Caridina sumatrensis De Man, 1892

Caridina sumatrensis De Man, 1892 View in CoL

( Figure 4E, F, 6)

Caridina weberi var. sumatrensis De Man, 1892: 375 View in CoL , pl. 22, fig. 23g, Type locality: Deli, Sumatra, Indonesia, Type material: Lectotype, ZMA De 102603, ovigerous female (CL 5.3 mm) (designated by Cai & Naiyanetr, 2024). Kemp, 1918a: 99; Pillai, 1964: 43.

Caridina weberi sumatrensis View in CoL – Bouvier, 1904: 132; Bouvier, 1905: 75, 83; Kemp, 1918b: 292, Bouvier, 1925: 247, fig. 567; Johnson, 1961: 46; Kazmi et al., 2002.

Caridina sumatrensis View in CoL – Wowor et al., 2004: 343, fig. 6p, q; Cai & Shokita, 2006: 246, fig. 6C–F; Cai et al., 2007: 285, fig. 7; Cai & Naiyanetr, 2024: 774, fig. 2, 3.

Materials examined. 9 females (CL 3.91–4.49 mm), 3 males (CL 2.51–2.94 mm)( MUMNH-CAR053 , used for measurement in description), Mae Klong River , Tha Maka District, Kanchanaburi Province, Thailand, 13.8679°N, 99.8167°E, coll. W. Siriwut & W. Manonai, 19 April 2019 GoogleMaps ; 1 female (CL 4.10 mm)( MUMNH-CAR054 ), Mae Klong River , Photharam District, Ratchaburi Province, Thailand, 13.6318°N, 99.8162°E, coll. W. Siriwut & W. Manonai, 19 April 2019 GoogleMaps ; 4 females (CL 3.29–4.21 mm)( MUMNH-CAR055 ), Mae Klong River , Photharam District, Ratchaburi Province, Thailand, 13.7152°N, 99.8492°E, coll. W. Siriwut & W. Manonai, 19 April 2019 GoogleMaps ; 3 females (CL 3.73–4.29 mm)( MUMNH-CAR056 ), Mae Klong River , Photharam District, Ratchaburi Province, Thailand, 13.7393°N, 99.8420°E, coll. W. Siriwut & W. Manonai, 19 April 2019 GoogleMaps ; 4 females (CL 3.57–4.08 mm) (used for measurement in description); 4 males (CL 2.41–2.93 mm) ( MUMNH-CAR706 , used for measurement in description), Klong Bang Tanod River , Photharam District, Ratchaburi Province, Thailand, 13.6537°N, 99.8116°E, coll. E. Jeratthitikul & K. Macharoenboon, 8 August 2019 GoogleMaps .

Description. Cephalothorax and cephalic appendage. CL 3.57–4.60 mm (median = 4.08 mm, n = 13), width 2.65–3.48 mm (median = 2.92 mm, n = 13). Rostrum with basal ridge, slightly bent down, frequently reaching near the end of antennular peduncle (at least reaching beyond the end of second segment of antennular peduncle), 0.50–0.60

(median = 0.55, n = 13) times as long as CL ( Fig 6A, B). Rostral formula based on 13 individuals: (4–6) + 17–21 / 3–6. Antennal spine placed below inferior orbital angle. Pterygostomian margin subrectangular. Eye well-developed, anterior end reaching to 0.59–0.84 (median = 0.71, n = 13) of first segment of antennular peduncle. Antennular peduncle 0.46–0.55 (median = 0.51, n = 13) times as long as carapace, first segment 1.60–2.15 (median = 1.80, n = 13) times as long as second segment, second segment 1.03–1.33 (median = 1.16, n = 13) times as long as third segment. Tooth on distolateral margin of first segment of antennular peduncle prominent. Stylocerite reaching to 0.59–0.74 (median = 0.70, n = 13) of first segment of antennular peduncle. Scaphocerite 2.50–2.97 (median = 2.75, n = 13) times as long as wide, distal margin with short plumose setae.

Branchial formula. Podobranch on second maxilliped well-developed. Third maxilliped possesses one small and one large arthrobranch. Pleurobranchs present on all pereopods. Third maxilliped with epipod. Ultimate segment of endopod with a row of strong spinules at proximal ⅔ of posterior margin, ending with one large claw, 5–7 spiniform setae on distal ⅓ of posterior margin, 0.74–0.91 (median = 0.83, n = 10) times as long as penultimate segment. Exopod long and slender, with a tuft of long setae at tip.

