Athanas manticolus sp. nov.

(Figs. 1–5, 6A–C)

Type material. 1 ovigerous female, cl 4.6 mm, OUMNH.ZC. 2014-01-002, Vietnam, Nha Trang Bay, north of Nha Trang, Hon Chong Beach, 12º16'27''N 109º12'19''E, subtidal sand bottom adjacent to coral reef, depth 4–5 m, suction pump, in burrow of Bigelowina phalangium (OUMNH.ZC. 2014-01-003), coll. Z. Ďuriš and A. Šobáňová, 17 September 2013.

Description. Small-sized shrimp with subcylindrical body; carapace and abdomen surface smooth, without setae (Fig. 1). Carapace with small post-rostral tubercle on mid-dorsal line; cardiac notch deep (Figs. 1, 2 A, B); pterygostomial angle poorly marked, broadly rounded, not protruding anteriorly (Fig. 2 A); rostrum short, not overreaching distal margin of first article of antennular peduncle, broad at base, distally narrowing, dorsal margin with seven minute teeth not counting slightly up-raised acute tip (Fig. 2 A–C); extra-corneal teeth reduced to shallow bumps; supra-corneal and infra-corneal teeth not distinct (Fig. 2 A, B).

Eyes relatively small compared to body, largely exposed in dorsal and lateral view, with normally pigmented corneas; distal margin without tubercle or spiniform process (Fig. 2 A, B).

Antennular peduncle stout; first article with very strong, anteriorly pointed tooth on mesioventral carina; stylocerite stout, reaching or almost reaching distal margin of second article, distally subacute; second article short, slightly wider than long in dorsal view; lateral antennal flagellum with relatively short accessory branch departing from fifth joint, aesthetascs present from third joint to tip of accessory branch (Fig. 2 A, B). Antenna with very stout basicerite ending in subacute distoventral tooth; scaphocerite broadly subrectangular, reaching far beyond end of antennular peduncle, with small distolateral tooth and anteriorly convex blade; carpocerite stout, reaching far beyond scaphocerite (Fig. 2 A, B).

Mouthparts (mandible, maxillule, maxilla, first and second maxillipeds) typical for Athanas, as illustrated (Fig. 3 A–F). Third maxilliped slender, pediform; antepenultimate article slightly compressed, about five times as long as maximum width; penultimate article about three times as long as wide; ultimate article most slender, about seven times as long as wide, with two long stiff setae on tip; coxa with distally bluntly produced lateral plate; arthrobranch absent (Fig. 3 G).

First pereiopods (= chelipeds) moderately enlarged compared to body size, subequal in size and subsymmetrical in shape, carried folded with ventral portion of palm fitting in ventrally depressed merus (Figs. 1, 4, 6A); ischium about four times as long as wide, dorsal margin with several slender spiniform setae, ventral margin with triangular tooth proximal to mid-length; merus not particularly expanded, with ventral surface conspicuously depressed, ventrolateral margin rugose, with small, irregular teeth, dorsal margin smooth; carpus distally widening, vase-shaped, smooth, ventral surface depressed proximally; palm subcylindrical, distinctly twisted, ventrolateral surface with conspicuous tubercle, remaining surface smooth, without setal brushes; fingers somewhat curved following twisted axis of palm, slightly shorter than palm; finger cutting edges with small, subtriangular teeth proximally (Fig. 4 A–D).

Second pereiopod slender; ischium and merus unarmed; carpus composed of five articles with ratio approximately equal to (proximal to distal) 6:1:1:1:2; chela simple, slender, longer than fifth carpal artcle, fingers much longer than palm (Fig. 5 A, B). Third pereiopod moderately slender; ischium with two small, ventrolateral spiniform setae and small, stout distodorsal seta; merus about 4.7 times as long as maximum width (at about midlength), distoventral angle not produced; carpus much more slender than merus, half as long as merus, about four times as long as wide; propodus at least six times as long as wide, without spiniform setae on ventral margin except for one barely discernable, short spiniform seta adjacent to dactylus; dactylus slender, simple, strongly curved distally, about half propodus length (Fig. 5 C). Fourth pereiopod generally similar to third pereiopod, however, with one spiniform seta on ischium and much more slender merus (Fig. 5 D, E). Fifth pereiopod with unarmed ischium; merus slender, about six times as long as wide; carpus about half length of merus; propodus very slender, long, cleaning brush reduced to two distal rows of setae; dactylus more curved than that of third or fourth pereiopod, otherwise similar (Fig. 5 F).

First to fourth abdominal somites with ventrally rounded pleura, pleuron of fifth somite with blunt, slightly protruding posteroventral angle; sixth somite with subtriangular articulated plate and bluntly produced posterolateral angle (Figs. 1, 2 D). Uropod with lateral lobe of protopod ending in acute tooth; exopod with long, slender, distolateral spiniform seta; diaeresis nearly straight (Fig. 2 E). Telson moderately broad, conspicuously tapering distally; dorsal surface with two pairs of long spiniform setae with their bases situated at about 1/4 (anterior pair) and 3/5 (posterior pair) of telson length; posterior margin nearly straight, each posterolateral angle with one pair of slender spiniform setae, mesial much longer than lateral; four long, posteriorly directed plumose setae and four shorter, more dorsally directed setae present between mesial spiniform setae (Fig. 2 E, F).

Colour pattern. Body largely semitransparent covered with red chromatophores arranged in randomly oriented, narrow, short streaks; broad, white to pale-yellow, mediodorsal band extending from rostral tip to posterior margin of telson, this band interrupted between first and second, and second and third abdominal somites, respectively; rostrum, antennules, antennae, uropods and telson white; chelipeds hyaline-whitish, remaining pereiopods and pleopods colourless; eggs reddish brown (Fig. 6A–C).

