Caridina mertoni Roux, 1911

Figs 2L, 8, 25G

Caridina mertoni Roux, 1911: 84 .

Caridina mertoni – Bouvier 1925: 191, figs 398–408. — de Mazancourt et al. 2019a: 166, 169–170.

Material examined

Lectotype (here designated)

INDONESIA • ♂, cl 3.8 mm; Kei Besar Island, Elat; 1908; H. Merton leg.; DNA voucher: CA056; NMB 693 a.

Paralectotypes

INDONESIA – Kei Besar Island • 1 ♂, cl 2.7 mm, 1 ♀, cl 4.1 mm; same collection data as for lectotype; NMB 693 a • 1 ♂, cl 3.8 mm; same collection data as for lectotype; MNHN-IU-2018-1819 • 1 ♂, cl 3.4 mm; same collection data as for lectotype; MNHN-IU-2015-1820 • 1 ♂, cl 3.1 mm, 1 ♀ ovig., cl 4.8 mm; Warka; 1908; H. Merton leg.; NMB 693 b • 1 ♀, cl 4.3 mm; Enralang; 1908; H. Merton leg.; NMB 693 c .

Other material

SOLOMON ISLANDS – Kolombangara Island • 1 ♂, cl 2.9 mm; Manolu River; 08°05.312´S, 157°00.813´E; 28 m a.s.l.; 10 Nov. 2015; P. Keith, C. Lord and G. Marquet leg.; MNHN-IU- 2017-2108 • 1 ♂, cl 3.8 mm; same collection data as for preceding; MNHN-IU- 2017-2107 • 1 ♂, cl 3.7 mm; same collection data as for preceding; DNA voucher: CA1505; MNHN-IU- 2017-2109 • 1 ♀ ovig., cl 3.9 mm; same collection data as for preceding; MNHN-IU- 2018-2815 • 1 ♂, cl 4.0 mm; Sulumuni River; 08°02.253´S, 157°09.257´E; 148 m a.s.l.; 12 Nov. 2015; P. Keith, C. Lord and G. Marquet leg.; MNHN-IU- 2018-2816 • 1 ♀, cl 6.2 mm; same collection data as for preceding; MNHN-IU- 2018-2817. – Malaita Island • 1 ♂, cl 4.5 mm; Tanana River; 09°17.383´S, 167°07.012´E; 276 m a.s.l.; 16 Jun. 2015; D. Boseto leg.; DNA voucher: CA2000; MNHN-IU- 2018-2818 • 1 ♂, cl 4.6 mm; same collection data as for preceding; MNHN-IU- 2018-2819 • 1 ♀, cl 5.6 mm; same collection data as for preceding; MNHN-IU- 2018-2820 • 1 ♂, cl 4.4 mm; Wairahuta River; 09°16.967´S, 161°07.285´E; 258 m a.s.l.; 17 Jun. 2015; D. Boseto leg.; MNHN-IU- 2018-2821 • 1 ♀, cl 5.5 mm; same collection data as for preceding; MNHN-IU- 2018-2822 • 1 ♀, cl 5.6 mm; same collection data as for preceding; MNHN-IU- 2018-2823 .

Description

CEPHALOTHORAX. Carapace (Fig. 8m) smooth, glabrous, suborbital angle obscure, largely fused with antennal spine angle; pterygostomian margin rectangularly rounded. Rostrum (Fig. 8 m–o) straight or slightly curved down, 0.6–1.1 of cl, sometimes slightly inclined distally, reaching as far as distal end of antennular peduncle. 17–24 dorsal teeth closely set, leaving 0.0–0.25 unarmed distally except for one or two subapical teeth, 2–5 post-orbital teeth present. 4–9 teeth present of ventral margin. Number of dorsal teeth on rostrum before first ventral tooth 12–19. Eyes well developed, anterior end reaching to 0.70–0.77 length of basal segment of antennular peduncle. Antennular peduncle 0.64 (♀) – 0.81 (♂) times as long as carapace. Anterolateral angle pointed, reaching to 0.40 length of second segment; second segment distinctly longer than third segment. Stylocerite reaching to 0.77–0.80 length of basal segment of antennular peduncle.

