Hemigrapsus penicillatus (De Haan, 1835)

Hemigrapsus penicillatus (De Haan, 1835) View in CoL # ( Fig. 40C, D View Fig , inset)

? Heterograpsus penicillatus View in CoL — Stimpson 1858b: 104 [part: Hong Kong material only]; Stimpson 1907: 126 [part: Hong Kong material only].

? Brachynotus penicillatus View in CoL — Koelbel 1897: 712, pl. 1(5, 6); Gordon 1931: 552.

? Hemigrapsus penicillatus View in CoL — Gee 1926: 164; Shen 1940a: 237; Morton and Morton 1983: 246, fig. 11.18(13); VCS Lai et al. 2006: 57, 3 unnumb. figs.

Hemigrapsus penicillatus View in CoL — Bravo et al. 2021: tab. 2; present record.

Taxonomy: Asakura and Watanabe (2005), Mingkid et al. (2006).

Type: Lectotype ò RMNH D 200, and paralectotypes in RMNH and MNHN (designated by Yamaguchi and Baba 1993; see also Fransen et al. 1997); the type lots contain individual(s) of H. takanoi ( Asakura and Watanabe 2005) .

Type locality: Japan, locality unspecified.

Distribution: East Asia: verified from various localities in Taiwan, Japan, Korea and Pacific coast of Russia ( Asakura and Watanabe 2005; S Lee et al. 2013; Marin 2013; Ng et al. 2017a); possible distribution in China remains to be verified; and doubtfully from Hawaii ( Castro 2011).

Habitat: Intertidal; under boulders on mudflats, estuaries, lagoons and sheltered beaches ( Asakura and Watanabe 2005).

Remarks: Past records under the name Hemigrapsus penicillatus (De Haan, 1835) were demonstrated by Asakura and Yamaguchi (2005) to consist of H. penicillatus sensu stricto and the morphologically similar H. takanoi Asakura & Yamaguchi, 2005, both species originally described from Japan. These two species differ more consistently, in larger males, by the size of setal patch in relation to the chela, and configuration of pigmentation on external maxillipeds, pterygostomian region, and, in some cases, the anterior thoracic sternites and pleon (see also Mingkid et al. 2006; Marin 2013).

Using these criteria to examine the local material, we also recognize two subtly distinct forms: from eastern sites (e.g., in vicinity of Tolo Channel) where the setal patch on the male chela is relatively smaller, being approximately half of the chela height ( Fig. 40D View Fig inset), the chela is externally covered by sparse dark dots with those on the third maxillipeds and pterygostomian regions slightly larger ( Fig. 40D View Fig ); whereas material from western sites (e.g., around Lantau Island), have a comparatively larger setal patch on the male chela and the external surface is grayish but not spotted ( Fig. 40F View Fig inset), with the third maxillipeds and pterygostomian region covered with relatively smaller dark dots ( Fig. 40F View Fig ). This distinctness of both forms is supported by preliminary molecular results (HTS, unpublished data).

These two forms are tentatively identified as H. penicillatus (eastern: Fig. 40C, D View Fig , inset) and H. takanoi (western: Fig. 40E, F View Fig , inset). They, however, differ slightly from their respective Japanese and Northeast Asian counterparts. For H. penicillatus , the local form had never been observed to be decorated with dark round spots as large, and the dark spots do not extend to the anterior thoracic sternites and pleon, as shown by Asakura and Yamaguchi (2005: figs. 8–10) and Marin (2013: fig. 2). As for H. takanoi , the local form has a relatively inflated chela palm with the external surface unspotted (vs. less inflated with with numerous scattered small dark dots; Asakura and Yamaguchi 2005: fig. 3; Marin 2013: fig. 1). As such, more morphological and molecular investigations are needed to be done on these two taxa in Hong Kong.