Etymology. The new species name refers to its association with a nannosquillid stomatopod (see below), being a combination of the Latinised Greek word mantis (stomatopods are popularly known as mantis shrimps) and the Latin word colō (dweller, alluding to a burrow-dwelling life style).

Distribution. Presently known only from the type locality, in Nha Trang Bay, Vietnam.

Ecology. The holotype of Athanas manticolus sp. nov. was collected on a shallow (4–5 m) subtidal sand flat at the bottom of a coastal coral reef; the substrate consisted mainly of compacted fine sand. The shrimp was pumped from a burrow together with its presumable host, the burrowing stomatopod Bigelowina phalangium (Fabricius, 1798). Bigelowina phalangium (Fig. 6 D) is a medium-sized mantis shrimp (total length of the collected specimen ~ 60 mm) constructing deep U-shaped burrows in intertidal and shallow subtidal (usually less than 10 m) sediments (Ahyong 2001). It is presently unknown whether A. manticolus sp. nov. is an obligate or facultative dweller in stomatopod burrows and in the former case whether it is associated only with B. phalangium or with several stomatopod species and/or other burrowing animals.

Remarks. Athanas manticolus sp. nov. is unique within the genus Athanas in the combination of four morphological characters: (1) mid-dorsal line of the carapace with a low but conspicuous post-rostral tubercle; (2) rostrum with a series of minute teeth; (3) extra-corneal teeth reduced to shallow bumps, infra-corneal and supraorbital teeth not distinct; and (4) third and fourth pereiopods lacking spiniform setae on the ventral margin of the propodus (Figs. 2 A–C, 5C–E).

The only other species of Athanas with a dorsal dentition is Athanas dentirostris Anker, Jeng and Chan, 2001, presently known only from the type locality in northern Vietnam. However, A. dentirostris has stronger rostral teeth, well-developed extra-corneal and infra-corneal teeth (the former reduced, the latter absent in A. manticolus sp. nov.), and a dense setal brush on the major chela (not found in A. manticolus sp. nov.) (cf. Anker et al. 2001). This species appears to be morphologically much closer to the widespread A. japonicus Kubo, 1936 than to the herein described new species.

Athanas manticolus sp. nov. appears to be most closely related to Athanas daviei Anker, 2011, presently known only from the northern Great Barrier Reef. The two species have many similarities, especially in the general shape of the frontal margin of the carapace, as well as in the shape and proportions of the chelipeds and walking legs (cf. Anker 2011). However, A. daviei has neither rostral teeth nor post-rostral tubercle (characteristic of A. manticolus sp. nov.), but on the other hand has spiniform setae on the propodus of the third and fourth pereiopods (absent in A. manticolus sp. nov.).

Athanas manticolus sp. nov. shares some characters, e.g., the absence of infra-corneal teeth, with Athanas iranicus Anker, Naderloo & Marin, 2010 from Iran; Athanas ahyongi Anker & Komai, 2010 from Madagascar and Japan; and Athanas shawnsmithi Anker, 2011 from the northern Great Barrier Reef. However, these three species differ from A. manticolus sp. nov. by the absence of rostral dentition and post-rostral tubercle, as well as by the differently shaped chelipeds (especially A. iranicus and A. shawnsmithi); A. iranicus also differs by the much longer second article of the antennular peduncle (cf. Anker & Komai 2010; Anker et al. 2010; Anker 2011). None of the remaining species of Athanas is morphologically close to A. manticolus sp. nov. (cf. De Man 1911; Holthuis 1951; Chace 1955; Banner & Banner 1960, 1973, 1978; Chace 1988; Bruce 1990; Anker 2003; Anker & Jeng 2007; Anker & Ahyong 2007; Anker & Marin 2007).

The colour pattern of Athanas manticolus sp. nov. is unique within the Alpheidae (A. Anker, pers. obs.) in the arrangement of the red chromatophores on the carapace and abdomen, resembling unorganised reddish “hairs” (Fig. 6A–C). In most other species of Athanas with an overall similar colour pattern (reddish body with a whitish or yellowish mediodorsal band), the chromatophores are grouped in smaller or larger dots, as in Athanas amazone Holthuis, 1951, A. japonicus (cf. Anker & Jeng 2007), A. shawnsmithi, A. daviei (cf. Anker 2011), or form a broad longitudinal band, as in A. ahyongi (cf. Anker & Komai 2010).

Athanas manticolus sp. nov. is the third species of Athanas reported to be associated with stomatopods, the other two being Athanas squillophilus Hayashi, 2002 from Japan and A. amazone from the Mediterranean Sea, both morphologically very different from the new species (cf. Holthuis 1951; Froglia & Atkinson 1998; Hayashi 2002). In addition, another species of Athanas, presumably closely related to A. ahyongi Anker & Komai, 2010, is known to be associated with larger lysiosquillid stomatopods in the Philippines and Indonesia, based on underwater photographs (Kuiter & Debelius 2009: p. 159; A. Anker, pers. obs.). The burrowing host of the Madagascar specimens of A. ahyongi remains unknown, but based on the substrate and shape of the burrow entrance it may be either a stomatopod or a callianassid ghost shrimp (A. Anker, pers. obs.). Thus, associations between shrimps of the genus Athanas and burrowing stomatopods (Squillidae, Lysiosquillidae, Nannosquillidae) appear to be relatively common and likely more stomatopod-associated species will be found in the future.