PEREIOPODS. Slender P1 (Fig. 8a): chela about 1.8–2.1 times as long as wide, dactylus 2.9–4.5 times as long as wide, 1.1–2.0 length of palm; carpus 1.9–2.6 times as long as wide, with shallow excavation on anterior margin. P2 (Fig. 8b): more slender and longer than first pereiopod: chela 1.9–2.5 times as long as wide, dactylus 3.6–5.0 times as long as wide, 1.4–2.1 times length of palm; carpus 4.4–5.6 times as long as wide. P3 (Fig. 8c): dactylus (Fig. 8e) 2.8–3.4 times as long as wide (terminal spiniform setae included), with 5–6 spiniform setae on flexor margin in addition to terminal one; propodus 12.8–18.3 times as long as wide, 4.5–6.7 times as long as dactylus. P5 (Fig. 8d): dactylus (Fig. 8f) 2.6–4.5 times as long as wide, with 27–44 spiniform setae on flexor margin; propodus 15.6–25.1 times as long as wide, 4.8–9.0 times as long as dactylus.

ABDOMEN. Typical dorsal hump over third abdominal somite, sixth abdominal somite 0.71 times as long as carapace, 1.7 times as long as fifth somite, slightly shorter than telson.

TELSON (Fig. 8i). 2.7 times as long as wide, with four pairs of dorsal spinules and one pair of dorsolateral spinules; posterior margin with a median process, distal setae short, lateral pair slightly shorter or longer than intermediate setae (5–8).

MALE PLEOPODS. Pl1 (Fig. 8j): endopod subtriangular, 1.6 times as long as wide, 0.20 times as long as exopod, with appendix interna placed at distal end. Pl2 (Fig. 8k): appendix masculina reaching 0.54 times length of endopod; appendix interna reaching 0.87 of appendix masculina.

PRE- ANAL CARINA (Fig. 8g). Without spine.

UROPODAL DIAERESIS (Fig. 8h). With 8–14 spinules.

EGGS (Fig. 8l). Size: 0.44–0.49 × 0.24–0.29 mm.

Habitat

This species prefers fresh and well-oxygenated waters. It is found from the middle to the higher course of rivers. They are more abundant in areas situated above waterfalls where predators are less numerous.

Colour pattern (Fig. 25G)

The colour of the body is hyaline with many red dots and oblique red bands.

Distribution

Caridina mertoni is known from Indonesia (Grand-Kei island and Waigeo (Roux 1928)) and the Solomon Islands (Kolombangara and Malaita).

Remarks

Our specimens from Solomon Islands look like the type specimens: rostrum with presence of 2–3 postorbital teeth (vs 2–5 in type specimens), 17–24 dorsal teeth (vs 20–23) and 4–9 ventral teeth (vs 4–7); P1 carpus 1.9–2.6 times as long as wide (vs. 2.0–2.5); P2 carpus 4.6–5.6 times as long as wide (vs 4.4–5.1). P3 dactylus with 5–6 spiniform setae (vs 5–6), propodus 4.8–6.7 times as long as dactylus (vs 4.5–5.9); P5 dactylus with about 27–39 spiniform setae (vs 36–44), propodus 18.2–25.1 times as long as width (vs 15.6–21.4) and dactylus 2.6–4.5 times as long as wide (vs 2.8–4.1); number of spinules on uropodal diaresis 10–13 (vs 8–14); small eggs 0.44–0.49 × 0.28–0.29 (vs 0.44–0.46 × 0.24–0.26 mm). Some values given by Bouvier (1925) are also similar: P3 dactylus with 5–6 spiniform setae (vs 5–6 according to Bouvier (1925)), P5 dactylus with about 30–35 spiniform setae (vs 27–39), telson with 5 intermediate setae as long as or slightly longer than the lateral pair (vs 2–4 pairs of intermediate setae, lateral pair no longer than intermediate). The type specimens exhibit a shorter rostrum than those collected from Solomon Islands: 0.6–0.8 of cl (vs 09–1.1). However, the rostrum length widely used in Caridina taxonomy might not be as reliable as previously thought. It is highly plastic and varies with environmental parameters (de Mazancourt et al. 2017b).