Pseudohesperocyclops loeiensis, Brancelj & Boonyanusith & Sanoamuang, 2024

Brancelj, Anton, Boonyanusith, Chaichat & Sanoamuang, Laorsri, 2024, A new cyclopoid genus (Copepoda, Crustacea) from a deep aquifer in northeastern Thailand with comments on peculiar sampling sites and local fauna, Raffles Bulletin of Zoology 72, pp. 71-83 : 74-78

Pseudohesperocyclops loeiensis , new species

( Figs. 2A–D , 3A–E , 4A–C , 5A–E (female))

Type locality. Well on Mr. Ken-Yen Chen’s property filling ten plastic reservoirs (volume of 10 m 3 each), Phurua district, Loei province, Thailand. Coordinates: 10° 17′ 02.73″ E, 17° 20′ 19.24″ N, altitude 636 m a.s.l. ( Figure 1 ). Only reservoirs No. 3 and No. 10 were sampled .

Material examined. Holotype: adult female, total body length 685 µm, completely dissected, mounted in glycerol on a slide, and sealed with nail polish (access number THNHM-IV-20274). Collected on 12 March 2023, by A. Brancelj, L. Sanoamuang, and N. Sanoamuang. No allotype. Paratype: one female stored in 70% ethanol (access number THNHM-IV-20275). All material was deposited at the Thailand Natural History Museum, Pathum Thani, Thailand. The paratype specimen was collected at the same place and on the same date as the holotype .

Description. Female: total body length, measured from tip of rostrum to posterior margin of caudal rami, 685−707 µm (mean: 699 µm; n=3); prosome/urosome length ratio about 1.5 ( Fig. 2A ). Preserved specimens colourless, naupliar eye not discernible. Total body length/width ratio about 3.5 (specimens narcotised before fixation); prosome with numerous small narrow and elongated ovoid pits in bilaterally symmetrical pattern, present also on urosome but anal segment. Rostrum triangular, small, with rounded tip, with two sensilla. Integument smooth, not strongly chitinised, without visible cuticular windows. Cephalosome slightly shorter than wide, representing 28% of body length, with the greatest width at the posterior margin. Hyaline free margins of Pd1–Pd3 dorsally smooth but Pd4–Pd5 serrated. Genital double somite about 1.5 times as wide as long, tapering posteriorly ( Figs. 2B, C ), with serrated hyaline free margin, both dorsally and ventrally. Copulatory pore small, positioned at 1/3 length of somite. Seminal receptacle large; circular in shape, extended laterally in posterior genital segment ( Fig. 2C ). Urosomite segments 3 and 4 with serrated hyaline free margin, both dorsally and ventrally. Anal somite with rows of spinules distally from ventral to dorsolateral section. Anal operculum well developed, rectangular with rounded corners, free margin smooth. Two large sensilla at base of operculum ( Fig. 2B ).

Caudal rami ( Figs. 2A, B ; 3A, B ). Elongated, parallel, about 2.4 times as long as wide, with a ridge along dorsal surface and lateral integumental pore at proximal 1/4 of ramus length. Anterolateral accessory seta (I) apparently absent. Anterolateral seta (II) soft, plumose, inserted at 3/4 length of ramus, few spinules at its base. Posterolateral seta (III) robust, pinnate, as long as caudal ramus. Outer terminal seta (IV) plumose, about 3.5 times as long as caudal ramus, without breaking plane. Inner terminal seta (V) plumose, without breaking plane, longest. Terminal accessory seta (VI) slim, about 1/2 length of caudal ramus. Dorsal seta (VII) articulated, plumose, inserted near base of inner terminal seta (V), as long as caudal ramus.

Antennule ( Fig. 2A , 3C ). 11-segmented, not reaching posterior margin of cephalothorax ( Fig. 2A ). Armature formula: 7.2.6.2.2.2.3.2+ae.2.2+ae.7+ae. Segments 2, 4 and 5 shortest; segment 5 with spiniform seta. Aesthetascs on segments 8 and 10 small, slim; on terminal segment slim, as long as accompanied seta; all forming acrothek.

Antenna ( Fig. 3D ). 4-segmented, comprising coxobasis and 3-segmented Enp. Coxobasis with two smooth seta on inner distal corner. Robust pinnate seta on outer apical corner represents Exp, reaching middle of Enp-2. Enp-1 with one smooth seta at 2/3 length of inner margin; group of spinules along outer margin. Enp-2 about 1.5 times as long as wide, with five smooth setae (two laterally, one subapically, two apically). Enp-3 about twice as long as wide, with seven smooth apical setae of different lengths, two of them long, about 3 times as long as segment bearing them.

Mandible ( Fig. 3E ). Comprising coxa and basis. Gnathobase with strongly chitinised teeth, ventralmost teeth robust and slightly obtuse, with two smooth seta dorsally. Basis shorter than wide, with two long plumose setae representing Exp; shorter bare seta representing Enp, respectively; long setae about 10 times as long as short seta.

