Parapseudoleptomesochra phayaoensis, Koompoot & Sanoamuang, 2021

Koompoot, Kamonwan & Sanoamuang, La-orsri, 2021, Parapseudoleptomesochra phayaoensis, a new species of copepod (Copepoda: Harpacticoida: Ameiridae) from a cave in northern Thailand, Invertebrate Zoology 18 (1), pp. 1-15 : 3-11

Parapseudoleptomesochra phayaoensis sp.n.

Figs. 1–8 .

ETYMOLOGY. The specific name phayaoensis is taken after the type locality, Phayao Province. The name is with the Latin suffix “ -ensis ”, which refers to the type locality.

TYPE LOCALITY. Chom Sin cave , Ban Tham Subdistrict , Dok Kham Tai District , Phayao Province, Northern Thailand (19°04′ 52.68″ N, 100°04′24.74″ E), 443 m above sea level. The cave is about 15 m long, with one single horizontal gallery. Most of the cave is completely dark with little airflow. A pool filled with percolating water about 4 m in diameter, is located in the inner part of the cave, and is not connected to any surface water. On the collecting date (10 June 2016), the following water parametersweremeasured:temperature 26.6 °C, pH 7.3, a conductivity of 639.3 µS cm –1, dissolved oxygen 4.7 mg L –1, nitrate concentration 1.1 mg L –1 and orthophosphate concentration 0.56 mg L –1.

MATERIAL EXAMINED. Holotype: one adult female ( NHMUK 1009 ), dissected and mounted in glycerol on one slide; allotype, one adult male ( NHMUK 1010 ), dissected and mounted in glycerol on one slide; paratypes, eleven adult females ( NHMUK1011–1021 ), undissected and preserved in 70% ethanol in a 1.5 mL microtube. All specimens were collected on 10 June 2016 by K. Koompoot.

DESCRIPTION OF FEMALE. Body length (measured from anterior margin of rostrum to posterior of caudal rami, excluding caudal setae), 575–609 µm (n = 5; mean = 591 µm), fusiform ( Fig. 1A–C ). Prosome/urosome ratio 1.8 with largest width along posterior margin of cephalothorax. Naupliar eye not discernible. Rostral tip short and small. Cephalothorax nearly ovoid on lateral view, proportional length/ width cephalothorax about 1.0. Integument of cephalic shield bearing several pairs of sensilla on dorsal surface ( Fig. 1D, E ). Posterior margin of prosomites smooth dorsally ( Fig. 1F ).

Fifth pedigerous somite, thoracic somite ( Fig. 2A ) with serrated posterior margin, ornamented with transverse rows of tiny spinules on lateral view. Genital double-somite ( Fig. 2A ) 0.6 times as long as wide, with short rows of minute spinules laterally on proximal half and a transverse row above its posterior margin, hyaline fringe serrated on posterior margin. Genital complex with single copulatory pore, seminal receptacles curve and strongly sclerotized. P6 reduced, fused into a small plate on each side of copulatory pore, without armature ( Fig. 5A ). Urosomites 3–4 with a continuous row of minute spinules above posterior margins; with serrated hyaline frills on posterior margins ( Figs 2B–D , 5A ). Anal somite ( Figs 2E, F , 5A, B ) with short row of spinules on dorsal surface; posterior margin consisting of prominent spinules on dorsal, lateral and ventral views.

Anal operculum ( Figs 2E, F , 5B ) convex, reaching beyond somite, with frill on its margin.

Caudal rami ( Figs 2E–F , 3A , 5A, B ) subconical, about 1.2 times as long as wide, slightly divergent, armed with seven elements. Armature consists of one short anterolateral external accessory seta (seta I) and a long anterolateral external seta (seta II). Posterolateral seta (seta III) about 1.9 times as long as caudal ramus, with three large spinules at base of distal posterolateral seta. Outer terminal seta (seta IV) without breaking plane, pinnate at distal end, about 3.7 times as long as caudal ramus. Inner terminal seta (seta V) slightly enlarged base and relatively long, without breaking plane, pinnate at distal end, about 20 times as long as caudal ramus. Inner accessory seta (seta VI) smooth, about 2.4 times as long as caudal ramus. Dorsal seta (seta VII) articulated, arising near posterior inner edge, about 3.7 times as long as caudal ramus.

