Onychocamptus satunensis, Boonyanusith, Chaichat, Saetang, Thanida, Wongkamheng, Koraon & Supiyanit Maiphae,, 2018

Boonyanusith, Chaichat, Saetang, Thanida, Wongkamheng, Koraon & Supiyanit Maiphae,, 2018, Onychocamptus Daday, 1903 from Thailand, with descriptions of two new species and two new records (Crustacea, Copepoda, Harpacticoida, Laophontidae), ZooKeys 810, pp. 45-89 : 47-52

Onychocamptus satunensis sp. n. Figs 2, 3, 4, 5, 6, 7, 8, 23A

Material examined.

Holotype. Adult female, dissected and mounted onto one slide, collected from type locality on 30 July 2015 (PSUZC-PK2002-01). Allotype. One adult male, dissected and mounted onto one slide, (PSUZC-PK2002-02), all collected from type locality on 20 January 2016. Paratypes. One undissected adult ovigerous female paratype mounted onto one slide (PSUZC-PK2002-03), and one undissected adult male paratype, mounted onto one slide (PSUZC-PK2002-04), coll. C Boonyanusith and K Wongkamheng; type locality on 30 July 2015 and 20 January 2016, respectively.

Additional material.

One adult ovigerous female and one adult male, both collected from type locality on 2 April 2015 and stored in 70% ethanol, deposited in the collection of the first author (CB).

Type locality.

Prawattisart cave, Muang district, Satun Province, southern Thailand, 6°42'55.82"N, 100°05'19.17"E. The cave is in an isolated, wedge-shaped, limestone hill. It is surrounded by irrigation canal and paddy fields, but there are no connections between water in and outside cave. Beyond entrance of the cave there is a long horizontal gallery, with approximately 5-10 m high and approximately 2-3 m wide. At some place there are two openings, which are large enough for entry, indicating a complex tunnel system. The collecting point is a part of a large water body inside the cave, fulfilled by approximately 10-50 cm depth of water. Water depth varies according to season, but it has never dried out. Water was turbid and flowed slowly. Water temperature was 25.5 °C, pH 7.8, conductivity 360 µS cm-1, dissolved oxygen 4.9 mgL-1.

Etymology.

The specific name satunensis is derived from the name of Satun Province, where the species was collected. The name is a noun in the genitive singular, masculine.

Differential diagnosis.

Laophontidae . Body gradually tapering posteriorly. Cephalothorax with internal sausage-like structure, and internal rounded structures. Posterior margin of cephalothorax and body somites (except penultimate and anal somite) with sensillum-bearing tubercles. Second and third urosomite partly fused ventrally in female, representing genital double-somite. Caudal rami approximately 2.5 times as long as wide, with one transverse inner row of spinules near insertion of dorsal seta. Caudal seta IV and V fused. Allobasis of antenna without abexopodal seta. Endopodal lobe of P5 with three, and exopod with four pinnate setae. Male P3 enp-2 with apophysis on outer distal corner, reaching tip of enp-3. Exopod of male P5 with three setae, outer seta as long as supporting segment. Male P6 reduced, with outer seta and inner bipinnate seta apically; inner seta approximately twice as long as outer one.

Description of adult female.

Body (Fig. 2A). Total body length, measured from tip of rostrum to posterior margin of caudal rami, 401-445 µm (mean 419 µm, n = 3; 445 µm in holotype); preserved specimen colourless. Body covered with setules (Fig. 8E, F), cylindrical; gradually tapering posteriorly, with maximum width at posterior part of cephalothorax. Prosome approximately 1.3 times as long as urosome (including caudal rami) (Fig. 2A). Rostrum small, completely fused to cephalothorax. Cephalothorax as long as wide, approximately 0.5 times the length of prosome, just under integument with anterior internal structure comprising three parts; each of which sausage-like, and with internal rounded structures near distal margin (Figs 2A, B, 8A, B). Cephalothorax and all free thoracic somites with sensillum-bearing tubercles along posterior margin (Fig. 2A, B). Second and third urosomite fused ventrally (Fig. 2D), distinct dorsally and laterally (Fig. 2 A–C), original division between sixth thoracic somite and first abdominal somite, with dorsal sensillum-bearing tubercles (Fig. 2C). Genital field ribbon-shaped, with seta representing P6 at outer distal corner (Fig. 2D). The remnant of first abdominal somite (posterior half of genital double-somite) with lateral sensillum-bearing tubercles (Fig. 2C, D). Posterior margin of genital double-somite and fourth urosomites with outer sensillum-bearing tubercles; posterior half of genital double-somite and fourth urosomite with posterior setules dorsally (Fig. 2C) and small spinules ventrally (Fig. 2D) between sensillum-bearing tubercles. Penultimate urosomite with posterior setules dorsally and laterally, with one posterior row of spinules ventrally. Anal somite as long as wide, with arch row of long spinules posterior to anal operculum (Figs 2A, C, 3A, 8D), with ventrolateral row of minute spinules near insertion of caudal rami (Fig. 2D). Anal operculum poorly developed, with minute spinules along posterior margin (Figs 2C, 3A, 8D).

