Phyllodiaptomus (P.) roietensis, Sanoamuang & Watiroyram, 2020

Sanoamuang, La-orsri & Watiroyram, Santi, 2020, Phyllodiaptomus (Phyllodiaptomus) roietensis, a new diaptomid copepod (Copepoda, Calanoida) from temporary waters in Thailand and Cambodia, with a key to the species, ZooKeys 911, pp. 1-20 : 1

Phyllodiaptomus (P.) roietensis sp. nov. Figs 2 , 3 , 4 , 5 , 6 , 7 , 8

Type locality.

A pool in the rice field at Ban Nakae, Khilek Subdistrict, Pathum Rat District, Roi Et Province, northeastern Thailand; pH of water 8.6, water conductivity 126 µS cm-1.

Type material.

Holotype: one adult male completely dissected (NHMUK 2019.7, one slide), Ban Nakae (15°37'37"N, 103°28'06"E), Khilek Subdistrict, Pathum Rat District, Roi Et Province, northeastern Thailand; collected on 12 June 1999 by L. Sanoamuang. Allotype: one adult female completely dissected (NHMUK 2019.8, one slide); same data as for holotype. Paratypes: two adult females and three adult males undissected preserved in 70% ethanol (NHMUK 2019.9-13), one adult female completely dissected (KKU-COP-2019-S-01); one adult female with eggs and three adult males undissected preserved in 70% ethanol (KKU-COP-2019-T-01); same data as for holotype.

Other localities.

(1) a temporary pond, Ban Non Lakki (15°10'55"N, 102°23'46"E), Than Lalot Subdistrict, Phimai District, Nakhon Ratchasima Province, northeastern Thailand; collected on 17 October 2017 by N. Plangklang; (2) a roadside canal, Tropeang Chouk village (no geographical co-ordinates), Baray District, Kampong Thom Province, central Cambodia; collected on 14 June 2007 by R. Chaicharoen; (3) a temporary pond, Kropeu village (no geographical co-ordinates), Steung Sen District, Kampong Thom Province, central Cambodia; collected on 14 June 2007 by R. Chaicharoen.

Description of adult female.

Total body length measured from anterior margin of rostrum to posterior margin of caudal rami, 0.9-1.3 mm. Rostrum (Fig. 3G ) with bifid process in distal margin, pointed backward; each with short spine at tip. Prosome length: urosome plus caudal rami ratio about 2.6:1, ratio of width to length of prosome = 1:2.4, urosomites 1-3 = 1.3:3.0:1.1, caudal ramus = 1:1.5. Prosome (Figs 2A , 3A ) ovoid, cephalosome with transversal groove in anterior part of somite length; Pdg 4 and 5 fused, partly separated laterally, with few tiny hair-like spinules scattered laterally (Fig. 3B, C ). Pdg 5 (Figs 2C, E , 3C-F ) with asymmetrical postero-lateral wings; right one rounded; left one longer and triangular; each wing with dorsal and posterior spines (former spine slightly larger than later one). Urosome (Figs 2A , 3A ) with asymmetrical genital double-somite. Genital double-somite (Figs 2C-E , 3C-F ) longer than urosomite 2, anal somite and caudal ramus combined. Left side with obviously laterally dilated proximal part of genital-double segment; dilatation dorsally with large and blunt spine distally, tip of spine oriented medially. Right side with slightly dilated proximal part of genital double-somite; elongated into triangular outgrowth with blunt spine at tip; spine orientated ventro-laterally. A pair of gonopores located beneath genital operculum, at about one-half length of genital double-segment. Adult female bears one egg sac with 20-25 eggs (Fig. 2A ). Urosomite 2 symmetrical, very short. Anal somite (Figs 2C, D , 3A ) as long as wide; anal operculum small, free margin convex. Caudal rami (Fig. 2A, D ) symmetrical, with row of setules along inner and outer margins. Ramus with six setae (seta II-VII), subequal in length, all plumose but dorsal (VII); dorsal seta articulated, longest.

