Athanas polymorphus Kemp, 1915

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 : 294-301

publication ID	https://doi.org/ 10.5281/zenodo.13229368
persistent identifier	https://treatment.plazi.org/id/03EE7B58-A873-CC61-4DEB-B938FB52FD4A
treatment provided by	Felipe
scientific name	Athanas polymorphus Kemp, 1915
status

Treatment

Athanas polymorphus Kemp, 1915 View in CoL

( Figs. 8- 13 View Fig View Fig View Fig View Fig View Fig View Fig , 20e, f View Fig )

Athanas polymorphus Kemp, 1915: 295 View in CoL , figs. 31, 32; Tattersall,

1921: 370; Miya, 1991: 1197; Bruce & Coombes, 1997: 325. Athanas View in CoL near polymorphus View in CoL – Banner & Banner, 1966b: 24, fig. 2.

Material examined. – 1 male (CL 5.3 mm)*, 1 male (CL 5.5 mm, dissected)*, 1 male (CL 5.2 mm), 1 juv. male (CL 3.1 mm)*, 1 juv. female (CL 2.6 mm)*, ZRC 2003.0085 View Materials , Sungei Buloh mangrove, Singapore, at low tide, under dead wood and debris, coll. Y. Cai & A. Anker, 10 Feb.2000 ; 1 male (CL 4.9 mm)*, 1 female (CL 4.8 mm)*, 1 male (CL 4.1)*, ZRC ZRC 2003.0086 View Materials , Sungei Buloh mangrove, Singapore, at low tide, in mud under debris, coll. Y. Cai, 28 Feb.2000 ; 1 female (CL 3.0 mm), MNHNNa 13688, Lim Chu Kang mangrove, Singapore, in mud under mangrove roots, coll. A. Anker & D. C. J. Yeo, 16 Jan.2002 .

* specimens illustrated.

Description. – Specimens from Singapore. Carapace slightly hirsute due to numerous erected setae ( Fig. 9a View Fig ). Rostrum laterally compressed, acute, usually reaching to mid-length of second article of antennular peduncle ( Figs. 9a, b View Fig ); rostral carina feebly marked posterior to eyestalks. Extra-corneal and infra-corneal teeth well developed, acute ( Fig. 9a View Fig ). Eyes exposed in dorsal and lateral views, with large, well pigmented cornea. Pterygostomial angle with a small tooth projecting anteriorly ( Fig. 9a View Fig ); this tooth is slightly larger in some specimens ( Fig. 9c View Fig ).

Antennular peduncles with second article as long as or shorter than first article; stylocerite acute, clearly exceeding distal margin of first article, but not reaching mid-length of second article ( Figs. 9 a, d View Fig ); ventro-mesial carina with acute tooth ( Fig. 9d View Fig ); outer flagellum biramous, fused portion composed of five-seven articles; shorter ramus with several (e.g., four) groups of aesthetascs. Antenna with basicerite bearing acute ventro-lateral tooth; scaphocerite oval and slightly elongate ( Fig. 9e View Fig ), disto-lateral spine strong, exceeding antennular peduncles; carpocerite exceeding 3/4 of scaphocerite.

Mouthparts not species-specific, typical for Athanas . Third maxilliped slender ( Fig. 9f View Fig ); tip of ultimate segment with one superior spine and one slender, elongate inferior spinelike seta ( Fig. 9g View Fig ); arthrobranch absent.

First chelipeds highly variable in shape and symmetry. Chelipeds of large adult males subsymmetrical, left and right pereiopods differing only slightly in proportions and armature ( Figs. 10 View Fig , 11 View Fig ); ischium stout, with 1 small dorsal spine; merus elongated, 5-6 times as long as wide at ischiomeral articulation, ventrally excavated, outer margin serrated with teeth, inner margin straight; carpus cup-shaped, distal margin with lobes; palm more or less oval, somewhat twisted, flat on one side, lower margin with a series of small proximal tubercles and a larger tubercle situated approximately on palm mid-length ( Figs. 10b View Fig , 11a View Fig ); fingers distally curved (especially dactylus ventrally), about 0.5 times as long as palm; cutting edges of pollex either armed with small serrated teeth – type A ( Fig. 10 View Fig ), or armed with a large rectangular tooth bearing serrations distally – type B ( Fig. 11 View Fig ); dactylus either finely serrated – type A, or with a rounded tubercle situated basal to the dactylus middle – type B ( Fig. 11 View Fig ). Chelipeds of some males asymmetrical in shape but more or less equal in size; larger cheliped of type B ( Figs. 13 View Fig a-c); smaller cheliped different in proportions and shape of chela, especially fingers being longer, more slender, with cutting edges serrated ( Figs. 13 View Fig d-f). First chelipeds of smaller and subadult males usually asymmetrical and unequal – type C ( Figs. 12 View Fig l-n); major cheliped with ischium slender and more elongated than in types A and B; merus with one triangular tooth on outer margin ( Figs. 12l, m View Fig ); carpus cup-shaped, more slender and slightly longer than in types A and B; chela with palm slightly inflated, with ( Fig. 12k View Fig ) or without ( Fig. 12m View Fig ) tubercles on lower margin; fingers only slightly curved and unarmed or finely serrated; minor cheliped of male ( Fig. 12n View Fig ) similar to that of some females ( Fig. 12o View Fig ), with merus and carpus elongated, cylindrical, and chela slender, not inflated. Other males and larger females with chelipeds strongly unequal and asymmetrical; major chelipeds with shapes and proportions very different from those of males – type D ( Figs. 12 View Fig a-i), fingers either armed, with pollex bearing one large tooth ( Fig. 12c View Fig ), or serrated ( Fig. 12 h View Fig ); minor chelipeds of females as described above, however with carpus distinctly longer ( Figs. 12d, e, i View Fig ). When not used, chelipeds are held folded under cephalothorax with the chela applied against the merus ( Figs. 8 View Fig , 20 f View Fig ).

