Athanas japonicus Kubo, 1936

Anker, Arthur, 2003, Alpheid Shrimps From The Mangroves And Mudflats Of Singapore. Part I. Genera Salmoneus, Athanas And Potamalpheops, With The Description Of Two New Species (Crustacea: Decapoda: Caridea), Raffles Bulletin of Zoology 51 (2), pp. 283-314 : 301-311

Athanas japonicus Kubo, 1936

( Figs. 14-19 )

Athanas japonicus Kubo, 1936: 43 , pl. 13; Miya & Miyake, 1968: 139, figs. 4-6; Nishimura & Suzuki, 1971: 84, pl. 27, fig. 8; Banner & Banner, 1973: 308, fig. 4; Wadley, 1978: 13, figs. 6a-b; Miyake, 1982: 41; Takeda, 1982: 29; Miya, 1995: 283, 287; Hayashi, 1994: 4, figs. 267b-d, 268d, 270g, 271; Bruce & Coombes, 1997: 325; Nomura et al., 1998: 42, fig. 1 H; Nomura & Asakura, 1998: 28.

Athanas lamellifer Kubo, 1940: 102 , figs. 3-5; Nakazawa & Miyake, 1957: 776, fig. 2240.

Material examined. – Athanas cf. japonicus A: 1 male (CL 3.5 mm)* and 1 female (CL 3.3 mm)*, ZRC 2003.0087 , belt of muddy sand in front of Lim Chu Kang mangrove, N Singapore, small shallow pool, under debris, low tide, coll. A. Anker, 16 Jan.2002. Athanas cf. japonicus B: 1 male (CL approx. 3.5 mm)*, ZRC 1979.4 .6.15, Ponggol Beach, Singapore, at about LSWT, muddy sand with stones, coll. D. Johnson, 07 Apr.1969, id. D. Johnson as “ Athanas tenuipes De Man ” (J11, 895) .

Extra-limital material – Athanas cf. japonicus C: 2 males (CL 3.4 and 3.7 mm)* QM-W26809, Cooya Beach, Mossman, Queensland, muddy sand at low tide, specimens obtained with yabby pump from burrow of a mud-skipper (Periopthalmidae, possibly Periphthalmodon sp.), coll. A. Anker, July 2001 .

Athanas cf. japonicus D: 1 female (CL 2.9 mm)*, NTM Cr-009968, Channel Island , near Darwin, Northern Territory, Australia, near Bridge, 12 34.9’ S, 130 55.4’ E, Site 3, LWS, hand collection, coll. M. Burke, 01 Jul.1992.

Athanas japonicus series from Japan: 2 males (CL 3.3 and 3.2 mm), 1 female (CL 4.6 mm), MNHN-Na 13764*, Arita Bay, Kushimoto , Wakayama Pref., intertidal, under rock, coll. K. Nomura, 30 Mar.1994 ; 2 males (CL 5.1 and 5.2 mm), MNHN-Na 13711, Arita Bay, Kushimoto , Wakayama Pref., intertidal, under rock, coll. K. Nomura, 28 Mar.1997 ; 2 males (CL 4.1 and 3.9 mm), 1 ovigerous female (CL 4.0 mm), MNHN-Na 13705, Okuda, Chita , Aichi Pref., intertidal, under rock, coll. M. Kasiwara, 08 Sep.1994 ; 6 males (CL 5.2, 4.7, 4.5, 5.5, 5.0 and 4.3 mm), 1 female (CL 4.7 mm), 1 ovigerous female (CL 4.4 mm), MNHN-Na 13640*, Yamaguchi Bay , Yamaguchi, intertidal, under rock, coll. G. Itani, May.1995 ; 2 males (CL 4.7 and 5.0 mm) and 1 female (CL 3.1 mm), MNHNNa 13701, mouth of Hidaka River, Gobou , Wakayama Pref., intertidal, under rock, coll. G. Itani, 27 Sep.1996 ; 1 male (CL approx. 5.1 mm) and 1 ovig. female (CL 5.4 mm), MNHN-Na 13713, Sasebo , Nagasaki pref., intertidal, under rock, coll. K. Nomura, 23 Jun.2001 ; 1 specimen (CL not measured), MNHNNa 13674, Hazama, Tateyama, near Kominato , Chiba Pref., intertidal, under rock, coll. K. Nomura, 15 May.1996 ; 1 female (CL 4.3 mm), MNHN-Na 13717, Banda, Tateyama, near Kominato , Chiba Pref., intertidal, under rock, coll. K. Nomura, 17 May.1996 ; 2 males (CL 5.1 and 3.8 mm), 1 ovig. female (CL 4.7 mm), MNHNNa 13685, Kominato , Chiba Pref., intertidal, under rock, coll. K. Nomura, 24 May.1994 ; 3 ovig. females (CL 3.9, 4.4 and 5.6 mm), MNHN-Na 13635 (from YMP 1812 ), Sunabe, Chyatan, Okinawajima , intertidal, under rock, coll. K. Nomura, 29 Mar.1998 .

