Zoosyst. Evol. 100 (4) 2024, 1211-1230 | DOI 10.3897/zse.100.129089 Ree BERLIN A new species of Thermocyclops Kiefer, 1927 (Crustacea, Copepoda, Cyclopoida, Cyclopidae) from temporary habitats, with a discussion on the diversity and distribution of the genus in Thailand Thanida Saetang', Kamonwan Koompoot?, Santi Watiroyram?, Supiyanit Maiphae!* 1 Animal Systematics and Ecology Speciality Research Unit (ASESRU), Department of Zoology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand 2 Diversity of Family Zingibeaceae and Vascular Plant of Its Applications Research Unit, Walai Rukhavej Botanical Research Institute, Mahasarakham University, Kantarawichai District, Maha Sarakham 44150, Thailand 3 Division of Biology, Faculty of Science, Nakhon Phanom University, Nakhon Phanom 48000, Thailand 4 Biodiversity Center Kasetsart University (BDCKU), Kasetsart University, Bangkok 10900, Thailand https://zoobank. org/C526568E-EBE2-46E5-A58A-D54C2ACCC04F Corresponding author: Supiyanit Maiphae (supiyanit.m@ku.ac.th) Academic editor: Kay Van Damme @ Received 5 June 2024 # Accepted 16 August 2024 Published 2 September 2024 Abstract Thermocyclops Kiefer, 1927, is a genus of Cyclopidae, one of the most diverse families among cyclopoids. To date, 13 species of this genus have been recorded in Thailand. Through intensive sampling of rice fields in central Thailand and temporary waters in northeastern Thailand, one new species, Thermocyclops oryzae sp. nov., was discovered. This new species is clearly distinguished from other Thermocyclops by the presence of a serrated lobe on the posterior surface of the medial expansion of the basipodite of the fourth swimming leg. Moreover, it can be distinguished from its congeners by (i) ornamentation on the genital double-somite, suc- ceeding two urosomites and caudal ramus; (11) the length and width ratio of the caudal ramus; (111) the length ratio of the innermost terminal seta (VI) and the outermost terminal seta (III); (iv) the number of setae on the second endopodal segment of the antenna; (v) projection and ornamentation on the intercoxal sclerites of the first to fourth swimming legs; (vi) the surface ornamentation of the medial margin of the basipodite of the first to fourth swimming legs; and (vii) the relative length of two apical spines of the third endopodal segment of the fourth swimming leg. The present discovery increases the number of species in this genus in Thailand to 14. A pictorial key to all species is proposed, and their ecologies and distributions within Thailand are updated and discussed. Key Words Diversity, habitat preference, niche heterogeneity, temporary habitat, Thailand, Thermocyclops oryzae sp. nov. Introduction A total of 170 copepod species have been found in fresh- water habitats in Thailand (Saetang et al. 2020; Sano- amuang and Dabseepai 2021; Saetang and Maiphae 2023). Cyclopidae is one of the most diverse families of cyclo- poids. Approximately 66 valid species of Thermocyclops Kiefer, 1927, have been recorded worldwide (Walter and Boxshall 2024), 13 of which have been found in Thai- land (Sanoamuang 1999; Wongrat and Pipatcharoenchai 2003; Alekseev and Sanoamuang 2006; Proongkiat 2006; Wansuang and Sanoamuang 2006; Chittapun et al. 2009; Koompoot 2010; Watiroyram 2012; Boonyanusith 2013; Karanovic et al. 2017; Maiphae et al. 2023; Soe and Sa- noamuang 2023). Most of these species are widely dis- tributed, while a few have a restricted distribution. The latter group includes two recently described species in Thailand that are restricted to caves: 7’ parahastatus Karanovic, Koomput & Sanoamuang, 2017 and T° thai- landensis Karanovic, Koomput & Sanoamuang, 2017. Copyright Saetang, T. et al. 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. P22 However, more species can be expected, particularly in special habitats that are less explored than lakes, such as caves and temporary water bodies. This is a general fact in tropical zooplankton, where considerable diversi- ty remains to be explored (Brendonck et al. 2022). Rice fields are an example of temporary habitats that provide a unique form of complex temporary habitats (Edirisinghe and Bambaradeniya 2006). They encompass the differ- ent characteristics of each phase through which organ- isms pass during a cultivation cycle. Water levels and dry periods in rice fields are important features of transient aquatic ecosystems that affect not only the diversity and community structures of species but also the life histories of microscopic