Antennule ( Figs. 3B–D , 6A ) eight-segmented and elongate, longer than cephalothorax. Aesthetasc on fourth segment not reaching beyond tip of last segment. Setal formula: I (1), II (9), III (5), IV (2, 1+ae), V (4). VI (2), VII (5), VIII (6). Segment 1 with one smooth seta and row of spinules, with cuticular tube on anterior surface ( Fig. 1B ).

Antenna ( Figs 3E, F , 6B ) composed allobasis, two-segmentedEnpandone-segmentedExp. Allobasis unarmed, about 1.5 times as long as wide, with row of spinules along outer margin. Enp-1 about 2.8 times as long as wide, unarmed and unornamented. Enp-2 with nine elements: with two surface frills subdistally, armed laterally with two pinnate spines and one slender seta; ornamentation consist of two large spinules distally on anterior surface, apical armature consisting of five geniculate setae, longest one fused basally to additional smaller and slender seta. Exp with three strong apical setae.

Labrum ( Fig. 6C ) subtriangular, well-sclerotized, ornamented with a row of teeth on distal margin.

Mandible ( Fig. 6D ) elongated coxa and wide based. Gnathobase robust, with three slightly curved teeth ventrally and a row of many teeth along distal edge, one unipinnate seta dorsally. Mandibular palp two-segmented, comprising basis and one-segmented endopod. Basis unarmed and unornamented. Endopod segment slender, with five smooth setae apically.

Maxillule ( Fig. 6E ) with strong praecoxal arthrite and two long, smooth setae on aboral surface, two smooth setae on inner distal margin, four apical setae (three unipinnate strong setae and one smooth slender seta) and one seta proximally on oral margin. Coxal endite with three smooth setae. Basis with five smooth setae apically. Exp and Enp absent.

Maxilla ( Figs 4A , 6F ) composed of syncoxa, basis and one-segmented Enp. Syncoxa with row of spinules on anterior surface, proximal endite completely reduced, distal endite armed with two unipinnate spines and one smooth seta. Basis drawn out into robust unipinnate claw and one unipinate seta. Enp reduced to minute segment, with two smooth setae.

Maxilliped ( Fig. 6G ) comprising syncoxa, basis and one-segmented Enp. Syncoxa with row of spinules along inner margin and one pinnate seta. Basis stout, about 1.8 times as long as wide, with a row of spinules along inner median margin. Enp represented by distal unipinnate claw.

P1–P4: ( Fig. 7A–D ) biramous, with threesegmented Exp and Enp; Exp longer than Enp on P2–P4, shorter on P1. Armature of P1–P4 as follows (legend: inner/outer spine or seta; inner/ terminal/outer; Arabic numerals represent setae; Roman numerals represent spines).

Exopod

1 2 3 P1 0/I 1/I 0/2/II P2 0/I 1/I 1/2/II P3 0/I 1/I 1/2/II P4 0/I 1/I 2/2/II

Endopod

1 2 3 1/0 0/0 1/2/0 1/0 1/0 1/2/0 1/0 1/0 1/2/0 1/0 1/0 1/2/0

P1 ( Figs 4B , 7A ) coxa; with three rows of spinules on anterior surface and two short rows of spinules on outer margin. Basis with one outer and one inner pinnate spine; row of spinules along outer distal margin, and near base of exopod. Exp-1 with one outer spine on distal margin. Exp-2 with one outer spine on distal margin and one pinnate seta at inner distal margin. Exp-3 with two strong outer spines and two apical geniculate setae. Enp-1 long, about 3 times as long as wide, extending nearly middle half of Exp-3, with one inner pinnate seta distally. Enp-2 unarmed. Enp-3 with two strong apical setae and one thin inner distal seta. All segment of exopod and endopod ornamented with small spinules and hair-like spinules along outer and inner margins, and exopodal segments also with spinules along distal margin.

