Dardanus aspersus ( Berthold, 1845 )

Osawa, Masayuki, 2013, Identity of Pagurus watasei (Crustacea: Decapoda: Anomura: Paguroidea), Species Diversity 18 (1), pp. 39-44 : 39-43

Dardanus aspersus ( Berthold, 1845)

( Figs 1 , 2 )

Pagurus aspersus Berthold, 1845: 45 (type locality: China); 1846: 21, pl. 2, fig. 1.

Pagurus diogenes .—De Haan 1849: 208; Terao 1932, pl. 57, fig. 2. [not Cancer diogenes Linnaeus, 1758 (= Petrochirus diogenes (Linnaeus, 1758) ]

Pagurus watasei Terao, 1913: 380 , text-fig. 3. [type locality: Komenotsu , Satsuma (now located in Izumi City, Kagoshima Prefecture, Kyushu, southern Japan)]

Dardanus diogenes .— Gee 1925: 159; Miyake 1965: 644, fig. 1080.

Dardanus aspersus .— Holthuis and Sakai 1970: 96; Miyake 1978: 64, text-fig. 23, pl. 1, fig. 2; 1982: 109, pl. 37, fig. 2; 1998: 109, pl. 37, fig. 2; Yamaguchi and Baba 1993: 275, fig. 74; Asakura 2006: 34, figs. 27, 28; McLaughlin et al. 2007: 96, 2 unnumbered figs.

Material examined. Komenotsu, Satsuma , 20 April 1896, collected by Mitsukuri and Hara, holotype of Pagurus watasei , female (cl 16.7 mm), UMUTZ-Crs-33 . No locality and date records, collected by Tokyo Higher Normal School, 1 male (cl 14.0 mm), UMUTZ-Crs-c110 . Nagasaki Prefecture, 1912, collected by Kaneko, 1 ovigerous female (cl 13.5 mm), UMUTZ-Crs-c112. Nagasaki Prefecture, 1 male (cl 13.6 mm), UMUTZ-Crs-c195 .

Redescription of holotype of Pagurus watasei . Shield ( Fig. 1A, B ) approximately as long as broad; dorsal surface with tufts of stiff setae laterally and broad, U-shaped suture on posteromedian part; anterolateral margins terraced. Rostrum broadly triangular, nearly reaching tips of blunt lateral lobes.

Ocular peduncles ( Fig. 1B ) slightly depressed dorsoventrally, stout, 0.6 of shield length; corneas somewhat dilated, broader than bases of peduncles, 0.4 of peduncular length; ocular acicles subquadrate, each with 3 or 4 small spines on anterior margin.

Antennular peduncles ( Fig. 1B ) slightly overreaching distal corneal margins.

Antennal peduncles ( Fig. 1B ) slender, overreaching bases but not reaching distal margins of corneas; antennal acicle slender, overreaching base of fifth peduncular segment, terminating in small bifid spine, mesial margin with row of small spines partially obscured by stiff setae.

Carpus of third maxilliped with 2 tiny spines on distal half of ventral margin.

Left cheliped ( Fig. 1C ) massive, appreciably larger than right. Chela broadly subovate in general outline, 1.4 times longer than wide; outer surface convex, covered with numerous short tubercles each bearing sharp corneous spinule and tuft of short, stiff setae; fingers without hiatus, each with row of blunt teeth and terminating in small, plate-like claw. Dactylus slightly longer than palm. Palm with row of small corneous-tipped spines on upper margin and row of blunt spines on lower margin. Carpus with sparse small spines on outer surface; upper margin with row of moderately large, sharp, corneous-tipped spines increasing in size distally. Merus with row of small spines on ventromesial and on ventrolateral margin, ventromesial spines pronounced.

Right cheliped ( Fig. 1D ) short. Chela elongate subtriangular in general outline, 1.9 times longer than wide; fingers without hiatus, each with row of blunt teeth and terminating in large, plate-like claw. Dactylus about 1.3 times as long as palm; outer surface with small tubercles near upper margin, each tubercle bearing corneous spinule and tuft of stiff setae. Palm slightly convex on outer face, covered with short, transverse ridges each bearing tuft of short, stiff setae, ridges near upper and lower margins and on fixed finger with 1 or 2 corneous spinules each; upper margin with row of sharp corneous-tipped spines; lower margin nearly straight, rounded. Carpus with small corneous-tipped spines on upper side and short, transverse ridges on lower side of outer surface; upper margin with row of moderately large, sharp corneous-tipped spines. Merus also with row of small corneous-tipped spines on ventromesial margin; ventrolateral margin distally with 2 small corneous-tipped spines.

