Athanas sydneyensis, Anker, Arthur & Ahyong, Shane T., 2007

Anker, Arthur & Ahyong, Shane T., 2007, Description of two species in the alpheid shrimp genus Athanas Leach, 1814, with remarks on A. amazone Holthuis, 1951 (Decapoda, Caridea), Zootaxa 1563, pp. 17-30 : 18-23

Athanas sydneyensis n. sp.

( Figs. 1 , 2 )

Type material: Holotype: 1 female, CL 4.8 mm, TL ca. 12.0 mm, AM P62764, mid-stream between Juno Head and Hungry Beach, Hawkesbury River, New South Wales ( NSW), Australia, 33°34’S, 151°16’E, depth 10 m, sandy mud, coll. A. Jones et al., 9 Nov 1982. Paratypes: 1 female, CL 2.7 mm, TL ca. 7.5 mm, AM P62760, near Hungry Beach, Hawkesbury River, NSW, Australia, 33°34.5’S, 151°16.5’E, depth 4 m, sandy mud, Smith MacIntyre grab, coll. A. Jones et al., 17 May 1982; 1 female, CL 2.2 mm, TL ca. 6.0 mm, AM P 62761, 300 m NE of Green Point, Hawkesbury River, NSW, Australia, 33°34.0’S, 151°13.5’E, depth 5 m, sandy mud, coll. A. Jones & A. Murray, 17 May 1982; 1 female, CL 3.2 mm, TL ca. 9.0 mm, AM P62762, between Juno Head and Hungry Beach, Hawkesbury River, NSW, Australia, 33°34.5’S, 151°16’E, depth 4 m, sandy mud, coll. A. Jones et al., 26 May 1981; 1 female, CL 2.3 mm, TL ca. 6.5 mm, AM P62763, between Juno Head and Hungry Beach, Hawkesbury River, NSW, Australia, 33°34.5’S, 151°16’E, depth 4 m, sandy mud, coll. A. Jones et al., 27 May 1983.

Description: Body elongate, slender. Carapace glabrous, not setose. Rostrum laterally compressed, slightly descending, with subacute tip, not reaching mid-length of second segment of antennular peduncle ( Fig. 1 A), proximally broadened; rostral carina slight, posteriorly not reaching rostral base ( Fig. 1 B). Extracorneal spine acute, triangular, not reaching anterior margin of cornea ( Fig. 1 A, B); infra-corneal and supracorneal spine absent. Eyes largely exposed in dorsal and lateral views; cornea well pigmented ( Fig. 1 A, B). Pterygostomial region rounded, not protruding anteriorly.

Antennular peduncle with second segment subequal to dorsally visible portion of first segment and equal to third segment ( Fig. 1 B, C); stylocerite acute, reaching mid-length of second segment; ventromesial carina with well developed, acute spine; lateral flagellum biramous, fused portion composed of about five segments ( Fig. 1 B). Antenna with basicerite bearing acute ventrolateral spine; scaphocerite exceeding antennular peduncle ( Fig. 1 B, C), oval, lateral margin straight, anterior margin broadly convex, reaching beyond distlateral spine ( Fig. 1 C); carpocerite exceeding scaphocerite by 1/5 of scaphocerite length ( Fig. 1 A, C), reaching far beyond distal margin of antennular peduncle.

Mouthparts without specific features, typical for genus. Third maxilliped slender, ultimate segment 1.5 times as long as penultimate segment, about half as long as antepenultimate segment; tip of ultimate segment setose, without spiniform setae.

Female chelipeds subsymmetrical in shape, subequal in size ( Figs. 1 D–G, 2 A, B); ischium elongate, almost as long as merus, ventral margin irregularly toothed, distally projecting, dorsal margin proximally with group of three to five slender spiniform setae ( Fig. 1 D–G); merus elongate, ventromesially slightly depressed, ventrolateral margin irregularly toothed; ventral surface furnished with numerous setae; carpus subequal to merus, distally widening, unarmed, setose ventrally; chela laterally compressed, ventral margin of palm concave at pollex base; fingers slightly shorter than palm, more or less gaping, tips crossing, cutting edges armed proximally with broadly triangular teeth, distally unarmed or armed with inconspicuous, irregular teeth, one chela of larger individuals with pronounced teeth on dactylus and pollex ( Fig. 1 D). Male chelipeds unknown.

