Thermocyclops oryzae, Saetang & Koompoot & Watiroyram & Maiphae, 2024

Saetang, Thanida, Koompoot, Kamonwan, Watiroyram, Santi & Maiphae, Supiyanit, 2024, 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, Zoosystematics and Evolution 100 (4), pp. 1211-1230 : 1211-1230

Thermocyclops oryzae sp. nov.

Type locality.

Central Thailand, Suphan Buri Province, Bang Pla Ma District, Phai Kong Din Subdistrict; 14 ° 19 ' 41.4 " N, 100 ° 15 ' 05.5 " E; rice field.

Other localities.

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 .

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 .

Northeastern Thailand, Sakon Nakon Province, Akat Amnuai District, Samakkhi Phatthana Subdistrict, Ban Nong Sam Kha ; 17 ° 19 ' 41.5 " N, 103 ° 52 ' 38.2 " E; temporary roadside canal; 16 June 2022; leg. S. Watiroyram .

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 .

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 .

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 .

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 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-PK 2010-01 and PSUZC-PK 2010-02 .

Allotype. • One adult male, dissected and mounted onto two slides, collected from the same locality as the holotype: PSUZC-PK 2010-03 and PSUZC-PK 2010-04 .

Paratype. • One adult female, dissected and mounted onto two slides, collected from the same locality as the holotype: PSUZC-PK 2010-05 and PSUZC-PK 2010-6 .

Other specimens examined.

Ten adult females, collected 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 characters: female, (i) 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 (III), (iii) second endopodal segment of antenna with 8 setae, (iv) round projections on the distal margin of intercoxal sclerite of P 1 – P 4 with spinules, (v) intercoxal sclerite of P 1 – P 3 ornamented with one intermittent row of spinules on posterior surface, (vi) intercoxal sclerite of P 4 ornamented with spinules arranged in two arcs on the anterior surface, and two transverse rows of spinules on the posterior surface, (vii) medial margin of basis of P 4 with serrate lobe, (viii) inner apical spine of third endopodal segment of P 4 length about 0.9 times as long as outer spine, (ix) exopodal and endopodal segments of P 1 – P 4 with tiny spinules on posterior surface.

Description of the adult female.

Body (Fig. 1 A ). Total body length measured from anterior margin of rostrum to posterior margin of caudal rami, ranging from 768–990 µm (mean 894 µm, n = 3; 990 µm in holotype).

Prosome (Figs 1 A, B , 2 A, B , 3 C ) composed of cephalothorax and three free prosomites (second to fourth pedigerous somites). Surface of prosome pitted. Cephalothorax and second pedigerous somites smooth along posterior margin (Figs 2 A, B , 3 C ); third and fourth pedigerous somites coarsely serrated along posterior margin (Figs 1 B , 2 B arrow).

Urosome (Figs 1 C – E , 2 C, D , 3 D, E, G , 10 A ) composed of fifth pedigerous somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Fifth pedigerous somite ornamented with two dorsal sensilla and with dense pattern of tiny spinules on dorsal and lateral surface. Genital double-somite about as long as wide, with two dorsal sensilla; dorsal and ventral surfaces with irregular but mostly 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 surface; dorsal surface ornamented with tiny spinules; ventral surface unornamented. Caudal rami (Figs 1 C – E , 2 D , 3 F ). cylindrical, parallel, about 3.5–4.1 times as long as wide (mean 3.8, n = 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 4 A , 6 C ) trapezoidal, with nine teeth between two blunt lateral corners, posterior surface ornamented with two rows of long hairs.

A 1 (Figs 3 A , 4 B, 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. 3 A ).

A 2 (Figs 3 B , 4 D, E , 6 A, B ) composed of coxa, basis, 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. 4 D ) ornamented with one oblique row of inner spinules along proximal part, one longitudinal row of inner spinules along middle part; posterior surface (Fig. 4 E ) 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 row of tiny spinules along inner margin. ENP 1 with one inner smooth seta. ENP 2 with 7–8 inner smooth setae. ENP 3 with seven apical setae. Posterior surface of each endopodal segment ornamented with one longitudinal row of outer spinules.

Mandible (Fig. 5 A, B, F ) composed of coxa and palp. Coxal gnathobase with eleven chitinized teeth and two pinnate setae; anterior surface ornamented with one row of three spinules. Palp reduced, with one short smooth seta and two plumose setae.

Maxillule (Figs 5 C , 6 D, F ) composed of praecoxa and two-segmented palp, representing one-segmented coxobasis 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, 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 surface ornamented with tiny spinules. Exopod reduced into one smooth seta near proximal part of coxobasis. Endopod with three apical smooth setae.