Ambulatory legs ( Fig. 2A, B ) relatively short; second pereopods generally similar on right and left sides but third pereopods noticeably dissimilar to each other (dactylus, propodus, and carpus of left third pereopod stouter and with stronger armature than those of right); most spines corneous-tipped and most tubercles bearing slender corneous spinule; tufts of short and long stiff setae present on spines, tubercles, and ridges, particularly numerous on left third pereopod. Dactyli 1.3 (right second pereopod)–1.6 (left third) times longer than propodi, lengths 7.2–7.3 (right and left second), 8.4 (right third), and 4.9 (left third) times respective proximal widths; dorsal margins each with row of small spines; lateral and mesial surfaces flattened, each with shallow longitudinal sulcus on midline, on left third pereopod, lateral surface also with scattered rounded and low tubercles. Propodi 2.8 (right second and third pereopods), 3.0 (left second), and 2.0 (left third) times respective proximal widths, somewhat tapering distally and convex ventrally; dorsal, lateral, and ventral surfaces of right second, left second, and right third pereopods with occasionally granulate, short, transverse ridges (dorsal ridges each with 1 or 2 corneous spinules), but on left third pereopod, dorsal surface with irregular, longitudinal double row of small spines, lateral surface with 4 longitudinal rows of tubercles, ventral margin with row of blunt spines; lateral surface of left third pereopod flattened, but those of right second, left second, and right third slightly convex. Carpi each with dorsal row of small spines, but on right third pereopod, these reduced in size; lateral surfaces each with median row of short transverse ridges, distal ridges denticulate on left third pereopod. Meri unarmed on dorsal margins; lateral surfaces with short, sparse transverse ridges; ventral margins with some tiny spines or protuberances, these pronounced on left third pereopod, but obsolete on right third.

Fourth pereopods ( Fig. 2C ) semichelate. Dactyli distinctly longer than palm, each with dorsal row of small corneous-tipped spines; preungual process absent. Propodi each with small, corneous-tipped spine near dorsodistal end; rasp well developed, consisting of numerous small, subovate scales. Carpi each with dorsal row of sharp, corneous-tipped spines.

Sixth thoracic sternite with anterior lobe narrow, rounded, and with tuft of stiff setae anteriorly.

Second to fifth pleomeres ( Fig. 1A ) with unpaired left pleopods; second to fourth pleopods well developed, triramous; fifth pleopod short, biramous, with endopod greatly reduced in size; short, subtriangular plate present between fourth and fifth pleopods. Sixth pleonal tergite ( Fig. 2D ) unarmed, widened posteriorly, approximately as long as wide, divided into 2 parts by distinct transverse groove crossing at nearly half length; lateral indentations narrow; posterior part with deep median groove. Telson ( Fig. 2D ) with posterior lobes broadly subtriangular, unequal (left lobe larger), separated by narrow median cleft; terminal margins strongly oblique, each with 6 or 7 small corneous-tipped spines extending onto lateral margins.

Coloration. See Miyake (1978: 65, pl. 1, fig. 2; 1998: pl. 37, fig. 2) and McLaughlin et al. (2007: 97, unnumbered fig.).

Distribution. Boso Peninsula and Toyama Bay southward on both coasts of Honshu and Kyushu in Japan, Taiwan, East and South China Seas, Andaman Sea; 20–50 m ( McLaughlin 2002; Asakura 2006).

Habitat. Gastropod shells, often encrusted with sea anemones, on sandy-mud substrates ( McLaughlin et al. 2007).

Remarks. The holotype of Pagurus watasei agrees well with the previous descriptions of Dardanus aspersus (e.g., Miyake 1978, 1998; McLaughlin et al. 2007) in every diagnostic aspect, particularly in the stout ocular peduncles with dilated corneas, the markedly unequal chelipeds with the left chela covered with numerous tubercles each bearing a corneous spinule, and the flattened lateral surfaces of the dactylus and propodus of the left third pereopod. Terao (1913) described the coloration of his material of Pagurus watasei preserved in alcohol and formalin, and this is also consistent with that reported for Dardanus aspersus (e.g., Miyake, 1998: 111, pl. 38, fig. 2; McLaughlin et al. 2007: 96, unnumbered fig.) in the presence of numerous red spots on the carapace, pleonal tergites, and pereopods, darker coloration on the dactyli of the ambulatory legs than on their proximal segments, and a broad purple band on the median part of each ocular peduncle; the characteristic color pattern of the ocular peduncle is still preserved in the holotype of Pagurus watasei . Thus, this taxon is considered to be identical with Dardanus aspersus and is placed in the synonymy of that species.

In addition to the holotype of P. watasei , three other specimens identified with this taxon by Terao were examined, although one of them (UMUTZ-Crs-c112) was not included in Terao’s (1913) description. One male (UMUTZ-Crs-c195) is now in poor condition (dry and partially fragmental), but the other two specimens are still in good condition and preserved in ethanol. As in the holotype, these two specimens display the diagnostic characters of Dardanus aspersus , including the broad purple band on the median part of each ocular peduncle.