animals (Edirisinghe and Bambaradeniya 2006; Watanabe 2019). Moreover, rice fields are dynam- ic and undergo rapid physical, chemical, and biological changes. The heterogeneous composition of rice fields provides various niches for microscopic animals and con- tributes to their richness and biodiversity (Bambaradeni- ya et al. 2004). As reported in previous studies, copepods are often among the first groups of zooplankton to arrive and dominate in sampled ponds (Frisch and Green 2007). The rapid dispersal and dominance of certain cyclopoid copepods during early colonization are due to their rapid individual development and ability to store sperm. Given that cyclopoid copepods can survive periods of drought in the sediment of temporary ponds, initial and early col- onization by cyclopoids is likely to have a significant ef- fect on propagule banks and future plankton communities when such ponds refill (Frisch and Green 2007). The present study investigates the diversity of this ge- nus in temporary habitats, including rice fields, temporary canals, and temporary ponds. In a prior survey of five rice fields in central Thailand, 22 samples were collected, and a total of 9 species of this genus were found (Maiphae et al. 2023). Among them, an undescribed species of 7hermocy- clops was found that exhibited clear morphological differ- ences from known species. Moreover, this unknown Ther- mocyclops was also discovered in zooplankton samples collected from seven temporary habitats in northeast Thai- land. Therefore, the present study proposes one new spe- cies of Thermocyclops and provides detailed descriptions and illustrations of both females and males. In addition, a pictorial key to identify Thermocyclops species found in Thailand was proposed, the present diversity of the genus was updated, and its distribution in Thailand was discussed. Materials and methods Twenty-two samples were qualitatively collected be- tween November 2022 and January 2024 from five rice fields in Suphan Buri Province, Central Thailand, using a plankton net with a 60 um mesh. They were immediately preserved in 70% ethanol. Environmental variables, including pH, water temperature, conductiv- ity, salinity, total dissolved solids, dissolved oxygen, and chlorophyll, were measured using a calibrated YSI zse.pensoft.net Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand EXO Multiparameter Sonde and YSI EXO Handheld Display 599150. In addition, specimens of the new spe- cies collected from six temporary roadside canals and one temporary pond in northeastern Thailand between May and July 2022 were examined. All adult males and females were sorted using an Olympus SZ40 stereo microscope. Each specimen was dissected and mounted on a slide in glycerin, which was then sealed using nail varnish. The specimens’ morphological characteristics were examined and identified using an Olympus CH2 com- pound microscope. Drawings of complete and dissected specimens were made by using a camera lucida connect- ed to the microscope. The final versions of the drawings were made using Adobe Illustrator 2024 software (ver- sion 28.2). Specimens for digital photographs were tak- en using an Olympus BX51 compound microscope with an Olympus DP21 digital camera system. Specimens for scanning electron microscopy (SEM) were dehydrated in graded ethanol concentrations and then transferred to pure isoamyl acetate. The specimens were subjected to the critical point drying process, mounted on stubs, coat- ed with gold, and examined with a scanning electron mi- croscope (LEO 1450 VP). The specimens were identified to the species level in accordance with Ishida (2002), Mirabdullayev et al. (2003), and Holynska (2006). The descriptive terminol- ogy proposed by Huys and Boxshall (1991) was adopted. The abbreviations used in the text and figures are as fol- lows: Al = antennule, ae = aesthetasc, s = spine, A2 = antenna, P1—P6 = first to sixth swimming legs, ENP1 (2, 3) = first (second and third) segment of endopod, EXP1 (2, 3) = first (second and third) segment of exopod, G.S. = genital double-somite. All materials were deposited in the reference collection of the Princess Maha Chakri Sirindhorn National History Museum, Prince of Songkla University, Songkhla, Thailand. Results Systematics Order CYCLOPOIDA Burmeister, 1834 Family CYCLOPIDAE Rafinesque, 1815 Genus Thermocyclops Kiefer, 1927 Type species. Zhermocyclops oithonoides (Sars G.O., 1863). Thermocyclops oryzae sp. nov. https://zoobank.org/384503A9-CDF6-4B54-8E62-1A5098C81F5B