Second pereiopod slender ( Fig. 1 H); ischium slightly shorter than merus; carpus five-segmented, first article longer than four others combined; ratio of carpal segments (from proximal to distal) approximately: 8: 1: 1: 1: 3; chela simple, slightly longer than distal carpal article, fingers longer than palm. Third pereiopod slen- der ( Fig. 1 G); ischium with two ventrolateral spiniform setae, dorsal margin with small distal spiniform seta; merus, carpus and propodus unarmed, merus about eight to ten times as long as broad; dactylus about 0.6 times propodus length, simple, slender, slightly curved.

Pleura of first to fifth abdominal somites with rounded posteroventral angles; sixth somite with articulated triangular flap posteroventrally ( Fig. 1 K). Uropod with protopod (sympodite) bearing distally two subacute lobes ( Fig. 1 J); diaeresis straight, distolateral spiniform seta small. Telson ( Fig. 1 J) widest at proximal third, distally tapering, with two pairs of slender dorsal spiniform setae; posterior margin medially convex, with two pairs of slender posterolateral spiniform setae, mesial almost twice as long as lateral.

Gill formula typical for genus: pleurobranchs above P1–P5; podobranch and arthrobranch absent; straplike epipods (mastigobranchs) on coxae of Mxp3 and P1–P3; setobranchs on coxae of P1–P4; exopods on Mxp1–Mxp3, rudimentary exopods on P1–2.

Colour in life unknown. Size: CL 2.2–4.8 mm, TL ca. 6.0–12.0 mm.

Etymology: The new species is named after the Australian city of Sydney, situated near the type locality.

Type locality: Hawkesbury River, Sydney, New South Wales, Australia.

Habitat: All specimens were dredged from sand–mud bottoms at depths between 4 and 10 m.

Distribution: Presently known only from the type locality near Sydney, Australia.

Remarks: Athanas sydneyensis n. sp., is most closely related to A. phyllocheles Banner & Banner, 1983 presently known only from the type series of 13 males and two ovigerous females, dredged from 345–450 m off La Réunion in the southwestern Indian Ocean ( Banner & Banner 1983). However, the new species differs in several characteristics from A. phyllocheles , as summarized in Table 1 .

We believe that some of these differences, e.g., the proportion of the articles in the third pereiopod (8, 9), the length of the scaphocerite compared to that of the antennular peduncle (6), the carpus/merus ratio in the chelipeds (7), and the relative lengths of the dactylus and propodus of the third maxilliped (10) are taxonomically reliable. In view of the intraspecific polymorphism of the chelipeds reported in A. phyllocheles ( Banner & Banner 1983) , other differences on these appendages appear to be less significant. The chelipeds of A. sydneyensis n. sp., are somewhat “intermediate” between the chelipeds of the smaller male paratype of A. phyllocheles with TL 8.7 mm ( Banner & Banner 1983, fig. 14 l, m) and the juvenile paratype of unknown sex with TL 6.5 mm (idem., fig. 14 n, o). At TL 12.0 mm, however, the holotype of A. sydneyensis n. sp. is considerably larger than the aforementioned specimens of A. phyllocheles . Although both A. sydneyensis n. sp. and A. phyllocheles live on soft bottoms, the bathymetry is very different: A. sydneyensis n. sp. was collected in relatively shallow water (6–10 m) of an estuary, whereas A. phyllocheles was collected from much deeper water (345–450 m) off the coast of an oceanic island.

