Atyoida tahitensis (Stimpson 1860)

(Figure 4)

Atyoida tahitensis Stimpson, 1860: 28 [type locality: Tahiti, French Polynesia].

Not Atya serrata – Edmondson, 1935: 14, fig. i.

Not Atyoida pilipes - Keith et al. 2013: 72-73 (partim).

Not Atyoida pilipes - Keith et al. 2002: 38-39.

Material examined:

Neotype (here designated): FRENCH POLYNESIA. TAHITI. Mahina, 1♂ cl 5.6mm (MNHN-IU-2018-3290; DNA: CA2376), 17°32.241’S, 149°29.269’W, April, 1995, 114m a.s.l., coll. J. Poupin, E. Tavosso .

FRENCH POLYNESIA. TAHITI. Papehere river, 1♂ immature, cl 3.1mm (MNHN-IU-2018-3283), 1♀ ovig., cl 5,8mm (MNHN-IU-2018-3284; DNA: CA2060), 1♀ ovig., cl 7.7mm (MNHN-IU-2018-3285; DNA: CA2381), 1♀ ovig., cl 6.8 mm (MNHN-IU-2018-3286; DNA: CA2382), 1♀, cl 7,8mm (MNHN-IU-2018-3287; DNA: CA2384), 1♀, cl 7,1mm (MNHN-IU-2018-3288), and 1♀, cl 6.8mm (MNHN-IU-2018-3289; DNA: CA2387), 17°49.719’S, 149°17.067’W, October 02, 2017, 16m a.s.l., coll. G. Marquet, P. Tiberghien.- Mahina river, 1♀ ovig., cl 6.4mm (MNHN-IU-2018-3291; DNA: CA2378), and 1♀, cl 6.4mm, 17°32.241’S, 149°29.269’W, April, 1995, 114m a.s.l., coll. J. Poupin, E. Tavosso. MOOREA. Afeareatu river, 1juv., cl 4.5mm (MNHN-IU-2018-3292; DNA: CA2380), 1♂, cl 4.4mm (MNHN-IU-2018-3293; DNA: CA2065) and 1♂, 4.6mm (MNHN-IU-2018-3294; DNA: CA2064), 17°32.629’S, 149°48.555’W, November 05, 2017, 139m a.s.l., coll. G. Marquet, P. Tiberghien. RURUTU. Puputa river, 1♀, cl 5.7mm (MNHN-IU-2018-3295; DNA: CA2057) and 1♀, 6,7mm (MNHN-IU-2018-3296), 22°27.009’S, 151°21.061’W, September 26, 2017, 99m a.s.l., coll. G. Marquet, P. Tiberghien. COOK ISLANDS. RAROTONGA. Avana river, 1♂, cl 5.4mm (MNHN-IU-2018-3297; DNA: CA2372), 1♀, cl 6.7mm (MNHN-IU-2018-3298; DNA: CA1978) and 1♀, cl 7.4 (MNHN-IU-2018-3299; DNA: CA1977), 21°14.462’S, 159°43.546’W, November 07, 2010, 12m a.s;l., coll. P. Gerbeaux, P. Keith; G. Marquet. MANGAREVA. Gatavake river, August 1986, 1♀ ovig., cl 6.1mm, 1♀, cl 6.0mm and 1♂, cl 3.6mm (USNM 231705).

Description

Cephalothorax. Rostrum short (Fig. 4n), 0.2-0.3 of cl, reaching near to end of basal segment of antennular peduncle, with dorsal margin convex, apex slightly ventrally, ventral margin unarmed; Antennal spine fused with inferior orbit angle, acute; pterygostomian margin acute.

Eyes well developed. Antennular peduncle stout, 0.40 (♀) - 0.70 (♂) times as long as carapace; basal segment shorter than half length of antennular peduncle, second segment longer than third segment. Stylocerite reaching 0.81-0.94 length of the basal segment of antennular peduncle.

Pereiopods. Epipods on first 4 pereiopods. P1 and P2 similar in size and shape. Chelae dimorphic, caridinoid in shape in males and atyoid in females. ♂ P1 (Fig. 4b) chela about 1.8-3.7 times as long as wide, movable finger 3.2- 5.0 times as long as wide1.1-7.4 times length of palm; ♀ P1 (Fig. 4a) chela 2.0-3.9 times as long as wide, dactylus 3.9-6.0 times as long as wide, with tufts of long setae distally, carpus excavated strongly anteriorly, 0.8-1.2 times as long as wide. ♂ P2 chela 1.8-4.0 times as long as wide: movable finger 3.9-5.3 times as long as wide, 1.4-7.4 times length of palm; ♀ P2 (Fig. 4c) chela 1.9-3.9 times as long as wide, dactylus 3.9-5.3 times as long as wide, with tufts of long setae distally, P2 carpus excavated strongly anteriorly, 1.0-1.9 times as long as wide. P3 (Fig. 4d) with row of setae on outer surface of each joint, very short dactylus (Fig. 4f) ending in a strong claw, 2.2-3.7 times as long as wide (terminal spine included) with 3-6 spines on flexor margin in addition to the terminal spine; propodus 3.9-7.1 times as long as wide, 1.8-3.5 times as long as dactylus. P5 (Fig. 4e) with setae only present on merus; dactylus (Fig. 4g) short 1.7-4.4 as long as wide with 5-13 spines on flexor margin; propodus 6.0-10.4 times as long as wide, 2.7-8.8 times as long as dactylus.