Caudal rami (Figs 2C, D, 3A). Slightly convergent, 2.5 times as long as wide, with one transverse row of inner spinules near insertion of caudal seta (VII) (Figs 2C, 3A). Anterolateral accessory seta (I) minute, close to anterolateral seta (II), both subapical. Posterolateral seta (III) inserted on minute pedestal. Outer terminal seta (IV) slender, fused at base with inner terminal seta (V), the latter longest, without fracture plane, approximately 0.6 times as long as body length. Inner accessory seta (VI) slender. Dorsal seta (VII) tri-articulate, inserted at quarter of rami. Length ratio of caudal setae to ramus length, from seta I to seta VII of the holotype: 0.4: 0.8: 1.3: 0.7: 9.7: 0.7: 1.1.

The ovigerous female bears one oval egg sac with eight eggs, located ventrally between pair of fifth legs.

Antennule (Fig. 3B, C). Short, 5-segmented. First segment with medial and distal rows of spinules. Armature formula: I-[1], II-[8], III-[7+(1+aesthetasc)], IV-[1], V-[9+acrothek]. Aesthetasc on third segment robust, fused basally to one seta. Apical acrothek on fifth segment slender, consisting of one aesthetasc fused basally to two slender smooth seta.

Antenna (Fig. 3D). Comprising coxa, allobasis, and 1-segmented endopod and exopod. Coxa without ornamentation. Allobasis with one row of inner spinules, with 1-segmented exopod; the latter with two apical and two lateral bipinnate setae. Free endopodal segment with one strong, sharp spine, and one seta at distal third of segment; the former accompanied by several strong, short spinules; distal end with six elements: one minute seta, one slender, bipinnate seta, two geniculate setae, and two strong, smooth spines.

Mandible (Fig. 3E). Gnathobase with strong, chitinised teeth and lateral pinnate seta. Mandibular palp short, 1-segmented, with five slender setae sub-equal in length.

Maxillule (Fig. 4A). Composed of robust precoxa, coxa, basis, endopod fused to basis, and 1-segmented free exopod. Precoxal arthrite with six strong apical spines and one slender lateral seta. Coxa with cylindrical endite bearing two smooth setae, one of which robust. Basis with cylindrical endite bearing three setae, one of which robust. Endopod incorporated to basis, with three setae. Exopod free, 1-segmented, with two sub-equal apical setae.

Maxilla (Fig. 4B). Composed of syncoxa, allobasis, and 1-segmented endopod. Syncoxa with two endites; proximal endite with three apical pinnate setae, distal endite with two pinnate and one slender apical seta, outer margin with spinules. Allobasis with apical drawn out into claw, with one anterior and one posterior seta. Endopod 1-segmented, with two smooth apical setae.

Maxilliped (Fig. 4C). Subchelate, 3-segmented, comprising syncoxa, basis, and endopod. Syncoxa with one pinnate seta at inner distal corner. Basis with two transverse rows of outer spinules, one of which near base of endopod. Endopod drawn out into strong claw, with one minute seta near its base.

P1 (Fig. 4D). Coxa with longitudinal row of outer setules. Basis with one outer bipinnate spine and one inner spine near insertion of endopod, with longitudinal row of anterior spinules medially, with long setules along inner margin. Both rami 2-segmented. Exopod reaching proximal third of enp-1; exp-1 with one bipinnate outer spine, with one row of outer spinules; exp-2 with three outer spines, two apical geniculate setae, with outer spinules and inner setules. Enp-1 approximately seven times as long as wide, with outer spinules and inner setules; enp-2 with one median strong outwardly curved claw-like smooth spine and one slender inner seta, with few outer spinules.

P2 (Fig. 5A, B). Coxa with oblique row of spinules on anterior surface near outer margin, with row of spinules at distal outer corner. Basis with outer spine. Rami with 3-segmented exopod and 2-segmented endopod; endopod reaching tip of exp-2. Exp-1 with one outer bipinnate spine; exp-2 with one outer bipinnate spine and one inner plumose seta; exp-3 with three outer bipinnate spines, two apical elements (of which outer one spiniform seta with outer spinules and inner setules, inner element one plumose seta), and one inner plumose seta. All segments of exopod with row of outer spinules and inner setules. Enp-1 without armature, enp-2 with two apical and two inner plumose setae. All segments of endopod with row of outer spinules and long inner setules.

P3 (Fig. 5C). Coxa, basis, and segmentation of rami as in P2. Outer element of basis one long seta. Endopod reaching tip of exp-2. Exp-1 with one outer bipinnate spine; exp-2 with one outer bipinnate spine and one inner plumose seta; exp-3 with three outer bipinnate spines, two apical elements (of which outer one spiniform seta with outer spinules and inner setules, inner element one plumose seta), and one inner plumose seta. Ornamentation of exopod as in P2. Enp-1 without armature; enp-2 with one outer bipinnate seta, two apical, and three inner plumose setae. Outer and inner margins of segments of endopod with setules.