Several other species of Athanas are characterized by extremely slender, scythe-shaped dactyli on the third to fifth pereiopods. However, only three of them appear to be more closely related to A. sydneyensis n. sp.: A. gracilipes Banner & Banner, 1978 , dredged from 365-385 m in the South China Sea, off Hong Kong ( Banner & Banner 1978); A. tenuipes de Man, 1910, collected from 72 m off Sulawesi, Indonesia (de Man 1911); and A. amazone Holthuis, 1951 known from several localities in the eastern Atlantic, including the Mediterranean Sea ( Holthuis 1951; Crosnier & Forest 1973; Froglia & Argenti 1993).

Athanas gracilipes was described on the basis of two fragmentary specimens, both without chelipeds. Although Banner & Banner (1983) did not contrast A. phyllocheles with A. gracilipes , these two species are possibly closely related, and both are similar to A. sydneyensis n. sp. The only significant differences between A. gracilipes and the other two species are: (1) the slightly shorter rostrum, not reaching distal margin of the first segment of the antennular peduncle; (2) the presence of small, triangular infra-corneal spines; (3) the more slender second pereiopod; and (4) the different proportional lengths of articles in the third pereiopod, e.g., the dactylus being only half length of the propodus (instead of 3/ 5 in A. sydneyensis n. sp., and 1/ 3 in A. phyllocheles ). In this last feature, and generally in the proportions of the articles of the third pereiopod, A. gracilipes is closer to A. sydneyensis , n. sp., differing from it mainly in (1) the presence of infra-corneal spines; (2) the shorter stylocerite, only slightly exceeding the distal margin of the first segment of the antennular peduncle; (3) the more slender antennular peduncle, with the second segment 1.5 times as long as broad (vs. 1.2 times in A. sydneyensis n. sp.); (4) the shorter scaphocerite, not exceeding distal margin of the antennular peduncle; (5) the much more slender second pereiopod; (6) differently shaped telson, with lateral margins straight, not convex, as in A. sydneyensis n. sp. (cf. Fig. 1 and Banner & Banner 1978, fig. 3).

Athanas tenuipes is presently known only from the possibly juvenile holotype, which, like A. gracilipes , lacks both chelipeds. A complete specimen, possibly assignable to A. tenuipes , was recently collected in southern Vietnam (Anker & Marin unpubl.). Athanas tenuipes differs from A. sydneyensis n. sp., but also from A. gracilipes and A. phyllocheles by (1) the carpocerite being much shorter than the scaphocerite; (2) the lateral spine of the scaphocerite exceeding the anterior margin of the blade; (3) the telson being more slender, with a slightly emarginated posterior margin (cf. de Man 1911, 1915); and possibly also several features on the chelipeds (A. Anker pers. obs.). Further, A. tenuipes differs from A. gracilipes by the much longer stylocerite, exceeding mid-length of the second segment of the antennular peduncle, and from A. phyllocheles by the presence of small infra-corneal spines. Banner & Banner (1978) assumed that the type of A. tenuipes , with TL 7 mm, is immature, and that this may account for the slight differences between A. tenuipes and A. gracilipes . However, we feel that both A. gracilipes and A. tenuipes should be treated as valid species until more material of A. gracilipes becomes available.

The eastern Atlantic A. amazone Holthuis, 1951 ( Fig. 5 ) has many affinities with A. sydneyensis n. sp., and is also closely related to A. phyllocheles , to such degree that in the description of the latter species Banner & Banner (1983) added that "when enough mature specimens from the tropical Atlantic and Mediterranean are studied, it may be found that their forms show such variation that A. phyllocheles may be considered to be a synonym". However, the chelipeds of A. phyllocheles differ in many ways from those of A. amazone . In adult males of A. phyllocheles the chelipeds are more or less asymmetrical in shape, and subequal in shape, the chelae are rounded to oval-shaped and laterally compressed in both sexes (at least in adults), whereas in adult males of A. amazone the chelipeds are both strongly asymmetrical in shape and unequal in size ( Fig. 5 A), the chelae are sub-rectangular, not oval, flattened only on “mesial” side ( Fig. 5 C, E). In A. phyllocheles , the merus is not expanded and relatively slender, whereas in A. amazone , the merus is conspicuously expanded and stouter in both sexes, especially in males ( Fig. 5 A). The major chelipeds of A. phyllocheles and A. amazone also differ in the relative proportions of the ischium to the merus, and the merus to the carpus; for instance, in A. phyllocheles the carpus is much shorter than the merus (at least in adults), while in A. amazone these articles are subequal. In our opinion, these differences are sufficient to reject Banner’s tentative assumption of the synonymy of A. phyllocheles with A. amazone . Athanas sydneyensis n. sp., can be separated from A. amazone by (1) the absence of the infra-corneal spines; and (2) the more elongated ischium of the major cheliped.