* Specimens illustrated.

Description. – Specimens from Lim Chu Kang, Singapore ( Athanas cf. japonicus A). Carapace sparsely setose. Rostrum laterally compressed, acute, slightly exceeding distal margin of first article of antennular peduncle ( Fig. 14b ). Extra-corneal and infra-corneal teeth well developed, acute, supra-corneal teeth absent. Eyestalks largely exposed in dorsal and lateral views; cornea well pigmented, occupying latero-anteror and lateral, but not the most medio-proximal section ( Fig. 14a ). Pterygostomial angle rounded, not projecting anteriorly, without acute tooth.

Antennular peduncles with second article shorter than first; stylocerite acute, reaching from 1/3 to almost mid-length of second article; ventro-mesial carina with well developed, acute tooth; outer flagellum biramous, fused portion composed of 4 articles. Antenna with basicerite bearing acute ventro-lateral tooth; scaphocerite not exceeding antennular peduncles, oval-shaped, anterior margin broadly convex, lateral spine strong; carpocerite only slightly shorter than scaphocerite, not reaching to distal margin of antennular peduncles.

Mouthparts not species-specific, typical for Athanas . Third maxilliped slender; tip of ultimate segment with long setae, without stout spines; arthrobranch absent.

Male first chelipeds very asymmetrical in shape, subequal in size ( Figs. 14d, g ). Major cheliped ( Figs. 14 d-f) with ischium short, stout; merus robust, elongated, broadened distally, shallowly excavated on ventral side ( Fig. 14e ), outer margin armed with eight teeth, two small proximal teeth, followed more distally by two larger teeth, one large triangular tooth situated approximately on mid-length of merus margin, and three medium-sized to small, distal teeth ( Fig. 14d ); inner margin of merus straight; carpus robust, cup-shaped, distal margin with lobes; palm more or less oval in cross-section, with inner side flattened and forming an angle with ventral side, outer margin of ventral side with three tubercles situated approximately at palm mid-length ( Fig. 14e ); fingers distally curved, about 0.3 times as long as palm; dactylus irregularly and slightly serrated; pollex armed with a large, rectangular tooth, followed distally by a hiatus ( Fig. 14f ); outer surface of dactylus and pollex densely covered with fine setae, obscuring direct view of cutting edges. Minor cheliped ( Figs. 14 g-i) different from major cheliped mainly by shape and armature of chela; ischium and merus similar, latter being more slender compared to that of major cheliped; number and development of teeth on outer margin almost as in major cheliped; carpus similar but slightly shorter; chela very different from that of major cheliped by shape and armature of chela; chela suboval, lower margin of palm with tubercles; fingers long and slender, about 0.7 of palm length, more gradually curved; cutting edges irregularly serrated ( Fig. 14i ).

