Atyoida chacei, Mazancourt & Marquet & Keith, 2024

Atyoida chacei sp. nov.

urn:lsid:zoobank.org:act:E409BE2B-D026-46D1-BE44-9CD5B34FC8E0

Figures 3B View Figure 3 , 4 View Figure 4 and 9B View Figure 9

- Atyoida cf. pilipes —Lorang et al., 2020 [45]: 300, Figure 1 View Figure 1 ;

- Atya serrata —Miyake, 1938 [10]: 111;

- Atyoida pilipes —Chace, 1983 [44]: 13, Figures 5–8 View Figure 5 View Figure 6 View Figure 7 View Figure 8 (part).—Maciolek and Ford, 1987 [13]: 628.—Nelson et al., 1996 [14]: 11.—Buden et al., 2001 [15]: 260.—Leberer and Cai, 2003 [18]: 354.—March et al., 2003 [20]: 126.—Page et al., 2007 [21]: 139, Figure 1 View Figure 1 (part); 2008 [46]: 73, Figure 4 View Figure 4 (part).—Benstead et al., 2009 [16]: 459.

Material examined

Type material:

PALAU: Babeldaob Island . Holotype: MNHN-IU-2024-439 (DNA: CA1858 ), 1 ♂, cl 4.7 mm, Tireloich river ( Station 3 ), 07 ◦ 41.417 ′ N, 134 ◦ 37.754 ′ E, 28 February 2011, coll. M. Castelin, P. Keith, P. Gerbeaux, G. Marquet and L. Taillebois. GoogleMaps Paratypes: MNHN-IU-2024- 440 (DNA: CA1859 ), 1 ♂, cl 4.7 mm, MNHN-IU-2024-441 (DNA: CA1863 ), 1 ♂, cl 4.5 mm, and MNHN-IU-2024-442 (DNA: CA1860 ), 1 ♀, cl 7.5 mm, same data as holotype. CA1863, no locality data. USNM 104901 : GoogleMaps 6 ♀ ovig., cl 5.9–7.3 mm and 1 ♀, cl 4.9 mm, Arakitaoch river ( station 241 ), 7 ◦ 32.836 ′ N, 134 ◦ 35.782 ′ E, 18 October 1955, coll. H.A. Fehlmann. USNM 104926 : GoogleMaps 1 ♂, cl 4.2 mm, 1 ♀ ovig., cl 6.0 mm and 4 ♀, cl 4.0 mm– 6.8 mm, Station 170-A , 27 November 1956, coll. H.A. Fehlmann. USNM 105280 : 1 ♀, cl 5.8 mm, South Fork of Arakitaoch river (station 170- A), 7 ◦ 31.556 ′ N, 134 ◦ 34.206 ′ E, 15 November 1956, coll. H.A. Fehlmann. GoogleMaps Arakabesan Island : USNM 172586 : 1 ♀ ovig., cl 7.0 mm, below reservoir , station 2 A 14-01 , 9 August 1976, coll. G. Bright.

FEDERATED STATES OF MICRONESIA: Pohnpei Island . MNHN-IU-2024-443 (DNA: CA1869 ): 1 ♂, cl 4.6 mm, MNHN-IU-2024-444 : 1 ♀, cl 5.1 mm, MNHN-IU-2024-445 (DNA CA1870 ): 1 ♀ ovig., cl 6.7 mm and MNHN-IU-2024-446 ( DNA CA 1871), Senipehn river ( Station 7 ), 06 ◦ 51.906 ′ N, 158 ◦ 16.010 ′ E, March 12 2012, 95 m a.s.l., coll. M. Castelin, P. Keith, P. Gerbeaux, G. Marquet, and L. Taillebois. ZMB 8926 : GoogleMaps 4 ♀, cl 4.7–6.1 mm, February 1880, coll. O. Finsch.

Comparative material:

Atyoida pilipes (Newport, 1947) : See [45].

Atyoida tahitensis Stimpson, 1860 : See [45].

Description

Cephalothorax. Rostrum short ( Figure 4o–q View Figure 4 ), 0.2–0.4 of cl, reaching near to or slightly beyond end of basal segment of antennular peduncle, with dorsal margin convex, ventral margin usually unarmed, sometimes with 1–2 teeth; antennal spine fused with inferior orbit angle, acute; pterygostomian margin acute.

Eyes well-developed. Antennular peduncle stout ( Figure 4o View Figure 4 ), 0.46 (♀)–0.65 (♂) times as long as carapace; basal segment shorter than half length of antennular peduncle, second segment longer than third segment. Stylocerite reaching near to or slightly beyond end of basal segment of antennular peduncle.