Maxilla (Figs 5 D , 6 E ) 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 endite with two apical pinnate setae. Basis with claw-like endite and one pinnate seta. ENP 1 with two pinnate setae. ENP 2 with one pinnate and two smooth setae.

Maxilliped (Fig. 5 E ) 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. ENP 1 with one inner pinnate seta; anterior surface ornamented with one row of inner spinules. ENP 2 with one inner pinnate and two inner smooth setae.

P 1 – P 4 (Figs 2 E , 7 A – D , 8 A – D , 9 A – G ) composed of intercoxal sclerite, coxa, basis, three-segmented exopod, and three-segmented endopod. Armature formula of P 1 – P 4 as in Table 1 .

P 1 (Figs 7 A, B , 9 A , 10 B, D ). Intercoxal sclerite subquadrate; distal margin with round projection bearing 6-7 spinules; anterior surface unornamented; posterior surface ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; anterior surface 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. Basis with one outer plumose seta and one inner pinnate spine, distal tip of inner spine reaching middle of ENP 2; 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. EXP 1 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 surface ornamented with dense pattern of tiny spinules. EXP 2 with one pinnate outer spine and one inner plumose seta; anterior surface ornamented as in EXP 1. EXP 3 with two pinnate outer spines, two apical plumose setae, and two inner plumose setae; anterior surface ornamented as in EXP 1 except one row of spinules along distal margin of segment. ENP 1 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. ENP 2 two inner plumose setae; anterior surface ornamented as in ENP 1. ENP 3 with one outer plumose seta, two apical elements (outer element: one pinnate spine; inner element: one plumose seta), and three inner plumose setae; anterior surface ornamented as in ENP 1.

P 2 (Figs 7 C, D , 9 B , 10 C ). Intercoxal sclerite subquadrate; distal margin with round projection bearing 4–5 spinules; anterior surface unornamented; posterior surface ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; intermittent longitudinal row of hair-like spinules on lateral margin; 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 bases of exopod and endopod; and one intermittent row of spinules near base of endopod; posterior surface ornamented with one row of spinules in distal part of medial expansion. EXP 1 and EXP 2, 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 surface ornamented with one row of spinules along distal margin of segment, and dense pattern of tiny spinules. EXP 3 with two pinnate outer spines, two apical elements (outer element: one pinnate spine; inner element: one plumose seta), three inner plumose setae; posterior surface ornamented as in EXP 1. ENP 1 with one inner plumose seta; anterior surface ornamented with one longitudinal 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 pattern of tiny spinules. ENP 2 two inner plumose setae; anterior and posterior surfaces ornamented as in ENP 1. ENP 3 with one outer plumose seta, two apical elements (outer element: one pinnate spine; inner element: one plumose seta), three inner plumose setae; anterior surface ornamented with one row of spinules along distal margin; posterior surface ornamented as in ENP 1.

P 3 (Figs 8 A, B , 9 C , 10 E ). Intercoxal sclerite subquadrate; distal margin with round projection bearing 5–6 spinules; anterior surface unornamented; posterior surface ornamented with one intermittent row of spinules. Coxa with one inner plumose seta; anterior surface ornamented 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 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. 8 A ). Both EXP 1 –3 and ENP 1 –3 as in P 2.

P 4 (Figs 2 E , 8 C, D , 9 D – G , 10 F, G ). Intercoxal sclerite subquadrate, distal margin with round projection bearing 6 spinules; anterior surface ornamented with one intermittent row of spinules; posterior surface ornamented with two intermittent rows of spinules. Coxa with one inner plumose seta; anterior surface ornamented 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 spinules along subdistal part; posterior surface ornamented with one distal serrate lobe close to inner margin. EXP 1 and EXP 2 as in P 2, except posterior surface unornamented along distal margin. EXP 3 as in P 2, except anterior surface without longitudinal row of inner setules. ENP 1 and ENP 2 as in P 2. ENP 3 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.

P 5 (Figs 1 F , 10 A ) composed of coxobasis and one-segmented 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.

P 6 (Fig. 1 C, E ) reduced to simple cuticular plate inserted 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. 11 A ). Total body length measured from anterior margin of rostrum to posterior margin of caudal rami, ranging from 686–789 µm (mean 748 µm, n = 3, 789 µm in allotype).

Urosome (Figs 11 B – D , 12 A – C ) composed of fifth pedigerous somite, genital somite, three free urosomites, and anal somite with caudal rami. Fifth pedigerous somite 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 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 operculum; and posterior margin with spinules on both ventral and dorsal surfaces. Caudal rami cylindrical, parallel, about 3.7–3.9 times as long as wide; inner margin without 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 11 B – D , 12 B, C , arrows). Each ramus with six setae: innermost terminal seta (VI) 1.4–1.5 times as long as outermost terminal seta (III).

