A new species of Cerapus (Amphipoda, Senticaudata, Ischyroceridae) from Mae Klong Estuary, with a discussion on their nesting and types of mating behaviour

Chanikan Katnoum; Tosaphol Saetung Keetapithchayakul; Azman Abdul Rahim; Koraon Wongkamhaeng

doi:10.3897/zse.99.107974

Abstract

The first representative of the genus Cerapus in the Gulf of Thailand, Cerapus rivulus sp. nov., is described from specimens sampled from Mae Klong Estuary, the inner Gulf of Thailand. The main identifying characteristics of this new amphipod species are pereonites 1 and 2 without constriction; male gnathopod propodus palm transverse with long posterior defining tooth and well-developed anterodistal recurved tooth adjacent to propodus articulation; pereopod 6 coxa without fine fringe setae ventrally, basis with setae on posterior margin; and telson with deep cleft. An updated identification key for the 25 known species in the genus is also presented. A discussion on their nesting and types of mating behaviour is provided.

Key Words

Amphawa, Cerapus, mating behaviour, nesting behaviour

Introduction

Lowry and Berents (1996) recognised five genera of tube building amphipods in the Cerapodini (Cerapus Say, 1817, Runanga Barnard, 1961, Paracerapus Budnikova, 1989, Bathypoma Lowry & Berents, 1996 and Notopoma Lowry & Berents, 1996). In 2018, Berents and Lowry (2018) proposed a new genus from Australia (Kapalana Berents and Lowry 2018). The tubicolous genus Cerapus can be recognised by: 1) antenna 1 without vestigial accessory flagellum, 2) antenna 1 peduncular article 1 posterior margin with strong posterior projection, 3) gnathopod 2 of adult male, carpochelate, subchelate in female, 4) pereopod 5 with the distal part directed posteriorly, 5) dactyli of pereopods 6 and 7 with 1–2 small accessory spines, 6) pleopods 2 and 3 with inner rami reduced, 1-articulate, 7) uropod 1 with the outer margin of the ramus dentate, 8) uropod 2 uniramus, outer margin of the ramus dentate, without robust setae and 9) uropod 3 uniramous, ramus vestigial bearing recurved spines (Lowry and Berents 1996; Souza-Filho and Serejo 2014; Berents and Lowry 2018; Nurshazwan et al. 2020).

Most species of Cerapodini are found on the soft bottom of estuaries and various coastal habitats, i.e. seagrass beds, algal beds, mangrove forests and coral reefs (Shen 1936; Lowry and Berents 2002; Lowry and Berents 2005; Nurshazwan et al. 2020). There are various types of tubes, with Lowry and Berents (2005) classifying Cerapus tubes into three types: the detrital tube, algal tube and sandy tube. Most tubes are constructed in a turf of the interwoven tube with various substrates attached, including hydroids, algae, fleshy and calcareous gorgonians and sponges (Lowry and Thomas 1991). The study of Nurshazwan et al. (2020) reported 23 species, but did not include C. longicervicum Lim, Park & Min, 2008 from South Korea (Lim et al. 2008). Adding the newly-discovered C. rivulus sp. nov., there are now a total of 25 Cerapus species worldwide. From that, only six species of Cerapus have been described in the waters of Southeast Asia, including Singapore: C. tubularis Say, 1817; Thailand: C. chaomai Lowry & Berents, 2002 and C. yuyatalay Lowry & Berents, 2002; Korea: C. longirostris Shen, 1936 and C. longicervicum Lim, Park & Min, 2008; Malaysia: C. bumbumiensis Nurshazwan, Ahmad-Zaki & Azman, 2020. However, there have been no recorded species from the South China Sea, including the Gulf of Thailand (Lowry and Berents 2002; Lim et al. 2008; White 2015; Nurshazwan et al. 2020; Azman 2022).

The present study describes Cerapus rivulus sp. nov. as a new species from the Gulf of Thailand. A distribution map with brief biological notes and a key to the world species of the genus are also provided.

Materials and methods

The Cerapus sampling was carried out using the experimental model set, based on Aikins and Kikuchi (2001). The experimental models were set up around Mae Klong estuarine for two and four months (Fig. 1).