P2 ( Figs. 4C–D 7B ) coxa; with one row of spinules on anterior surface and two short rows of spinules on outer margin. Basis with one outer spine; row of spinules along outer distal margin, and near base of endopod. Exp 1–2 with one outer spine on distal margin, Exp-2 with one additional pinnate seta at inner distal margin and an outer bipinnate spine. Exp-3 with two outer spines, two apical pinnate setae (one is spiniform), and inner pinnate seta. Enp-1–2 with inner pinnate seta at distal outer margin. Enp-3 with an inner seta and two apical setae. All segment of exopod ornamented with small spinules and hair-like spinules along outer and inner margins, and exopodal segments also with spinules along distal margin. Enp-1 ornamented with spinules and hair-like spinules along outer and inner margins. Enp-2–3 ornamented with spinules along outer and distal margins.

P3 ( Figs 4E , 7C ) similar to P2, except basis with slender outer seta. Enp-2 with longer inner seta, reaching to tip of outer apical seta on Enp- 3. All segment of exopod and endopod ornamentation similar to P2. Enp-3 with one inner pinnate seta and two apical pinnate setae.

P4 ( Fig. 7D ) coxa, basis and Exp similar to those in P2, except basis with one outer spine. Exp-3 with two outer spines, two apical pinnate setae (one is spiniform), and two inner pinnate setae. Enp-2 with a long inner seta, reaching to tip of outer apical seta on Enp-3. Enp-3 with one inner pinnate seta and two apical pinnate setae. All segment of exopod and endopod ornamentation similar to P2.

P5 ( Figs 4F , 7E ): with reduced baseoendopod, with one outer seta. Exp subquadrate, with three smooth setae; inner and outer setae subequal in length, middle seta shortest.

DESCRIPTION OF MALE.( Fig.8A ). Body length 395 µm (measured from anterior margin of rostrum to apex of caudal rami, excluding caudal setae), smaller than female, habitus, general ornamentation of body somites as in female except for typical sexual dimorphism in genital segment, geniculate antennules and P1 basis.

Caudal rami ( Fig. 8A ) about 1.0 times as long as wide, slightly shorter than those of female. Armature and ornamentation as in female.

Antennule ( Fig.8B ) geniculate, ten-segmented, aesthetasc on apical acrothek of segment 5, reaching almost tip of antennule. First segment similar to female. Setal formula as follow: I (1), II (9), III (6), IV (2), V (2+ae), VI (1), VII (1), VIII (1), IX (3), X (8). All setae smooth, except setae on second segment ornamented with one unipinnate and one pinnate and seven smooth setae. Fifth segment ornamented with three spinules on anterior surface.

Antenna, labrum, mandible, maxillule, maxilla, and maxilliped as in female.

P1–P5 ( Fig. 8C–D ) with same segmentation and majority of ornamentation similar to female but P1 with a modified inner basal spine ( Fig. 8C ).

P6 ( Fig. 8A ) completely fused to genital somite, with one smooth seta on each side of posterior margin.

Figures

Fig. 1. Parapseudoleptomesochra phayaoensis sp.n., SEM photographs, female: A — habitus, lateral view; B — rostral area of cephalothorax, ventroanterior view (arrow indicates a cuticular tube); C — frontal part of cephalothorax with appendages, lateral view; D — cephalothorax, lateral view; E — two sensilla on cephalothorax; F — tergites of free prosomites with coxa and basis of P2–P4. Рис. 1. Parapseudoleptomesochra phayaoensis sp.n., СЭМ, самка: A — вид сбоку; B — ростральнаЯ область головогруди, передневентрально (стрелка укаЗывает на кутикулЯрную трубку); C — фрон- тальнаЯ часть головогруди с конечностЯми, вид сбоку; D — головогрудь, вид сбоку; E — две сенсиллы на головогруди; F — тергиты свободных сегментов просомы с коксой и баЗисом ног 1–4.

