Elaphoidella thailandensis, Watiroyram, Santi, Brancelj, Anton & Sanoamuang, La-Orsri, 2015

Watiroyram, Santi, Brancelj, Anton & Sanoamuang, La-Orsri, 2015, Two new stygobiotic species of Elaphoidella (Crustacea: Copepoda: Harpacticoida) with comments on geographical distribution and ecology of harpacticoids from caves in Thailand, Zootaxa 3919 (1), pp. 81-99 : 82-90

Elaphoidella thailandensis sp. nov.

( Figs. 1 –5)

Etymology. Elaphoidella thailandensis sp. nov. is named after Thailand, where it was found for the first time. The name is a noun composed from the name Thailand, and the Latin suffix –ensis, denoting a place (meaning: “from Thailand ”).

Type locality. Tham Khun Cave is located in Ban Chomphu Nuea, Chomphu Subdistrict, Noen Maprang District (Phitsanulok Province, Northern Thailand). The coordinates of the entrance are: 16° 39΄ 55.8˝ N, 100° 39΄ 14.6˝ E, 140 m above sea level. The cave is about 50 m long, represented by one horizontal gallery, 1 to 3 m high. Its water bodies directly depend on precipitation during rainy season (May–October) and persist throughout the year; there is no other subterranean water inside. Part of the cave is dimly lighted due to the large entrance hole. Leaf litter and other organic matter can easily be transported into the cave either by wind through the entrance or by gravity and water flow through fissures in the roof. Water dripping from the ceiling was collected directly in several jars (volume 1–3 L) left there by visitors, who attend a Buddha statue in the cave, which is situated 10 m from the entrance. In addition to the jars, in their vicinity, there are 5–10 small pools (volume of 50 mL to 1 L) also filled by dripping water. Specimens of the new species were collected from epikarstic drips in the two jars and four small pools. On the collecting date (13 August 2010), water temperature was 25.8 °C, pH 8.0, and a conductivity of 320 µ S cm −1 for the jar which animals were selected as the type specimens.

Material examined. Holotype: adult female, completely dissected and mounted on a slide: NHMUK 2011.2089. Allotype: adult male, completely dissected and mounted on a slide: NHMUK 2011.2090. Paratypes: three females with egg sacs and two males (stored in 70% alcohol): NHMUK 2011.2091–2095; two females with egg sacs and one male (stored in 70% alcohol): KKU-COP-2011-002. All material collected by S. Watiroyram, 13 August 2010.

Description. Female. Body length, measured from anterior margin of rostrum to posterior end of caudal rami, 510–540 µm (mean = 520 µm, n = 5); elongated, subcylindrical, depigmented. Thoracic somites, genital doublesomite, abdominal somites with several rows of dorsal spinules ( Fig. 1 A). Naupliar eye absent. Rostrum small, fused to cephalothorax. Cephalothorax smooth, with four pairs of sensilla and without integumental windows. Posterior margins of thoracic and abdominal somites dorsally serrated. Thoracic somites with one (3rd) or two pairs (1st & 2nd) of dorsal sensilla. Genital double-somite wider than long, without trace of division between genital and third urosomites, with two pairs of dorsal sensilla and row of strong spinules along ventrodistal margin, interrupted in middle ( Fig. 1 B). Genital complex ( Fig. 1 B) with single large copulatory pore, copulatory duct bell-shaped; paired seminal receptacles well developed. Fourth urosomite with ventrolateral row of robust spinules along distal margin, interrupted in middle; with pair of dorsal sensilla. Fifth urosomite with continuous row of ventral spinules along distal margin; with one pair of dorsal sensilla. Anal somite with large anal operculum. The latter with 10–11 rounded teeth (outer most teeth on each side forming triangular flattened plate with round tip curved outwards), not reaching distal end of anal somite; flanked by pair of sensilla and with median row of tiny spinules between the latter ( Fig. 1 C). Four (exceptionally five or six) strong and robust ventral spinules, decreasing in length from innermost; near inner basal corner of each ramus ( Fig. 1 B).