Type locality. Central Thailand, Suphan Buri Prov- ince, Bang Pla Ma District, Phai Kong Din Subdistrict; 14°19'41.4"N, 100°15'05.5"E; rice field. Zoosyst. Evol. 100 (4) 2024, 1211-1230 Other localities. (1) Northeastern Thailand, Bueng Kan Province, So Phisai District, Kham Kaeo Subdistrict, Ban Kham Kaeo; 18°05'32.0"N, 103°31'52.3"E; temporary roadside canal; 3 June 2022; leg. S. Watiroyram. (2) Northeastern Thailand, Sakon Nakhon Province, at the boundary between Ban Muang-In Plaeng District; 17°48'49.0"N, 103°35'19.8"E; temporary roadside canal; 16 May 2022; leg. S. Watiroyram. (3) Northeastern Thailand, Sakon Nakon Province, Akat Amnuai District, Samakkhi Phatthana Sub- district, Ban Nong Sam Kha; 17°19'41.5"N, 103°52'38.2"E; temporary roadside canal; 16 June 2022; leg. S. Watiroyram. (4) Northeastern Thailand, Udon Thani Province, Nam Som District, Ban Yuak Subdistrict, Ban Champa Thong; 17°43'37.8"N, 102°11'20.4"E; temporary roadside canal; 19 June 2022; leg. S. Watiroyram. (5) Northeastern Thailand, Udon Thani Province, Kumphawapi District, Nong Wa Subdistrict, Ban Nong Wa; 17°01'33.9"N, 102°58'55.8"E; temporary roadside canal; 18 June 2022; leg. S. Watiroyram. (6) Northeastern Thailand, Ubon Ratchathani Province, Samrong District, Bon Subdistrict, Ban Kho Bon; 15°04'47.2"N, 104°48'00.9"E; temporary roadside canal; 3 May 2022; leg. S. Watiroyram. (7) northeast Thailand, Ubon Ratchathani Province, Pho Sai District, Lao Ngam Subdistrict, Ban Pong Pao; 15°45'54.7"N, 105°23'33.0"E; temporary 5) pond; 5 May 2022; leg. S. Watiroyram. Material examined. Holotype. « One adult female, dissected and mounted onto two slides, central Thailand, Suphan Buri Province, Bang Pla Ma District, Phai Kong Din Subdistrict, 27 March 2023, leg. T. Saetang and S. Maiphae; PSUZC-PK2010-01 and PSUZC-PK2010-02. Allotype. « One adult male, dissected and mounted onto two slides, collected from the same locality as the holotype: PSUZC-PK2010-03 and PSUZ.C-PK2010-04. Paratype. « One adult female, dissected and mounted onto two slides, collected from the same locality as the holotype: PSUZC-PK2010-05 and PSUZC-PK2010-6. Other specimens examined. Ten adult females, col- lected from those other seven localities and deposited in the collection of the second author (KK); two adult males, collected from the type locality and deposited in the collection of the fourth author (SM). Differential diagnosis. Thermocyclops oryzae sp. nov. differs from congeneric species in the following charac- ters: female, (1) caudal ramus elongate, about 3.5—4.1 times as long as wide, (ii) innermost terminal seta (VI) 1.1—1.3 times as long as outermost terminal seta (II), (111) second endopodal segment of antenna with 8 setae, (iv) round pro- jections on the distal margin of intercoxal sclerite of P1—P4 with spinules, (v) intercoxal sclerite of PI—P3 ornamented with one intermittent row of spinules on posterior surface, (vi) intercoxal sclerite of P4 ornamented with spinules Wis arranged in two arcs on the anterior surface, and two trans- verse rows of spinules on the posterior surface, (vii) medial margin of basis of P4 with serrate lobe, (viii) inner apical spine of third endopodal segment of P4 length about 0.9 times as long as outer spine, (1x) exopodal and endopodal segments of P1—P4 with tiny spinules on posterior surface. Description of the adult female. Body (Fig. 1A). To- tal body length measured from anterior margin of rostrum to posterior margin of caudal rami, ranging from 768— 990 um (mean 894 um, n= 3; 990 um in holotype). Prosome (Figs 1A, B, 2A, B, 3C) composed of cephalo- thorax and three free prosomites (second to fourth pediger- ous somites). Surface of prosome pitted. Cephalothorax and second pedigerous somites smooth along posterior margin (Figs 2A, B, 3C); third and fourth pedigerous somites coarse- ly serrated along posterior margin (Figs 1B, 2B arrow). Urosome (Figs 1C—E, 2C, D, 3D, E, G, 10A) composed of fifth pedigerous somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Fifth pedig- erous somite ornamented with two dorsal sensilla and with dense pattern of tiny spmules on dorsal and lateral surface. Genital double-somite about as long as wide, with two dorsal sensilla; dorsal and ventral surfaces with irregular but most- ly transverse short striae; coarsely serrated hyaline frill along posterior margin. Lateral arms of seminal receptacle slightly curved posteriorly. Two free urosomites with irregular but mostly transverse short striae dorsally and ventrally and