Antennule (Fig. 4A ) symmetrical, 25-segmented, reaching beyond the end of caudal setae. Setal formula (Roman numerals in parentheses refer to segment number): 1+ae (I), 3+ae (II), 1+ae (III), 1(IV), 1+ae (V), 1 (VI), 1+ae (VII), 1+sp (VIII), 2+ae (IX), 1 (X), 1 (XI), 1+ae+sp (XII), 1 (XIII), 1+ae (XIV), 1 (XV), 1+ae (XVI), 1 (XVII), 1 (XVIII), 1+ae (XIX), 1 (XX), 1 (XXI), 2 (XXII), 2 (XXIII), 2 (XXIV), 4+ae (XXV).

Antenna (Fig. 4B ) biramous. Coxa and basis with one and two inner setae on distal corner, respectively. Exp-1-7 with 1, 3, 1, 1, 1, 1, and 1 inner seta, respectively; Exp-7 with three additional apical setae. Enp-1 with two inner median setae. Enp-2 with eight inner and seven apical setae.

Mandible (Fig. 4C ) with six strongly chitinized teeth and one dorsal seta on gnathobase. Basis with four inner setae. Enp-1 with four inner distal setae; Enp-2 with nine apical setae plus tiny spinules along posterior surface. Exp-1-4 with 1, 1, 1, 3 setae, respectively.

Maxillule (Fig. 4D ) with 13 setae on praecoxal arthrite. Coxal endite and coxal epipodite with four and nine setae, respectively. Proximal and distal endites each with four setae; basal exite with a single seta. Enp with seven apical setae. Exp with six setae.

Maxilla (Fig. 4E ) with two praecoxal and two coxal endites; each with three apical setae. Allobasis with three setae. Enp-1 and 2 with three setae each.

Maxilliped (Fig. 4F ) with four endites on syncoxa, with 1, 2, 3, 4 apical setae respectively. Basis with three setae along median margin. Enp-1-6 with 2, 3, 2, 2, 2, 4 setae, respectively.

P1-P4 (Fig. 5A-D ) with round and bare intercoxal sclerite. Coxa with inner seta. P1 basis with reduced outer seta. Exp longer than Enp, Exp and Enp three-segmented except P1 Enp bi-segmented. Armature formula of P1-P4 as follows (Arabic and Roman numerals indicate number of setae and spines, respectively; outer-inner or outer-apical-inner indicate seta/spine):

P5 (Fig. 5E ) asymmetrical. Coxa with blunt, stout spine on distal outer margin. Basis with thin, bare seta on distal outer margin, reaching beyond 3/4 of Exp-1. Exp-1 sub-rectangular, more than twice as long as wide, longer than Enp. Exp-2 triangular, right side stout and shorter than left one; with row of strong spinules along margins and proximolateral spine at basal Exp-3; with two longitudinal grooves on anterior view (Fig. 5F, G ). Exp-3 represented by small distal prominence produced into short distolateral spine and longer medial spine. Enp subconical, Enp-1 slightly rectangular. Enp-2 tipped with circular row of spinules.

Description of adult male.

Body length (Figs 6 , 7A ) without caudal setae, 0.8-1.1 mm (mean = 1.0 mm, n = 5), smaller than female. Prosome length: urosome plus caudal rami ratio about 2.1:1, ratio of width to length of prosome = 1:2.1, urosomites 1-5 = 2.3:1.0:1.0:1.3:1.0, caudal ramus = 1:1.9. Prosome similar to that of female except lateral wings on Pdg 5. Lateral wings (Figs 6A , 7B-D ) asymmetrical, round on right and more triangular on left side; posterior spine on right wing larger compared to left side. Urosome (Figs 6A, B , 7A ) 5-segmented, asymmetrical, curved downward to right side. Genital somite (Figs 6 , 7B ) dilated postero-laterally on right side, with spine at distal outer corner; longer than that on Pdg 5 wings. Genital aperture located on mid-ventral region. Urosomites 2-3 (Figs 6B , 7D ) without ornamentation. Urosomite 4 (Fig. 6A, B ) with irregularly dilated posterior margin. Anal somite (Fig. 6A, B ) asymmetrical and twisted to right side. Caudal rami (Figs 6A, B , 7E, F ) asymmetrical, right ramus with two triangular prominences: one proximolateral and one distoventral; setation similar to female.