All other species of Athanas bearing slender, scythe-shaped dactyli on the walking legs are more distantly related to A. sydneyensis n. sp. For instance, A. hongkongensis Bruce, 1990 can be distinguished from the new species by the proportions of the dactylus to the propodus on the third to fifth pereiopods; A. dentirostris Anker, Jeng & Chan, 2001 by the dorsally dentate rostrum; A. squillophilus Hayashi, 2002 by the presence of a strong pterygostomial spine; also, all three species have differently shaped chelipeds ( Bruce 1990; Anker et al. 2001; Hayashi 2002).

Figures

FIGURE 1. Athanas sydneyensis n. sp., female, holotype, CL 4.8 mm, AM P 62764, Hawkesbury River, New South Wales, Australia. A – frontal region, lateral view; B – same, dorsal view; C – right antennule and antenna, dorsal view; D – right cheliped, lateral view; E – merus and ischium of right cheliped, mesial view; F – left cheliped, lateral; G – merus and ischium of left cheliped, mesial view; H – right second pereiopod, lateral view; I – right third pereiopod, lateral view; J – tail fan, dorsal view; K – tailfan, right lateral view. Scale bar: A, B, D – H, J, K = 1.0 mm; C, H = 0.5 mm.

FIGURE 2. Athanas sydneyensis n. sp., female, paratype, CL 3.2 mm, AM P 62762, Hawkesbury River, New South Wales, Australia. A – left cheliped, lateral view; B – right cheliped, lateral view. Scale bar = 1.0 mm.

FIGURE 5. Athanas amazone Holthuis, 1951: male, CL 4.9 mm, MNHN-Na 13748, Banyuls-sur-Mer, southern France: A – habitus; B – major cheliped, chela and distal carpus, mesial view; male, CL 3.2 mm, MNHN-Na 8806, Pointe Noire, Congo: C – major cheliped, chela and distal carpus, ventral view; D – same, ventromesial view; E – same, dorsomesial view; F – same, basis and ischium, ventromesial view; G – same as B, fingers in slightly different angle (entire cheliped illustrated by Crosnier & Forest 1973, fig. 48); ovigerous female, CL not measured, MNHN-Na 1745, Cap l'Abeille, Banyuls-sur-Mer, southern France, H - minor cheliped, lateral view. Scale bars = 1 mm.

Tables

TABLE 1. Differences between Athanas phyllocheles Banner & Banner, 1983 and A. sydneyensis n. sp.

Features / Species	A. phyllocheles	A. sydneyensis n. sp.
1. Rostrum lateral view	slender, with tip slightly ascending	more robust, tip slightly descending
2. Rostrum, dorsal view	proximally not broadened	proximally broadened, convex
3. Extra-corneal spines	reaching anterior margin of eyes	not reaching anterior margin of eyes
4. Anterolateral margin of cara- pace (antennal region)	concave	convex
5. Stylocerite	slightly exceeding distal margin of first segment of antennular peduncle	reaching almost middle of second seg- ment of antennular peduncle
6. Scaphocerite	not reaching end of antennular peduncle	clearly exceeding antennular peduncle
7. Major cheliped, carpus	shorter than merus	subequal to merus
8. Third pereiopod, propodus	almost 15 times as long as broad	8–10 times as long as broad
9. Third pereiopod	dactylus / propodus ratio 1/3	dactylus / propodus ratio 1/2
10. Third maxilliped, dactylus: propodus ratio	~1.3	~1.5
10. Bathymetry	345–450 m	6–10 m