Phyllodiaptomus (P.) parachristineae, Sanoamuang & Watiroyram, 2023

Sanoamuang, Laorsri & Watiroyram, Santi, 2023, Phyllodiaptomus parachristineae, a new species of copepod (Copepoda, Calanoida, Diaptomidae) from the floodplain of the lower Mekong River Basin in Thailand and Cambodia, ZooKeys 1168, pp. 403-424 : 403

Phyllodiaptomus (P.) parachristineae sp. nov.

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

Phyllodiaptomus (P.) sp.: Sanoamuang and Dabseepai (2021): 7, 19, 22.

Phyllodiaptomus (P.) sp.: Chaicharoen and Sanoamuang (2022): 1, 6-7, 9, 11-12; fig. 2u.

Type locality.

A temporary pond, near Km 6 of the road no. 2214, Nong Om Subdistrict, Thung Si Udom District, Ubon Ratchathani Province, northeastern Thailand (14°49'14"N, 104°59'09"E); water temperature 28.3 °C, pH 6.8, conductivity 67 µS cm-1.

Type material.

Holotype: one adult male completely dissected (THNHM-IV-20183, one slide), collected from the type locality on 11 June 2002, by L. Sanoamuang. Allotype: one adult female, completely dissected (THNHM-IV-20184, one slide). Paratypes: one adult female and three adult males, undissected (THNHM-IV-20185-20186); two adult females and five adult males, undissected (KKU-COP-2019-T-01), preserved in 70% ethanol; collected from the type locality on the same date as the holotype.

Other localities.

Thailand: eight temporary-water bodies from Ubon Ratchathani Province, northeast Thailand, sampled by P. Wansuang: (1) a temporary pond, Ban Don Yoong, Muang Sam Sip Subdistrict, Muang Sam Sip District, collected on 19 October 2002; (2, 3) roadside canals, along the road no. 2050 at Kms 25 and 43, Hua Na Subdistrict, Khemarat District, collected on 9 June 2002; (4) a roadside canal, along the road no. 2337 at Km 4, Pho Sai Subdistrict, Pho Sai District, collected on 9 June 2002; (5) a roadside canal, along the road no. 2248 at Km 94, Huai Kha Subdistrict, Buntharik District, collected on 10 June 2002; (6) a rice field, road no. 2248 at Km 65, Na Chaluai Subdistrict, Na Chaluai District, collected on 10 June 2002; (7) a temporary pond, along the road no. 2214 at Km 7, Khok Chamrae Subdistrict, Thung Si Udom District, collected on 11 June 2002; and (8) a temporary pond, Ban Na Sabaeng, Ka Bin Subdistrict, Kut Khaopun District, collected on 20 October 2002.

Twenty-one localities from Surin Province, northeast Thailand, were sampled by W. Yindee:

a roadside canal, Ban Doo Sok, Nong Ha Subdistrict, Samrong Thap District, collected on 7 December 1998;

a canal, Ban Nong Ha, Nong Ha Subdistrict, Samrong Thap District, collected on 7 December 1998;

a roadside canal, Ban Khon Kaen, Nong Ha Subdistrict, Samrong Thap District, collected on 7 December 1998;

a permanent pond, Ban Khon Kaen, Nong Ha Subdistrict, Samrong Thap District, collected on 7 December 1998;

a canal, Ban Nong Buaban, Nong Buaban Subdistrict, Rattanaburi District, collected on 7 December 1998;

a canal, Ban Chat, Nong Buaban Subdistrict, Rattanaburi District, collected on 7 December 1998;

a permanent pond, Ban Rawiang, Rawiang Subdistrict, Non Narai District, collected on 7 December 1998;

a canal, Ban Non, Don Rat Subdistrict, Rattanaburi District, collected on 7 December 1998;

a rice field, Ban Nonsadao, Nong Thap Subdistrict, Non Narai District, collected on 7 December 1998;

a temporary pond close to the Mun river, Tha Tum Subdistrict, Tha Tum District, collected on 9 December 1998;

a reservoir, Ban Nongbor, Ba Subdistrict, Tha Tum District, collected on 9 December 1998;

a canal, Ban Tato, Phrom Thep Subdistrict, Tha Tum District, collected on 9 December 1998;

a canal, Ban Phrai Khla, Phrai Khla Subdistrict, Chumphon Buri District, collected on 9 December 1998;

a canal, Ban Sri Chumpon, Chumpon Buri Subdistrict, Chumphon Buri District, collected on 9 December 1998;

a canal, Ban Kut Phatai, Kut Wai Subdistrict, Sikhoraphum District, collected on 10 December 1998;

a permanent pond, Ban Narong, Narong Subdistrict, Si Narong District, collected on 10 December 1998;

a reservoir, Ban Angkhor, Ban Chan Subdistrict, Sangkha District, collected on 10 December 1998;

Huay Saneng Dam, Chaniang Subdistrict, Mueang District, collected on 10 December 1998;

a canal, Ban Nayom, Khaen Subdistrict, Sanom District, collected on 11 December 1998;

a roadside canal, Sanom intersection, Sanom Subdistrict, Sanom District, collected on 11 December 1998; and

a roadside canal, Taphet intersection, Na Nuan Subdistrict, Sanom District, collected on 7 December 1998.

