Caridina maeklongensis, Macharoenboon & & Jeratthitikul & Ekgachai, 2024

Caridina maeklongensis , new species

( Figs. 2, 3, 4A–D)

Type materials. Holotype, ovigerous female (CL 3.44 mm; Fig. 2A) ( MUMNH-CAR064-9 ), Sai Yok Yai Waterfall , Sai Yok District, Kanchanaburi Province, Thailand, 14.4363°N, 98.8516°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; Paratypes, 7 females (CL 3.17–3.53 mm)( MUMNH-CAR064-1 , CAR 064-7, CAR 064-10, CAR 064-13, and CAR 064-15) ; 4 males (CL 2.87–3.25 mm) ( MUMNH-CAR064-2 to CAR 064-5), same collection data as for the holotype GoogleMaps ; 2 females (CL 3.55–3.97 mm) ( MUMNH-CAR062-1 and CAR062-2), Mae Plu Stream , Si Sawat District, Kanchanaburi Province, Thailand, 14.8043°N, 98.1822°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps .

Non-type materials. 13 females (CL 3.08–3.88 mm), 1 male (CL 2.76 mm)( MUMNH-CAR060 ), Phu Nong Pling Wetland , Thong Pha Phum District, Kanchanaburi Province, Thailand, 14.6278°N, 98.6073°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; 16 females (CL 3.20–4.16 mm)( MUMNH-CAR061 ), U-long Stream , Thong Pha Phum District, Kanchanaburi Province, Thailand, 14.7836°N, 98.6711°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; 8 females (CL 3.60–4.24 mm), 3 males (CL 3.13–3.25 mm)( MUMNH-CAR062 ), Mae Plu Stream , Si Sawat District, Kanchanaburi Province, Thailand, 14.8043°N, 98.1822°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; 6 females (CL 2.96–3.49 mm) ( MUMNH-CAR063 ), Huai Mae Khamin Waterfall , Si Sawat District, Kanchanaburi Province, Thailand, 14.6380°N, 98.9866°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; 5 females (CL 2.96–3.49 mm)( MUMNH-CAR064 ), Sai Yok Yai Waterfall , Sai Yok District, Kanchanaburi Province, Thailand, 14.4363°N, 98.8516°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps ; 4 females (CL 3.28–4.01 mm), 1 male (CL 2.61 mm)( MUMNH-CAR065 ), Khayeng Stream , Thong Pha Phum District, Kanchanaburi Province, Thailand, 14.6330°N, 98.5684°E, coll. E. Jeratthitikul, W. Siriwut & K. Macharoenboon, 25 June 2019 GoogleMaps .

Description. Cephalothorax and cephalic appendage. CL 3.17–3.97 mm (median = 3.44 mm, n = 7), width 2.12–3.06 mm (median = 2.47 mm, n = 7). Rostrum with basal ridge, slightly or moderately bent down, frequently reaching near the end of second segment of antennular peduncle, 0.38–0.54 (median = 0.46, n = 7) times as long as CL ( Fig. 2A, B). Rostral formula based on seven individuals: (3–4) + 9–14 / 1–4. Antennal spine placed below inferior orbital angle. Pterygostomian margin subrectangular. Eye well-developed, anterior end reaching to 0.48–0.70 (median = 0.55, n = 7) of the first segment of antennular peduncle. Antennular peduncle 0.47–0.59 (median = 0.55, n = 7) times as long as carapace, first segment 1.63–2.47 (median = 1.80, n = 7) times as long as second segment, second segment 1.03–1.47 (median = 1.30, n = 7) times as long as third segment. Tooth on distolateral margin of first segment of antennular peduncle prominent ( Fig. 2D). Stylocerite reaching to 0.54–0.77 (median = 0.65, n = 7) of first segment of antennular peduncle. Scaphocerite 2.49–2.69 (median = 2.63, n = 7) 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 ( Fig. 2E). Ultimate segment of endopod with a row of strong spinules at proximal ⅔ of posterior margin, ending with one large claw, 5–6 spiniform setae on distal ⅓ of posterior margin, 0.95–1.04 (median 1.00, n=7) 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. 3A, B).