Second pereiopod slender; ischium slightly shorter than merus; carpus five-articulated, first article longer than the sum of all other articles; ratio of carpal articles equal to (from proximal to distal): 5.5: 0.9: 0.9: 0.9: 1.8 ( Fig. 9h View Fig ); chela simple, longer than distal carpal article.

Third pereiopod slender ( Fig. 9i View Fig ); ischium armed with two spines; merus and carpus unarmed; propodus with two or three small slender spines one on inferior margin and one distal pair of spines; dactylus about 0.45 length of propodus, simple, slender, gradually curved ( Fig. 9i View Fig ). Fourth pereiopod in most aspects similar to the third pereiopod. Fifth pereiopod with ischium, merus, carpus and propodus unarmed; latter with several rows of grooming setae ( Fig. 9j View Fig ).

Abdominal segments with posterior ventral angles rounded (A1), angular (A3, A4) or pointed (A5); sixth segment (A6) with articulated triangular plate, and posterior angle bluntly producing ( Fig. 8 View Fig ). Uropod with diaeresis bearing a pointed tooth proximal to lateral spine, straight from this tooth to inner margin ( Fig. 9l View Fig ). Telson elongated, tapering distally, usually with two pairs of dorsal spines, sometimes with only three spines ( Fig. 9m View Fig ); posterior margin of telson medially convex, with two strong postero-lateral spines at each angle, median spines about 4 times longer than lateral spines.

Gill formula typical for majority of Athanas s. str (sensu Anker, in prep.): 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.

Largest specimens reaching approximately 5.5 mm CL (13- 14 mm TL).

Colour. – Ground colour grey-blue or brownish, densely covered with small reddish chromatophores, particularly concentrated on the almost brown dorsal part of the carapace; articulation area between the carapace and the abdomen bluish; carapace dorsally with three whitish to ivoryyellowish, transverse bands, two bands posterior to the rostrum, and one broad band proximal to the posterior margin; branchiostegites with several irregular white patches; rostrum brown; abdominal segments A2-4 and A6 dorsally with a whitish or yellowish, transverse patch, A1 only with a lateral whitish patch, A2, A3 and A5 with small whitish patch proximal to the posterior margin; telson and uropods dark brown, fringing setae whitish; legs semitransparent, with reddish chromatophores; antennular and antennal peduncles brownish, flagella reddish; first pereiopods reddish brown, outer side of the palm whitish with a reddish reticulation; fingers also reddish, tips white ( Figs. 20e, f View Fig ).

Habitat. – Athanas polymorphus has been collected on mudflats of a brackish lagoon ( Kemp, 1915), on mangal flats dominated by Sonneratia alba ( Miya, 1991) , and in rich mangrove forests, in mud, small pools and under rotten pieces of wood and bark (present report). In Singapore, A. polymorphus seems to be restricted to mangrove areas such as Sungei Buloh and Lim Chu Kang. However, several specimens of “ A. near polymorphus ” were collected under rocks on a gravel-sand beach, at Rayong, Gulf of Thailand ( Banner & Banner, 1966b).

Remarks. – Kemp (1915) provided a relatively good description of this species, accompanied by some figures. The types of A. polymorphus from the Chilka Lake in the State of Orissa, India, were deposited in the Indian Museum in Calcutta (IMC) and are not easily accessible for examination. Because of insufficiency of original figures, rarity of reports of A. polymorphus , and increasing number of species in the genus Athanas , a redescription of the type material of this species is desirable.