Figure 1.

Map showing the three river mouths along the Gulf of Thailand. Red circle represents the type locality of Cerapus rivulus sp. nov.

The Mae Klong River is located in west-central Thailand and passes through Kanchanaburi, Ratchaburi and Samut Songkhram before reaching the upper Gulf of Thailand. Along the river, there are urban and aquaculture zones which make this area important for fishing activities and aquaculture. The Mae Klong Estuary is situated in the Amphawa District of Samut Songkhram Province with salinity ranges from 0.05–2.00 ppt due to tide and water runoff.

The specimens were selected from experimental material and preserved in 95% ethanol. The male holotype and female paratype specimens were transferred from ethanol on to a glycerol slide for morphological study in the laboratory. Drawings were made using a camera lucida attached to an Olympus CH30 light microscope. The pencil drawings were scanned and digitally inked using a WACOM bamboo CTH-970 graphics board in Adobe Illustrator CC 2017, following the method described in Coleman (2003). Terminology for setae and mouthparts described by Zimmer et al. (2009).

The representative specimens were dehydrated with absolute ethanol, critical-point-dried using carbon dioxide, placed on holders and coated with gold for examination with an FEI Quanta 450 scanning electron microscope. Institutional abbreviation: THNHM, Thailand Natural History Museum, Bangkok, Thailand.

Systematics

Suborder Senticaudata Lowry & Myers, 2013

Infraorder Corophiida Leach, 1814 (sensu Lowry & Myers, 2013)

Parvorder Caprellidira Leach, 1814 (sensu Lowry & Myers, 2013)

Superfamily Photoidea Boeck, 1871

Family Ischyroceridae Stebbing, 1899

Subfamily Ischyrocerinae Stebbing, 1899

Tribe Cerapodini Smith, 1880

Genus Cerapus Say, 1817

Type species

Cerapus tubularis Say, 1817

Current species composition

Cerapus contains 24 species + 1 new species: C. tubularis Say, 1817, C. calamicola (Giles, 1885), C. longirostris Shen, 1936, C. erae Bulyčeva, 1952, C. benthophilus Thomas & Heard, 1979, C. alquirta (Barnard & Drummond, 1981), C. oceanicus Lowry, 1985, C. pacificus Lowry, 1985, C. cudjoe Lowry & Thomas, 1991, C. micronesicus Myers, 1995, C. thomasi Ortiz & Lemaitre, 1997, C. chaomai Lowry & Berents, 2002, C. yuyatalay Lowry & Berents, 2002, C. bundegi Lowry & Berents, 2005, C. murrayae Lowry & Berents, 2005, C. volucola Lowry & Berents, 2005, C. orteai Ortiz & Thomas, 2007, C. jonsoni Valério-Berardo, Thiago de Souza & Waiteman Rodrigues, 2008, C. longicervicum Lim, Park & Min, 2008, C. nudus Just, 2009, C. maculanigra Zeina & Asakura, 2017, C. ryanadamsi Drumm, 2018, C. slayeri Drumm, 2018, C. bumbumiensis Nurshazwan, Ahmad-Zaki & Azman, 2020; C. rivulus sp. nov.

Cerapus rivulus sp. nov.

https://zoobank.org/3074048C-ECA2-499C-A3D4-C54C6DAECB7C

Figs 2, 3, 4, 5, 6, 7, 8, 9, 10

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.

Type locality

Darunanukroh School (13°29'41.0"N, 99°55'25.3"E) Mae Klong River, Amphawa District, Samut Songkhram Province, Thailand.

Habitat

Freshwater and brackish water (0.05–2.03 ppt) in Mae Klong River of Amphawa District, Samut Songkhram Province, Thailand.

Etymology

The species is named after their habitat which is located in the river (Rivulus: Latin for river/stream).

Description

Based on holotype, male, size 10 mm, body elongated, cylindrical THNHM-lv-19376.

Head. (Fig. 3A) Eye medium, 0.1 mm (0.14× head length); rostrum short (0.16× length of head), acute; Head lateral cephalic lobe well-developed and distally round. Antenna 1 (Fig. 3B) anterior margin with short setae, posterior margin with long setae, about 0.4× the body length, peduncle 3.1× 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. 3C) 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.