First pereopod short ( Fig. 3A); chela 1.63–2.35 (median = 1.98, n = 6) times as long as wide, 1.09–1.53 (median = 1.26, n = 6) times as long as carpus; tips of fingers rounded, with tuft of setae near tip; dactylus 0.98–1.27 (median = 1.05, n = 6) times as long as palm; carpus excavated distally, 1.52–2.26 (median = 1.74, n = 6) times as long as wide, 0.88–1.02 (median = 0.98, n = 6) times as long as merus; merus 2.33–3.04 (median = 2.78, n = 6) times as long as wide, 1.31–2.16 (median = 1.72, n = 6) times as long as ischium.

Second pereopod more slender than first pereopod ( Fig. 3B); chela long, 2.40–3.56 (median = 2.83, n = 6) times as long as wide, 0.72–0.78 (median = 0.74, n = 6) times as long as carpus, tips of fingers round, with tuft of setae near tip; dactylus 1.19–1.66 (median = 1.52, n = 6) times as long as palm; carpus slender, 4.57–6.09 (median = 5.10, n = 6) times as long as wide, 1.10–1.27 (median = 1.14, n = 6) times as long as merus; merus 4.06–5.93 (median = 5.31, n = 6) times as long as wide, 1.52–1.80 (median = 1.63, n = 6) times as long as ischium.

Third pereopod not sexually dimorphic ( Fig. 3C); dactylus with 5–7 spiniform setae on flexor margin ( Fig. 3D), 2.97–3.41 (median = 3.20, n = 6) times as long as wide (including terminal claw), terminating with one large claw; propodus with numerous spiniform setae on lateral and posterior margin, 8.36–10.82 (median = 9.35, n = 6) times as long as wide, 3.55–4.42 (median 4.05, n = 6) times as long as dactylus; carpus with 2–4 spiniform setae on posterior margin of outer surface, the distal seta largest, the other setae minute, 4.47–6.05 (median = 4.81, n = 6) times as long as wide, 0.59–0.70 (median = 0.63, n = 6) times as long as propodus; merus with three large spiniform setae on posterior margin of outer surface, 6.16–6.80 (median = 6.50, n = 6) times as long as wide, 1.89–2.27 (median = 1.99, n = 6) times as long as carpus; ischium with one spiniform seta.

Fifth pereopod slender ( Fig. 3E); dactylus with 24–38 spiniform setae on flexor margin ( Fig. 3F), 3.40–3.70 (median = 3.65, n = 5) times as long as wide (including terminal claw), terminating with one large claw; propodus with numerous spiniform setae on posterior margin, 10.61–14.51 (median = 13.43, n = 5) times as long as wide, 3.66–4.71 (median = 4.11, n = 5) times as long as dactylus; carpus with 2–3 (mode = 3, n = 5) spiniform setae on posterior margin of outer surface, the distal seta largest, the other setae minute, 4.19–4.89 (median = 4.37, n = 5) times as long as wide, 0.45–0.50 (median = 0.49, n = 5) times as long as propodus; merus with two large setae on posterior margin of outer surface, 5.73–7.23 (median = 6.35, n = 5) times as long as wide, 1.54–1.64 (median = 1.59, n = 5) times as long as carpus; ischium without spiniform setae.

Pleopods (n = 4). Endopod of male first pleopod subtriangular ( Fig. 3G, H), wider proximally, 2.05–2.56 (median = 2.21, n = 4) times as long as width, 0.38–0.48 (median = 0.43, n = 4) times exopod length, with elongated appendix interna, emerged near the tip. Appendix masculina of second male pleopod rod-shaped ( Fig. 3I, n = 4), with numerous setae, 0.70–0.73 (median = 0.71, n = 4) times as long as endopod (including distal setae). Appendix interna slender, reaching 0.69–0.76 (median = 0.7, n = 4) times of appendix masculina length ( Fig. 3J).