P 4 (Fig. 6A). Coxa with row of outer long spinules. Basis with one slender outer seta. Rami with 3-segmented exopod and 2-segmented endopod; endopod reaching tip of exp-1. Exp-1 with one outer bipinnate spine; exp-2 with one outer bipinnate spine and one inner plumose seta; exp-3 with two outer bipinnate spines, two apical elements (of which outer one spiniform seta with outer spinules and inner setules, inner element one plumose seta), and one inner plumose seta. Ornamentation of exopod as in P2 and P3. Enp-1 without armature, with long inner subdistal spinules and smaller outer spinules; enp-2 with one outer bipinnate seta, one apical plumose seta, and one inner plumose seta.

Armature formula of P1−P4 as in Table 1.

P 5 (Figs 6B, C, 23A). Baseoendopod and exopod separated, with setules as on figures. Baseoendopod with basal seta and three pinnate setae on endopodal lobe, with spinules at base of distalmost seta. Exopod with four pinnate setae; innermost one longest.

P6 (Fig. 2D). Reduced to minute prominence at outer distal corner of genital field, with one short, slender seta.

Description of adult male.

Body (Fig. 6D). Total body length, measured from tip of rostrum to posterior margin of caudal rami, 352−410 µm (mean 374 µm, n = 3; 410 µm in allotype); preserved specimen colourless. Prosome approximately 1.3 times as long as urosome (Fig. 6D). Cephalothorax as long as wide, 0.5 times the length of prosome, internal sausage-like structure as in female, with two internal rounded structures. All free thoracic somites with sensillum-bearing tubercles along dorsal posterior margin, but fifth thoracic somite (first urosomite) with additional row of posterior setules dorsally (Fig. 6D). Second and third urosomite completely separated. Second urosomite with dorsal sensillum-bearing tubercles along posterior margin (Fig. 6D). Fourth urosomite without lateral protuberances, with lateral sensillum-bearing tubercles, with one posterior row of dorsal setules and ventral spinules. Ornamentation on next three urosomites as in female (Fig. 6E). Anal somite and anal operculum as in female.

Caudal rami as in female (Fig. 6D, E).

Antennule (Fig. 7A). 8-segmented, geniculate, with three segment distal to geniculation. First segment with proximal and subdistal outer spinules. Armature formula I-[1], II-[9], III-[7], IV-[2], V-[9+(1+aesthetasc)], VI-[1], VII-[1], VIII-[7+acrothek)]. Aesthetasc on fifth segment robust, fused basally to one seta. One pinnate seta on fifth segment. Apical acrothek on eighth segment small, consisting of one aesthetasc fused basally to two slender smooth seta.

Rostrum, antenna, mouthparts and P1, P2 (not shown) as in female.

P3 (Fig. 7B). General shape as in female but both rami 3-segmented. Endopod reaching tip of exp-2. Exp-3 with three outer bipinnate spines, two apical elements (of which outer one spiniform robust seta with outer spinules and inner setules, inner element one smooth spiniform seta), and one inner plumose seta. Enp-2 with inner seta and outer apophysis on outer distal corner reaching tip of enp-3, with long outer spinules and few inner setules; enp-3 with two inner and two apical plumose setae.

P 4 (Fig. 7E). General shape as in female but exp-3 relatively shorter and with stronger elements. Exp-3 with two outer bipinnate spines, two apical elements (of which outer one spiniform robust seta with outer spinules and inner setules, inner element one spiniform seta), and one inner plumose seta.

Armature formula of P1-P4 as in Table 1.

P5 (Fig. 6E, F). With outer basal seta arising from long setophore; without endopodal lobe. Exopod with three setae, outermost slender and slightly longer than segment, approximately 1/3 times as long as the middle seta.

P6 (Fig. 6E). Reduced to one minute rectangular protuberance, with outer plumose seta and inner bipinnate seta; inner seta approximately twice as long as outer one and reaching posterior margin of next urosomite.

Variability.

The right P2 enp-2 lacks the proximalmost inner seta (Fig. 5B), and one additional small inner seta on the P5 exopod was observed (Fig. 6B) in the holotype. The P3 enp-3 of the allotype possesses two inner setae. Also, on the right ramus the setae possess outer and inner setules (Fig. 7B), but those of the left ramus possess inner spinules (Fig. 7C, D).

Onychocamptus satunensis sp. n. is the only species of Onychocamptus with internal sausage−like structure on cephalothorax (Figs 2A, B, 8 A–C), differing from other members. O. satunensis sp. n. is most similar to O. tratensis sp. n., both species sharing the following remarkably characters: 1) absence of abexpodal seta on allobasis, 2) presence of 4 setae on exopod of antenna, 3) presence of 2 outer spines on P4 exp-3, 4) presence of 4 setae on exopod of P5 of the female, and 5) presence of 3 setae on exopod of P5 of the male. The southern Thai species ( O. satunensis sp. n.), however, can be distinguished from the eastern one ( O. tratensis sp. n.) by the presence of internal sausage−like structure, the presence of internal rounded structures, and the relative length of outer seta on P3 enp-2. Comparative study between two Thai new species and their congeners is provided in Table 3.

Distribution.

This species is known from the type locality only.