Zoosyst. Evol. 99 (2) 2023, 557-574 | DOI 10.3897/zse.99.107974 > PENSUFT. eee BERLIN 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!?: 1 Department of Zoology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand 2 Biodiversity Center Kasetsart University, Bangkok 10900, Thailand 3 Marine Ecosystem Research Centre, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia https://zoobank. org/1549A BF3-4A 14-448 B-89AF-549F 2088 D947 Corresponding author: Koraon Wongkamhaeng (koraon@gmail.com) Academic editor: Luiz F. Andrade @ Received 14 June 2023 # Accepted 9 November 2023 @ Published 4 December 2023 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 pere- onites 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 Notopo- ma 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 ac- cessory flagellum, 2) antenna 1 peduncular article 1 pos- terior margin with strong posterior projection, 3) gnatho- pod 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|-ar- ticulate, 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 Ber- ents 1996; Souza-Filho and Serejo 2014; Berents and Lowry 2018; Nurshazwan et al. 2020). Most species of Cerapodini are found on the soft bot- tom 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, al- gae, 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. /ongicervicum Copyright Katnoum, C. etal. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 558 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. tubu- laris 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 exper- imental 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). aS , = ye , The Gulf of Thailand Sp. nov. zse.pensoft.net | ==<_ » Cambodia ? ao -_-: ae Le F ’ Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand The Mae Klong River is located in west-central Thai- land and passes through Kanchanaburi, Ratchaburi and Samut Songkhram before reaching the upper Gulf of Thai- land. 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 Am- phawa 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 ma- terial 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 luci- da 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 diox- ide, placed on holders and coated with gold for exam- ination with an FEI Quanta 450 scanning electron mi- croscope. Institutional abbreviation: THNHM, Thailand Natural History Museum, Bangkok, Thailand. Zoosyst. Evol. 99 (2) 2023, 557-574 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 spe- cies + 1 new species: C. tubularis Say, 1817, C. calamicola (Giles, 1885), C. /ongirostris Shen, 1936, C. erae Bulyée- va, 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. yuvatalay Lowry & Berents, 2002, C. bundegi Lowry & Berents, 2005, C. murrayae Lowry & Berents, 559 2005, C. volucola Lowry & Berents, 2005, C. orteai Or- tiz & Thomas, 2007, C. jonsoni Valério-Berardo, Thiago de Souza & Waiteman Rodrigues, 2008, C. longicervicum Lim, Park & Min, 2008, C. nudus Just, 2009, C. maculan- igra Zeina & Asakura, 2017, C. ryvanadamsi 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 2-10 Material examined. Holotype. THAILAND « 4, 10 mm: Samut Songkhram Province, Mae Klong River, Daruna- nukroh 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 4, 5 9; 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 Songkh- ram Province, Thailand. 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). zse.pensoft.net 560 Etymology. The species is named after their habitat which 1s located in the river (Rivu/us: 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 (0.14x head length); rostrum short (0.16 length of head), acute; Head lateral cephalic lobe well-developed and distally round. Antenna I (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 an- tenna 1, setation similar to antenna 1; peduncle article 5 subequal to article 4. 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 acces- sory 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. Maxil- la I (Fig. 6E) inner plate small without seta; outer plate with 7 apical robust setae; palp biarticulate, with 6 ser- rated 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 I (Fig. 3D, E) length ratio from basis to dactylus 2.6:1:1:1.7:1.8; coxa 2x as broad as deep, carpus subequal length to propodus, lobate posteri- or margin with setae and plumose setae, anterior margin less setae; propodus oval, length 1.7 the width, poste- rior margin with setae and plumose setae, palm oblique, serrated and with setae; dactylus well developed, palmar margin serrated, crenulated posterior margin withone ro- bust 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 mas- sive, length 1.6x the width, palm margin transverse with long posterior defining tooth and well-developed antero- distal recurved spine adjacent to propodus articulation; propodus length 2x 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 dacty- lus 14:6:4.5:4:5.5:3.5; coxa 2.2x 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 antero- distal setae. zse.pensoft.net Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand Pereopod 4 (Fig. 4B) length ratio from basis to dac- tylus 12.5:6.5:6:4:5:3; coxa 1.8x 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 postero- distal 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 dac- tylus 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 anteri- or 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 dac- tylus 8.5:2:4:3:5:3; coxa lobate, about 1.3< as broad as deep; basis length 1.6x the width, with setae on posterior margin; ischium subrectangular, length 1.25 width; mer- us 2.1x< 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 | seta on anterior side. Pereopod 7 (Fig. 4E) length ratio from basis to dacty- lus 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 mar- gin; ischium subrectangular, length 1.5x the width; merus 2x 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 ar- ticles; outer ramus broader than inner ramus, with 2 ar- ticles, first article is the largest. Pleopod 2 (Fig. 5B) pe- duncle 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 3x as long as inner ramus; single article; inner ramus re- duced, about 1.75 as long as broad, single article with 1 plumose seta. Urosome. (Fig. 