with coarsely serrated hyaline frill along posterior margin. Anal somite with two dorsal sensilla at base of anal operculum; with spinules present along posterior margin on ventral sur- face; dorsal surface ornamented with tiny spinules; ventral surface unornamented. Caudal rami (Figs 1C—E, 2D, 3F). cylindrical, parallel, about 3.54.1 times as long as wide (mean 3.8, m = 13; 4.1 in holotype); inner margin without hairs; dorsal and ventral surfaces with dense pattern of tiny spinules. Each ramus with six setae: innermost terminal seta (VI) 1.1—1.3 times as long as outermost terminal seta (III). Labrum (Figs 4A, 6C) trapezoidal, with nine teeth be- tween two blunt lateral corners, posterior surface orna- mented with two rows of long hairs. Al (Figs 3A, 4B, C) 17-segmented. Armature formula (number of segment-[number of setae + aesthetasc (ae) + spine (s)]) of each segment as follows: 1-[8], 2-[4], 3-[2], 4-[6], 5-[4], 6-[1+s], 7-[2], 8-[1], 9-[1], 10-[0], 11-[1], 12-[1+ae], 13-[0], 14-[1], 15-[2], 16-[2+ae], 17-[7+ae]. Last two antennular segments bearing hyaline membrane on ventral surface (Fig. 3A). A2 (Figs 3B, 4D, E, 6A, B) composed of coxa, ba- sis, and three-segmented endopod. Coxa rectangular, unarmed and unornamented. Basis cylindrical, with one outer bipinnate seta and two inner smooth setae along distal corner; anterior surface (Fig. 4D) ornamented with one oblique row of inner spinules along proximal part, one longitudinal row of inner spinules along middle part; posterior surface (Fig. 4E) ornamented with one oblique row of outer and inner spinules along proximal part, one longitudinal row of outer spinules in middle part, field of tiny spinules near base of inner setae, and one longitudinal zse.pensoft.net 1214 row of tiny spinules along inner margin. ENP1 with one inner smooth seta. ENP2 with 7-8 inner smooth setae. ENP3 with seven apical setae. Posterior surface of each endopodal segment ornamented with one longitudinal row of outer spinules. Mandible (Fig. 5A, B, F) composed of coxa and palp. Coxal gnathobase with eleven chitinized teeth and two pinnate setae; anterior surface ornamented with one row AN AN WN I i \ WN v3 \ \ / it \ fd \ ‘AN if \ Hh \ IX ‘A Ss sh Bape Se ae ASS rade a ee Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand of three spinules. Palp reduced, with one short smooth seta and two plumose setae. Maxillule (Figs 5C, 6D, F) composed of praecoxa and two-segmented palp, representing one-segmented coxoba- sis and one-segmented endopod. Praecoxal arthrite with three smooth and one pinnate apical spine. Praecoxa with seven inner elements; one short naked proximalmost seta, one sub-proximal plumose seta, three middle smooth setae, ig 9 74 Figure 1. Thermocyclops oryzae sp. nov., female holotype. A. Habitus, dorsal view; B. Fourth pedigerous somite; C. Urosome, dorsal view; D. Urosome, ventral view; E. Urosome, lateral view; F. P5. Scale bars: 100 um. zse.pensoft.net Zoosyst. Evol. 100 (4) 2024, 1211-1230 1215 yee Ja BR, rin Figure 2. Digital photographs. Thermocyclops oryzae sp. nov., female, collected from a type locality. A. Cephalothorax, lateral view; B. Second to fourth pedigerous somites, lateral view (arrow indicates coarsely serrated posterior margin); C. Genital dou- ble-somite and P5, ventral view; D. Caudal rami, ventral view; E. P4 basis, lateral view (arrow indicates serrate lobe). two distal smooth setae; group of tiny spinules present at base of short naked proximalmost seta. Coxobasis with one spiniform and two smooth setae apically; anterior sur- face ornamented with tiny spinules. Exopod reduced into one smooth seta near proximal part of coxobasis. Endo- pod with three apical smooth setae. Maxilla (Figs 5D, 6E) composed of praecoxa, coxa, basis, and two-segmented endopod. Praecoxal endite with two apical pinnate setae. Coxa with two endites; proximal endite with one apical plumose seta; distal en- dite with two apical pinnate setae. Basis with claw-like endite and one pinnate seta. ENP1 with two pinnate setae. ENP2 with one pinnate and two smooth setae. Maxilliped (Fig. SE) composed of syncoxa, basis, and two-segmented endopod. Syncoxa cylindrical, with three inner pinnate setae; anterior surface ornamented with one group of spinules in middle part of segment. Basis with two inner pinnate setae; long spinules present on medial margin and anterior surface; posterior surface ornamented with two rows of outer spinules. ENP1 with one inner pinnate seta; anterior surface ornamented with one row of inner