Antennule (Figs 6C , 7G, H ) asymmetrical, with geniculated right side. Right antennule 22-segmented, with setal formula as 1+ae (I), 3+ae (II), 1+ae (III), 1 (IV), 1+ae (V), 1 (VI), 1+ae (VII), 1+sp (VIII), 2+ae (IX), 1+sp (X), 1+sp (XI), 1+ae+sp (XII), 1+ae+sp (XIII), 2+ae+sp (XIV), 2+ae+sp (XV), 2+ae+sp (XVI), 1+sp (XVII), 1+sp (XVIII), 2+ae+sp (XIX), 3+sp (XX), 2 (XXI), 4+ae (XXII); geniculated between segments 18 and 19; segment 20 (antepenultimate) with serrated process distally (3-4 teeth), and with longitudinal hyaline membrane along outer margin.

Left antennule, antenna, mouthparts, and P1-P4 as in female.

P5 (Figs 6D , 8A, G ) intercoxal sclerite with rounded lobe on free margin. Right P5: coxa with acute, stout spine on posterior lobe. Basis (Fig. 8B, G ) with large proximomedial triangular lamella at one-fourth length of inner margin; with large three-lobed chitinous medial prominence on posterior surface; distal outer margin with long, thin seta, slightly extending beyond Exp-1. Enp (Fig. 8B, H, G ) with bi-lobed distal margin, tipped with spinules and hyaline lamella on inner and outer lobes, respectively; reaching downward to approximately one-third of Exp-2. Exp-1 (Fig. 8A, B, H ) with semi-circular knob on distomedial margin; distolateral margin with small acute process. Exp-2 (Fig. 8C, H ) elliptic, with three accessory lateral spines, one proximal, middle, and distal on lateral margin. Principal lateral spine articulated, located at two-third length of Exp-2, flat, thick, digitiform, with sharp tip; long, with approximately half of segment bearing it; slightly twisted in posterolateral direction. End claw (Figs 6D , 8A ) medially sickle-shaped, slender towards tip, more than 1.5 times as long as Exp-2; medial margin serrated with row of tiny spinules.

Left P5 (Figs 6D , 8D ): coxa with moderate strong seta inserted on posterior lobe at distal inner corner, slightly shorter than distal margin of basis. Basis with flap of longitudinal hyaline lamella at medial margin; with long, thin seta at posterolateral margin, extending to approximately half of Exp-1. Exp-1 (Fig. 8F ) tapering towards posterior margin, medial margin concave, with field of setules and tiny spinules. Exp-2 smaller than Exp-1, conical; with large seta at mid-length of medial margin, as long as Exp-2 and apical process combined; with few setules proximally and widespread with spinules distally along inner margin, thickness of spinules increased from proximal to distal; apical process stout, bare, and blunt-tip. Enp (Fig. 8F, J ) bi-segmented, longer than Exp-1, Enp-2 tipped with row of spinules distally.

Differential diagnosis.

Phyllodiaptomus (P.) roietensis sp. nov. with the male P5 Exp-2 displays an affinity to the subgenus Phyllodiaptomus sensu Dumont et al. (1996): the lateral side of the right Exp-2, medially concave in posterior view, principal lateral spine inserted on distal to mid-outer margin and three accessary spines arranged from proximal, middle, and distal, respectively; the left Exp-2 with patch of strong spinules along medial margin.

The male of the new species has serrated outgrowth on the antepenultimate segment of the right antennule. The right caudal ramus with small chitinous spine near distal margin on ventral side and triangular prominence along proximal one-third length of outer margin. The P5 intercoxal sclerite produced, with convex distal margin. The right P5 with (1) short, strong spine on posterior lobe of coxa, (2) triangular hyaline lamella on proximal inner margin and large chitinous outgrowth on posterior surface of basis, (3) acute distal outer corner of Exp-1 (4) Exp-2 oval and concave, with strong, flat, curved principal spine and three accessary spines, and (5) bi-lobed Enp. The left P5 with long and narrow hyaline lamella along inner margin, Exp-2 with patch of strong spinules along medial margin, and bi-segmented Enp.

