Genus
Johngarthia Türkay, 1970
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TYPE SPECIES. —
Gecarcinus planatus Stimpson, 1860
, by original designation.
OTHER SPECIES. —
Johngarthia lagostoma (H. Milne Edwards, 1837)
;
J. malpilenis (Faxon, 1893)
;
J. weileri (Sendler, 1912)
;
J. cocoensis Perger, Vargas & Wall, 2011
.
DIFFERENTIAL GENERIC DIAGNOSIS
Gecarcinus
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and
Johngarthia
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are uniform with respect of selected characters: proepistome hardly discernible, inserted under the lower margin of narrow front ( Fig. 7D
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,
Gecarcinus ruricola
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; for
Johngarthia lagostoma
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see Tavares 1989: fig. 9, as
Gecarcinus
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; for
Johngarthia weileri
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see N. K. Ng et al. 2007: fig. 6H, as
Gecarcinus
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); male gonopore emerging far from P5 coxo-sternal condyle ( Fig. 7B, C,
G
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View FIG
. ruricola); for
J. planata
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(see Guinot 1979: fig. 54D; Ehrardt 1968, as
Gecarcinus
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; Guinot & Bouchard 1998: fig. 25A, as
Gecarcinus
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); for
J. weileri
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(see N. K. Ng et al. 2007: fig. 4H, as
Gecarcinus
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); sternite 1 as a small triangular tooth, not separated by suture from sternite 2; sternite 2 semi-ovate; suture 2/3 horizontal or V-shaped; no suture 3/4, without lateral trace; completely fused sternites 3 + 4 with straight, obliquely directed margins, thus not restricted at level of P1 ( Fig. 7B, C,
G
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View FIG
. ruricola); suture 7/8 rather short; sternite 8 not developed medially, the posterior emargination reaching sternite 7 at level of very a narrow median bridge at level of suture 7/8; another weak median bridge at level of suture 6/7 ( Fig. 7B, C,
G
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View FIG
. ruricola), or only some traces of such bridges (
G. lateralis
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,
G. quadratus
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), or indistinct bridges (
Johngarthia
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); deep median line only sternite 7 ( Fig. 7B, C,
G
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View FIG
. ruricola). No exposed portion of sternite 8 when pleon is folded.
Johngarthia
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differs from
Gecarcinus
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by the already known traits ( Türkay 1970; Cuesta et al. 2007; Perger et al. 2011) and by the locking structures. Instead of a button covered by setae in
Gecarcinus ruricola
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( Fig. 7B
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) and
G. quadratus
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(see Köhnk et al. 2017: fig. 19c, d), there is a large, oblique prominence covered by setae in
Johngarthia
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( Guinot & Bouchard 1998: fig. 25A, as
G. planatus
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); but in both genera the pleonal sockets are not delineated, so the locking is no longer functional.
A stridulatory apparatus characterises species of
Johngarthia
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and
Gecarcinus
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, but it is quite distinct from those of
Leptograpsodes
( Figs 1G
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; 2C, D
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),
Discoplax
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( Figs 6A
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; 11A
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) and
Epigrapsus
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, all three with a suborbital pars stridens and a plectrum on cheliped merus. Oblique rows of tubercles on the subhepatic region are rubbed by the tuberculated cheliped merus in
G. quadratus
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and by the cheliped palm in
G. lateralis
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(see Klaassen 1973: figs 5, 6; Abele et al. 1973: fig. 1; Davie et al. 2015a). It was shown that in
G. lateralis
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stridulation was part of communication system transmitted by substrate vibration ( Klaassen 1973).
In
Gecarcinus
and
Johngarthia
the pterygostomial region is glabrous. Setal tufts of dense setae are located along the first pleonal somites instead of between the pereiopods ( Rathbun 1918: figs 163, 165).