Maxillule ( Fig. 4A ). Comprising robust praecoxa, coxobasis, 1-segmented Enp. and Exp. represented by single soft seta. Arthrite of praecoxa with seven robust lateral spines, six of them smooth; proximal one longest, pinnate. Three strong claw-like spines similar in length apically and one strong seta laterally. Coxobasis with three elements: one pinnate and two unipinnate setae apically. Enp with three smooth setae apically; smooth seta next to them represents Exp.

Maxilla ( Fig. 4B ). 4-segmented. Praecoxa and coxa fused, with three endites; proximal one with one pinnate and one bare seta, middle one with one spiniform seta; distal endite elongated, with two setae apically, unequal in length. Allobasis with strong claw-like basal endite with additional two spiniform extrusions along concave margin; two setae at base of claw; longer one slightly shorter as claw, robust, unipinnate; other one positioned laterally, shorter and slim. Enp 2-segmented, proximal segment with two robust bare setae; distal segment with one robust seta apically, accompanied by two shorter setae subapically.

Maxilliped ( Fig. 4C ). 4-segmented, composed of syncoxa, basis and 2-segmented Enp. Syncoxa with one endite at distal end, with two robust unipinnate setae, unequal in length. Basis with row of robust short spinules on distal outer corner, few spinules along inner margin; two setae unequal in length along medial margin. Enp-1 with one long, strong pinnate seta. Enp-2 with three setae; one pinnate and one smooth apically, one smooth subapically.

Intercoxal sclerites in P1–P4 (Figs. 5A–D). Unornamented, distal margin broadly concave, minute rounded projections only slightly overreaching distal margin of sclerite. Coxa rectangular, with three long rows of minute spinules along distal margin on P1 but few robust spinules on outer distal margin on P2–P4. Long plumose seta at inner distal angle of P1–P4 coxae. Bases of P1–P4 roughly trapezoidal, with soft plumose seta on outer margin. Inner and outer distal corners with sharp points, but inner margin of P1 as rounded process with several long hairs at tip. Basis of P1 with long spiniform seta on inner margin.

Exp and Enp of P1–P4 2-segmented. Most of setae on Exp-2 and Enp-2 as long or slightly longer as ramus bearing them, soft, plumose. Exp-2 spines/setae formula as: 3.4.3.3 / 5.5.5.5, respectively. Enp-2 spines and setae formula: 1.1.1.1 and 5.6.6.4. Complete armament of P1–P4 as in Table 3.

P 1 (Fig. 5A). Basis with long and slim medial spine reaching middle of Enp-2. Exp-1 as long as wide, rather small. Exp-2 about 1.3 times as long as wide. Spines on Exp small, with blunt tips. Enp-2 about 1.5 times as long as wide; apical spine as long as segment bearing it, strong with blunt tip.

P2 (Fig. 5B). Exp-1 slightly longer than wide, rather small. Exp-2 about 1.5 times as long as wide; spines with rather blunt tips. Enp-1 as long as wide, Enp-2 1.8 times as long as wide; apical spine as long as segment bearing it, slightly curved, with blunt tip.

P3 (Fig. 5C). Exp and Enp identical to P 2 in shape, armament and proportions. Apical spine on Enp-2 as long as segment bearing it, slim, slightly curved, with sharp tip.

P4 (Fig. 5D). Exp and Enp similar to P2 and P 3 in shape and proportions; apical spine on Enp-2 slightly longer than segment bearing it, slim, straight, with sharp tip.

P5 ( Figs. 2 B–D ; 5E). Baseoendopod completely fused to Pd5; Exp 1-segmented with one long soft bare seta and one short spiniform one. Setae on baseoendopod and Exp similar in length. Long seta and spiniform seta on Exp inserted close to each other.

P6 ( Figs. 2B, D ). Small, simple cuticular plate positioned dorsolaterally on genital double somite, with two minute spines and a longer, soft seta dorsally.

Male. Unknown.

Variability. Not recorded.

Etymology. The specific epithet alludes to the species type locality province, e.g., the Loei province in northeastern Thailand.

Figures

Fig. 2. Pseudohesperocyclops loeiensis, new genus, new species, female; A, paratype; B–D, holotype. A, habitus; B, urosome; C, genital double somite (ventral view); D, genital double somite (lateral view). Scale bars: A, 0.1 mm; B–D, 0.05 mm.

Fig. 3. Pseudohesperocyclops loeiensis, new genus, new species, female; A–E, holotype. A, anal somite and caudal rami (dorsal view); B, anal somite and caudal rami (ventral view); C, antennule; D, antenna; E, mandible. Scale bars: 0.05 mm.

Fig. 4. Pseudohesperocyclops loeiensis, new genus, new species, female; A–C, holotype. A, maxillule; B, maxilla; C, maxilliped. Scale bars: 0.05 mm.

Fig. 1. A, map of Thailand with indication of sampling sites (red circle); B, detailed locations of sampling sites in Hug Jang Loei Garden & Resort (HJL I well (30 m deep), HJL II well (80 m deep), and Mr. Chen’s well (120 m deep) in Dan Sai and Phurua districts, respectively, Loei province (northeast Thailand); C, sampling site of the new species, Pseudohesperocyclops loeiensis, new genus, new species in Mr. Chen’s containers (Photo: Laorsri Sanoamuang).