Abdomen. Sixth abdominal somite 0.44–0.52 (median = 0.48, n = 7) times carapace length, 1.13–1.48 (median = 1.29, n = 7) times as long as fifth somite, 0.76–0.93 (median = 0.84, n = 7) times as long as telson ( Fig. 2A). Telson 2.33–2.79 (median = 2.60, n = 7) times as long as wide, with 3–4 pairs of dorsal spiniform setae and one pair of dorsolateral spiniform setae ( Fig. 2K). Distal margin of telson subtriangular, posteromedian projection absent or greatly reduced, with 6–8 moveable plumose setae that are subequal in length ( Fig. 2L). Uropodal diaeresis with 13–19 short moveable spiniform setae ( Fig. 2M). Preanal carina subtriangular, with a few setae, without a spine ( Fig. 2N). Eggs. Ovigerous females with few eggs (25– 35 eggs per individual; n = 3). Size of eye-developed eggs 0.82–0.93 × 0.51–0.60 mm (n = 30).

Colour in life. Female and male shrimps exhibit distinct colouration. Male body is translucent, decorated with scattered small dark spots ( Fig. 4A). Colour of female shrimps is variable, as dark blue, copper, or brown ( Fig. 4B–D). Rostrum is yellowish-orange. Cephalic region is decorated with gold, orange, and brown stripes. Each abdominal somite furnished dorsally with conspicuous yellow-orange bands. Eggs are dark brown to dark orange.

Distribution and habitat. Based on the present study, the distribution range of the new species is limited to the upper part of the Mae Klong Basin in western Thailand ( Fig. 5). They are commonly found in aquatic vegetation near stream banks or ponds located near waterfalls or headwaters.

Etymology. The specific name is from its type locality, the Mae Klong Basin.

Remarks. The phylogenetic tree suggests a sister relationship between the new species and C. sumatrensis ( Fig. 1). These two species resemble each other in having similar P1 and P2, and appendix interna on the endopod of the first pleopod in males. However, they can be distinguished by the following diagnostic features (a comparison of key characters among spine, length in absent without a 0.60 mm maeklongensis new species subequal, or reduced subtriangular 13 19 –,, high present 0.93 – 0.51 × C. – 6 8 setae greatly subtriangular 0.82 – & Pandya vary shorter or. spine) spines spines babaulti C., 1918 Bouvier, Bouvier from; 1918, 2019 Richard 8 intermediate, setae fractionally, length longer lateral the than absent rounded 21 12 – without subtriangular a, present 1.0 – mm 0.9 – × 0.62 0.50 (– 4 spine length a mm. sumatrensis 1892, Man De) study (this, in subequal present subtriangular 22 – 15 without high,, present × 0.29 0.24 0.46 – C 9 – setae 6 subtriangular – 0.41 Mazancourt) longer setae ones spine 0.25 mm 1892; 2020 a – weberi . C Man, De 1892, Man,. et al, intermediate lateral than present rounded 21 17– without, present 0.19 0.42 × De setae high 0.35 – from – 11 (6 on telson projection telson of telson diaeresis on endopod Characters setae Plumose Posteromedian distal end on end of Distal Setae uropodal on Preanal carina Appendix interna male Pl of 1 Egg size species is presented in Table 3). The rostrum of the new species is relatively shorter when compared to C. sumatrensis (reaching near the end of second segment of antennular peduncle vs reaching near the end of antennular peduncle). The rostral teeth of the new species are fewer than those of C. sumatrensis , including the dorsal teeth (9–14 vs 12–17), the ventral teeth (1–4 vs 3–6), and the postorbital teeth (3–4 vs 4–6). The new species possesses a greatly reduced or absent posteromedian projection on the distal end of the telson, whereas this character is well-developed in C. sumatrensis . Lastly, eggs of the new species are much larger than C. sumatrensis (0.82–0.93 × 0.51–0.60 mm vs 0.41–0.46 × 0.24–0.29) ( De Man, 1892; Cai et al., 2007; this study).