Fig. 2. Parapseudoleptomesochra phayaoensis sp.n., SEM photographs, female: A — 5th pedigerous somite and genital double-somite, lateral view; B — 2nd (genital) and 3rd urosomites, dorsal view; C — 4th and 5th urosomites, dorsal view; D — 4th and 5th urosomites, lateral view; E — anal somite and caudal rami, dorsal view; F — anal somite and caudal rami, lateral view. Рис. 2. Parapseudoleptomesochra phayaoensis sp.n., СЭМ, самка: A — сегмент с 5-й парой ног и генитальный двойной сегмент, вид сбоку; B — 2-й (генитальный) и 3-й сегменты уросомы, вид сверху; C — 4-й и 5-й сегменты уросомы, вид сверху; D— 4-й и 5-й сегменты уросомы, вид сбоку; E — анальный сегмент и каудальные ветви, вид сверху; F — анальный сегмент и каудальные ветви, вид сбоку.

Fig. 3. Parapseudoleptomesochra phayaoensis sp.n., SEM photographs, female: A — left caudal ramus, dorsal view; B — last two segments of antennule, lateral view; C — first two segments of antennule, anterior view; D — 4th to 6th segments of antennule, anterior view; E — distal tip of antennal endopod, anterior view; F — Exp of antenna, lateral view. Рис. 3. Parapseudoleptomesochra phayaoensis sp.n., СЭМ, самка: A — леваЯ каудальнаЯ ветвь, вид сверху; B — два дистальных членика антеннул, вид сбоку; C — два проксимальных членика антеннул, видспереди;D — 4–6-йчленики антеннул,видспереди;E —дистальный отдел Эндоподита антеннул, вид спереди; F — ЭкЗоподит антенны, вид сбоку.

Fig. 4. Parapseudoleptomesochra phayaoensis sp.n., SEM photographs, female: A — mouth appendages, lateral view; B — P1, anterior; C — P2 Enp, anterior view; D — P2 Exp-3, anterior view; E — P3 Exp-3, anterior view; F — P5, lateral view. Рис. 4. Parapseudoleptomesochra phayaoensis sp.n., СЭМ, самка: A — околоротовые конечности, вид сбоку; B — нога 1, вид сбоку; C — вид спереди; D — дистальный членик ЭкЗоподита 2-й ноги; E — дистальный членик ЭкЗоподита 3-й ноги, вид спереди; F — нога 5, вид сбоку.

Fig. 5. Parapseudoleptomesochra phayaoensis sp.n., female (holotype): A — urosomites 2–5 with caudal rami, ventral view (arrow indicates a copulatory pore); B — caudal rami, dorsal view. Scale bar 0.1 mm. Рис. 5. Parapseudoleptomesochra phayaoensis sp.n., самка (голотип): A — сегменты уросомы 2–5 с каудальными ветвЯми, вид сниЗу (стрелка укаЗывает на копулЯтивную пору); B — каудальные ветви, вид сверху. МасШтаб 0,1 мм.

Fig. 6. Parapseudoleptomesochra phayaoensis sp.n., female (holotype): A — antennule; B — antenna; C — labrum; D — mandible; E — maxillule; F — maxilla; G — maxilliped. Scale bar 0.1 mm. Рис. 6. Parapseudoleptomesochra phayaoensis sp.n., самка (голотип): A — антеннула; B — антенна; C — лабрум; D — мандибула; Е — максиллула; F — максилла; G — максиллипед. МасШтаб 0,1 мм.

Fig. 7. Parapseudoleptomesochra phayaoensis sp.n., female (holotype): A — P1; B — P2; C — P3; D — P4; E — P5. Scale bar 0.1 mm. Рис. 7. Parapseudoleptomesochra phayaoensis sp.n., самка (голотип): A — нога 1; B — нога 2; C — нога 3; D — нога 4; E — нога 5. МасШтаб 0,1 мм.

Fig. 8. Parapseudoleptomesochra phayaoensis sp.n., male (allotype): A — urosome, P5 and P6; B — antennule; C — a modified spine on basis of P1; D — P5. Scale bar 0.1 mm. Рис. 8. Parapseudoleptomesochra phayaoensis sp.n., самка (аллотип): A — уросома, ноги 5 и 6; B — антеннула; C — иЗмененный Шип на баЗисе ноги 1; D — нога 5. МасШтаб 0,1 мм.