Cambodia: Nine localities were sampled by R. Chaichareon:

a canal, Mong Rusey, preytouch, Dub Krasaing, Battambong Province (12°49'52"N, 103°24'22"E), collected on 9 June 2007;

a canal, Ochrov, Nimith, Acphiwatt, Bantaen Meanchey Province (13°37'15"N, 102°42'58"E), collected on 9 June 2007;

a ricefield, Srey Sophol, Teuk Thla, Teuk Thla, Bantaen Meanchey Province (13°34'55"N, 102°53'05"E), collected on 9 June 2007;

a canal, Srey Sophol, Teuk Thla, Teuk Thla, Bantaen Meanchey Province (13°34'46"N, 102°54'49"E), collected on 9 June 2007;

a temporary pond, Strung Treng District, Strung Treng Province (13°17'11"N, 106°06'20" E), collected on 10 June 2007;

a permanent pod, Snourl, Sreicha, Meanchey, Kratie Province (11°58'48"N, 106°23'16"E), collected on 22 October 2007;

a swamp, Snourl, Snourl, Prek Kdey, Kratie Province (13°08'09"N, 106°26'19"E), collected on 22 October 2007;

a permanent pond, Snourl, Ksen, Kratie Province (12°13'08"N, 106°26'07"E), collected on 22 October 2007; and

a canal, Kratie District, Kratie Province (12°15'57"N, 106°25'42"E), collected on 22 October 2007.

Diagnosis.

Male. Right antennule with a serrated spine on segment XX. Urosomites 2 and 3 without hairs ventrally. Caudal rami symmetrical. P5: intersclerite plate produced into a round lobe distally. Right P5: coxa with moderate spine on posterior lobe; right basis with semi-circular lamella on inner medial margin; Exp-1 with outer distal margin produced into acute tip; Exp-2 spherical to oval with principal lateral spine inserted at 1/3 length of outer margin; tiny distal accessory spine; Enp one-segmented. Left P5: basis with long, narrow lamella; Exp-2 with spinular field on inner margin; Enp two-segmented.

Female. Pedigerous somites 4 and 5 completely fused. Pedigerous somite 5 with asymmetrical wings: right wing round with two strong spines, left wing triangular with one strong spine. Genital double-somite incompletely fused dorsolaterally, with right dorsolateral spine. Exp-2 without lateral spine.

Description of adult male.

Body length, without caudal setae, 0.9-1.1 mm (mean = 1.0 mm, n = 5; Fig. 2A ). Prosome ovoid, ~ 2.5 × as long as urosome (Fig. 2A ). Rostrum with bifid process on distal margin (Fig. 2B ). Cephalosome with transversal groove dorsally at anterior part of somite. Pediger 4 separated dorso-laterally from pediger 5 (Fig. 2E ). Pediger 5 asymmetrical; right postero-lateral wing triangular in dorsal view but round on the left wing; posterior spines larger than dorsal spine; spines on right wing relatively larger than those on the left wing (Fig. 2E, F ).

Urosome (Fig. 2C-E ) with five somites, unornamented. Genital somite dilated postero-laterally on right side, shorter than wide, with a minute spine on posterolateral corner. Urosomites 2-4 as long as wide. Anal somite asymmetrical, twisted to right side (Fig. 2C ). Caudal rami symmetrical, each ramus 2.5 × as long as wide, inner margin hairy (Fig. 2C, D ). Each ramus with six setae, subequal in length and size, plumose: dorsal seta bare and thinner than others.

Antennule (Fig. 3 ): asymmetrical, not reaching beyond the end of caudal setae. Left antennule (Fig. 3A-C ): 25-segmented. Armature formula as in Table 1 .

Right antennule (Fig. 3D-H ) 22-segmented. Armature formula as in Table 2 . Segment XX (antepenultimate) with spine modified into comb-like (4 teeth) process (Fig. 3H ).

Antenna (Fig. 4A ): coxa and basis with one and two bare setae on inner distal corner, respectively. Enp two-segmented. Enp-1 with two setae along inner margin; Enp-2 with nine setae along inner margin, seven setae apically; all setae bare. Exp seven-segmented: Exp-1-6 with 1, 3, 1, 1, 1, 1 setae along inner margin; Exp-7 with one seta on inner margin and three setae apically; all setae bare.

