Dentodiaptomus orientalis, Sanoamuang & Watiroyram, 2021

Sanoamuang, Laorsri & Watiroyram, Santi, 2021, A new species of copepod (Copepoda: Calanoida) from the floodplain of the lower Mekong River Basin in Thailand and Cambodia, with an amended diagnosis of the genus Dentodiaptomus Shen & Tai, 1964, Raffles Bulletin of Zoology 69, pp. 414-427 : 416-422

publication ID	https://doi.org/ 10.26107/RBZ-2021-0061
publication LSID	lsid:zoobank.org:pub:28532173-0DA0-45C2-8AF6-263E1A49CE78
persistent identifier	https://treatment.plazi.org/id/E0456C4A-13B0-4880-BB57-FB3CFE55706B
taxon LSID	lsid:zoobank.org:act:E0456C4A-13B0-4880-BB57-FB3CFE55706B
treatment provided by	Felipe
scientific name	Dentodiaptomus orientalis
status	sp. nov.

Treatment

Dentodiaptomus orientalis , new species

( Figs. 2–7 View Fig View Fig View Fig View Fig View Fig View Fig )

Type locality. A roadside canal in Okreng , Sambo District, Kratie Province, Cambodia. The geographic coordinates are 13°08′04.15″N, 106°02′20.65″E GoogleMaps .

Material examined. Holotype: one adult male (THNHM- Iv-18782), dissected and mounted in glycerol on one slide. Allotype: one adult female (THNHM-Iv-18783), dissected and mounted in glycerol on one slide. Paratypes: three adult males and three adult females (THNHM-Iv-18784), undissected and preserved in 70% ethanol in one microtube; and, three adult males and three adult females, (KKU-COP- 2021- T01 ), undissected and preserved in 70% ethanol in one microtube. All specimens collected from the type locality on 11 February 2007 by Rachada Chaicharoen .

Other localities. (1) a permanent pond, Kratie District, Kratie Province, Cambodia ; two males collected on 11 February 2007; (2) a permanent pond, Kampong Svay District , Kampong Thom Province, Cambodia ; two males collected on 9 June 2007; (3) a temporary pond, Bakan District , Pursat Province, Cambodia ; two males collected on 10 June 2007; (4) a roadside canal, Boeung Khnar District , Pursat Province, Cambodia ; two males collected on 21 October 2007; (5) a permanent pond, Slor Prah District , Pursat Province, Cambodia ; two males collected on 21 October 2007; (6) a temporary pond, Ban Dong Pleuy, Tansoom District , Ubon Ratchathani Province, Thailand ; three males and one female collected on 9 June 2002; (7) a pond in a rice field, Ban Samrong , Tansoom District, Ubon Ratchathani Province, Thailand ; two males and one female collected on 9 June 2002; (8) a temporary pond, Road Number 24 (Km 9), Muang Det Sub-district , Det Udom District, Ubon Ratchathani Province, Thailand ; two males collected on 11 June 2002; (9) a temporary pond, Road Number 2213 (Km 2), Nayia District , Ubon Ratchathani Province, Thailand ; two males collected on 11 June 2002; and, (10) a temporary pond, Road Number 2172 (Km 18), Pibool Mungsahan District , Ubon Ratchathani Province, Thailand ; two males collected on 21 October 2002. Specimens from Cambodia and Thailand were collected by Rachada Chaicharoen and Panna Wansuang, respectively.

Description of adult male. Body length ( Figs. 2A View Fig , 3A View Fig ) excluding caudal setae, 1.63–1.70 mm (mean = 1. 62 mm, n = 5), smaller and slender than female. Prosome about twice as long as urosome, without ornamentation. Cephalosome with dorsal suture representing fused ascestral segments (cephalon and the first thoracic somite). Rostral spines with two teethlike processes on anterior margin. Pedigers 4 and 5 ( Fig. 3A View Fig ) completely separated, slightly asymmetrical, pediger 5 wings with minute hyaline spines (left spine slightly larger than right spine). Urosome ( Fig. 3B, C View Fig ) five-segmented, asymmetrical. Genital somite ( Fig. 3B View Fig ) slightly enlarged at right distal corner, tipped with a minute spine apically. Urosomites 2–5 ( Fig. 3C View Fig ) without ventral ornamentation. Caudal rami ( Fig. 3B, C View Fig ) with row of setules along inner margin, five plumose setae (seta II–VI), and bare dorsal (VII) seta; dorsal seta thinner than others, but longest.