spinules. ENP2 with one inner pinnate and two inner smooth setae. P1—P4 (Figs 2E, 7A—D, 8A—D, 9A—G) composed of intercoxal sclerite, coxa, basis, three-segmented exopod, and three-segmented endopod. Armature formula of P1— P4 as in Table 1. zse.pensoft.net 1216 Table 1. Armature formula of P1—P4 in Thermocyclops oryzae sp. nov. (Arabic numerals representing setae and Roman numerals representing spine from outer-inner or outer-apical-inner margins). Swimming Coxa _ Basis EXP ENP legs 1 2 3 1 2 3 Pl 0-1 1-| +1] +1 W,2,2 0-1 O-2 1,11,3 P2 0-1 1-0 |--l 1 I,l1l,3 O01 O2 1,11,3 P38 0-1 1-0 |-l -1 I,ll,3 O-1 O2 1,11,3 P4 0-1 1-0 -l 1 I,ll,3 0-1 O-2 1,11,2 Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand P1 (Figs 7A, B, 9A, 10B, D). Intercoxal sclerite subquadrate; distal margin with round projection bear- ing 6-7 spinules; anterior surface unornamented; pos- terior surface ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; anterior sur- face ornamented with one longitudinal row of hair-like spinules laterally and three rows of tiny spinules along distal margin; posterior surface ornamented with one oblique row of hair-like spinules near the lateral margin. Figure 3. Scanning electron micrographs. Thermocyclops oryzae sp. nov., female, was collected from Kumphawapi District, Udon Thani Province, northeastern Thailand. A. Antennule and cephalothorax; B. Endopodal segments of antenna; C. Free prosomites, dor- sal view; D. Urosomites lateroventral view; E. Anal somite, dorsal view; F. Caudal rami, dorsal view; G. Anal somite, ventral view. zse.pensoft.net Zoosyst. Evol. 100 (4) 2024, 1211-1230 Basis with one outer plumose seta and one inner pin- nate spine, distal tip of inner spine reaching middle of ENP2; anterior surface ornamented with two rows of tiny spinules between bases of exopod and endopod, one row of spinules at base of endopod, one row of spinules at base of inner spine, one row of inner tiny spinules along proximal margin of segment, and long setules on median margin of basis. EXP1 with one pinnate outer spine and \ ty }) } Wr wig WS 1217 one inner plumose seta; anterior surface ornamented with one longitudinal row of outer spinules and one longitudi- nal row of inner setules; one row of tiny spinules at base of outer spine; and one row of spinules along distal mar- gin of segment; posterior surface ornamented with dense pattern of tiny spinules. EXP2 with one pinnate outer spine and one inner plumose seta; anterior surface orna- mented as in EXP1. EXP3 with two pinnate outer spines, /= (Ss \\ ss \= (x |= Figure 4. Thermocyclops oryzae sp. nov., female holotype. A. Labrum; B. Antennule, segments 1-10; C. Antennule, segments 11-17; D. Coxa and basis of antenna, anterior surface; E. Antenna, posterior surface. Scale bar: 100 um. zse.pensoft.net 1218 two apical plumose setae, and two inner plumose setae; anterior surface ornamented as in EXP1 except one row of spinules along distal margin of segment. ENP1 with one inner plumose seta; anterior surface ornamented with one longitudinal row of outer setules and one row of spinules along distal margin of segment; posterior surface ornamented with dense pattern of tiny spinules. ENP2 two inner plumose setae; anterior surface ornamented as in ENP1. ENP3 with one outer plumose seta, two apical elements (outer element: one pinnate spine; inner ele- ment: one plumose seta), and three inner plumose setae; anterior surface ornamented as in ENP1. P2 (Figs 7C, D, 9B, 10C). Intercoxal sclerite sub- quadrate; distal margin with round projection bearing 4—S spinules; anterior surface unornamented; poste- rior surface ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; intermittent longitudinal row of hair-like spinules on lateral margin; Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand two rows of tiny spinules in proximal part; and two rows of tiny spinules along distal margin. Basis with one outer plumose seta; anterior surface ornamented with one row of tiny spinules near outer seta; one row of tiny spinules at base of exopod; one row of tiny spinules between bas- es of exopod and endopod; and one intermittent row of spinules near base of endopod; posterior surface orna- mented with one row of spinules in distal part of medi- al expansion. EXP1 and EXP2, each with one pinnate outer spine and one inner plumose seta; anterior surface ornamented with one longitudinal row of outer spinules and one longitudinal row of inner setules; one row of tiny spinules at base of outer spine; and one row of