Figure 2.

Cerapus rivulus sp. nov. A. Holotype male lateral (THNHM -19377); B. A specimen in its tube with protruding head and antennae; C. Paratype female front (THNHM-19379).

Figure 3.

Cerapus rivulus sp. nov., holotype, male (THNHM -19377). A. Habitus of the male holotype; B. Antenna 1; C. Antenna 2; D. Gnathopod 1; E. Palm of gnathopod 1; F. Gnathopod 2; G. Palm of gnathopod 2. Scale bars: 0.2 mm.

Upper lip (Fig. 6F) symmetrical, notched, with small setulae apically. Lower lip (Fig. 6G) with inner lobe, smooth, setulose on inner and outer lobes. Mandibles (Fig. 6A, 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× as long as article 3, with 17 marginal setae; article 3 with 10 long setae. Maxilla 1 (Fig. 6E) 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. 6D) outer plate broader than inner plate, with 12 simple setae; inner plate with 12 setae.

Pereon. Gnathopod 1 (Fig. 3D, E) length ratio from basis to dactylus 2.6:1:1:1.7:1.8; coxa 2× 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× 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. 3F, 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× the width, palm margin transverse with long posterior defining tooth and well-developed anterodistal recurved spine adjacent to propodus articulation; propodus length 2× the width, with two acute spines and 1 rounded projection on posterior margin, with long setae on anterior and posterior margins; dactylus length 3× the width, with long setae on posterior margin and one seta on anterior margin.

Pereopod 3 (Fig. 4A) length ratio from basis to dactylus 14:6:4.5:4:5.5:3.5; coxa 2.2× as broad as deep, with 2 anterodistal setae; basis length 2.2× 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.

Figure 4.

Cerapus rivulus sp. nov., holotype, male (THNHM -19377). A. Pereopod 3; B. Pereopod 4; C. Pereopod 5; D. Pereopod 6; E. Pereopod 7. Scale bars: 0.2 mm.

Pereopod 4 (Fig. 4B) length ratio from basis to dactylus 12.5:6.5:6:4:5:3; coxa 1.8× as broad as deep, with a anterodistal seta; basis, length 1.9× 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. 4C) length ratio from basis to dactylus 8:3:4.5:3:5.5: 3; coxa 1.2× 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. 4D) length ratio from basis to dactylus 8.5:2:4:3:5:3; coxa lobate, about 1.3× as broad as deep; basis length 1.6× the width, with setae on posterior margin; ischium subrectangular, length 1.25× width; merus 2.1× 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. 4E) length ratio from basis to dactylus 9:3:5:3:5:3; coxa lobate, about 1.6× as broad as deep; basis length 2.25× the width, with setae on anterior margin; ischium subrectangular, length 1.5× the width; merus 2× 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. 5A) 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. 5B) peduncle with 2 retinacula, without setae; outer ramus 3.1× as long as inner ramus, with a single article; inner ramus reduced, 1.6× as long as broad, 1 plumose seta and single article. Pleopod 3 (Fig. 5C) peduncle with 2 retinacula, without plumose setae distomarginally; outer ramus 3× as long as inner ramus; single article; inner ramus reduced, about 1.75× as long as broad, single article with 1 plumose seta.

Figure 5.

Cerapus rivulus sp. nov., holotype, male (THNHM -19377). A. Pleopod 1; B. Pleopod 2; C. Pleopod 3; D. Uropods 1–3 and Telson; E. Uropod 1. Scale bars: 0.1 mm.

Figure 6.

Cerapus rivulus sp. nov., holotype, male (THNHM -19377). A. Left mandible; B. Right mandible; C. Maxilliped; D. Maxilla 2; E. Maxilla 1; F. Upper lip; G. Lower lip. Scale bars: 0.1 mm.