Pereiopods. Epipods on first four pereiopods. P1 and P2 similar in size and shape. Chelae dimorphic, ortmannioid in shape (palm present, Figure 4b,d View Figure 4 ) mostly in males and atyoid (palm virtually absent, Figure 4a,c View Figure 4 ) mostly in females. P1 ( Figure 4a,b View Figure 4 ) chela about 1.9–4.2 times as long as wide, movable finger 3.9–5.9 times as long as wide, 1.7–2.0 times length of palm with tufts of long setae distally, carpus excavated strongly anteriorly, 1.0–1.3 times as long as wide. P2 ( Figure 4c,d View Figure 4 ) chela 2.2–3.9 times as long as wide: dactylus 3.7–6.3 times as long as wide, 2.4 times length of palm with tufts of long setae distally, P2 carpus excavated strongly anteriorly, 1.0–1.8 times as long as wide. P3 ( Figure 4e View Figure 4 ) with row of setae on outer surface of merus, very short dactylus ( Figure 4f View Figure 4 ) ending in a strong claw, 1.7–3.2 times as long as wide (terminal spine included) with 2–6 spines on flexor margin in addition to the terminal spine; propodus 3.0–6.6 times as long as wide, 2.5–3.7 times as long as dactylus. P5 ( Figure 4g View Figure 4 ) with setae only present on carpus; dactylus ( Figure 4h View Figure 4 ) short, 2.1–3.5 times as long as wide with 8–18 spines on flexor margin; propodus 5.9–13.4 times as long as wide, 3.3–5.6 times as long as dactylus.

Abdomen. Sixth abdominal somite 0.45 times length of carapace, 1.2 times as long as fifth somite, 0.79 times as long as telson.

Telson ( Figure 4k View Figure 4 ) 2.4–2.8 times as long as wide, with from two to eight pairs of dorsal spinules, often not in pairs, one pair of dorsolateral spinules near dorsal end; posterior margin rounded with 8–11 plumose intermediate setae distinctly longer than lateral ones.

Male Pl1 ( Figure 4l View Figure 4 ): Endopod subtriangular, 3.4 times as long as wide, reaching 0.59 times length of endopod, with a distinct appendix interna near distal end of endopod.

Male Pl2 ( Figure 4m View Figure 4 ): Appendix masculina reaching 0.58 times length of endopod, inner and distal surface densely lined with long spines; appendix interna at basal 0.27 times length of appendix masculina, extending to distal 0.33 times length of appendix interna.

Preanal carina triangular ( Figure 4j View Figure 4 ) without spine.

Uropodal diaeresis ( Figure 4i View Figure 4 ) with 15–20 spinules.

Eggs ( Figure 4n View Figure 4 ): undeveloped: 0.31–0.29 mm × 0.52–0.51 mm.

Etymology

A. chacei sp. nov. is named in honor of Fenner A. Chace, Jr (1908–2004) as an acknowledgement to his posthumous cooperation with us on the study of Atya -like shrimps of the Indo-Pacific region and for being the first to suggest that the Atyoida from Palau may belong to a distinct species.

Colour pattern

Body transparent, flanks whitish ornamented with numerous dark blue-black spots and stripes all over the body.

Distribution

Reported only from Babeldaob Island and Pohnpei Island in Micronesia.

Habitat

This species is largely rheophile and prefers fresh and fast-flowing waters.

Remarks

Atyoida chacei sp. nov. resembles A. pilipes and A. tahitensis ( Table 3 View Table 3 ) by its short, unarmed, bent rostrum, as well as by the proportions between the joints of pereiopods and the presence of ortmannioid and atyid chelae. The absence of caridinoid chelae in males or in females in these three species distinguishes them from A. serrata (Bate, 1888) and A. bisulcata Randall, 1840 . Indeed, in these two species, the chelae are trimorphic: atyoid, caridinoid, and ortmannioid (see [44]).

Due to their high morphological variability, finding diagnostic characters to separate A. chacei sp. nov. from A. pilipes or A. tahitensis turned out to be a difficult task (see Table 3 View Table 3 ), so much so that they could be considered to be cryptic species, as they can only be distinguished by the following characters:

- Frequently, presence of one or more teeth on the ventral margin of the rostrum, vs. always 0 in A. pilipes and A. tahitensis . This character was already highlighted by Chace (1983): “Of 613 specimens with complete rostra from the Palau Islands, 270 have no ventral rostral teeth, 240 have 1, 97 have 2, 5 have 3, and 1 has 4”;

- Two–eight pairs of dorsal spinules, often not in pairs for A. chacei sp. nov. (vs. one–five pairs of dorsal spinules, often not in pairs for A. pilipes , vs. from two to four pairs of dorsal spinules, often in pairs for A. tahitensis );

- Posterior margin rounded with from 8 to 11 plumose intermediate setae distinctly longer than lateral ones (vs. 4 to 9 plumose intermediate setae distinctly longer than lateral ones for A. pilipes , vs. with 6 to 10 plumose intermediate setae distinctly longer than lateral ones for A. tahitensis );

- By the size of undeveloped eggs (0.51–0.52 mm × 0.29–0.31 mm (vs. 0.47–0.60 mm × 0.31–0.39 mm for A. pilipes , vs. 0.55–0.70 mm × 0.29–0.54 mm for A. tahitensis )).

Nevertheless, following an integrative taxonomy framework, their genetic distinctiveness (16S p-distances: 9–15%) 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., [47–49]).