The new material from Singapore agrees rather well with the original description, including the detailed description of the colour pattern. However, some important differences between the type-specimens and the specimens from Singapore do not allow the present description to be considered as a formal redescription of A. polymorphus . Some of these differences may be due to inaccuracies in Kemp’s illustrations. However, one of the main differences between the two populations concerns the development of the first chelipeds in females. Kemp (1915) noted that from 27 of his Chilka specimens only nine were males, and that only these males exhibited the three “ types ” I, II and III of the polymorphic first chelipeds (hence the specific name proposed by Kemp). The other 18 specimens of the original type-series of A. polymorphus were females, all of which had almost symmetrical and slender first chelipeds, with a small, unarmed chela (cf. Kemp, 1915: fig. 31a). Among the 10 specimens collected in Singapore both males and females present a very pronounced polymorphism in the shape of the first chelipeds. Several types of chelipeds can be recognized in this population: some major chelipeds are apparently typical of males, others are found in both males and females, and the most undeveloped minor chelipeds are found only in a few small and possibly immature females. At least three adult females from Singapore have a robust major cheliped, with an armed chela (cf. Fig. 12 View Fig ), and minor cheliped typical to many species from A. dimorphus group, a condition never observed in the 18 females collected from Chilka Lake.

There are also some other important differences between the Chilka and Singapore specimens. Kemp (1915) reported that his specimens of A. polymorphus had either four or five articles in the carpus of the second pereiopod. However, all specimens of A. polymorphus from Singapore had five articles in the carpus of the second pereiopod. According to Kemp’s drawings, the rostrum is longer and more slender in specimens from the Chilka Lake than in the present specimens from Singapore. Also, in A. polymorphus from Chilka the “pterygostomian tooth” arises above the pterygostomial angle (cf. Kemp, 1915: fig. 32a), while in all specimens from Singapore this tooth is actually represented by a small acute anterior projection of the pterygostomial angle itself ( Figs. 9a, c View Fig ). The antennules of A. polymorphus seem to be more slender and more elongated, at least according to Kemp’s figure 32b, compared to Singapore material (cf. Fig. 9b View Fig ). The shape of the scaphocerite is also different: it is slightly longer and less broad in A. polymorphus (cf. Kemp, 1915: fig. 32c and present Fig. 9e View Fig ). In larger males, the number of teeth on the lateral margin of the merus of the first chelipeds is approximately 20 in A. polymorphus from Chilka, while it never exceeds 10 in specimens from Singapore. Kemp also noted and illustrated the variation in the number of carpal articles in the second pereiopod: some of the Chilka specimens apparently had only four articles instead of the normal five. Seven specimens from Singapore examined especially for this feature all had a normal, five-articulated carpus in the second pereiopod.

The specimens from Singapore appear to be closer to “ A. near polymorphus ” collected “under rocks on a gravel-sand beach” in Rayong, Thailand ( Banner & Banner, 1966b). The main reasons, for which Banner & Banner (1966b) did not assign the specimens from Rayong unambiguously to Kemp’s species are the same as the doubts about the identity of the present specimens from Singapore, namely the presence of strongly asymmetrical chelipeds in both sexes (including a robust major cheliped in females), and the acute pterygostomial tooth arising from the pterygostomial angle itself (not above it), and being much stronger.

It is not clear whether the above mentioned differences are of taxonomic importance or simply reflect an intra-specific, geographical variation. Without having the possibility to examine Kemp’s type-series of A. polymorphus and Banner’s specimens of A. near polymorphus , the specimens from Singapore are tentatively assigned to A. polymorphus , and the species is considered as polymorphic, with a high plasticity of the first chelipeds. Collections on the shores of Chilka Lake, India, the type-locality of A. polymorphus (or examination of the type-material at the IMC) and Rayong, Thailand will be necessary to conclude whether A. polymorphus is indeed a highly variable species or a species complex. If Kemp’s drawings of A. polymorphus are correct, a new species must be established for the present specimens from Singapore and possibly those from Rayong, Thailand (A. near polymorphus in Banner & Banner, 1966b). Similarly, the identity of specimens from northern Australia reported with some doubts as A. polymorphus by Bruce & Coombes (1997) remains to be determined.

Athanas polymorphus can be easily distinguished from the majority of other Athanas species by the presence of a small acute tooth on the pterygostomial angle. The only other species having an anteriorly produced pterygostomial tooth and a slender, simple dactylus on the third to fifth pereiopods is A. squillophilus Hayashi from southern Hokkaido, Japan ( Hayashi, 2002). This stomatopod-associated species differs from A. polymorphus in having the pterygostomial tooth much more pronounced, the corneas somewhat reduced, and the chelae of the first chelipeds furnished with long and fine filtering setae.

Distribution. – Chilka Lake, Orissa, eastern India ( Kemp, 1915); northern Gulf of Thailand ( Banner & Banner, 1966b); Singapore (present study); Darwin, Northern Territory, Australia (Bruce & Coombes, 1997).