Caudal ramus ( Fig. 1 A–C) approximately conical, about 1.5 times as long as wide, with well-developed dorsal keel; rami slightly divergent. Inner margin with several strong lateral spinules; distal margin with row of strong ventral spinules. Each ramus with 7 setae; seta I very small, ventral to seta II; setae II, III, VI and VII bare; anterolateral seta (II) inserted at about proximal third of caudal ramus; posterolateral seta (III) as long as setae II, VI, and VII and all approximately as long as caudal ramus; outer terminal seta (IV) about three times as long as caudal ramus, unipinnate, without breaking plane; inner terminal seta (V) long, distal two-thirds pinnate, fracture plane not visible; inner terminal seta (VI) thin; dorsal seta (VII) thin, inserted close to inner distal corner of ramus.

Antennule ( Fig. 2 A) relatively short, eight-segmented, not reaching posterior margin of cephalothorax ( Fig. 1 A). Aesthetasc on fourth segment cylindrical, with rounded tip and reaching slightly beyond tip of antennule. Second aesthetasc on terminal segment long and slim. Setal formula as follows: 1, 8, 5, 2+A, 1, 3, 2, 7+A. All setae thin and bare. No surface ornamentation.

Antenna ( Fig. 2 B) robust, with allobasis; one-segmented Exp and Endp. Allobasis with one thin seta and few spinules on the middle of outer margin. Exp with two apical smooth and two subapical unipinnate setae. Endp with two strong, sharp outer spines accompanied by several strong, shorter spinules of different lengths; three geniculate and one normal seta, and one strong and sharp spine on distal end of segment.

Mandible ( Fig. 2 C) short and robust, with two strongly chitinized teeth on gnathobase; with short, smooth seta at dorsal corner and dorsal pore. Mandibular palp two-segmented; one seta on proximal segment (basis) and four setae on distal segment (endopod). All setae thin and bare.

Maxillule ( Fig. 2 D) composed of robust praecoxa, coxa, and basis. Praecoxal arthrite with six strong apical spines and bare seta on anterior surface. Coxa with cylindrical endite bearing pinnate seta. Basal endite with two smooth and one pinnate setae. Endp and Exp represented by three thin, smooth setae at about half-way the outer margin.

Maxilla ( Fig. 2 E) two-segmented, composed of syncoxa and allobasis. Syncoxa with rows of outer spinules and two endites; proximal endite with two short pinnate setae, distal endite with two short pinnate setae and one longer, smooth seta. Allobasis drawn out into strong serrate claw with one accompanying seta. Endp represented by three smooth setae.

Maxilliped ( Fig. 2 F) three-segmented, composed of syncoxa, basis, and one-segmented Endp. Basis 2.5 times as long as wide, with about 20 outer spinules equal in length; with a short, smooth proximal seta. Endp drawn out into strong, acutely curved claw; slightly longer than basis and ornamented with several spinules in distal half; accessory armature represented by short seta at base of endopodal claw.

P1–P4 with bare intercoxal sclerite (Figs. 3B, C, D). P1–P3 with three-segmented Exp and two-segmented Endp.

P1 (Fig. 3A) basis with thin inner seta and robust outer spine. Endp and Exp segments with several strong outer spinules. Endp-1 with one strong spine-like inner seta. Endp-2 shorter than Endp-1, with three apical, bare setae; innermost very short, middle one geniculate and longest, outermost normal, the latter about 0.7 times as long as middle one. Exp-1, 2 and 3 with strong unipinnate outer spine. Exp-3 with strong unipinnate seta, and two long geniculate distal setae.

P2 (Fig. 3B) basis with robust outer spine. Endp-1 small, shorter than wide, without inner armature. Endp-2 twice as long as wide, with spiniform outer terminal seta, long pinnate inner terminal seta and inner-distal spinule. Exp-1 as long as Exp-2, with one strong, blunt spine at distal outer corner. Exp-2 with strong blunt outer spine and strong spiniform seta at distal inner margin. Exp-3 2.5 times as long as wide, shorter than Exp-1 and Exp-2 combined; with outer blunt sub-distal spine, one terminal spine and two terminal setae. Inner apical seta soft and pinnate, slightly shorter than outer terminal spine. Middle apical seta unipinnate, as long as Exp.

