taxonID	type	description	language	source
ADFF785E4AB25672B2F53B6336FBD91E.taxon	description	Figs 2, 3, 4, 5, 6, 7, 8, 9, 10	en	Katnoum, Chanikan, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul, Wongkamhaeng, Koraon (2023): A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour. Zoosystematics and Evolution 99 (2): 557-574, DOI: http://dx.doi.org/10.3897/zse.99.107974, URL: http://dx.doi.org/10.3897/zse.99.107974
ADFF785E4AB25672B2F53B6336FBD91E.taxon	materials_examined	Material examined. Holotype. THAILAND • ♂, 10 mm; Samut Songkhram Province, Mae Klong River, Darunanukroh School; 13 ° 29 ' 41.0 " N, 99 ° 55 ' 25.3 " E; 5 m depth; 10 Apr 2021; C. Katnoum leg.; THNHM-lv- 19376. Paratype. THAILAND • 5 ♂, 5 ♀; same data as for holotype • THNHM-lv- 19379.	en	Katnoum, Chanikan, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul, Wongkamhaeng, Koraon (2023): A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour. Zoosystematics and Evolution 99 (2): 557-574, DOI: http://dx.doi.org/10.3897/zse.99.107974, URL: http://dx.doi.org/10.3897/zse.99.107974
ADFF785E4AB25672B2F53B6336FBD91E.taxon	etymology	Etymology. The species is named after their habitat which is located in the river (Rivulus: Latin for river / stream).	en	Katnoum, Chanikan, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul, Wongkamhaeng, Koraon (2023): A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour. Zoosystematics and Evolution 99 (2): 557-574, DOI: http://dx.doi.org/10.3897/zse.99.107974, URL: http://dx.doi.org/10.3897/zse.99.107974
ADFF785E4AB25672B2F53B6336FBD91E.taxon	description	Description. Based on holotype, male, size 10 mm, body elongated, cylindrical THNHM-lv- 19376. Head. (Fig. 3 A) Eye medium, 0.1 mm (0.14 x head length); rostrum short (0.16 x length of head), acute; Head lateral cephalic lobe well-developed and distally round. Antenna 1 (Fig. 3 B) anterior margin with short setae, posterior margin with long setae, about 0.4 x the body length, peduncle 3.1 x the length of flagellum peduncle article 1 with proximoventral swelling, peduncle article 3 subequal to peduncle article 2, both are slender, several aesthetascs, flagellum with 5 articles, article 1 being the longest, flagellum article 5 the shortest with 1 aesthetasc. Antenna 2 (Fig. 3 C) anterior margin with short setae, posterior margin with long setae, slightly shorter than antenna 1, setation similar to antenna 1; peduncle article 5 subequal to article 4. Upper lip (Fig. 6 F) symmetrical, notched, with small setulae apically. Lower lip (Fig. 6 G) with inner lobe, smooth, setulose on inner and outer lobes. Mandibles (Fig. 6 A, B) left incisor with 4 teeth; right lacinia mobilis 4 - cuspidate (4 teeth); right mandible with 3 broad accessory spines; molar triturative; molar flake absent; palp elongated, robust; article 2 1.3 x as long as article 3, with 17 marginal setae; article 3 with 10 long setae. Maxilla 1 (Fig. 6 E) inner plate small without seta; outer plate with 7 apical robust setae; palp biarticulate, with 6 serrated apical robust setae and 4 subapical setae. Maxilla 2 (Fig. 6 D) outer plate broader than inner plate, with 12 simple setae; inner plate with 12 setae. Pereon. Gnathopod 1 (Fig. 3 D, E) length ratio from basis to dactylus 2.6: 1: 1: 1.7: 1.8; coxa 2 x as broad as deep, carpus subequal length to propodus, lobate posterior margin with setae and plumose setae, anterior margin less setae; propodus oval, length 1.7 x the width, posterior margin with setae and plumose setae, palm oblique, serrated and with setae; dactylus well developed, palmar margin serrated, crenulated posterior margin withone robust seta. Gnathopod 2 (Fig. 3 F, G) carpochelate, length ratio from basis to dactylus 3: 1: 2: 3.5: 3: 2.5; coxa broader than deep, subequal to coxa 1; basis longer than wide, with 2 marginal setae on anterior margin; carpus massive, length 1.6 x the width, palm margin transverse with long posterior defining tooth and well-developed anterodistal recurved spine adjacent to propodus articulation; propodus length 2 x the width, with two acute spines and 1 rounded projection on posterior margin, with long setae on anterior and posterior margins; dactylus length 3 x the width, with long setae on posterior margin and one seta on anterior margin. Pereopod 3 (Fig. 4 A) length ratio from basis to dactylus 14: 6: 4.5: 4: 5.5: 3.5; coxa 2.2 x as broad as deep, with 2 anterodistal setae; basis length 2.2 x the width, anterior margin with 10 setae; merus with 3 anterodistal setae and 3 posterodistal plumose setae; carpus with 2 anterodistal setae and 2 posterodistal setae; propodus with 3 anterodistal setae. Pereopod 4 (Fig. 4 B) length ratio from basis to dactylus 12.5: 6.5: 6: 4: 5: 3; coxa 1.8 x as broad as deep, with a anterodistal seta; basis, length 1.9 x the width, anterior margin with 8 setae; ischium subequal to merus, with 4 posterodistal setae; merus without ridges, with a posterodistal plumose seta; carpus with an anterodistal