Female first chelipeds very asymmetrical in shape and unequal in size. Major cheliped ( Figs. 14 j-l) robust; ischium elongated (almost twice as long as in male major cheliped); merus slender, shallowly excavated on ventral side, lateral margin with one large triangular tooth situated approximately on mid-length, and several (4-5) smaller teeth situated on distal half; carpus cup-shaped, almost twice as long as carpus in male major cheliped; chela subcylindrical, flattened on one side; lower margin of palm unarmed; fingers slightly less than half length of palm, gradually curved, cutting edges serrated, outer surface of fingers, mostly dactylus, with dense row of fine setae. Minor female cheliped ( Figs. 14m, n ) slender, much smaller and less robust than major cheliped; ischium elongate subequal to merus, carpus about 0.6 length of merus, elongate, cylindrical; chela simple, slender, fingers about 0.8 length of palm, simple, unarmed, slightly and gradually curved, with some tufts of setae.

Second pereiopod with ischium shorter than merus; carpus five-articulated, first article longest; ratio of carpal articles equal to (from proximal to distal): 5: 1: 1: 1: 2 ( Fig. 14o ); chela simple, longer than distal carpal article, but shorter than proximal article, fingers with tufts of setae.

Third pereiopod slender, proportions of articles as illustrated ( Fig. 14p ); ischium armed with two spines; merus and carpus unarmed; propodus unarmed; dactylus about 0.5 length of propodus, simple, slender, gradually curved ( Fig. 14p ), with a very subtle convexity on ventral margin. Fourth pereiopod similar to third pereiopod. Fifth pereiopod with ischium, merus, carpus and propodus unarmed; latter with several rows of grooming setae.

Abdominal segments with posterior ventral angles rounded (A2), angular (A3-5); sixth segment (A6) with articulated triangular plate. Uropod with diaeresis well developed and straight, lateral spine rather small. Telson broadly ovalrectangular, tapering distally, with two pairs of dorsal spines; posterior margin of telson broad, slightly convex, with two postero-lateral spines at each angle, median spines less than twice as long as lateral spines ( Fig. 14c ).

Gill formula as in majority of Athanas s. str.: pleurobranchs on P1-P5; podobranch and arthrobranch absent; exopods on Mxp1-Mxp3; strap-like epipods (mastigobranchs) on Mxp3 and P1-P3; setobranchs on P1-P4.

Both adult specimens rather small: 3.3 mm and 3.5 mm CL, approximately 9 mm TL.

Colour. – Dull reddish, with whitish medio-dorsal stripe; the reddish colour is due to numerous pinkish or red chromatophores dispersed over the whole body except for chelae (few on lateral side), second to fifth pereiopods, flagella of antennule and antenna, and the medio-dorsal longitudinal band.

Habitat. – Both specimens from Lim Chu Kang, probably forming a mating pair, were collected on a several meters large belt of dark, muddy sand with various debris (natural and artificial) lying around or being partly immerged in the mud or sand, only a few metres from some mangrove trees. Both specimens were found in a few centimetres of water remaining in a small depression under a piece of dead wood at low tide. Not a single Athanas was collected from the very soft and deep mud occupying large surfaces in this area.

Remarks. – The type of Athanas japonicus upon which Kubo’s (1936) description and illustrations were based, was an ovigerous female of 10 mm TL from Mitajiri (Yamaguchi Bay), although Kubo stated that two adult males were also collected at the same locality. Only the cheliped of the male was illustrated (cf. Kubo, 1936: pl. XIII, fig. C). The stylocerite of the female type reaches according to Kubo’s drawings (cf. Kubo, 1936: pl. XIII, figs. A, G) to only about one third of length of the second article of the antennular peduncle, and the rostrum to the distal margin of the same article. The male cheliped does not have a strong dentition on the outer margin of the merus but bears instead very small and spaced teeth, while the cutting edges of fingers are apparently unarmed. Furthermore, the carpus is half as long as the merus, and about 0.8 times as long as the palm. The infra-corneal teeth are more protruding than the extra-corneal teeth. The posterior margin of the telson is convex only in its median portion (cf. Kubo, 1936: pl. XIII, fig. M). The colour has been described as «deep blue, hence the new Japanese name» ( Kubo, 1936). The types of A. japonicus were apparently deposited in the Fisheries University in Tokyo (Miya & Miyake, 1968), but could not be located during a recent inspection of the collections of this institution (K. Nomura, pers. com.).