Female with asymmetrical Pdg 5 wings, left wing more elongated in posterio-lateral direction; posterior and dorsal spines short and strong. Genital double-somite with posterolateral directed process on right side. One pair of genital spines on lateral side slightly symmetrical and strong. P5 Exp-2 with conveyor canal on anterior surface. P5 with bi-segmented Enp.

Etymology.

The specific name roietensis is taken after the type locality, Roi Et Province. The name with the Latin suffix "- ensis " is the adjective for a location.

Distribution.

Known only from four temporary water bodies from Roi Et and Nakhon Ratchasima provinces, Thailand and Kampong Thom Province, Cambodia (Fig. 1 ). Presence of specimens was recorded in early monsoon period. The new species is rare, as it was found in 0.4% of all the localities sampled in Cambodia. The new species was found together with six diaptomids including Dentodiaptomus javanus (Grochmalicki, 1915), Eodiaptomus sanoamuangae Ranga Reddy & Dumont, 1998, Mongolodiaptomus calcarus (Shen & Tai, 1965), M. malaindosinensis (Lai & Fernando, 1978), Neodiaptomus laii Kiefer, 1974, and Phyllodiaptomus (Phyllodiaptomus) christineae Dumont, Ranga Reddy & Sanoamuang, 1996.

Figures

Figure 1. Distribution of Phyllodiaptomus (P.) roietensis sp. nov. and P. (P.) surinensis. Key: black square = city, black circle = P. (P.) roietensis sp. nov., black triangular = P. (P.) surinensis, blue arrows indicate water flow direction.

Figure 2. Phyllodiaptomus (P.) roietensis sp. nov., female: A habitus, dorsal view B cephalosome with rostrum, lateral view C lateral wings on Pdg 5 and urosome (without caudal rami), dorsal view D urosome, ventral view E Pdg 5 with P 5 and genital double-somite, lateral view from left side.

Figure 3. Phyllodiaptomus (P.) roietensis sp. nov., female: A habitus, dorsal view B Pdg 4, lateral view C Pdg 5 and genital double-somite, dorsal view D Pdg 5 and genital double-somite spines, lateral view from left side E Pdg 5 and genital double-somite spines, lateral view from right side F Pdg 5 and genital double-somite, lateral view G rostral spines.

Figure 4. Phyllodiaptomus (P.) roietensis sp. nov., female: A antennule B antenna C mandible D maxillule E maxilla F maxilliped.

Figure 5. Phyllodiaptomus (P.) roietensis sp. nov., female: A P 1 B P 2 C P 3 D P 4 E P 5 F, G right and left P 5 Exp- 2 (black arrows indicate longtitudinal ridges) A-E posterior view F, G anterior view.

Figure 6. Phyllodiaptomus (P.) roietensis sp. nov., male: A habitus, dorsal view B urosome, ventral view C right antennule, with grey objects indicating antennular spines D P 5, with grey and dotted objects indicating hyaline lamella and chitinous prominences respectively, posterior view.

Figure 7. Phyllodiaptomus (P.) roietensis sp. nov., male: A habitus, dorsal view B Pdg 5 and genital somite, dorsal view C Pdg 5 lateral wing, left view D Pdg 5, genital somite and urosomites 2 and 3, ventrolateral view E, F right caudal ramus in dorsal (E) and ventral (F) views G, H right antennule (white arrows indicate spines on segments 8, 10 - 18, 20.

Figure 8. Phyllodiaptomus (P.) roietensis sp. nov., SEM photographs, male: A P 5 in posterior view B right P 5 basis, Exp- 1 and Enp, posterior view C right P 5 Exp- 2 in posterior view (white arrows indicate accessory spines) D left lobe of P 5, posterior view E left P 5 Exp- 2 and Enp, posterior view F left P 5 Enp, posterior view G P 5, anterior view H right P 5 Exp- 1 - 2 and Enp, anterior view I left P 5 basis, Exp and Enp, anterior view J left P 5 Enp (white arrow indicates Enp segmented point), anterior view.