Urosome. (Fig. 5D) Uropod 1 (Fig. 5E) biramous; peduncle 2.1× as long as wide, with 3 dorsodistal setae; outer ramus shorter than peduncle, 1.5× 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. 5D) uniramous; peduncle 3.75× as long as broad, 6.3× as long as vestigial ramus; ramus with 1 row of short setae and a terminal seta. Uropod 3 (Fig. 5D) uniramous; peduncle 2.7× as long as wide, with one seta on inner margin; ramus vestigial, inconspicuously small with 2 hooks. Telson (Fig. 5D) deeply cleft, 0.5× 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. 7A). Similar to male, except for the following: Antenna 1 (Fig. 7B) with fewer setae and fewer aesthetascs. Antenna 2 (Fig. 7C) more slender than in male. Gnathopod 1 (Fig. 7D, E) dactylus posterior margin serrated, with one spine. Gnathopod 2 (Fig. 7F, 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. 8C) coxa larger, about 2.7× as broad as deep, about 6.3× 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.

Figure 7.

Cerapus rivulus sp. nov., paratype, female (THNHM -19379). A. Habitus of the female paratype; B. Antenna 1; C. Antenna 2; D. Gnathopod 1; E. Palm of gnathopod 1; F. Gnathopod 2; G. Palm of gnathopod 2. Scale bars: 0.2 mm.

Figure 8.

Cerapus rivulus sp. nov., paratype, female (THNHM -19379). A. Pereopod 3; B. Pereopod 4; C. Pereopod 5; D. Pereopod 6; E. Pereopod 7. Scale bars: 0.2 mm.

Figure 9.

Cerapus rivulus sp. nov., paratype, female (THNHM -19379). A. Pleopod 1; B. Pleopod 2; C. Pleopod 3; D. Uropods 1–3 and Telson. Scale bars: 0.1 mm (A–C); 0.2 mm (D).

Figure 10.

Cerapus rivulus sp. nov., paratype, female (THNHM -19379). A. Maxilliped; B. Maxilla 2; C. Maxilla 1; D. Upper lip; E. Lower lip; F. Left mandible; G. Right mandible. Scale bars: 0.2 mm.

Remarks

Cerapus rivulus sp. nov. is similar to C. nudus and C. longirostris which has synapomorphic character states, such as: (1) pereonites 1–2 without constriction; (2) pereopod 5 merus without plumose seta on posterior lobe; (3) pereopod 6 coxa without setae on ventral margin; (4) uropod 1 without hook on ventrodistal margin. They are distinguished by the following: (1) head subequal in length to pereonites 1 + 2 [C. nudus longer than pereonites 1 + 2, C. longirostris subequal to pereonites 1 + 2]; (2) gnathopod 2 propodus twice as long as wide [C. nudus and C. longirostris less than twice as long as wide]; (3) telson deeply cleft (> 50%) [C. nudus and C. longirostris semi-cleft]; (4) telsonic lobe with 19–20 hooks in two transverse rows [C. nudus with ten recurved hooks on three transverse rows and C. longirostris with eight recurved hooks on two transverse rows.

This study brings the number of identified Cerapus species from Southeast Asia to seven. Cerapus rivulus sp. nov. can be separated from Southeast Asian congeners by a combination of characteristics as follows (other species in paratheses): absence of constriction between pereonite 1 and 2 (present in C. yuyatalay, C. bumbumiensis and C. longicervicum); antenna 1 peduncular article 1 shorter than article 3 (longer in C. chaomai, C. bumbumiensis and C. longicervicum); gnathopod 2 propodus with tooth in male (without tooth in C. chaomai, C. yuyatalay, C. bumbumiensis and C. longicervicum); telson fused with pleonite 3 (not fused in C. yuyatalay, C. bumbumiensis, and C. longicervicum); telson with more than ten hooks (fewer than ten in C. bumbumiensis).

C. tubularis was described from Long Island Sound, New York, U.S.A. and after that reported in Japan by Morino (1976). However, Lowry and Berents (1989) re-described C. tubularis and excluded the record of Morino (1976). Lastly, White (2015) reported Cerapus sp. in Singapore and noted that the amphipod resembles C. tubularis and possibly was introduced to Singapore. The presence of C. tubularis in the eastern Pacific and South China Sea is still unclear and needs clarification.

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.

Figure 11.