Left antennule ( Fig. 4A View Fig ) 25-segmented, not extending beyond tip of caudal rami. Setal formula (Arabic numerals = number of setae, Roman numerals = segment numbers): 1(I), 3+a (II), 1+a (III), 1(IV), 1+a (V), 1 (VI), 1+a (VII), 1+s (VIII), 2+a (IX), 1 (X), 1 (XI), 1+a+s (XII), 1 (XIII), 1+a (XIV), 1 (XV), 1+a (XVI), 1 (XVII), 1 (XVIII), 1+a (XIX), 1 (XX), 1 (XXI), 2 (XXII), 2 (XXIII), 2 (XXIV), 5+a (XXV).

Right antennule ( Fig. 3D View Fig ) 22-segmented, geniculated between segment 18 and 19, with setal formula as: 1+a(I), 3+a (II), 1+a (III), 1 (IV), 1+a (V), 1 (VI), 1+a (VII), 1+s (VIII), 2+a (IX), 1+s (X), 1+s (XI), 1+a (XII), 1+a+s (XIII), 2+a+s (XIV), 2+a+s (XV), 2+a (XVI), 1+s (XVII), 1+s (XVIII), 1+a+2s (XIX), 2+s (XX), 2 (XXI), 5+a (XXII); segment 20 (antepenultimate segment) with smooth process reaching distal end of later segment.

Antenna ( Fig. 4B View Fig ) biramous. Coxa small, with inner seta distally. Basis with two inner setae distally. Exp-1–6 with 1, 3, 1, 1, 1, and 1, respectively. Exp-7 with one inner seta and three setae apically. Enp two-segmented: Enp-1 with two inner median setae and small spinules on distal outer margin; Enp-2 with eight inner setae subapically and six setae apically; both segments with row of spinules along distal outer margin.

Mandible ( Fig. 4C View Fig ) with seven strongly chitinised teeth; two three-cusped, three two-cusped, and one mono-cusped teeth; with one dorsal seta on gnathobase. Basis with one seta proximally and three setae distally along inner margin. Enp two-segmented; Enp-1 with four inner setae distally, Enp-2 with nine setae apically and transverse row of tiny spinules on posterior surface. Exp four-segmented, with setal formula as 1, 1, 1, 3.

Maxillule ( Fig. 4D View Fig ) with eight strong spiniform setae distally; five slender setae subapically on praecoxal arthrite. Coxal endite and coxal epipodite with four and seven setae, respectively. Basal endite with three setae proximally and four setae distally; basal exite with outer seta. Enp with eight setae distally. Exp with six setae.

Maxilla ( Fig. 4E View Fig ) with three setae on both praecoxal endites. Coxal endite with three setae on proximal and distal endites. Allobasis with three setae. Enp two-segmented, with three setae each.

Maxilliped ( Fig. 4F View Fig ) with four endites on syncoxa, with setal formula as 1, 2, 3, 4; distal inner corner protruded into subspherical lobe, ornamented with tiny spinules. Basis with three inner setae distally, ornamented with tiny spinules proximally. Enp six-segmented, setal formula as 2, 3, 2, 2, 2, 4.

P1–P4 ( Fig. 5A–D View Fig ) with biramous, three-segmented rami except P1, and two-segmented Enp. Intercoxal sclerite bare. Coxa with distal inner pinnate seta. P1–P3 basis bare. P4 basis with reduced outer seta distally. Armature formula of P1–P4 as shown in Table 1.

(The Arabic and Roman numerals indicate the number of setae and spines, respectively; outer-inner or outer-apical-inner indicate seta/spine) P5 ( Figs. 2B–D View Fig , 5E–H View Fig ) asymmetrical, right leg enlarged. Distal margin of intercoxal sclerite straight. Right P5: coxa with finger-like extension on distal outer corner, accompanied with one small hyaline spine inserted on posterior surface. Basis ( Figs. 2B, C View Fig , 5E View Fig ) elongated, about 1.5 as long as wide; without hyaline lamella on inner margin; no projection on posterior surface; sensory seta on distal outer margin short. Exp-1 ( Figs. 2B, C View Fig , 5E View Fig ) shorter than wide, with acute process at distal outer corner and semi-circular posterior knobs on distal margin. Exp-2 ( Figs. 2B, C View Fig , 5E, F View Fig ) slightly oval, about twice as long as wide, with lateral ridge on posterior surface ending with acute spine. Lateral spine ( Figs. 2B, C View Fig , 5E, F View Fig ) articulated, curved backward, acutely pointed, 0.1 times as long as Exp-2, inserted sub-distally, close to end claw. End claw ( Figs. 2B, C View Fig , 5E View Fig ) sickle-shaped, robust, with acute tip, about as long as Exp-2. Enp ( Fig. 2B, C View Fig ) rectangular, reaching slightly beyond Exp-1, tipped with spinules.