Athanas lamellifer Kubo was separated from A. japonicus mainly because of the much longer stylocerite, exceeding the second article of the antennular peduncle, the distinctly shorter carpus of the major cheliped (being only one quarter as long as the merus), and the shorter dactylus of the third pereiopod (cf. Kubo, 1936: pl. XIII, fig. J; 1940: figs. 4G, H). Furthermore, in A. lamellifer the infra-corneal teeth are less protruding compared to the extra-corneal teeth, whilst the rostrum is more slender and slightly longer. The posterior margin of the telson is rather broadly convex. The merus of the larger cheliped is only slightly serrated, both in females and males; the cutting edges are also serrated, but without a large tooth on the pollex, at least in Kubo’s specimens. The colour of A. lamellifer has been described as uniformly deep reddish brown, with a white medio-dorsal band and white tips of uropods and telson (cf. Kubo, 1940: fig. 5).

Athanas ohsimai Yokoya seems to be very close to A. japonicus , but can be separated from both A. japonicus and A. lamellifer by the pollex being much shorter than the dactylus, and also by the pterygostomial angle anteriorly produced, the shorter rostrum and the presence of epipods on the first four pereiopods ( Yokoya, 1936; Miya & Miyake, 1968; Hayashi, 1994).

In a major revision of Japanese species of Athanas, Miya & Miyake (1968) reported and illustrated an important intra-specific variation in A. japonicus , and placed A. lamellifer in synonymy with A. japonicus . According to Miya & Miyake (1968), the intra-specific variability of A. japonicus affects the width and the length of the rostrum, the length of the stylocerite, the development and the armature of chelipeds and the colour pattern. Considerable differences in the length of the stylocerite are rather unusual for Alpheidae , but variations in size, shape and armature of chelipeds, along with sexual dimorphism, occur in several other species of Athanas , including A. polymorphus Kemp , A. phyllocheles Banner & Banner and A. dimorphus Ortmann (see Kemp, 1915; D. M. Banner & A. H. Banner, 1973; A. H. Banner & D. M. Banner, 1983; see also above).

A series of specimens of A. japonicus from different Japanese localities situated in temperate and subtropical waters, including Yamaguchi Bay (a locality very close to the type-locality), was examined for comparison with the Singapore material. The chelipeds of these specimens are indeed quite different, as are the length of the stylocerite and the development of orbital teeth. The figures of two adult males from Yamaguchi Bay ( Figs. 17 , 18 ) and of an adult female from Arita Bay ( Fig. 19 ) show well the differences between Singapore and Japanese specimens, and also within the Japanese material. The length of the rostrum and the stylocerite is obviously different between the male from Yamaguchi and the female from Arita (cf. Figs. 17a , 19a ). The chelipeds of these specimens are also quite different from those of the type female described and illustrated by Kubo (1936) and also from the chelipeds illustrated by Miya & Miyake (1968). In large males from Yamaguchi, the lateral margin of the merus is armed with strong teeth, and the pollex bears a large process on the margin opposable to the dactylus ( Fig. 17e ). Furthermore, the palm of both chelae bears a series of tubercles on the lower margin, absent in the chelae of original male specimens of A. japonicus and A. lamellifer (cf. Kubo, 1936, 1940). Very small tubercles are also present on the major cheliped in the female from Arita ( Fig. 19d ). Most larger specimens from the Japanese series have subsymmetrical chelipeds armed with a tooth on the pollex, but some (e.g., one male and one female from Yamaguchi) have asymmetrical chelipeds, with the major cheliped as described above, and the smaller cheliped slender and not enlarged, typical of the females of many species of dimorphus group; other specimens have more slender chelipeds, without a tooth on the fixed finger.