seta and 2 posterodistal setae; propodus with 4 posteromarginal setae; dactylus with unguis. Pereopod 5 (Fig. 4 C) length ratio from basis to dactylus 8: 3: 4.5: 3: 5.5: 3; coxa 1.2 x as broad as deep; basis globular, length equals to width; ischium subrectangular; merus posterior lobe with 1 plumose seta, smaller anterior lobe with 1 seta; carpus smaller than merus, posterior lobe with fine hair, bearing a seta; propodus subovate; dactylus unguis with 2 accessory hooks. Pereopod 6 (Fig. 4 D) length ratio from basis to dactylus 8.5: 2: 4: 3: 5: 3; coxa lobate, about 1.3 x as broad as deep; basis length 1.6 x the width, with setae on posterior margin; ischium subrectangular, length 1.25 x width; merus 2.1 x as long as broad with distal setae on both sides; carpus as long as broad, with 3 long setae on anterodistal corner and 2 long setae on posterodistal corner; propodus with 2 anterodistal long setae and 1 short marginal seta; dactylus unguis with 2 accessory hooks, with 1 seta on anterior side. Pereopod 7 (Fig. 4 E) length ratio from basis to dactylus 9: 3: 5: 3: 5: 3; coxa lobate, about 1.6 x as broad as deep; basis length 2.25 x the width, with setae on anterior margin; ischium subrectangular, length 1.5 x the width; merus 2 x as long as broad with distal long setae on both sides; carpus as long as broad broad, with 1 marginal seta and 3 long setae on anterodistal corner and 3 long setae on posterodistal corner; propodus with 3 marginal setae on both sides and 8 long posterodistal setae; dactylus unguis with 2 accessory hooks. Pleon. Pleopods 1 to 3 decreasing in size. Pleopod 1 (Fig. 5 A) peduncle bearing 2 retinacula, without setae; outer ramus slightly shorter than inner ramus, with 6 articles; outer ramus broader than inner ramus, with 2 articles, first article is the largest. Pleopod 2 (Fig. 5 B) peduncle with 2 retinacula, without setae; outer ramus 3.1 x as long as inner ramus, with a single article; inner ramus reduced, 1.6 x as long as broad, 1 plumose seta and single article. Pleopod 3 (Fig. 5 C) peduncle with 2 retinacula, without plumose setae distomarginally; outer ramus 3 x as long as inner ramus; single article; inner ramus reduced, about 1.75 x as long as broad, single article with 1 plumose seta. Urosome. (Fig. 5 D) Uropod 1 (Fig. 5 E) biramous; peduncle 2.1 x as long as wide, with 3 dorsodistal setae; outer ramus shorter than peduncle, 1.5 x longer than inner ramus, with outer row of spinules and 1 large apical robust seta, inner ramus with a large apical robust seta, corona of short robust setae surrounding large terminal robust seta. Uropod 2 (Fig. 5 D) uniramous; peduncle 3.75 x as long as broad, 6.3 x as long as vestigial ramus; ramus with 1 row of short setae and a terminal seta. Uropod 3 (Fig. 5 D) uniramous; peduncle 2.7 x as long as wide, with one seta on inner margin; ramus vestigial, inconspicuously small with 2 hooks. Telson (Fig. 5 D) deeply cleft, 0.5 x the length of uropod 3, each lobe with 19 or 20 recurved hooks in two rows and an apical seta. Female (Figs 7 - 10) (Sexually dimorphic characters). Based on allotype (THNHM-iv- 19379), length 3.5 mm (Fig. 7 A). Similar to male, except for the following: Antenna 1 (Fig. 7 B) with fewer setae and fewer aesthetascs. Antenna 2 (Fig. 7 C) more slender than in male. Gnathopod 1 (Fig. 7 D, E) dactylus posterior margin serrated, with one spine. Gnathopod 2 (Fig. 7 F, G) slightly larger than gnathopod 1; carpus triangular, posterodistal corner with plumose setae and normal setae; propodus palm not serrated, with plumose setae and simple setae; dactylus posterior margin crenulated. Pereopod 5 (Fig. 8 C) coxa larger, about 2.7 x as broad as deep, about 6.3 x longer than the basis width; basis slightly globular; dactylus with 2 accessory hooks; with a pair of oostegites on each segment from 4 to 6.	en	Katnoum, Chanikan, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul, Wongkamhaeng, Koraon (2023): A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour. Zoosystematics and Evolution 99 (2): 557-574, DOI: http://dx.doi.org/10.3897/zse.99.107974, URL: http://dx.doi.org/10.3897/zse.99.107974
ADFF785E4AB25672B2F53B6336FBD91E.taxon	distribution	Geographic distribution. The Cerapus are distributed worldwide and mainly inhabit marine and brackish water (Fig. 11) (Lowry and Thomas 1991; Lowry and Berents 2002; Drumm 2018; Nurshazwan et al. 2020). Interestingly, C. rivulus sp. nov. was found in freshwater and brackish water (salinity less than 3 ppt), so this is the first report for freshwater habitats. They were dominant in the coarse filter substrate used for benthos sampling because the tubes are retained on the coarse filter.	en	Katnoum, Chanikan, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul, Wongkamhaeng, Koraon (2023): A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour. Zoosystematics and Evolution 99 (2): 557-574, DOI: http://dx.doi.org/10.3897/zse.99.107974, URL: http://dx.doi.org/10.3897/zse.99.107974