The morphology of the new species is also similar to that of C. weberi (see summary in Table 3). However, it differs from C. weberi in several characteristics. The rostrum of the new species is relatively longer than that of C. weberi (reaching to base or around the middle of second segment of antennular peduncle vs reaching to base or near middle of second segment of antennular peduncle). The dorsal teeth are fewer in the new species (9–14 vs 11–23 in C. weberi ). However, the number of ventral teeth shows considerable overlap between the two species (1–4 vs 2–5 in C. weberi ), and the new species possesses a larger number of postorbital teeth compared to C. weberi (3–4 vs 0–2). The new species has a shorter antennular peduncle than that of C. weberi (0.47– 0.53 as long as CL vs 0.64 as long as CL). It also possesses a stouter P5 dactylus (3.40–3.70 as long as wide vs 3.9–5.2 as long as wide in C. weberi ), but contains fewer spiniform setae (24–38 vs 47–66 in C. weberi ). The characteristics of the distal end of the telson also differ between the new species and C. weberi . In the new species, the distal end of the telson is subtriangular in shape (vs rounded in C. weberi ), it possesses a greatly reduced or absent posteromedian projection (vs well-developed in C. weberi ), and has fewer spiniform setae (6–8 vs 6–11 in C. weberi ). Furthermore, the size of the eggs in the new species is much larger than those in C. weberi (0.82–0.93 × 0.51–0.60 mm vs 0.35–0.42 × 0.19–0.25 mm) ( De Man, 1892; de Mazancourt et al., 2020). Additionally, the distributions of these two species do not overlap. Caridina weberi is distributed in Indonesia (Sumba, Halmahera), Papua New Guinea, and the Solomon Islands ( de Mazancourt et al., 2020), while the new species occurs only in the Mae Klong Basin in mainland Southeast Asia. Moreover, the distant phylogenetic placement ( Fig. 1), and high genetic divergence (12.04%; Table 2), strongly support the conclusion that they are distinct species.

In terms of genetic divergence, the new species showed the closest divergence to the sequence identified as C. cf. babaulti . This sequence was retrieved from the GenBank database (MN399172). It has been used in a previous study and was stated to have been collected from West Bengal, India ( Klotz et al., 2019). Caridina babaulti was originally described from Central India ( Bouvier, 1918). Its distribution range covers the areas of Central, Western, and Southern India ( Pandya & Richard, 2019). It was recently recorded as an introduced ornamental pet that can establish populations in open waters in Europe ( Maciaszek et al., 2021). Morphologically, the new species shared a few characteristics with C. babaulti , including the absence of a posteromedian projection and the number of spinules on the uropodial diaeresis. Both species carry large-sized eggs (0.82–0.93 × 0.51–0.60 mm in the new species vs 0.9–1.0 × 0.50–0.62 mm in C. babaulti ), and are characterised as landlocked species ( Pandya & Richard, 2019, de Mazancourt et al., 2021, 2023; Hamasaki et al., 2021). However, the new species differs from C. babaulti by having a shorter rostrum (reaching near the end of second segment of antennular peduncle vs reaching to middle of third segment antennular peduncle in C. babaulti ), fewer dorsal teeth (9–14 vs 14–25 in C. babaulti ), stouter P1 chelae (1.63–2.35 vs 2.2–2.6 as long as wide in C. babaulti ), fewer spiniform setae on P3 dactylus (5–7 vs 7–10 in C. babaulti ), fewer spiniform setae on P5 dactylus (24–38 vs 30–45 in C. babaulti ), and subtriangular distal end of telson (vs rounded in C. babaulti ) ( Bouvier, 1918; Pandya & Richard, 2019).