As none of the chelipeds illustrated by Miya & Miyake (1968) or examined personally on present specimens from Japan were identical to the chelipeds of Athanas cf. japonicus from Lim Chu Kang mangrove in Singapore, it is quite possible that the latter belong to an undescribed species within what appears to be the A. japonicus complex. The most obvious difference between the specimens of A. cf. japonicus from Lim Chu Kang and other specimens of the A. japonicus complex is the very robust merus of both chelipeds, armed with very strong serrated teeth on the lateral margin. However, Hayashi (1994) illustrated the first chelipeds of a male from Japan, which are quite similar to those of A. cf. japonicus from Lim Chu Kang. Until the true status of Kubo’s A. japonicus is determined, the taxonomic status of A. cf. japonicus from Singapore will remain unclear. The only literature records of A. japonicus outside of Japan are from Australia: Darwin, Northern Territory ( Banner & Banner, 1973; Bruce & Coombes, 1997) and Moreton Bay, Queensland ( Wadley, 1978). Banner & Banner’s (1973) female specimen from Darwin is closer to A. lamellifer in the confirmation of orbital teeth and in all cheliped features, and similar to A. japonicus only in the length of the stylocerite. The ischium of the third pereiopod of the specimen from northern Australia bears only one spine instead of two, as in A. japonicus from Japan ( Fig. 17g , not mentioned for the type) and A. lamellifer (cf. Kubo, 1940: fig. 4G). An immature female recently collected near Darwin ( Figs. 15 l-o) is referable to the A. japonicus complex, mainly because of the very slender dactylus of the third pereiopod. This female bears two perfectly symmetrical chelipeds, which are very similar to the minor chelipeds of many other Athanas species ( Fig. 15m ).

Wadley (1978) listed A. japonicus in the key to the epibenthic shrimps of Moreton Bay, and provided two superficial figures of the anterior carapace. More recently, two male specimens of A. cf. japonicus were collected by the author with the aid of a yabby pump from a burrow of a mud-skipper (Periopthalmidae) near Mossman, North Queensland ( Figs. 15 a-k). In several features (length of the stylocerite, length of the carpus in the minor first cheliped, dactylus of the third pereiopod) these specimens are similar to the type of A. japonicus , however, there are also some important differences to both Japanese and Singapore material (compare Figs. 15 , 17 , 19 ).

The specimen from Ponggol Beach, Singapore (ZRC 1979.4.6.15) was collected and initially identified by D. Johnson as Athanas tenuipes De Man. However , this record remained unpublished. Athanas tenuipes was described by De Man (1910) upon a specimen lacking first pereiopods, and has not been reported since the original description. After having examined De Man’s original description and figures ( De Man, 1911, 1915) the conclusion was reached that the Ponggol specimen is different from A. tenuipes sensu De Man , and instead, presents several features of the A. japonicus complex. This specimen ( Fig. 16 ) is here tentatively assigned to the A. japonicus complex. The rostrum of A. cf. japonicus from Ponggol is significantly longer than in A. tenuipes (cf. De Man, 1915: pl. III, fig. 8), whilst the telson, although heavily damaged, is much broader (cf. De Man, 1915: fig. 8b). The dactylus of the walking legs in A. cf. japonicus from Ponggol is less slender than in A. tenuipes (cf. De Man, 1915: fig. 8d), and the ischium of the third pereiopod bears two spines instead of one as in A. tenuipes . Also, the stylocerite is much longer and the infra-corneal tooth much more developed in the Ponggol specimen compared to A. tenuipes ; these features however are considered to be variable within the A. japonicus complex. Furthermore, A. tenuipes is apparently a species from deeper water (the type has been dredged from 72 m), while the specimen from Ponggol has been collected intertidally, possibly in the same type of habitat as A. japonicus . Notably, A. cf. japonicus from Ponggol seems to differ from specimens of A. cf. japonicus from Lim Chu Kang and Mossman (compare Fig. 16 with Figs. 15 and 17 , respectively), and also from the Japanese specimens of A. japonicus , especially in the more excavated merus of the first chelipeds ( Fig. 16d ).

