MALE GENITAL CHARACTERS Whereas the traditional differentiating characters of Plagusiidae are well established, sternal and male genital features must be documented. Proepistome either roughly triangular and prolonged inside median frontal incision (N. K. Ng et al. 2007: fig. 6D), or shorter, blunt and not deeply inserted into front. Thoracic sternum subcircular ( Fig. 8J, K ) ( Schubart & Ng 2000: fig. 1D; Naderloo 2011: fig. 18f). Sternite 1 (narrow, triangular) and sternite 2 (of variable size and shape) forming a variously shaped, single piece located at a more or less lower level, but presence of suture 1/3, lined by setae. Suture 2/3 well marked, straight or curved. Sternites 3 and 4 completely fused without external mark, being only crossed medially by thick row of setae. Posterior emargination on sternite 8 low ( Plagusia , Davusia and Guinusia ). Sternite 8 wide, developed, exposed medially ( Fig. 8L ). Median line extending on sternite 8 and 7. (It should be noted that a long median line is already present [from somite 8 to 5] in the megalopa of Guinusia dentipes , as shown by Gonzáles-Gordillo et al. [2000: fig. 1C]). Male gonopore ( Fig. 8L ), in posteriormost location in relation to sternite 8, and penis very close to P5 coxa; however, junction of episternite 7 with sternite 8, thus gonopore separated: Plagusia depressa (Fabricius, 1775) (see H. Milne Edwards 1834, 1837, 1844, Atlas, pl. 23, fig. 3d; Guinot 1979: 209, fig. 52E), P. squamosa (see N. K. Ng et al. 2007: fig. 4C), Guinusia dentipes (see Karasawa & Kato 2001: fig. 2.17, as P.dentipes ), and Davusia glabra (see Guinot 1979: pl. 18, fig. 9, as Plagusia glabra ; 2007: 29); Guinot et al. 2013: figs 23B, 33B, C). Penis short, consisting of wide sclerotised portion and small papilla. Presence of strong, efficient press button, with remarkable microstructure, likely functional throughout life in females ( Guinot & Bouchard 1998: 678, 680, figs 23D, 26F). Vulva with operculum, of varying complexity (see Guinot et al. 2013: 48; McLay & Sal Moyano 2016). Pleonal somites 3-5 fused, but sutures still evident.

MOLECULAR ANALYSIS AND LARVAL MORPHOLOGY

Based on a molecular analysis and larval morphology, three main phylogenetic clusters have been recognised by Schubart & Cuesta (2010): Davusia , phylogenetically basal to other plagusiids; another cluster including P. depressa (type species), P. squamosa , P. immaculata Lamarck, 1818 , and P. speciosa Dana, 1852 ; a third cluster consisting of the two species of Guinusia , G. chabrus and G. dentipes .

We do not find any close similarities between Plagusiidae and Leptograpsodidae n. fam .

Figures

FIG. 8. — Pleon, thoracic sternum and genital region of Grapsoidea: A, D, G, J, M, thoracic sternum (brushed) with pleon; B, E, H, K, N, thoracic sternum (brushed) without pleon; C, F, I, L, O, genital region with gonopore and penis: A-C, Grapsidae: Grapsus grapsus Lamarck, 1801, ♂ 23.8 ×26.9 mm, Antilles, MNHN-IU-2013-10764 (=MNHN-B24641);D-F, Glyptograpsidae:Glyptograpsus jamaicensis (Benedict,1892),♂ 32.8 ×37.4 mm,Jamaica,MNHN-IU-2017-8401 (= MNHN-B127715); G-I, Percnidae: Percnon planissimum (Herbst, 1804), ♂ 29.7× 27.7 mm, Réunion Island,MNHN-IU-2010-19798 (=MNHN-B24534);J-L, Plagusiidae: Plagusia squamosa (Herbst, 1790), ♂ 43.6 ×46.3 mm, Marquesas Islands, MNHN-IU-2011-8947; M-O, Xenograpsidae: Xenograpsus testudinatus N. K. Ng, Huang & Ho, 2000, ♂ 21.8 ×23.8 mm, NE Coast of Taiwan, MNHN-IU-2013-14995 (= MNHN-B30314). Scale bars: 10 mm.