Mandible (Fig. 4B ): ca 7 cuspidate teeth dorsally and three small triangular teeth on cutting blade ventrally; one bare seta on coxal gnathobase dorsally. Basis with four bare setae: one proximally and three distally along inner margin. Enp-1 with four setae on inner distal corner. Enp-2 with nine setae apically; two oblique rows of spinules along outer margin. Exp-1-3 each with one seta on inner margin; Exp-4 with three setae apically; all setae bare.

Maxillule (Fig. 4C ): praecoxal arthrite with nine strong setae laterally and four slender submarginal setae. Coxal endite with four setae; coxal epipodite with nine setae; two proximal-most setae smaller than others. Two basal endites fused to segment bearing them: proximal and distal endite, each with four setae apically; basal exite with one short seta. Enp-1 and Enp-2 each with four setae apically, proximal segment fused to basis. Exp with six setae apically.

Maxilla (Fig. 4D ): praecoxa fused to coxa. Proximal and distal endites on praecoxa with four and three setae apically, respectively. Two coxal endites with three setae apically each. Allobasis with three setae apically. Enp four-segmented: Enp-1-3 with one inner seta each, Enp-4 with three setae apically.

Maxilliped (Fig. 4E ): four medial lobes on syncoxa: setal formula 1, 2, 3, 4, respectively; subdistal inner margin produced into a spherical lobe ornamented with densely tiny spinules. Basis with three setae along medial margin, with a row of tiny spinules proximately. Enp-1-6 with 2, 3, 2, 2, 2, and 4 setae, respectively.

P1-P4 (Fig. 5A-D ): each with a round and bare intercoxal sclerite. All coxae with bi-pinnate setae on inner distal margin. P1-P3 basis without setae; a reduced bare seta on outer margin of P4. Exp longer than Enp; two-segmented Enp and three-segmented Exp on P1, three-segmented Enp and Exp on P2-P4. Armature formula of P1-P4 as in Table 3 .

P5 (Figs 5E, F , 6A ): intercoxal sclerite fused to coxa, produced into a rounded lobe distally (Fig. 5F1 ). Right P5: coxa with an acute, strong spine on posterior surface. Basis subrectangular, larger than that on the left side; semi-circular lamella at the middle of inner margin; short longitudinal ridge at proximal half of posterior surface; short, thin seta on the distal outer margin. Enp one-segmented, distal half tapering, tipped with tiny spinules; reaching beyond 1/3 of Exp-2, close to insertion of its principal lateral spine on outer margin. Exp-1 shorter than wide, with a bifid knob at inner margin; distolateral margin with a small acute process. Exp-2 oval with two lateral spines. Principal lateral spine articulated, located at 1/3 length of Exp-2 outer margin, thick, S-shaped, with a sharp curved tip, reaching the distal margin of segment. Accessory lateral spine minute, close to insertion of end-claw. End-claw sickle-shaped, with a blunt tip; ~ 1.5 × as long as Exp-2.

Left P5 (Figs 5E, F , 6A ): coxa with thin seta on posterior lobe near distal inner corner; longer, slender than spine on right coxal segment. Basis with narrow hyaline lamella along 3/4 distal length of inner margin; with a small seta at distal outer margin. Exp-1 triangular, tapering towards distal end, medial margin concave with a field of long setules. Exp-2 smaller than Exp-1, bulbous, with a strong pinnate seta at mid-length of medial margin, with a field of long setules proximally, and a field of tiny spinules distally. Apical hyaline process, thumb-like, with blunt tip. Enp two-segmented, shorter than Exp-1; Enp-1 unarmed. Enp-2 longer than Enp-1, slightly tapering distal end, tipped with a row of tiny spinules.

Description of adult female.

Body length, without caudal setae, 0.9-1.2 mm (mean = 1.1 mm, n = 5), slightly larger than male (Fig. 7A ). Prosome: urosome ratio ~ 2.4:1. Prosome similar to that of males, but lateral wings on pedigerous somites 4-5 completely fused. Lateral wings on pediger 5 asymmetrical: round on right side, triangular on left side; right wing with two strong spines; left wing with one spine (Fig. 7B ). Urosome 3-segmented, with asymmetrical genital double-somite (Fig. 7A , 7E ). Genital double-somite longer than urosomite 2, anal somite, and caudal rami combined, but incompletely fused dorsolaterally on right side (Fig. 7B, C, E ). Right side with a small spine at proximal 1/2 of segment. Left side with bulged margin proximally compared to right side. A pair of gonopores and copulatory pores located centrally at ~ 1/2 length of genital double-somite, beneath a genital operculum. Urosomite 2 symmetrical, shorter than wide. Anal somite (Fig. 7A, E ) as long as wide; anal operculum small with convex free margin.

Antennule symmetrical; left antennule, antenna, mouthparts, and P1-P4 as in male.