Pereopods. Epipod present on first four pereopods. Chelae of first and second pereopods well-developed ( Fig. 6E, F).

First pereopod short ( Fig. 6E); chela 2.11–2.66 (median = 2.18, n = 11) times as long as wide, 1.31–1.62 (median = 1.48, n = 11) times as long as carpus; tips of fingers rounded, with tuft of setae near tip; dactylus 0.91–1.26 (median = 1.07, n = 11) times as long as palm; carpus excavated distally, 1.40–1.83 (median = 1.67, n = 11) times as long as wide, 0.78–1.10 (median = 0.96, n = 11) times as long as merus; merus 2.44–2.93 (median = 2.62, n = 11) times as long as wide, 1.15–2.14 (median = 1.84, n = 11) times as long as ischium.

Second pereopod more slender than first pereopod ( Fig. 6F); chela long, 2.71–3.40 (median = 2.84, n = 11) times as long as wide, 0.65–0.87 (median = 0.74, n = 11) times as long as carpus, tips of fingers round, with tuft of setae near tip; dactylus 1.17–2.20 (median = 1.80, n = 11) times as long as palm; carpus slender, 4.63–6.69 (median = 5.72, n = 11) times as long as wide, 0.43–0.75 (median = 0.54, n = 11) times as long as merus; merus 5.00–7.41 (median = 5.83, n = 11) times as long as wide, 1.24–2.15 (median = 1.54, n = 11) times as long as ischium.

Third pereopod not sexually dimorphic ( Fig. 6G); dactylus with 4–6 spiniform setae on flexor margin ( Fig. 6H), 2.23–3.13 (median = 2.65, n = 9) times as long as wide (including terminal claw), terminating with one large claw; propodus with numerous spiniform setae on lateral and posterior margin, 8.49–11.53 (median = 9.71, n = 9) times as long as wide, 4.34–5.67 (median = 4.50, n = 9) times as long as dactylus; carpus with 3–5 spiniform setae on posterior margin of outer surface, the distal seta largest, the other setae minute, 4.13–5.36 (median = 4.69, n = 9) times as long as wide, 0.50–0.69 (median = 0.66, n = 9) times as long as propodus; merus with 4–5 large spiniform setae on posterior margin of outer surface, 6.25–6.96 (median = 6.67, n = 9) times as long as wide, 1.88–2.26 (median = 2.09, n = 9) times as long as carpus; ischium with one spiniform seta.

Fifth pereopod slender ( Fig. 6I); dactylus with 32–43 spiniform setae on flexor margin ( Fig. 6J, n = 9), 2.76–3.96 (median = 3.41, n = 9) times as long as wide (including terminal claw), terminating with one large claw; propodus with numerous spiniform setae on posterior margin, 12.39–14.45 (median = 13.61, n = 9) times as long as wide, 4.31–5.79 (median = 4.70, n = 9) times as long as dactylus; carpus with 3–5 spiniform setae on posterior margin of outer surface, the distal seta largest, the other setae minute, 4.65–5.78 (median = 5.05, n = 9) times as long as wide, 0.45–0.56 (median = 0.52, n = 9) times as long as propodus; merus with 2–4 (mode = 2, n = 9) large setae on posterior margin of outer surface, 6.12–7.45 (median = 6.91, n = 9) times as long as wide, 1.48–1.82 (median = 1.61, n = 9) times as long as carpus; ischium without spiniform setae.

Pleopods. Endopod of male first pleopod subtriangular ( Fig. 6O, P), wider proximally, 1.73–2.27 (median = 1.94, n = 7) times as long as width, 0.32–0.46 (median = 0.41, n = 7) times exopod length, with elongated appendix interna. Appendix masculina of second male pleopod rod-shaped ( Fig. 6Q, R), with numerous setae, 0.74–0.81 (median = 0.77, n = 7) times as long as endopod (including distal setae). Appendix interna slender, reaching 0.55–0.64 (median = 0.61, n = 7) times appendix masculina length.

Abdomen. Sixth abdominal somite 0.32–0.50 (median = 0.43, n = 10) times carapace length, 1.10–1.54 (median = 1.29, n = 10) times as long as fifth somite, 0.60–0.99 (median = 0.82, n = 10) times as long as telson ( Fig. 6A). Telson 2.33–2.96 (median = 2.71, n = 10) times as long as wide, with 3–4 pairs of dorsal spiniform setae and one pair of dorsolateral spiniform setae ( Fig. 6K). Distal margin of telson subtriangular, with a posteromedian projection, and 6–9 moveable plumose setae, subequal in length ( Fig. 6L). Preanal carina subtriangular, high, without a spine ( Fig. 6N). Uropodal diaeresis with 15–22 short moveable spiniform setae ( Fig. 6M).