De Haan (1849) reported Pagurus diogenes Fabricius, 1775 [as Fabricius, 1798; = Petrochirus diogenes (Linnaeus, 1758) ; cf. McLaughlin and Holthuis (2001)] from Japan and included Pagurus aspersus in the synonymy of that species. As was discussed at some length by McLaughlin and Holthuis (2001), De Haan’s (1849) misinterpretation led numerous subsequent authors to identify Dardanus aspersus with Pagurus diogenes or Dardanus diogenes . De Haan’s material is unquestionably referred to Dardanus aspersus as shown by Yamaguchi and Baba (1993: 275, fig. 74). Terao (1913) listed Pagurus diogenes in the catalogue of Japanese hermit crabs, although there was no material referred to that taxon available for his examination at that time, and he remarked that P. watasei was closely similar to P. diogenes , but distinguishable by the relatively longer left chela. Terao (1932: pl. 57, fig. 2) subsequently provided a color illustration of P. diogenes with a short description, both of which agree well with Dardanus aspersus , furthermore, the illustration shows the left chela as being much larger than that of the holotype of P. watasei . In the second description of D. aspersus, Berthold (1846 : pl. 2, fig. 1) had also given an illustration showing a similarly proportioned large left chela. These facts suggest that Terao (1913) misinterpreted the comparative sizes of the left chelae of Pagurus watasei and P. aspersus (as P. diogenes ). Nevertheless, such a difference can often be attributed to intraspecific variations; chela size generally varies to some degree in hermit crab species, particularly between males and females (for Dardanus aspersus , cf. Miyake 1978: pl. 1, fig. 2; 1998: 109, pl. 37, fig. 2; McLaughlin et al. 2007; 96, unnumbered fig.). Furthermore, Petrochirus diogenes is immediately distinguished from Terao’s (1913) taxon by the much longer and more slender ocular peduncles (cf. Williams 1984). It seems unlikely that Terao (1913) overlooked this distinction, because he correctly remarked that Pagurus watasei differed from Dardanus megistos (Herbst, 1804) (as Pagurus ) in having shorter ocular peduncles (for D. megistos , cf. Miyake 1998; McLaughlin et al. 2007).

Miyake (1951) gave an annotated list of anomurans recorded from Kii Peninsula, western Japan. His list included Pagurus watasei based on the published records by Terao (1913) and Shiino (1933); the latter author only reported P. watasei as a host of his new parasitic isopod Pagurion tuberculata Shiino, 1933 . Nevertheless, Miyake (1978) later suggested that Dardanus watasei might be identical with D. scutellatus based on his personal investigation, while in the same publication he questionably placed D. watasei under in the synonymy of D. scutellatus in a list of Japanese anomurans. Miyake (1982, 1998) did the same, and McLaughlin et al. (2010) also followed this synonymy in their checklist of the hermit crab species of the world. However, as has been shown above, D. watasei is actually a junior synonym of D. aspersus . Dardanus scutellatus is readily distinguished from D. aspersus by the comparatively slender ocular peduncles that are longer than the antennular peduncles, the non-dilated corneas, the lack of distinct corneous-tipped spines or tubercles on the outer face of the left chela, and the dorsally concave lateral surfaces of the dactylus and propodus of the left third pereopod (cf. Buitendijk 1937; Fize and Serene 1955; Haig and Ball 1988).

The original description of D. aspersus has been attributed frequently to Berthold (1846), a work containing illustrations of his new taxa of crustaceans, reptiles, and amphibians (e.g., Miyake 1978; McLaughlin et al. 2007, 2010), but the correct attribution is to Berthold (1845). This paper had the same title as the 1846 work but comprised a shorter, unillustrated text. In addition to D. aspersus, Berthold (1845) included descriptions of three other new crustacean taxa: one slipper lobster, Scyllarus haanii Berthold, 1845 [= Remiarctus bertholdii (Paul’son, 1875)], and two stomatopods, Squilla affinis Berthold, 1845 [= Oratosquilla oratoria (De Haan, 1844) ] and Gonodactylus edwardsii Berthold, 1845 [= Odontodactylus japonicus (De Haan, 1844) ], which have already been referred to the year 1845 (e.g., Manning 1995; Holthuis 2002).

Figures

Fig. 1. Dardanus aspersus (Berthold, 1845), holotype of Pagurus watasei Terao, 1913, female (cl 16.7mm), UMUTZ-Crs-33. A, entire animal, dorsal view; B, shield and cephalic appendages, dorsal view; C, left cheliped, outer view; D, right cheliped, outer view.

Fig. 2. Dardanus aspersus (Berthold, 1845), holotype of Pagurus watasei Terao, 1913, female (cl 16.7mm), UMUTZ-Crs-33. A, left second and third pereopods, lateral view; B, right second and third pereopods, lateral view; C, left fourth pereopod, lateral view; D, sixth pleonal tergite and telson, dorsal view.