P5 (Fig. 8 ) asymmetrical. Coxa with a blunt, stout spine on distal outer margin. Basis with a thin, bare seta on outer margin, reaching almost distal end of Exp-1. Exp-1 sub-rectangular, more than twice as long as wide, longer than Enp. Exp-2 triangular, with a row of strong spinules along both margins; right side stouter than left one (Fig. 8A ); left side with a longitudinal groove (i.e., a conveyor canal) on anterior view (Fig. 8B ). Exp-3 reduced, represented by a small segment on proximal outer margin of Exp-2, with one short spine and a longer medial spiniform seta apically. Enp one-segmented, conical, with a circular row of spinules apically.

Variation.

The male specimens of the new species have the P5 variations as follows: (1) right P5Exp-1: distal outer corner shape varies from triangular to round (Fig. 5F1 ); (2) right P5Exp-2: differences in size of a large distal outer spine; (3) left P5Enp: varies in length (Figs 5E, F ); (4) the comb-like process on segment XX of the right antennule has 4-5 teeth (Fig. 3H ).

Etymology.

The specific name parachristineae is a combination of the Greek prefix para -, meaning to resemble, and the specific name christineae, referring to the fact that the male P5 of the new species resembles Phyllodiaptomus (P.) christineae Dumont, Ranga Reddy & Sanoamuang, 1996 (Fig. 6B ).

Distribution.

At present, the new species have been found throughout the year in both temporary and permanent water bodies, like ponds, roadside canals, irrigation canals, puddles in rice fields, and reservoirs. The new species was prominently found at 30 sites in the Mun River Basin, which is one of the largest tributaries of the Mekong River in Thailand (Fig. 1 ). In Cambodia, the new species has been found in habitats similar to those in Thailand. However, it was recorded at only nine of the 252 sampled sites in the floodplain of Tonle Sap Lake and the Mekong River Basin (Fig. 1 ).

Temperatures in the waters where the new species was discovered range from 20.0-34.1 °C, pH 6.0-7.9, and conductivity 39.4-810.0 µS cm-1. The new species was always present with other diaptomid species, ranging from 2-6 species per sampled site. Co-occurrences of diaptomid species were Dentodiaptomus javanus (Grochmalicki, 1915), Eodiaptomus phuphanensis Sanoamuang, 2001a, Mongolodiaptomus botulifer (Kiefer, 1974), M. malaindosinensis (Lai & Fernando, 1978), M. dumonti Sanoamuang, 2001b, M. mekongensis Sanoamuang & Watiroyram, 2018, Neodiaptomus laii Kiefer, 1974, N. yangtsekiangensis Mashiko, 1951, Phyllodiaptomus (P.) surinensis Sanoamuang & Yindee, 2001, Tropodiaptomus oryzanus Kiefer, 1937, T. vicinus (Kiefer, 1930), and Vietodiaptomus blachei (Brehm, 1951). The co-occurrence of congeneric species was rare, with only one site with the new species and P. (P.) surinensis living together.

Figures

Figure 1. Sampling sites of Phyllodiaptomus (P.) parachristineae sp. nov. in Thailand (black dots) and Cambodia (red dots). Open black squares indicate cities.

Figure 2. Phyllodiaptomus (P.) parachristineae sp. nov., male: A habitus, dorsal view B rostrum C prosomite 5 and urosome, dorsal view D urosome, ventral view E prosomite 5 and urosome, right side in lateral view F left wing of prosomite 5.

Figure 3. Phyllodiaptomus (P.) parachristineae sp. nov., male, antennule: A-C left antennule A segments I-X B segments XI-XX C segments XXI-XXV D-H left antennule D segments I-IX 9 E segments X-XVII F segments XVIII-XIX G segments XX-XXII H a variation of segment XX.

Figure 4. Phyllodiaptomus (P.) parachristineae sp. nov., male: A antenna B mandible C maxillule D maxilla E maxilliped.

Figure 5. Phyllodiaptomus (P.) parachristineae sp. nov., male: A P 1 B P 2 C P 3 D P 4 E P 5 in anterior view F P 5 in posterior view F 1 a variation of right P 5 Exp- 1.

Figure 6. SEM pictures of the male's P 5 of Phyllodiaptomus (P.) parachristineae sp. nov. (A) and P. (P.) christineae (B; fig. 2 B in Sanoamuang and Dabseepai 2021, p. 9) (posterior view).

Figure 7. Phyllodiaptomus (P.) parachristineae sp. nov., female: A habitus, dorsal view B prosomite 5 and genital double-somite, dorsal view C genital double-somite, dorsal view D right spine on genital double-somite, lateral view E urosome with spermatophore, ventral view.

Figure 8. Phyllodiaptomus (P.) parachristineae sp. nov., female: A P 5, posterior view B P 5, anterior view.