spinules along distal margin of segment; posterior sur- face ornamented with one row of spinules along distal margin of segment, and dense pattern of tiny spinules. EXP3 with two pinnate outer spines, two apical ele- ments (outer element: one pinnate spine; inner element: Figure 5. Thermocyclops oryzae sp. nov., female holotype. A. Mandible; B. Cutting edge of mandibular gnathobase; C. Maxillule; D. Maxilla; E. Maxilliped; F. Mandibular palp (F. Shows the female paratype; other drawings show the holotype). Scale bar: 100 um. zse.pensoft.net Zoosyst. Evol. 100 (4) 2024, 1211-1230 A Figure 6. Scanning electron micrographs. Thermocyclops oryzae sp. nov., female, was collected from Kumphawapi District, Udon Thani Province, northeastern Thailand. A. Basis and endopodal segments of the antenna, posterior surface; B. Antennal basis, pos- terior surface; C. Labrum; D. Maxillule, anterior surface; E. Maxilla; F. Maxillule, posterior surface. zse.pensoft.net 1220 Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand Brg. iio tet 1 AY ATTY Figure 7. Thermocyclops oryzae sp. nov., female holotype. A. P1, anterior surface; B. Intercoxal sclerite of P1, posterior surface; C. P2, anterior surface; D. Intercoxal sclerite of P2, posterior surface. The dense pattern of tiny spinules shown in A, C is on the posterior surface. Scale bar: 100 um. one plumose seta), three inner plumose setae; posterior surface ornamented as in EXP1. ENP1 with one inner plumose seta; anterior surface ornamented with one lon- gitudinal row of outer setules and one row of spinules along distal margin; posterior surface ornamented with one row of spinules along distal margin and dense pat- tern of tiny spinules. ENP2 two inner plumose setae; anterior and posterior surfaces ornamented as in ENP1. ENP3 with one outer plumose seta, two apical elements (outer element: one pinnate spine; inner element: one plumose seta), three inner plumose setae; anterior sur- face ornamented with one row of spinules along distal margin; posterior surface ornamented as in ENP1. P3 (Figs 8A, B, 9C, 10E). Intercoxal sclerite subquad- rate; distal margin with round projection bearing 5—6 spinules; anterior surface unornamented; posterior sur- face ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; anterior surface or- namented with tiny spinules on lateral margin, three rows of tiny spinules along distal margin, and one row of tiny spinules near base of inner seta; posterior surface ornamented with one oblique row of hair-like spinules zse.pensoft.net close to outer margin. Basis with one outer plumose seta. Anterior surface of basis ornamented with one row of tiny spinules between bases of exopod and endopod, one intermittent row of spinules near base of endopod, three rows of tiny spinules close to inner and distal parts of medial expansion (Fig. 8A). Both EXP1—3 and ENP1-3 Asin RZ P4 (Figs 2E, 8C, D, 9D-G, 10F, G). Intercoxal scler- ite subquadrate, distal margin with round projection bearing 6 spinules; anterior surface ornamented with one intermittent row of spinules; posterior surface or- namented with two intermittent rows of spinules. Coxa with one inner plumose seta; anterior surface ornament- ed with one oblique row of tiny spinules in middle of the segment and two rows of tiny spinules along distal margin; posterior surface ornamented with one oblique row of tiny spinules in subproximal part, two oblique rows of spinules close to outer margin, one row of spinules along subdistal margin. Basis with one outer plumose seta; anterior surface ornamented with one row of spinules near base of endopod, one row of inner spinules along subproximal part, and one row of inner Zoosyst. Evol. 100 (4) 2024, 1211-1230 tL EE 1221 My y Pr TV HNITTNNN Figure 8. Thermocyclops oryzae sp. nov., female holotype. A. P3, anterior surface; B. Intercoxal sclerite of P3, posterior surface; C. P4, anterior surface; D. Protopodite of P4, posterior surface. The dense pattern of tiny spinules shown in A. and C. is on the posterior surface. Scale bar: 100 um. spinules along subdistal part; posterior surface orna- mented with one distal serrate lobe close to inner mar- gin. EXP1 and EXP2 as in P2, except posterior surface unornamented along distal margin. EXP3 as in P2, ex- cept anterior surface without longitudinal row of inner setules. ENP] and ENP2 as in P2. ENP3 with one outer plumose seta, two apical spines, and two inner plumose setae; inner apical spine about 0.9 times as long as the outer apical spine. P5 (Figs 1F, 10A) composed