Distribution of Cerapus spp.

Biological notes

Generally, tube-building amphipods build tubes using amphipod silk which is observed as silk strands adhering to the tip of the dactylar surface close to the pore on P3 and P4 (Kronenberger et al. 2012). Cerapus rivulus sp. nov. also presents this characteristic (Fig. 12). The outer surface of the tube consists of uniformly coarse sediment and detritus with a mix of fragmented fibres and algae (Fig. 2) (small tubes of juvenile attached to the larger tube) (Fig. 13A–D); the inner surface, on the other hand, exhibits a fine network of amphipod silk. Laboratory observations on C. rivulus sp. nov.: feeding behaviour, both antennae 1 and 2 were used to gather food and move chunks of organic material back inside their tube. From the gut content analysis, the major food items consist of fungus, algae, diatoms, organic substances and protozoa. Moreover, mating behaviour showed that males wander about the habitat investigating the tube of female individuals. During these encounters, males try to contact females with their antennae. After that, females withdraw the posterior part of the body into their tubes, while males use their urosome to stimulate the ventral surface of the female pleosome. These situations are assumed to be a possible prelude to mating (Fig. 14).

Figure 12.

Distal end of P3 and P4 of Cerapus rivulus sp. nov. Red dash line represents distal end of P3 dactylus with amphipod silk opening and yellow dash line represents distal end of P4 dactylus with amphipod silk opening.

Figure 13.

Cerapus rivulus sp. nov. A. Showing a mix of fragmented fibres and algae on its tube; B. Showing small tubes of juvenile attached on the larger tube; C. Uniformly coarse sediment on the outer surface of the tube; D. Ultrastructure of uniformly coarse sediment on the outer surface of the tube (scanning electron microscope); E. Ultrastructure of fine network of amphipod silks on the inner surface of the tube (scanning electron microscope).

Figure 14.

Series of mating of Cerapus rivulus sp. nov. (created from video of Suppl. material 1).