5D) Uropod I (Fig. 5E) biramous; pe- duncle 2.1 x as long as wide, with 3 dorsodistal setae; out- er ramus shorter than peduncle, 1.5 longer than inner ra- mus, 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 3.75x as long as broad, 6.3x 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 Zoosyst. Evol. 99 (2) 2023, 557-574 561 Pfr fsa ane ji WW Y AV ANN A ANN 4 at eel ball ae ‘Sl \ \ \ I Teper fufener (4 yn Xt a2 \N & <— 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. zse.pensoft.net 562 Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand 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. zse.pensoft.net 563 Zoosyst. Evol. 99 (2) 2023, 557-574 ere t TT Meee ht h nARRANS ARN ANS AAIWAR AA iy \ — aN} Pcl. Ra i —— fa <= Sr ee Se _ ——$—$— — 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. zse.pensoft.net 564 Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand 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. zse.pensoft.net Zoosyst. Evol. 99 (2) 2023, 557-574 565 h = < SS EI he fe i \ Fiza a tip of Wie eon Figure 7. Cerapus rivulus sp. nov., paratype, female (THNHM -19379). A. Habitus of the female paratype; B. Antenna 1; C. Anten- na 2; D. Gnathopod 1; E. Palm of gnathopod 1; F. Gnathopod 2; G. Palm of gnathopod 2. Scale bars: 0.2 mm. zse.pensoft.net 566 Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand B 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. zse.pensoft.net 567 Zoosyst. Evol. 99 (2) 2023, 557-574 Ee Ps29>> prrn P37 z pa 7S 7 "253. oF) i is | | / | Lae | te \— 4 zse.pensoft.net 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). 568 Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand y I) 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. zse.pensoft.net Zoosyst. Evol. 99 (2) 2023, 557-574 one seta on inner margin; ramus vestigial, inconspicuous- ly 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 I (Fig. 7B) with fewer setae and fewer aesthe- tascs. Antenna 2 (Fig. 7C) more slender than in male. Gnathopod I (Fig. 7D, E) dactylus posterior margin ser- rated, 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 se- tae; dactylus posterior margin crenulated. Pereopod 5 (Fig. 8C) coxa larger, about 2.7< as broad as deep, about 6.3x 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. 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 ventro- distal margin. They are distinguished by the following: (1) head subequal in length to pereonites 1 + 2 [C. nudus longer than pereonites 1 + 2, C. /ongirostris subequal to pereonites 1 + 2]; (2) gnathopod 2 propodus twice as long as wide [C. nudus and C. /ongirostris 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 trans- verse rows. ES = marine species &) = marine or brackish water species =freshwater or brakish water species = - “ =a : ee = = 7 is : 569 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 | peduncular article 1 shorter than article 3 (longer in C. chaomai, C. bumbumiensis and C. Jongicervicum); 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. Jongicervicum), 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 Mo- rino (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 distrib- uted 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. Biological notes. Generally, tube-building amphi- pods 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). 0 1100 2200 3300 km Figure 11. Distribution of Cerapus spp. zse.pensoft.net 570 Cerapus rivulus sp. nov. also presents this characteristic (Fig. 12). The outer surface of the tube consists of uniform- ly 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 | and 2 were used to gather food and move chunks of organic material back inside their tube. From the gut con- = { F 0.01 mm Katnoum, C. et al.: Cerapus rivulus from the Gulf of Thailand tent analysis, the major food items consist of fungus, algae, diatoms, organic substances and protozoa. Moreover, mat- ing 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). 0.05 mm mm ee eee eee = ? 0.01 mm 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. zse.pensoft.net Zoosyst. Evol. 99 (2) 2023, 557-574 eral Figure 13. Cerapus rivulus sp. nov. A. Showing a mix of frag- mented 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 Uropod 1 with conspicuously large lateral peduncular hook on ventrodistal MArgin..............ccceeeeceeeeeeeeeeeeeeeeeeeeaeees 2 JRO pOGel WithOUlineoksonWentreciStal ARGU, 22 e. catty fester tae ceacpeee dense detegrrea te agente lesnaenerPenage uoceheenenssphatecsareseqsees 5 REPS mes lA IWITMIOOMSUNICT Ol Mzecstteer sal cfs: ss wets Bean Moye elie on AB C. cudjoe Lowry & Thomas, 1991 PEleonites=Z WITHGUCOMSLFICLIGI eg, rata iim, ee rte Oe es Ns Pe ne PN Ba eee OEP ae oR Ae ee 3 Meadilomeerthanppereoinite: IeeZ.. -S..ee el ass... f cee feleeheees, parce sy Sheesh oes 1. eee let C. slayeri Drumm, 2018 RieaGh SUSE lal Wrimlei Sts tose he Oliike Stebtye eae. ulete sacne tea eddlillnatten oeeemue tists stom emeaeniee sweat eeae -seaaee ce team easel 4 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.................cccsccceeseeeseeeeees 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 ..............cccccecseecsecseecetscerseeesees C. thomasi Ortiz & Lemaitre, 1997 PEFEORIeS sl —ZIWITMOCIMSULICH OL). recstentste. 2 Sen POPPet atts v5. 2 Rectan UOTE ated 2 Ninh ad OPIS Lenn sut 0, Lacie. POPE ela! 2. fy sag EET ee 6 PELeomtes. | —ZIwithouk GOMStAICtIOM, <.7seahtes yee cee igs peLMde cos ce eh tees wpe haere rtuy coe Sllily s saccae tet twa gamed Jecre steers 12 TeRSGTiSNtiRelViGl Clic s. |. meme dates: oe mh Aree oe sete, 8 cemma dh wheres ysen. ome. assert ares, 0) tee ac mts ly fuk en oss pereierses 7 SS ioe ee MG ek a ape ee rE, eR we art ON se ee el oS oe ce i a eee a Boe a make ol 8 Antenna 2 shorter than antenna 1, peduncle article 4 shorter than 5.0... eee eee C. micronesicus Myers, 1995 Antenna 2 longer than antenna 1, peduncle article 4 longer than 5.............. C. longicervicum Lim, Park & Min, 2008 TELSOUp WICC uClohria= <0 Co/e) same .et Rem. 2, 2e00U. ames VOREES, 5 Sere Bee EO... eee Ree Ne an See eee inn eee 9 Telserew iti Shia OwrGle tt C50 507 yas ad, Rie Seed s,m, ce SERED oO absense. oe ote seat eas aes eect he ditennctmsanaseearerans