Dardanus crassimanus (H. Milne Edwards 1836 )

Celia, Maria, Malay, D., Miller, Allison K. & Komai, Tomoyuki, 2021, Hermit crabs (Crustacea: Decapoda: Anomura: Paguroidea) of the Northern Marianas, including new records and an updated checklist, Micronesica 2021 (1), pp. 1-29 : 9-10

Dardanus crassimanus (H. Milne Edwards 1836)

Material. 1 male, SL 3.3 mm ( UF 8614 ), Anatahan Island , station ANA-001 ; 1 female, SL 3.1 mm ( UF 8617 ), Anatahan Island , station ANA-003 ; 1 female, SL 3.5 mm ( UF 8615 ), Anatahan Island , station ANA-006; 1 ovigerous female, SL 4.6 mm and 1 male, SL 3.5 mm ( UF 8612 ), Pagan Island , station PAG-07 ; 1 female, SL 3 mm ( UF 58289 ), Agrihan Island , station AGR-003 ; 1 female, SL 3.5 mm ( UF 7447 ), Agrihan Island , station AGR-03 ; 1 female, SL 3.7 mm ( UF 8613 ), Agrihan Island , station AGR-06 ; 1 female, SL 5.1 mm ( UF 8611 ), Asuncion Island , station ASU-002 ; 2 females, SL 3.1-3.9 mm and 1 specimen still in shell ( UF 8618 ), Maug Islands , station MAUG-03 ; 1 male, SL 3 mm ( UF 8616 ), Maug Islands , station MAUG-02 ; 1 male, SL 6.2 mm ( UF 8619 ), Uracas Island , station URA-004 .

Additional material. 1 ovigerous female, SL 6.0 mm, 2 females, SL 3.6-4.4 mm, 1 male, SL 4.1 mm ( UF 33241 ), Asuncion Island , collected by D. Wooster 07/08/1975 ; 1 female, SL 6.0 mm ( UF 33234 ), Anatahan Island station 3, collected by D. Wooster 01/17/1975 .

Remarks. Dardanus crassimanus is usually identified on the basis of the distinctively tessellated margins on the lateral face of the left third pereopod propodus and dactyl, with a broad ridge on the propodus, a wide and deep sulcus traversing the propodus and dactyl, and a dense fringe of setae on the margins of the propodus and dactyl ( McLaughlin et al. 2007). The species is similar to Dardanus setifer , but D. setifer bears corneous-tipped spines on the ridge of the left third pereopod propodus and along each of the dorsal and ventral margin tessellations, characters lacking in D. crassimanus ( McLaughlin et al. 2007) . Moreover, D. crassimanus has long and dense setae on the left cheliped, while setae on the left cheliped are short and arranged in a rosette-like manner in D. setifer (Rahayu & Wahyudi 2007) . Another similar species is D. scutellatus , which differs in having an elongate palm of the left cheliped covered in short, stiff setae ( Malay et al. 2018).

The specimens from the Northern Marianas agree generally with D. crassimanus , however some differences were noted in the sculpturing and armature of the left third pereopod propodus and dactyl, particularly along the dorsal and ventral margin tessellations. In the Marianas specimens, the margins of the tessellations are sometimes less deeply incised and less regular in appearance than in McLaughlin et al. (2007), or sometimes the tessellations resemble short projections that are separated from each other and bear strong spines. The mid-propodus ridge was also variable in development. Moreover, the cheliped is not as setose as in specimens from Japan and Taiwan (cf. Miyake 1978, 1982; McLaughlin et al. 2007). A prominent fleshy protuberance between the third and fourth pleopods in adults of both male and female in D. crassimanus was noted by Miyake (1978: Japanese text, p. 59; 1982: 110). This structure was found in the Marianas specimens, however the degree of development varied from a short flap of chitinous membrane to a stout or elongate fleshy protuberance.

The present specimens from Marianas are much smaller in the body size than specimens from Japan and Taiwan. The latter specimens are quite large, exceeding 15 mm in the shield length ( Miyake 1978; McLaughlin et al. 2007). Wooster (1979) reported two color variants in the Marianas, a light form and a dark form. He also noted, and we corroborate, that D. crassimanus is common in the Northern Marianas yet uncommon in the Southern Marianas. Dardanus crassimanus is likely a species-complex, and careful comparison with the type material, including those of the synonymized taxa ( Pagurus sculptipes Stimpson 1858 ; Pagurus pavimentatus Hilgendorf 1879 ), combined with molecular work on topotypic material, will be needed to delineate the species boundaries.