of coxobasis and one-seg- mented exopod. Coxobasis with one outer seta. Exopod with one apical outer smooth seta and one subapical inner pinnate spine; length of the inner apical spine about 1.3 times as long as the outer apical seta. P6 (Fig. 1C, E) reduced to simple cuticular plate in- serted latero-dorsally on genital double-somite, with two subequal smooth spines and one smooth seta; seta about five times as long as spines; surface unornamented. Description of the adult male. Body (Fig. 11A). Total body length measured from anterior margin of rostrum to posterior margin of caudal rami, ranging from 686— 789 um (mean 748 um, 2 = 3, 789 um in allotype). Urosome (Figs 11B—D, 12A—C) composed of fifth pedigerous somite, genital somite, three free urosomites, and anal somite with caudal rami. Fifth pedigerous so- mite ornamented with two dorsal sensilla. Genital somite about 0.8 times as long as wide, with two dorsal sensilla, anterior and posterior surfaces with irregular but mostly zse.pensoft.net Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand . ire ie Fo et “ “a Alemany hice % cae * ¢ 7 wae Sa i tet i \\" \\, \ \ \ £ Figure 9. Digital photographs. Thermocyclops oryzae sp. nov., female, collected from a type locality. A. P1, posterior surface; B. P2, posterior surface; C. P3, posterior surface; D, E. P4, posterior surface; F, G. Apical spines of P4 ENP3. transverse short striae, and with coarsely serrated hyaline frill along posterior margin. Succeeding two urosomites with irregular but mostly transverse striae on both dorsal and ventral surfaces and with coarsely serrated hyaline frill along posterior margin. The fifth urosomite with coarsely serrated hyaline frill along posterior margin. Anal somite with two dorsal sensilla at base of anal oper- culum; and posterior margin with spinules on both ven- tral and dorsal surfaces. Caudal rami cylindrical, parallel, about 3.7—3.9 times as long as wide; inner margin with- out hairs; outer margin ornamented with one transverse row of spinules inserted at distance of 1/3 ramus length measured from anterior margin and at base of outermost terminal seta (III) (Figs 11B—D, 12B, C, arrows). Each ra- zse.pensoft.net mus with six setae: innermost terminal seta (VI) 1.4—-1.5 times as long as outermost terminal seta (III). Al (Fig. 13A—D) 17-segmented. Armature formula (number of segment-[number of setae + aesthetasc (ae) + spine (s)]) of each segment as follows: 1-[8+3ae], 2-[4], 3-[2], 4-[1], 5-[1], 6-[2], 7-[1], 8-[2], 9-[1+s], 10- [2], 11-[2], 12-[2], 13-[1+ae], 14-[2+ 1 plate-like mod- ified seta], 15-[1 + 2 plate-like modified setae], 16-[4], 17-[7+ae]. P6 (Fig. 11D) inserted latero-dorsally on genital so- mite with three smooth setae, length of the outermost seta about 1.4 times as long as the innermost seta, and middle seta about 0.6 times as long as the innermost seta; P6 flap ornamented with two rows of spinules. Zoosyst. Evol. 100 (4) 2024, 1211-1230 ot . SIS Let " \ Nis Figure 10. Scanning electron micrographs. Thermocyclops oryzae sp. nov., female, was collected from Kumphawapi District, Udon Thani Province, northeastern Thailand. A. PS and pediger 5 (arrow indicates P6); B. P1, anterior surface; C. P2, posterior surface; D. P1, posterior surface; E. P3, posterior surface; F. P4, anterior surface; G. Coxa and basis of P4, anterior surface; H. Coxa and basis of P4, posterior surface; I. EXP and ENP of P4, posterior surface; J. P4, posterior surface. zse.pensoft.net 1224 Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand Figure 11. Thermocyclops oryzae sp. nov., male allotype. A. Habitus, dorsal surface; B. Urosome, dorsal surface; C. Urosome, ventral surface; D. Urosome, lateral surface (arrows indicate rows of spinules on the caudal ramus). Scale bars: 100 um. Figure 12. Digital photographs. Thermocyclops oryzae sp. nov., male allotype. A. P6, lateral surface (arrows indicate two rows of spinules); B. Caudal rami, ventral surface (arrow indicates a row of spinules); C. Caudal rami, lateral surface (arrow indicates a row of spinules). zse.pensoft.net Zoosyst. Evol. 100 (4) 2024, 1211-1230 1225 A-D Figure 13. Thermocyclops oryzae sp. nov., A-B male allotype; C—D other specimens collected from type locality. A. Antennule, segments 1—9; B. Antennule, segments 10-17; C. Antennule, segments 1; D. Antennule, segments 10—13. Scale bar: 100 um. Prosome, A2, labrum, mandible, maxillule, maxilla, maxilliped, P1—P4 (not shown), and P5 (Fig. 11D) same as female. Variability. Morphological variabilities