Eggs. Ovigerous females with numerous eggs ( Fig. 3F, 6A). Size of eye-developed eggs 0.41–0.46 × 0.24–0.29 mm (n = 30).

Colour in life. Female and male shrimps exhibit distinct colouration. For specimens from the Mae Klong River, male body is translucent, decorated with scattered small dark spots ( Fig. 4E). Colour of female shrimps is frequently dark to light blue, decorated with scattered small dark spots ( Fig. 4F). Rostrum is yellowish-orange. Each abdominal somite furnished dorsally with conspicuous yellowish-orange bands. Eggs are brown to orange.

Distribution and habitat. Indonesia (Sumatra), Philippines, Singapore, Malaysia, Thailand, Myanmar, India, Pakistan ( Kemp, 1918a, b; Kazmi et al., 2002; Cai et al., 2007; Cai & Naiyanetr, 2024; this study). Based on the field survey in the Mae Klong Basin in this study, C. sumatrensis is restricted to the lower part of the basin ( Fig. 5), and commonly found in lowland rivers and their tributaries. They are found living on aquatic vegetation near the banks.

Remarks. The morphology of C. sumatrensis from the Mae Klong Basin in our collection closely matches with the original description ( De Man, 1892), redescription of type materials ( Cai & Naiyanetr, 2024), and descriptions in previous taxonomic literature (e.g., Kemp, 1918b; Pillai, 1964; Cai et al., 2007). Particularly, the characteristic of the slightly bent downward rostrum with a ridge at the base in our samples ( Fig. 6A, B) is in close agreement with illustrations by previous studies (i.e., De Man, 1892; Cai et al., 2007; Cai & Naiyanetr, 2024). Populations from Mae Klong Basin share a similar number of rostral teeth with those from the original description by De Man (1892), including the number of dorsal teeth (17–21 vs 16–20), ventral teeth (3–6 both in the Mae Klong population and the original description), and postorbital teeth (4–6 vs 5–6). The egg size of the Mae Klong population is also congruent with previous reports (0.41–0.46 × 0.24–0.29 mm vs 0.46–0.47 × 0.28–0.29 mm by Kemp, 1918b; 0.46 × 0.28 mm by Pillai, 1964; and 0.40–0.42 × 0.22–0.25 mm by Cai & Naiyanetr, 2024). However, the Mae Klong population possesses a slightly lower number of spiniform setae on the P5 dactylus (32–43 vs 36–57 by Kemp, 1918b; more than 40 by Cai et al., 2007; and 42–49 by Cai & Naiyanetr, 2024).

Originally, C. sumatrensis was proposed as a variant form of C. weberi , as “ Caridina weberi var. sumatrensis De Man, 1892 ”. Wowor et al. (2004) later elevated it as a valid species. This classification has been widely accepted in subsequent works ( Cai & Shokita, 2006; Cai et al., 2007; Cai & Naiyanetr, 2024). Caridina sumatrensis differs from C. weberi in several points (see summary in Table 3), including having a ridge at the base of rostrum (vs absent), longer rostrum (reaching near the end of third segment of antennular peduncle vs reaching to the base or near the middle of second segment of antennular peduncle), more dorsal teeth (16–20 vs 10–19, usually 13–14), more postorbital teeth (4–6 vs 0–2), shorter antennular peduncle (0.46–0.55 as long as CL vs 0.64 as long as CL), stouter P5 dactylus (2.76–3.96 vs 3.9–5.2 as long as wide), and the distal end of telson subtriangular (vs rounded) ( De Man, 1892; Cai et al., 2007, de Mazancourt et al., 2020; Cai & Naiyanetr, 2024; this study).

Caridina sumatrensis shares similarities with C. babaulti . However, several key morphological characteristics can be used to separate them. The P2 chela of C. sumatrensis is more slender than those of C. babaulti (2.71–3.40 vs 2.5–2.9), while the P3 dactylus of C. sumatrensis has fewer spiniform setae (4–6 vs 7–10). Caridina sumatrensis possesses a conspicuous posteromedian projection on the distal end of the telson. This feature is absent in C. babaulti . In addition, C. sumatrensis produces small-sized eggs, whereas the eggs of C. babaulti are much larger (0.41–0.46 × 0.24–0.29 mm vs 0.9–1.0 × 0.50–0.62 mm) ( Bouvier, 1918; Pandya & Richard, 2019).