P3 (Fig. 3C) basis with long and thin outer seta. Endp-1 shorter than wide. Endp-2 twice as long as wide, with spiniform outer terminal seta, long pinnate inner terminal seta and inner-distal spinule. Exp-1 as long as Exp-2, with strong, blunt outer-distal spine. Exp-2 with strong blunt outer spine and strong inner-distal spiniform seta. Exp-3 2.5 times as long as wide; with outer blunt spine, one terminal spine and two terminal setae, and strong inner-subdistal seta.

P4 (Fig. 3D) basis with long and thin outer seta. Endp absent, only remains represented by small thickening. Three-segmented Exp, Exp-1 and Exp-2 similar to those of P3. Exp-3 with two strong outer lateral spines and two smooth setae on inner margin. Two terminal setae: outer unipinnate one about twice as long as Exp-3; inner pinnate seta 5 times as long as Exp-3.

Armature formula of P1–P4 as follows (Arabic numerals = setae; Roman numerals = spines):

Exopod Endopod

1 2 3 1 2 P1 0-I 0-I 0-2,I-I 1-0 0-3-0 P2 0-I 1-I 0-2,I-I 0-0 0-1,I-0 P3 0- I 1-I 1-2 -II 0-0 0-1,I-0 P4 0- I 1-I 2-2 -II - - P5 (Fig. 3E) with separate Exp and baseoendopod, without surface ornamentation. Baseoendopod lobe relatively well developed, with four long, strong spiniform setae of unequal length; the second outermost longest; outermost longer than innermost, about 70% the length of second outer one. Baseoendopodal outer seta long and bare. Exp small, sub-oval, slightly longer than baseoendopodal lobe; with four setae of unequal length, decreasing in length from inner margin but the second inner one shortest, thin and bare; remaining setae long, robust and pinnate.

P6 ( Fig. 1 B) fused, small, forming single plate, with short, robust and pinnate seta on each side of copulatory pore.

Egg sac: slightly longer than genital double-somite, oval, with 9– 11 eggs.

Male. Slightly longer than female; body length, measured from anterior margin of rostrum to posterior of caudal rami, 590–630 µm (mean = 610 µm, n = 5), colorless, naupliar eye not discernible, no integumental window on cephalothorax and somites. Body similar to that of female but slightly more tapered posteriorly ( Fig. 4 A). Ornamentation of cephalothorax, thoracic somites, first urosomite, 4th, 5th urosomite, anal somite, similar to those of female. Genital somite and second urosomite with smooth posterior margin ventrally, third urosomite with row of strong spinules along ventrodistal margin ( Fig. 4 C). Anal operculum, antenna, mouthparts, P1 (Fig. 5A) and P2–P3 exopods (Fig. 5B, 5C) similar to those of female; P3 Exp-3 (Fig. 5C) with shorter, inner seta than in female.

Antennule ( Fig. 4 B) seven-segmented, geniculation between fifth and sixth segment. Ancestral third and fourth segment fused to form third segment. Fifth segment with spinous process in median anterior margin and accompanied by one seta. Sixth segment enlarged, spoon-like. Aesthetasc on fused third and fourth segment cylindrical, with rounded tip, not reaching to distal end of antennules. Aesthetasc on terminal segment shorter than on segment 3, about 1.5 times as long as last segment. Setal formula: 1, 9, (12+A), 1, 1, 0, 8+A.

P2 (Fig. 5B) Endp two-segmented, as long as Exp-1. Endp-1 small, shorter than wide, without inner seta or spine. Endp-2 twice as long as wide, with two apical setae; outer one shorter than supporting segment, robust and bare; inner seta long, bipinnate, reaching the distal end of Exp.

