Caridina bruneiana Choy, 1992

Caridina bruneiana Choy, 1992 View in CoL

( Figure 3)

In order to account for the morphological variability across its range, C. bruneiana Choy, 1992 is re-described here based on specimens from Mindoro. This re-description combined with the DNA analysis enabled us to remove all remaining doubts regarding the validity of this species.

Caridina bruneiana Choy, 1992 [ 64]: 49, Figs. 1–4 (Type locality: Negara Brunei Darussalam, on the upper reaches of Temburong River at Batang Duri, 04 ◦ 36 Į 05 ĮĮ N 115 ◦ 06 Į 45 ĮĮ E, altitude approx. 33 m) .

Caridina bruneiana View in CoL —Wowor et al., 2004 [ 59]: 343 (key), Fig. 7A–C; Cai et al., 2007 [ 60]: 284.

Material examined:

PHILIPPINES — 2 ♂ cl 2.8–3.1 mm, 2 ♀ ov. cl 4.3–4.4 mm; Roxas, Baroc River, Oriental Mindoro ; 12.6169, 121.4031 GoogleMaps ; 02.04.2013 ; coll. Freitag ; ZMB 32805 ( DNA 3161 and 3162) .

Comparative material:

Caridina bruneiana Choy, 1992

BRUNEI — 3 specimens; Temburong River tributary Sungai Seluju, small tributary near UBD field station ; 4.5638, 115.1486 GoogleMaps ; 90 m a.s.l .; 10.2018 ; coll. H. Freitag ; ZMB 34587 ( DNA 3421 and 3423) .

Caridina sumatrensis De Man, 1892

INDONESIA — Syntype, 1♀, cl 4.9 mm; Sumatra, Batak land, near Deli ; 12.1890 ; coll. C. Moesch ; MNHN-IU-2015-1758.— 1 ♀ ovig., cl 5.1 mm ; Java ; NMB 6. II. b.—Non type, 1♀, cl 6.0 mm ; ca. 5 km. Sfrom Deli Tua, Sungai Seruai , Deli, N. E. Sumatra ; 16.11.1984 ; coll. M. Kottelat ; RMNH. CRUS.D.54754 .

Description:

Cephalothorax. Antennal spine below the suborbital angle. Pterygostomian margin blunt. Rostrum ( Figure 3m –o): straight or slightly bent downward, 0.7–0.9 of cl, shorter or as long as the antennular peduncle, armed with 21–26 teeth on the dorsal margin, 3–4 of them situated on the carapace behind the orbital margin, ventral margin with 3–4 teeth. Rostral formula: (3–4) 21–26/3–4.

Eyes well developed, anterior end reaching to 0.68 length of the basal segment of the antennular peduncle. Antennular peduncle 0.71(♀)–0.85(♂) times as long as the carapace. Second segment shorter or the same length as the third. Stylocerite reaching the middle of the basal segment of the antennular peduncle.

Pereiopods. Epipods on the first four pereiopods. P1 ( Figure 3a): chela 2.2 times as long as wide, movable finger 4.1–4.8 times as long as wide, 1.6–1.8 times length of palm; carpus 1.8–2.2 times as long as wide. P2 ( Figure 3b) more slender and longer than P1 with chela 2.6 times as long as wide: movable finger 4.6–6.2 times as long as wide, 1.7–2.1 times the length of the palm; carpus 3.7–4.7 times as long as wide. P3 ( Figure 3c): slender, dactylus ( Figure 3e) short, 2.8–3.0 times as long as wide (terminal spiniform seta included) with 4 spiniform setae on the flexor margin in addition to the terminal spiniform seta; propodus 12.7–14.0 times as long as wide, 5.3–6.5 times as long as the dactylus. P5 ( Figure 3d): dactylus ( Figure 3f) short, 2.4–3.1 times as long as wide with 16–21 spiniform setae on the flexor margin; propodus 16.1–17.2 times as long as wide and 6.0–9.1 times as long as the dactylus.

Abdomen. Third abdominal somite with moderately convex dorsal profile. Sixth abdominal somite about 0.52–0.61 the carapace length and 1.45–1.75 times as long as the fifth somite, reaching 0.7–0.95 times the length of the telson.

Telson ( Figure 3i) with 2–4 pairs of dorsal spinules and one pair of dorsolateral spinules; posterior margin with a median process, rounded with 2–4 intermediate plumose setae shorter than the lateral ones, which bear thin lateral setulae on the inner margin.

Pl1 ( Figure 3j): Endopod of male triangular, 2.2–2.4 times as long as wide, reaching 0.27–0.34 times the exopod, with an appendix on the subdistal outer margin which reaches beyond the distal end of the endopod by half of its length.

Pl2 ( Figure 3k): Appendix masculina on the second pleopod reaching 0.51 times the length of the endopod; appendix interna reaching 0.35 times the appendix masculina.

Preanal carina ( Figure 3g) unarmed, higher in females than in males, with few long setae.

Uropodal diaeresis ( Figure 3h) weakly sigmoid, with 12–14 spinules.

Eggs ( Figure 3l) small, 0.34–0.43 × 0.22–0.24 mm (undeveloped).

Habitat: This species is found in the middle course of rivers.

Distribution: Known from Brunei, Singapore, and Mindoro Island (the Philippines).

Remarks:

Acombination of morphological characters makes the placement of this species within a species group difficult. Indeed, it can be brought close to the C. nilotica group as redefined by de Mazancourt et al. (2020) [ 65] with its antennal spine inferior to the suborbital angle, its sixth abdominal somite longer than half the carapace length, and its triangular endopod of the first male pleopod and its uropodal diaeresis with fewer than 15 spinules. However, the absence of apical teeth on the dorsal margin of its rostrum, its high pre-anal carina, and the absence of a dorsal hump on its third abdominal segment are characters more typical of the C. weberi and C. typus groups as defined by the same authors (de Mazancourt et al., 2020) [ 65]. Its telson, however, is unique by the setation on its distal margin with few intermediate plumose setae shorter than the lateral ones. Finally, its position within the molecular phylogeny presented here is poorly resolved, advocating further for its distinctiveness from all the other species groups.

From the high number of post-orbital teeth on the dorsal margin of the rostrum (3–4), this new species resembles Caridina sumatrensis , reported by Cai and Shokita (2006) [ 12] from Palawan Island. However, it can be easily distinguished by its antennal spine which is placed below the orbital angle (vs. fused), its higher number of dorsal teeth on the rostrum 21–26 (vs. 15–22), the lower number of intermediate plumose setae on the distal margin of the telson 2–4 (vs. 4–5) and intermediate setae being shorter than lateral ones (vs. intermediate longer than lateral), and the lower number of spinules on the diaeresis 12–14 (vs. 18–19). The probable sexual dimorphism of the pre-anal carina is interesting to note; the examination of more specimens from other localities will allow us to confirm it.

This is the first record of this species from the Philippines. It was originally described from Brunei and later found in Singapore (Cai et al., 2007 [ 60]). Since this species produces small-sized eggs, it is likely amphidromous and thus expected to have a wide distribution.

This species has been assessed as Least Concern for the IUCN Red List (De Grave and Cai, 2013 [ 66]).