taxonID	type	description	language	source
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	description	(Figs. 2, 3, 4 A – D)	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	materials_examined	Type materials. Holotype, ovigerous female (CL 3.44 mm; Fig. 2 A) (MUMNH-CAR 064 - 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; Paratypes, 7 females (CL 3.17 – 3.53 mm) (MUMNH-CAR 064 - 1, CAR 064 - 7, CAR 064 - 10, CAR 064 - 13, and CAR 064 - 15); 4 males (CL 2.87 – 3.25 mm) (MUMNH-CAR 064 - 2 to CAR 064 - 5), same collection data as for the holotype; 2 females (CL 3.55 – 3.97 mm) (MUMNH-CAR 062 - 1 and CAR 062 - 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. Non-type materials. 13 females (CL 3.08 – 3.88 mm), 1 male (CL 2.76 mm) (MUMNH-CAR 060), 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; 16 females (CL 3.20 – 4.16 mm) (MUMNH-CAR 061), 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; 8 females (CL 3.60 – 4.24 mm), 3 males (CL 3.13 – 3.25 mm) (MUMNH-CAR 062), 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; 6 females (CL 2.96 – 3.49 mm) (MUMNH-CAR 063), 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; 5 females (CL 2.96 – 3.49 mm) (MUMNH-CAR 064), 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; 4 females (CL 3.28 – 4.01 mm), 1 male (CL 2.61 mm) (MUMNH-CAR 065), 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.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	description	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. 2 A, 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. 2 D). 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. 2 E). 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. 3 A, B). First pereopod short (Fig. 3 A); 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. 3 B); 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. 3 C); dactylus with 5 – 7 spiniform setae on flexor margin (Fig. 3 D), 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. 3 E); dactylus with 24 – 38 spiniform setae on flexor margin (Fig. 3 F), 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. 3 G, 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. 3 I, 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. 3 J). 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. 2 A). 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. 2 K). Distal margin of telson subtriangular, posteromedian projection absent or greatly reduced, with 6 – 8 moveable plumose setae that are subequal in length (Fig. 2 L). Uropodal diaeresis with 13 – 19 short moveable spiniform setae (Fig. 2 M). Preanal carina subtriangular, with a few setae, without a spine (Fig. 2 N). 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. 4 A). Colour of female shrimps is variable, as dark blue, copper, or brown (Fig. 4 B – 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.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	distribution	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.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	etymology	Etymology. The specific name is from its type locality, the Mae Klong Basin.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF90FFBDFF4CF8B63517FD6F.taxon	discussion	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 P 1 and P 2, 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 P 5 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 (MN 399172). 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 P 1 chelae (1.63 – 2.35 vs 2.2 – 2.6 as long as wide in C. babaulti), fewer spiniform setae on P 3 dactylus (5 – 7 vs 7 – 10 in C. babaulti), fewer spiniform setae on P 5 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).	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF98FFB8FF41FD4B34E4FACF.taxon	description	(Figure 4 E, F, 6)	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF98FFB8FF41FD4B34E4FACF.taxon	materials_examined	Materials examined. 9 females (CL 3.91 – 4.49 mm), 3 males (CL 2.51 – 2.94 mm) (MUMNH-CAR 053, 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; 1 female (CL 4.10 mm) (MUMNH-CAR 054), Mae Klong River, Photharam District, Ratchaburi Province, Thailand, 13.6318 ° N, 99.8162 ° E, coll. W. Siriwut & W. Manonai, 19 April 2019; 4 females (CL 3.29 – 4.21 mm) (MUMNH-CAR 055), Mae Klong River, Photharam District, Ratchaburi Province, Thailand, 13.7152 ° N, 99.8492 ° E, coll. W. Siriwut & W. Manonai, 19 April 2019; 3 females (CL 3.73 – 4.29 mm) (MUMNH-CAR 056), Mae Klong River, Photharam District, Ratchaburi Province, Thailand, 13.7393 ° N, 99.8420 ° E, coll. W. Siriwut & W. Manonai, 19 April 2019; 4 females (CL 3.57 – 4.08 mm) (used for measurement in description); 4 males (CL 2.41 – 2.93 mm) (MUMNH-CAR 706, 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.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF98FFB8FF41FD4B34E4FACF.taxon	description	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 6 A, 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. 6 E, F). First pereopod short (Fig. 6 E); 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. 6 F); 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. 6 G); dactylus with 4 – 6 spiniform setae on flexor margin (Fig. 6 H), 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. 6 I); dactylus with 32 – 43 spiniform setae on flexor margin (Fig. 6 J, 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. 6 O, 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. 6 Q, 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. 6 A). 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. 6 K). Distal margin of telson subtriangular, with a posteromedian projection, and 6 – 9 moveable plumose setae, subequal in length (Fig. 6 L). Preanal carina subtriangular, high, without a spine (Fig. 6 N). Uropodal diaeresis with 15 – 22 short moveable spiniform setae (Fig. 6 M). Eggs. Ovigerous females with numerous eggs (Fig. 3 F, 6 A). 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. 4 E). Colour of female shrimps is frequently dark to light blue, decorated with scattered small dark spots (Fig. 4 F). Rostrum is yellowish-orange. Each abdominal somite furnished dorsally with conspicuous yellowish-orange bands. Eggs are brown to orange.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF98FFB8FF41FD4B34E4FACF.taxon	distribution	Distribution and habitat. Indonesia (Sumatra), Philippines, Singapore, Malaysia, Thailand, Myanmar, India, Pakistan (Kemp, 1918 a, 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.	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
03EFD249FF98FFB8FF41FD4B34E4FACF.taxon	discussion	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, 1918 b; 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. 6 A, 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, 1918 b; 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 P 5 dactylus (32 – 43 vs 36 – 57 by Kemp, 1918 b; 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 P 5 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 P 2 chela of C. sumatrensis is more slender than those of C. babaulti (2.71 – 3.40 vs 2.5 – 2.9), while the P 3 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).	en	Macharoenboon, Kongkit, , Varitsara Manonai, Jeratthitikul,, Ekgachai (2024): Caridina maeklongensis, a new landlocked freshwater shrimp species (Crustacea: Decapoda: Atyidae) from the Mae Klong Basin, Thailand. Raffles Bulletin of Zoology 72: 450-468, DOI: 10.26107/RBZ-2024-0033