In conclusion, the morphological variability shown here suggests that several species may be involved in what is believed to be A. japonicus . Examinations of morphology, colour patterns and morphometry of numerous specimens from Japan and elsewhere, and designation of a neotype of A. japonicus from the type-locality (or geographically close locality) in Japan will be necessary to resolve this complex.

Fig. 21. Variation of colour pattern in Potamalpheops tigger Yeo & Ng : a, specimen with rusty reddish pattern; b, young specimen with black spotted pattern (compare with Fig 20 , a, b).

Figures

Fig. 14. Athanas cf. japonicus Kubo, male (a-i, o, p) and female (j-n) from Lim Chu Kang, Singapore (ZRC 2003.0087): a, frontal region, dorsal view; b, same, lateral view; c, telson; d-n, first cheliped: d, male major cheliped, lateral view; e, same, mesial view; f, same, chela, distal palm and fingers; g, male minor cheliped, lateral view; h, same, mesial view; i, same, chela, distal palm and fingers; j, female major cheliped, mesial view; k, same, lateral view; l, same, chela, distal palm and fingers; m, female minor cheliped; n, same, carpus and chela; o, second pereiopod; p, third pereiopod. Scales: A (d, e, g, h), B (a-c, f, i-p), both scales: 1 mm.

Fig. 15. Athanas cf. japonicus Kubo, male from Cooya Beach, Mossmann, Queensland (QM-W26809): a, frontal region, dorsal view; b, same, lateral view; c, telson; d-i, first cheliped: d, major cheliped, lateral view; e, same, mesial view; f, same, chela; g, minor cheliped, mesial view; h, same, lateral view; i, same, carpus and chela; j, second pereiopod; k, third pereiopod. A. cf. japonicus, female from Channel Island, Darwin (NTM Cr009968): l, frontal region, lateral view; m, first cheliped (chelipeds symmetrical); n, second pereiopod; o, third pereiopod. Scale: 1 mm.

Fig. 16. Athanas cf. japonicus Kubo, male from Ponggol beach, Singapore (ZRC 1979.4.6.15): a, frontal region, dorsal view; b, same, lateral view; c, telson (damaged); d-h, first cheliped: d, major cheliped, lateral view; e, same, mesial view; f, minor cheliped, lateral view; g, same, mesial view; h, same, chela fingers; i, second pereiopod; j, third pereiopod. Scale: 1 mm.

Fig. 17. Athanas japonicus Kubo, male from Yamaguchi, Japan (MNHN-Na 13640): a, frontal region, dorsal view; b, same, lateral view; c, (major?) first cheliped, mesial view; d, same, lateral view; e, same, chela, distal palm and fingers; f, second pereiopod; g, third pereiopod; h, telson. Scales: A (c, d), B (a, b, e-h), both scales: 1 mm.

Fig. 18. Athanas japonicus Kubo, male from Yamaguchi (MNHN-Na 13640) first chelipeds: a, major cheliped, ventro-lateral view; b, minor cheliped, lateral view; c, same, chela. Scales: A (a, b), B (c), both scales: 1 mm.

Fig. 19. Athanas japonicus Kubo, female from Arita (MNHN-Na 13764): a, frontal region, dorsal view; b, same, lateral view; c, telson; d-g, first chelipeds: d, major cheliped, mesial view; e, same, lateral view; f, same, chela; g, minor cheliped; h, second pereiopod; i, third pereiopod; j, uropod. Scale: 1 mm.

Fig. 20. Colour patterns of some Alpheidae from Sungei Buloh, Singapore: a, b, Potamalpheops tigger Yeo & Ng; c, d, Potamalpheops johnsoni, new species; e, f, Athanas polymorphus Kemp. All more or less to scale.