Abdomen. Sixth abdominal somite 0.56 times of carapace, 1.4 time as long as fifth somite, 0.80 as long as telson.

Telson (Fig. 4j) 2.5-3.2 times as long as wide, with 2 to 3 pairs of dorsal spinules, often in pairs, one pair of dorsolateral spinules near dorsal end; posterior margin rounded with 6 à 13 plumose intermediate setae distinctly longer than lateral ones.

Pl1 (Fig. 4k): Endopod of male subtriangular, 2.6 times as long as wide, reaching 0.75 times of endopod, with a distinct appendix interna near distal end of endopod.

Pl2 (Fig. 4l): Appendix masculina of male reaching 0.78 times length of endopod, inner and distal surface densely lined with long spines; appendix interna at basal 0.36 times length of appendix masculina, extending to distal 0.36 length of appendix interna.

Triangular preanal carina (Fig. 4h) without spine.

Uropodal diaeresis (Fig. 4i) with 11-18 spinules.

Eggs (Fig. 4l): developed (visible eyes): 0.32-0.54 × 0.57-0.72mm; undeveloped: 0.33-0.39 × 0.55-0.57mm.

Habitat

The habitat of A. tahitensis (named A. pilipes in the papers cited below) has been particularly studied in Oponuhu Valley watershed (Moorea island) by Resh et al. (1990), Feldman (1996), Falvo (2013) and Goldstein (2016). A. tahitensis covers a broad elevation range from 2 to 335m (Resh et al. 1992). In this study, it represented only 5% of the shrimps found at three low elevation sites, 11% at three middle elevation sites and 30% at three high elevation sites. This distribution range is positively correlated with elevation and distance from stream mouth (Goldstein 2016). According to Falvo (2013), it is more strongly built and its appendages may also be better suited for gripping substrate and for withstanding strong current, explaining its ability to reach higher altitudes. Of the A. tahitensis caught, 143 were caught in leaf packs, 79 in riffles, 47 in banks without vegetation, 35 in pools, 26 in runs, and 6 in banks with vegetation.

Colour pattern

The body is blackish on its back, ornamented on its flanks with numerous bluish dots and longitudinal stripes (Fig. 6).

Distribution

See remarks below. This species (Fig. 7) is restricted to Cook Islands (Rarotonga) and in French Polynesia to Austral, Gambier and Society archipelagoes. Rapa in Austral archipelago and Mangareva in Gambier archipelago correspond respectively to the most southerly (27°35’S) and easterly extension (135°W) of the genus Atyoida, with A. tahitensis being present.

Remarks.

Atyoida tahitensis looks like A. pilipes by its short, unarmed, and bent rostrum, by the proportions between the joints of pereiopods and the egg size. Due to their high morphological variability, finding diagnostic characters to separate A. tahitensis from A. pilipes turned out to be a difficult task (see Table 2), so much that they could be considered to be cryptic species, as they can only be distinguished by the telson: 2 to 3 pairs of dorsal spinules, often in pairs for A. tahitensis (vs 1 to 5 pairs of dorsal spinules, often not in pairs for A. pilipes); posterior margin rounded with 6 to 13 plumose intermediate setae distinctly longer than lateral ones (vs posterior margin rounded with 4 to 9 plumose intermediate setae distinctly longer than lateral ones) and by their uropodal diaeresis with 11-18 spinules (vs 15-22 spinules). Nevertheless, following the integrative taxonomy framework, their genetic distinctiveness coupled with their discrete geographical distribution provides enough evidence to distinguish the two species as distinct taxa, as it was the case for other species of freshwater shrimps (e.g. Christodoulou et al. 2012; de Mazancourt et al. 2019; Choy et al. 2019a, b). One of us (GM) captured numerous specimens of “ Atyoida pilipes ” from Mangareva in 1986, which were deposited in the USNM (USNM 231705). Some specimens were re-examined. All have a telson with more than nine plumose intermediate setae on its posterior margin and less than 18 spinules on its uropodial margin. We can conclude that A. tahitenisis occurs in Mangareva but not A. pilipes . In Rapa and Mangareva islands “ Atya serrata ” were collected by the Mangarevan Expedition of Bernice Bishop Museum in 1934 (Edmondson 1935). We can affirm that it is A. tahitensis that is found at Rapa Island instead of A. serrata, which occurs in Indian Ocean (Chace 1983).

As the type locality of A. tahitensis described by Stimpson, is “In aquis dulcibus insulae Tahiti”, we affirm that all specimens genetically and morphologically similar to those of Tahiti belong to this species. The description of one specimen of A. tahitenis by Stimpson is very succinct and therefore not informative: “A. bisulcatae valde similis (an diversa?) sed rostro paullo breviore, latiore et magio depresso; flagelle externa antennularum quam internum dimidia breviore; et angulo postero-inferiore segmenti abdominis quinti minus acuto”. Chace (1983) considered A. tahitensis to be a junior synonym of A. pilipes . In this paper we demonstrate that A. pilipes and A. tahitensis are distinct species. Since the original type specimens were destroyed in the Great Chicago Fire of 1871, to prevent taxonomic confusion, we here designate an adult male specimen (cl 5.6mm) from Mahina river, Tahiti, as the neotype of Atyoida tahitensis (Stimpson 1860) . It is deposited in the MNHN (collection number: MNHN-IU-2018-3290).