Grapsidae MacLeay 1838
Creators: name: Guinot, Danièle
name: Ng, Ngan Kee
name: Rodríguez Moreno, Paula A.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Grapsidae

description: Family GRAPSIDAE MacLeay, 1838
INCLUDED GENERA. — Geograpsus Stimpson, 1858; Goniopsis De Haan, 1833; Grapsus Lamarck, 1801; Leptograpsus H. Milne Edwards, 1853; Metopograpsus H. Milne Edwards, 1853; Pachygrapsus Randall, 1840; Planes Bowdich, 1825.
REMARKS
Morphological comparison of Leptograpsodidae n. fam. with the family Grapsidae suffers from the lack of a consistent familial diagnosis for Grapsidae. In using the traditional and recently published grapsid morphological characters (Banerjee 1960; Guinot & Bouchard 1998; Poore 2004; N. K. Ng et al. 2007; Davie et al. 2015a; Köhnk et al. 2017), we propose the diagnostic features of the family, essentially based on the type species of all genera. The question whether some distinctive features warrant the separation of Grapsidae into subfamilies is not the topic of our study.
DIAGNOSIS
Carapace typically quadrilateral to quadrate; surface moderately flat, usually with marked striae, especially on branchial regions (Banerjee 1960: figs 1a-e, 5; Naderloo 2017: fig. 30.1), exceptionally faint in Planes (Chace 1951: table 1); anterolateral margins entire or with one, may be two, teeth behind exorbital angle; front wide, much broader than orbits, entire, strongly deflexed, widely overhanging epistome between short eyestalks; suborbital margin running vertically from orbital angle to meet end of suborbital crest directly, no overlap (N. K. Ng et al. 2007: fig. 5B); basal article of antenna immobile, bent; orbit small, open laterally; mxp3 leaving rhomboidal gape; both mxp3 merus and ischium with single longitudinal sulcus and lacking oblique setose crest (N. K. Ng et al. 2007: fig. 7D; Davie et al. 2015a: fig. 71- 2.27N); flagellum of exopodite usually present, may be strongly reduced or absent (Geograpsus); absence of stridulatory suborbital crest; pterygostomial region sparingly setose, with setae simple, plumose, never arranged in reticulated pattern; male chelipeds homochelous (except in Metopograpsus, merus usually with developed spines on anterodistal margin, fingers apically spoon-shaped; walking legs robust, distinctly flattened, usually armed with spines and bristles; mobile setae on dactylus of P2-P5; sterno-pleonal cavity without rim at level of telson, may be a faint rim; male gonopore next to articular membrane adjacent to P5 coxa (sternal emergence being proved by dissection), and opening in middle of sternite 8 thus far from suture 7/8 (except in Planes); penis elongate, narrow (e. g. Grapsus) or wide, short (e.g. Metopograpsus), partially calcified; G1 short, sinuous or slightly curved, even twisted, usually with dense setae on apical part; pleon with six free somites plus telson; pleonal-locking mechanism of press-button type always present (but absent in Geograpsus), functional throughout life, usually very marked, close to suture 5/6 or slightly remote (Goniopsis), with round or acute buttons, exceptionally developed and half-moon-shaped (Metopograpsus); small but distinct socket usually next to intestine (Hartnoll 1965; Guinot & Bouchard 1998: fig. 22; Köhnk et al. 2017: figs 16, 17); vulva with operculum (McLay & Sal Moyan 2016). Tufts of hydrophilic setae generally lacking, but may be present between P3/P 4 in some species of Grapsus, in Goniopsis, Metopograpsus, Pachygrapsus (Oliveira 2014: table 2) and chiefly in Geograpsus, the single terrestrial grapsid species (Greenaway 1988: fig. 7.2.B-D; Paulay & Starmer 2011).
ADDITIONAL CHARACTERS
For the sternal and male genital characters of Grapsidae that must be added, our diagnosis is based on the type genus Grapsus and its type species G. grapsus, but we have extended our study to numerous other genera.
Proepistome as a broad, more or less narrow, anteriorly convex (Grapsus) or straight (Goniopsis) septum, meeting frontal margin (Banerjee 1960: figs 2h, o, 4d; Komai et al. 2004: fig. 2B; N. K. Ng et al. 2007: fig. 6B; Bouchard et al. 2013: fig. 20D, F). Thoracic sternum wide (Fig. 8A, B) (Guinot & Bouchard 1998: fig. 22A-C); sternites 1-2 fused forming a small, more or less triangular plate, a trace of their separation may be however recognisable by a ridge or faint sulcus, lined by setae; suture 2/3 complete (Banerjee 1960: figs 1f, 4a, i); sternite 3 completely fused to sternite 4 without indication of a dorsally visible demarcation, thus absence of any suture 3/4; sutures 4/5-7/8 incomplete; sternite 7 with incomplete sulcus; suture 6/7 more obliquely directed forwards in Metopograpsus and Leptograpsus; episternite 7 variously shaped, for example extending posteriorly on the P5 coxa in Goniopsis (see Guinot 1979: fig. 52B); posterior emargination weak; sternite 8 very developed, largely exposed medially; no portion visible dorsally when the pleon is closed; suture 7/8 rather long, however shorter than preceding ones; median line long, present on sternite 8 and extending on sternite 7 (Fig. 8B, C: Grapsus grapsus) (Guinot & Bouchard 1998: fig. 22A: G. tenuicrustatus Herbst, 1783; fig. 22B, D: Metopograpsus latifrons). No medial bridge.