Key to world species of Cerapus

1	Uropod 1 with conspicuously large lateral peduncular hook on ventrodistal margin	2
–	Uropod 1 without hook on ventrodistal margin	5
2(1)	Pereonites 1–2 with constriction	C. cudjoe Lowry & Thomas, 1991
–	Pereonites 1–2 without constriction	3
3(2)	Head longer than pereonite 1+2	C. slayeri Drumm, 2018
–	Head subequal in length to pereonites 1+2	4
4(3)	Rostrum well developed, more than 20% of head length; antennal flagella 1 and 2 conspicuously short, composed of two or three articles; telson with 11 or 12 recurved spines	C. ryanadamsi Drumm, 2018
–	Rostrum conspicuously short, less than 20% of head length; antennal flagella 1 and 2 long, composed of more than three articles; telson with 9 or 10 recurved spines	C. thomasi Ortiz & Lemaitre, 1997
5(1)	Pereonites 1–2 with constriction	6
–	Pereonites 1–2 without constriction	12
6(5)	Telson entirely cleft	7
–	Telson semi-cleft	8
7(6)	Antenna 2 shorter than antenna 1, peduncle article 4 shorter than 5	C. micronesicus Myers, 1995
–	Antenna 2 longer than antenna 1, peduncle article 4 longer than 5	C. longicervicum Lim, Park & Min, 2008
8(7)	Telson with deep cleft (> 50%)	9
–	Telson with shallow cleft (< 45%)	10
9(8)	Telsonic lobe with 3–5 recurved spines on two transverse rows	C. bumbumiensis Nurshazwan, Ahmad-Zaki & Azman, 2020
–	Telsonnic lobe with 9–11 recurved spines on two transverse rows	C. yuyatalay Lowry & Berents, 2002
10(8)	Rostrum well developed, more than 20% of head length; antenna 2 longer than antenna 1; pereopod 5 merus without plumose seta on posterior lobe	C. benthophilus Thomas & Heard, 1979
–	Rostrum short, less than 20% of head length; antenna 2 shorter than antenna 1; pereopod 5 merus with more than one plumose seta on posterior lobe	11
11(10)	Pereopod 5 merus with three to six plumose setae at posterior lobe	C. jonsoni Valério-Berardo, Thiago de Souza & Waiteman Rodrigues, 2008
–	Pereopod 5 merus with seven to ten plumose setae at posterior lobe	C. murrayae Lowry & Berents, 2005
12(5)	Pereopod 6 coxa with long or short setae on ventral margin	13
–	Pereopod 6 coxa without setae on ventral margin	17
13(12)	Pereopod 5 merus without plumose seta on posterior lobe	C. longirostris Shen, 1936
–	Pereopod 5 merus with one or more than one plumose setae on posterior lobe	14
14(13)	Pereopod 5 with one plumose seta on posterior lobe	C. chaomai Lowry & Berents, 2002
–	Pereopod 5 merus with more than one plumose seta on posterior lobe	15
15(14)	Male gnathopod 2 palm without inner tooth	C. pacificus Lowry, 1985
–	Male gnathopod 2 palm with inner tooth	16
16(15)	Pereopod 5 merus with two plumose setae at posterior lobe	C. calamicola (Giles, 1885)
–	Pereopod 5 merus with three to six setae at posterior lobe	C. erae Bulyčeva, 1952
17(12)	Pereopod 5 merus without plumose seta on posterior lobe	18
–	Pereopod 5 merus with one or more than one plumose setae on posterior lobe	20
18(17)	Rostrum conspicuously short; pereopod 5 merus with one seta at posterior lobe	C. rivulus sp.nov.
–	Rostrum well developed; pereopod 5 merus without setae at posterior lobe	19
19(18)	Telsonic lobe with ten recurved hooks on three transverse rows	C. nudus Just, 2009
–	Telsonic lobe with eight recurved hooks on two transverse rows	C. longirostris Shen, 1936
20(17)	Pereopod 5 merus with one plumose seta on posterior lobe	C. alquirta (Barnard & Drummond, 1981)
–	Pereopod 5 merus with more than one plumose setae on posterior lobe	21
21(20)	Pereopod 7 basis with spines along posteroproximal margin	C. tubularis Say, 1817
–	Pereopod 7 basis without spines along posteroproximal margin	22
22(21)	Telson entirely cleft	23
–	Telson semi-cleft	24
23(22)	Rostrum well developed; antenna 2 longer than antenna 1	C. oceanicus Lowry, 1985
–	Rostrum conspicuously short; antenna 1 longer than antenna 2	C. erae Bulyčeva, 1952
24(22)	Telson with 6–7 longitudinal rows of spines	C. orteai Ortiz & Thomas, 2007
–	Telson with two transverse rows of spines	25
25(24)	Antenna 2 longer than antenna 1	C. maculanigra Zeina & Asakura, 2017
–	Antenna 1 longer than antenna 2	26
26(25)	Pereopod 5 merus with two plumose setae at posterior lobe	C. volucola Lowry & Berents, 2005
–	Pereopod 5 merus with four plumose setae at posterior lobe	C. bundegi Lowry & Berents, 2005

Acknowledgements

The authors thank Kasetsart University for providing a Master’s degree student scholarship through the Biodiversity Center Kasetsart University. This project is funded by the National Research Council of Thailand (NRCT) (Grant no. N25A660322). In remembrance and thanks also to Assistant Professor Pongrat Dumrongrojwattana for his invaluable advice on the nomenclature of the new taxa. We are grateful to Ms. Nattavadee Tipsut for provided information of gut contents in this study. We express our gratitude to Dr. Alan Myers, Dr. Jesser Fidelis de Souza Filho and Dr. Penny Berents for their valuable evaluations of a previous draft of the manuscript. Furthermore, we extend our appreciation to Dr. Luiz F. Andrade, the subject editor, for promptly facilitating and overseeing the publication process in a gracious manner. We thank the Department of Zoology, Faculty of Science, Kasetsart University, for the laboratory facilities.

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Supplementary material

Supplementary material 1

Video of mating of Cerapus rivulus sp. nov.

Chanikan Katnoum, Tosaphol Saetung Keetapithchayakul, Azman Abdul Rahim, Koraon Wongkamhaeng

Data type: mp4

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.

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