Left P5 ( Figs. 2B–D View Fig , 5E, G, H View Fig ) reaching posterior margin of right P5 Exp-1. Coxa as long as wide, with one small posterior seta inserted near inner corner distally. Basis trapezoidal, without hyaline lamella on inner margin; with one thin seta near outer corner distally and small knob-like outgrowth apically. Two-segmented Exp ( Figs. 2B–D View Fig , 5E View Fig ), Exp-1 fusiform, with field of tiny spinules at distal inner corner. Exp-2 ( Figs. 2E View Fig , 5E, G, H View Fig ) conical, smaller than Exp- 1; with few long setules and short spinules at proximal half of segment inner margin, one pinnate seta at 1/2 length of inner margin; and 6–10 denticles sub-terminally. Enp ( Figs. 2D View Fig , 5E View Fig ) unsegmented, longer than Exp-1, tipped with row of spinules distally.

Description of adult female. Body length ( Fig. 6A View Fig ), measured from anterior margin of rostrum to posterior margin of caudal rami, 1.65–1.77 mm (mean = 1. 70 mm, n = 5). Prosome as in male except pedigers 4 and 5 fused, with suture laterally. Pediger 5 with asymmetrical posterolateral wings ( Fig. 7A View Fig ), right wing posteriorly triangular in dorsal view, but rectangular on left side; each wing with one dorsal spine and one larger posterior spine. Urosome ( Fig. 6A, B View Fig ) symmetrical, three-segmented. Genital double-somite ( Figs. 6A, C View Fig , 7A View Fig ) symmetrical, separated dorsally, shorter than urosomite 2, anal somite and caudal ramus combined; slightly expanded proximally; with one pair of genital spines laterally, inserted directly on segment, sub-similar in size. Urosomite 2 symmetrical, shortest, usually beneath former segment. Anal somite ( Fig. 6C View Fig ) expanded distally; anal operculum small with posterior margin concave. Caudal rami, antennule, antenna, mouthparts, and P1–P4 similar to those in male.

P5 ( Figs. 6C–E View Fig , 7B, C View Fig ) slightly asymmetrical. Coxa with stout spine arising from posterior lobe located on distal outer margin. Basis trapezoidal, with short, bare seta on distal outer margin, reaching about 1/4 length of Exp-1. Exp-1 ( Figs. 6C–E View Fig , 7B, C View Fig ) rectangular, slightly curved, about twice as long as wide. Exp-2 slightly asymmetrical, right side more triangular, with acute tip, longitudinal conveyor canal on frontal view. Left side stouter, with blunt tip; with row of strong spinules along margins, more spinules on inner margin. Exp-3 ( Fig. 6C, D View Fig ) minute, as long as wide, not articulated; with two bare spines, lateral spine short, about 1/4 of apical spine. Enp ( Figs. 6E View Fig , 7B, C View Fig ) rectangular, about 4–5 times as long as wide, slightly shorter than Exp-1, with circular row of spinules terminally. Adult females with egg sac were not found in examined samples.

Variations. One of five females photographed by SEM showed a thin spine instead of a strong spine on P5 Exp-3. The left P5 Exp-2 of the males (n = 5) with the number of denticles varied from six to ten denticles on the distal inner margin that are clearly presented in frontal view.

Etymology. The specific epithet, orientalis (Latin, adj., of the east), alludes to the “Eastern region”, which includes Thailand and Cambodia, the countries where it was first recorded. The name is used as an adjective.

Geographic distribution. In Thailand, D. orientalis , new species, was found only in temporary water habitats in five localities in Ubon Ratchathani Province ( Fig. 1 View Fig ) during the rainy season (June and October). It was found together with 1–5 other diaptomids, including Eodiaptomus phuvongi Sanoamuang & Sivongxay, 2004 , Mongolodiaptomus malaindosinensis ( Lai & Fernando, 1978) , Neodiaptomus laii Kiefer, 1974 , Neodiaptomus songkhramensis Sanoamuang & Athibai, 2002 , and Vietodiaptomus blachei ( Brehm, 1951) . In Cambodia, the new species was recorded from six localities in three provinces; Kratie, Kampong Thom, and Pursat ( Fig. 1 View Fig ). It was recorded throughout the year and usually lived together with 1–3 other diaptomids, viz., E. phuvongi , E. phuphanensis Sanoamuang, 2001 , M. malaindosinensis , N. laii , Tropodiaptomus oryzanus Kiefer, 1937 , and V. blachei . This new species is very rare, as evidenced by the fact that it was isolated from 3.1% (5 from 163 localities) and 2.5% (6 from 236 localities) of the sampling localities in Thailand and Cambodia, respectively.