A male gonopore opening in the middle of sternite 8, thus far from suture 7/8, with a clear posteriormost location in relation to suture 7/8, occurs in all Grapsidae (Guinot 1979: fig. 52A) except in Planes. The penis emerges as a very thick, cylindrical tube (Fig. 8C) (Guinot 1979: fig. 52A-C; Sternberg et al. 1999; Karasawa & Kato 2001: fig. 2.19; N. K. Ng et al. 2007: fig. 4D; Guinot et al. 2013: fig. 23D), sometimes with a calcified proximal portion (e.g. in Metopograpsus). This pattern of genital disposition is shared by all examined genera, except by Planes (e.g. P. minutus), in which the gonopore is close to suture 7/8, the penis is short, lodged in a depression below suture 7/8, with only a tiny, hardly visible, sclerotised basal portion (Guinot 1979: fig. 52C).
Grapsids may swim; few of these do so extensively and exhibit significant swimming morphological adaptations, except species of Planes, which are wholly pelagic, clinging to floating marine animals such as sea turtles (Frick et al. 2011), and show fringes of setae on pereiopods for swimming ability (Hartnoll 1971: fig. 6d).
Leptograpsodidae n. fam. shares with Grapsidae: four postfrontal lobes, oblique striae on branchial regions, oblique ridges on the lateral surfaces of meri of P2-P5, an effective pleonal-locking mechanism, especially in Grapsus, in which the buttons on sternite 5 are generally acute (Köhnk et al. 2017: fig. 16a).
COMPARISON WITH LEPTOGRAPSODIDAE N. FAM.
Leptograpsodidae n. fam. (Figs 1-3) differs from Grapsidae by: the shape of carapace with strongly convex margins, the proepistome obviously inserted into the frontal margin, the pleonal sockets close to the border of pleonal segment 6 (vs close to the intestine and not bordered by lateral edge of the pleon in Grapsidae, Köhnk et al. 2017: figs 16, 17). Another distinctive feature is the persistence of the locking mechanism in adult females of Leptograpsodes (at least until cw carapace 20.6 mm), whereas it is lost in adult female grapsids. Pouches with tufts of hydrophilic setae are present between all pereiopods (generally absent in Grapsidae or, when present, only between P3/P4 such as in the terrestrial Geograpsu s).
The main sternal features that differentiate Leptograpsodidae n. fam. from Grapsidae are: thoracic sternum less widened; sternite 1-2 individualised with suture 1/2 present (no suture 1/2 or only a sulcus or ridge in Grapsidae); a bridge at level of suture 6/7 (absent in Grapsidae); sternite 8 not developed, unexposed medially, no median line at this level (much expanded and largely exposed medially, with median line on sternite 8, in Grapsidae); a small portion of sternite 8 and also a tiny proximal part of penis dorsally visible when pleon is folded (not visible in Grapsidae); sterno-pleonal rim at level of telson rather thick (no rim or only faint rim in Grapsidae).
Leptograpsodidae n. fam., the first gecarcinid subclade (Cardisoma, Discoplax and Tuerkayana n. gen.) and Grapsidae share the same pattern of the genital region, except that the penis of Grapsidae, instead to be basally wedged above the P5 coxo-sternal condyle, is fully developed at its exit.
Previously suggested (Cuesta et al. 1997; Schubart et al. 2006; Schubart & Cuesta 2010) but also questioned (Kitaura et al. 2002; Wetzer et al. 2009), the monophyly of Grapsidae (Leptograpodes being excluded) was confirmed by Ip et al. (2015: figs 1-3) based on five molecular markers, including mitochondrial DNA and nuclear protein-coding markers. These results, which corroborated the 2011 Schubart’s anlysis, showed with strong support: a paraphyletic Pachygrapsus (see also Wetzer et al. 2009; Schubart 2011; van der Meij & Schubart 2014); a paraphyletic Planes; Metopograpsus with clear differences in the number of zoeal stages (only 5) and also with distinctive morphological characters, so its basal position in the family (Cuesta et al. 2011: table 3; Landeira & Cuesta 2012; see also van der Meij & Schubart 2014). According to genetic studies, Metopograpsus was subdivided into two main clusters: the sister species M. thukuhar and M. messor on the one hand, and the remaining four species on the other (Fratini et al. 2018: fig. 2). From their phylogenetic tree, Wang et al. (2018a: fig. 1) found that M. quadridentatus Stimpson, 1858 and (Grapsus tenuicrustatus [Grapsus tenuicrustatus (Herbst, 1783) + Pachygrapsus crassipes] clustered in one branch with high nodal support value.
LARVAL CHARACTERS
From a larval point of view, the grapsids were divided into two groups: 1) a first group, weakly supported, consisting of the monophyletic Goniopsis and a big cluster of all the Grapsus species together with three species of Pachygrapsu s; 2) a second group that was a large assemblage of the remaining genera, e.g. the monophyletic Geograpsus, the monotypic Leptograpsus that branched off as a distinct clade, and all other species of Pachygrapsus (including the type species P. crassipes).
description: Published as part of 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), pp. 547-604 in Zoosystema 40 (26) on pages 572-574, DOI: 10.5252/zoosystema2018v40a26, http://zenodo.org/record/4336858