P3 (Fig. 5C) Endp-1 shorter than wide, without inner seta or spine. Endp-2 with long inner apophysis with harpoon-like tip, reaching slightly beyond Exp-3. Endp-3 about 1.5 times as long as wide, with two long, bare setae equal in length; two latter elements about 5 times as long as supporting segment.

P4 (Fig. 5D) Endp absent, only remains represented by small thickening. Exp three-segmented. Exp-1 and Exp-2 similar to those of P3 but slightly shorter and more robust. Exp-3 shorter than in female, about 1.2 times as long as wide, with the same armature complement as in female, with inner two setae comparatively shorter in male; apical outer spine transformed and antler-like in shape.

Additional ornamentation of P1-P4 as in Fig. 5A–D.

P5 (Fig. 5E) with distinct Exp and baseoendopod. Baseoendopodal lobe small, without armature. Outer baseoendopodal seta long and bare. Exp small, with three setae; inner subapical seta very small and bare, outer apical seta bare, inner apical one bipinnate, 2.5 times as long as outer apical seta.

P6 (Fig. 5E) fused to genital somite, with 2 minute spines.

Variability. There are variations in the number of spinules at the base of each caudal ramus; the number of spinules varies between 4 and 6, but at least one side always with four spinules.

Differential diagnosis. Elaphoidella thailandensis sp. nov. has the diagnostic features of the genus Elaphoidella based on the armature of the P5, shape of the female genital complex, and on the presence of a transformed spine on the male P4 Exp-3. Based on the male P4 Exp-3 armature formula and on the presence of an antler-like modified apical seta, as well as on the armature formula of the male and female P5, E. thailandensis is FIGURE 3. Elaphoidella thailandensis sp. nov., female (holotype): A, P1; B, P2; C, P3; D, P4; E, P5. Scale bar = 100 µm.

FIGURE 5. Elaphoidella thailandensis sp. nov., male (allotype): A, P1; B, P2; C, P3; D, P4; E, P5 and P6. Scale bar = 100 µm.

suggested to belong to group VIII (i.e. sewelli group) sensu Lang (1948). The two-segmented P1 Endp and the lack of Endp in P4 would suggest affinities with the genus Neoelaphoidella as defined by Apostolov (1985), which was separated from group X sensu Lang (1948). However, the new species belongs to group VIII of the genus Elaphoidella by having a transformed spine on P4 Exp- 3 in male, which do not fit with the proposal of Apostolov (1985). Elaphoidella thilandensis is easily distinguished from its congeners by a combination of morphological characters including P5 Exp and baseoendopod in females with four setae each; the absence of Endp of P 4 in both sexes (which is the most obvious discernible character of the new species); the two-segmented Endp P1; the setal formula 4, 5, 6 for Exp-3 P2–P4 (see table above). The new species is similar to E. coiffaiti Chappuis and Kiefer 1952 and E. reducta Rouch 1964 (both described from groundwater in France) in the lack of Endp on P4. However, these two European species differ from E. thailandensis by a three-segmented Endp P1. Additionally, the armature of the distal segments of Exp P2–P4 is in E. thailandensis , 4, 5, 6, versus 5, 6, 5 in E. coiffaiti and 5, 5, 5 in E. reducta .

Figures

FIGURE 1. Elaphoidella thailandensis sp. nov., female (holotype): A, habitus, dorsal view; B, genital double-somite, abdominal somites, and anal somite, ventral view; C, anal somite and caudal rami, dorsal view. Scale bars = 100 µm.

FIGURE 2. Elaphoidella thailandensis sp. nov., female (holotype): A, antennule; B, antenna; C, mandible; D, maxillule; E, maxilla; F, maxilliped. Scale bar = 100 µm.

FIGURE 4. Elaphoidella thailandensis sp. nov., male (allotype): A, habitus, dorsal view; B, antennule; C, genital somite, abdominal somites, and anal somite, ventral view; D, anal somite and caudal rami, dorsal view. Scale bars = 100 µm.