in female spec- imens were observed in 1) intercoxal sclerite of P1 of speci- mens from northeast Thailand is naked on the posterior sur- face (n= 7) (Fig. 10D), but one intermittent row of spinules present in specimens from central Thailand (n = 5) (Fig. 7B); 11) the inner apical spine of the third endopodal seg- ment of P4 shorter or as long as the outer apical spine (Figs 8C, 9E-G, 10F); and 111) P6 of one specimen from a tempo- rary pond in northeast Thailand has one short spine and one slender seta instead of three elements (Fig. 10A, arrow). Etymology. The specific name ‘oryzae’, which means rice, is derived from the habitat type (“rice”) of the type locality”. Co-occurring species. In our samples, the new taxon co-occurred with Cryptocyclops sp., Mesocyclops affin- is Van de Velde, 1987; M. aspericornis (Daday, 1906); M. ogunnus Onabamiro 1957; M. thermocyclopoides Harada, 1931; Microcyclops sp., Thermocyclops crassus (Fischer, 1853); 7: decipiens (Kiefer, 1929); T: operculif- er (Kiefer, 1930); 7. rylovi (Smirnov, 1928); 7. vermifer Lindberg, 1935; and T. wolterecki Kiefer, 1938. Distribution and ecology. Thermocyclops oryzae Sp. nov. 1s widespread in Thailand, both in the west and northeast. However, it has only been recorded in tem- porary habitats, including rice fields, temporary road- side canals, and temporary ponds. It was recorded in four out of 22 samples collected from five rice fields in Suphan Buri province during three planting seasons between November 2022 and January 2024. The en- vironmental parameters measured in the studied rice fields were as follows: water temperature ranged from 31.8-36.1 °C, conductivity ranged from 1176.5—1449.9 us cm-1, salinity ranged from 0.21—0.58 psu, total dis- solved solids ranged from 77-676 mg L-1, dissolved oxygen ranged from 7.54—7.54 mg L-1, pH 7.0-7.3, chlorophyll a ranged from 5.31—17.39 us L-1, and water depth was 10 cm with a substrate of mud. In addition, the temporary canals and temporary pond in the north- east, where this species was found, were not vegetated, but the grass and morning glory (Jpomoea) grew near the water’s edge. Pictorial keys to Thermocyclops species found in Thailand The pictorial key of the Thermocyclops species found in Thailand is presented in Fig. 14 to facilitate easy and quick identification. zse.pensoft.net 1226 Saetang, T. et al.: New Thermocyclops from temporary habitats, Thailand Species diversity and distribution of Thermocyclops in Thai water bodies In Thailand, Thermocyclops have been found in various types of freshwater habitats, including rice fields, ca- nals, lakes, and swamps (Sanoamuang 1999; Wongrat P4 intercoxal scerite without surface ornamentation a P4 ENP3: length of /) inner : outer apical spine < 1.5 I @® TF. thailandensis P4 ENP3: length of inner : outer apical spine > 2.0 A2 ENP2 A? ENP2 with 6 setae with 7 setae QT. incisus @) T. maheensis > x P4 intercoxal scerite: distal projection with large spinules so © TF. vermifer P4 intercoxal scerite: distal projection with tiny spinules Sy af TF. wolterecki with distal spinules ©) T. parahastatus G.S.: lateral arms of seminal receptacle slightly curved posteriorly 4 $0 um P4 basis: inner margin naked ee f sf id) \} t and Pipatcharoenchai 2003; Alekseev and Sanoamuang 2006; Proongkiat 2006; Wansuang and Sanoamuang 2006; Chittapun et al. 2009; Koompoot 2010; Watiroy- ram 2012; Boonyanusith 2013; Karanovic et al. 2017; Maiphae et al. 2023; Soe and Sanoamuang 2023). A total of 14 species have been recorded in Thailand to [1] Thermocyclops P4 intercoxal scerite with surface ornamentation —— P4 intercoxal scerite with row(s) of spinules P4 intercoxal scerite with row(s) of hairs ee \. | P4 ENP3: P4 ENP3: on / 7) inner apical spine inner apical spine t\ shorter than longer than > \ outer apical spine outer apical spine >> P4 basis: P4 basis: inner margin inner margin with serrate lobe | @ TF. operculifer © T. oryzae sp. nov. 4 Thermocyclops P4 intercoxal scerite with row(s) of hairs ae | ne : =a =a : . a »~ Sl > G.S.: lateral arms of seminal receptacle curved posteriorly = ie oh . mee 5, “ 2 4 P4 basis: inner margin with spinules or hairs P4 ENP3: length of P4 ENP3: length of inner : outer apical inner : outer apical spine 1.7-2.1 spine 2.6-4.5 P4 basis: P4 basis: inner margin inner margin > with hairs with spinules >}, } . 2 7 ——s << ied am 5 @ T. oblongatus gh T. taihokuensis PEA f + i' ay\ a (un @ TF. crassus | G.S.: surface with G.S.: surface without transverse rows of pits transverse rows of pits ag