A 1 (Fig. 13 A – D ) 17 - segmented. Armature formula (number of segment- [number of setae + aesthetasc (ae) + spine (s)]) of each segment as follows: 1 - [8 + 3 ae], 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 modified seta], 15 - [1 + 2 plate-like modified setae], 16 - [4], 17 - [7 + ae].

P 6 (Fig. 11 D ) inserted latero-dorsally on genital somite 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; P 6 flap ornamented with two rows of spinules.

Prosome, A 2, labrum, mandible, maxillule, maxilla, maxilliped, P 1 – P 4 (not shown), and P 5 (Fig. 11 D ) same as female.

Variability.

Morphological variabilities in female specimens were observed in i) intercoxal sclerite of P 1 of specimens from northeast Thailand is naked on the posterior surface (n = 7) (Fig. 10 D ), but one intermittent row of spinules present in specimens from central Thailand (n = 5) (Fig. 7 B ); ii) the inner apical spine of the third endopodal segment of P 4 shorter or as long as the outer apical spine (Figs 8 C , 9 E – G , 10 F ); and iii) P 6 of one specimen from a temporary pond in northeast Thailand has one short spine and one slender seta instead of three elements (Fig. 10 A , 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 affinis Van de Velde, 1987 ; M. aspericornis (Daday, 1906) ; M. ogunnus Onabamiro 1957 ; M. thermocyclopoides Harada, 1931 ; Microcyclops sp. , Thermocyclops crassus (Fischer, 1853) ; T. decipiens (Kiefer, 1929) ; T. operculifer (Kiefer, 1930) ; T. rylovi (Smirnov, 1928) ; T. vermifer Lindberg, 1935 ; and T. wolterecki Kiefer, 1938 .

Distribution and ecology.

Thermocyclops oryzae sp. nov. is widespread in Thailand, both in the west and northeast. However, it has only been recorded in temporary habitats, including rice fields, temporary roadside 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 environmental 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 µs cm- 1, salinity ranged from 0.21–0.58 psu, total dissolved 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 µs L- 1, and water depth was 10 cm with a substrate of mud. In addition, the temporary canals and temporary pond in the northeast, where this species was found, were not vegetated, but the grass and morning glory ( Ipomoea ) grew near the water’s edge.

Figures

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. P 5. Scale bars: 100 µm.

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 double-somite and P 5, ventral view; D. Caudal rami, ventral view; E. P 4 basis, lateral view (arrow indicates serrate lobe).

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, dorsal view; D. Urosomites lateroventral view; E. Anal somite, dorsal view; F. Caudal rami, dorsal view; G. Anal somite, ventral view.

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 µm.

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 µm.

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, posterior surface; C. Labrum; D. Maxillule, anterior surface; E. Maxilla; F. Maxillule, posterior surface.

Figure 7. Thermocyclops oryzae sp. nov., female holotype. A. P 1, anterior surface; B. Intercoxal sclerite of P 1, posterior surface; C. P 2, anterior surface; D. Intercoxal sclerite of P 2, posterior surface. The dense pattern of tiny spinules shown in A, C is on the posterior surface. Scale bar: 100 µm.

Figure 8. Thermocyclops oryzae sp. nov., female holotype. A. P 3, anterior surface; B. Intercoxal sclerite of P 3, posterior surface; C. P 4, anterior surface; D. Protopodite of P 4, posterior surface. The dense pattern of tiny spinules shown in A. and C. is on the posterior surface. Scale bar: 100 µm.

Figure 9. Digital photographs. Thermocyclops oryzae sp. nov., female, collected from a type locality. A. P 1, posterior surface; B. P 2, posterior surface; C. P 3, posterior surface; D, E. P 4, posterior surface; F, G. Apical spines of P 4 ENP 3.

Figure 10. Scanning electron micrographs. Thermocyclops oryzae sp. nov., female, was collected from Kumphawapi District, Udon Thani Province, northeastern Thailand. A. P 5 and pediger 5 (arrow indicates P 6); B. P 1, anterior surface; C. P 2, posterior surface; D. P 1, posterior surface; E. P 3, posterior surface; F. P 4, anterior surface; G. Coxa and basis of P 4, anterior surface; H. Coxa and basis of P 4, posterior surface; I. EXP and ENP of P 4, posterior surface; J. P 4, posterior surface.

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 µm.

Figure 12. Digital photographs. Thermocyclops oryzae sp. nov., male allotype. A. P 6, 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).

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 µm.