Pseudograeteriella longiaesthetascus, Sanoamuang & Boonyanusith & Brancelj, 2019

Sanoamuang, La-orsri, Boonyanusith, Chaichat & Brancelj, Anton, 2019, A new genus and new species of stygobitic copepod (Crustacea: Copepoda: Cyclopoida) from Thien Duong Cave in Central Vietnam, with a redescription of Bryocyclops anninae (Menzel, 1926), Raffles Bulletin of Zoology 67, pp. 189-205 : 191-196

Pseudograeteriella longiaesthetascus , new species

( Figs. 1 A–G, 2A–F, 3A–D [female]; 4A–D [male])

Type locality. A pool at Thien Duong Cave in Phong Nha-Ke Bang National Park, Quang Bin Province, Vietnam, located approximately 400 m from the tourist entrance. Coordinates of the entrance are 17°31′09.46″N, 106°13′17.80″E, altitude: 200 m a.s.l.

Material examined. Holotype: adult female, total body length 973 µm, completely dissected, mounted in glycerol on a slide and sealed with nail polish, NHMUK 2018.1013, collected on 21 March 2012 by L. Sanoamuang. Allotype: adult male, total body length 796 µm, completely dissected, mounted in glycerol on a slide and sealed with nail polish, NHMUK 2018.1014, collected on 21 March 2012 by L. Sanoamuang. Paratypes: two females without egg sacs and two males, sampled with the holotype, whole specimens are stored in 70% ethanol and deposited at the Khon Kaen University Science Museum; KKU–COP–2018.001–004. All specimens were collected at the same place and on the same date as the holotype .

Description. Female ( Figs. 1–3 ): total body length, measured from tip of rostrum to posterior margin of caudal rami, 960−973 µm (mean: 970 µm; n = 3), prosome/urosome ratio about 1.6 ( Fig. 1A ). Preserved specimens colourless, naupliar eye not discernible. Total body length/width ratio about 3.2, prosome with numerous sensilla, in bilaterally symmetrical pattern. Rostrum triangular, with rounded tip, bearing two sensilla ( Fig. 4B ). Integument smooth, not strongly chitinised, without any visible cuticular windows. Cephalothorax slightly shorter than wide, representing 43% of body length, with the greatest width near posterior margin. Posterior margins of Pd1–Pd5 smooth. Genital double-somite as long as wide, slightly tapering posteriorly ( Fig. 1A, C, D ). Copulatory pore small and oval-shaped, positioned at 1/3 length of somite; copulatory duct short, narrow, and sclerotised. Seminal receptacle about 1/4 of double-somite length, with short and wide anterior portion and well-developed, semi-circular posterior part ( Fig. 1D ). Ovipores situated dorsolaterally at 1/3 length of somite, covered with reduced P6 ( Fig. 1E ). Hyaline fringes of genital double-somite and two subsequent somites irregularly serrate both ventrally and dorsally. Anal somite with rows of spinules on posterior margin ventrally and laterally. Anal operculum reaching anterior margin of caudal ramus, free margin of operculum broadly rounded and smooth ( Fig. 1F ), two large sensilla present anteriorly to operculum.

Caudal rami ( Fig. 1D, F, G ): elongate and parallel, about 4.2 times as long as wide, with spinules at insertion of anterolateral seta (II) and posterolateral seta (III) ( Fig. 1F, G ). Anterolateral accessory seta (I) reduced. Anterolateral seta (II) pinnate, inserted at 3/4 length of ramus. Posterolateral seta (III) spiniform. Outer terminal seta (IV) completely reduced. Inner terminal seta (V) without breaking plane. Terminal accessory seta (VI) short and weak. Dorsal seta (VII) articulated, inserted near inner terminal seta. Length ratio of caudal setae II–VII to ramus length (excluding reduced seta IV): 0.2, 0.4, 5.2, 0.1 and 0.8, respectively. Relative length of caudal setae II–VII (excluding reduced seta IV): 1.0: 2.3: 29.9: 0.8: 4.8.

Antennule ( Fig. 2A ): 11-segmented, not reaching posterior margin of cephalothorax ( Fig. 1A ). Armature formula: 7.4.4.2.1.2.3.2+ae.2.2+ae.6+ae. Fourth and fifth segments short, fifth segment with spiniform seta. Aesthetascs on the eighth and penultimate segments inserted near anterodistal seta. Aesthetascs on segments 8 and 10, three and two times as long as corresponding anterodistal seta, respectively. The terminal segment with acrothek subapically, ae is about twice as long as adjacent seta.

Antenna ( Fig. 2B ): four-segmented, comprising coxobasis and three-segmented Endp. Coxobasis with one smooth seta on inner distal corner, without seta representing Exp, caudal surface adorned with several groups of spinules. Endp-1 with one smooth seta at 1/2 length of inner margin, adorned with several groups of spinules. Endp-2 about 1.5 times as long as wide, with eight smooth setae (six laterally, one subapically, one apically). Endp-3 about twice as long as wide, with seven smooth apical setae of different lengths, two of them robust, about seven times as long as segment bearing them.

Mandible ( Fig. 2C ): with coxa and short basis partly fused with coxa. Gnathobase with strongly chitinised teeth, ventralmost teeth very robust and slightly obtuse, with smooth seta dorsally. Mandibular palp small, one short, smooth seta, two long, plumose setae representing Exp and Endp, respectively, long setae about ten times as long as short seta.

Maxillule ( Fig. 2D ): with robust praecoxa and two-segmented palp, proximal segment of palp coxobasis, lateral one Endp. Arthrite of praecoxa bearing seven lateral spines, five of them smooth, proximal one minute, subproximal one robust and pinnate, three strong claw-like spines decreasing in length apically and one strong curved seta subapically. Coxobasis with three elements: one smooth and one robust bipinnate seta apically, smooth seta subapically. Endp with three smooth setae apically. Exp represented by one seta.

Maxilla ( Fig. 2E ): five-segmented. Endite of praecoxa with two unipinnate setae. Proximal endite of coxa with one pinnate seta, distal endite elongated, with two setae unequal in length apically. Basis with slim claw-like basal endite, with a row of minute spinules along concave margin. Two setae at base of claw, longer one as long as claw and robust, other one short and slim. Endp two-segmented, proximal segment with two robust setae, distal segment with one robust seta apically, accompanied by two shorter setae subapically.

Maxilliped ( Fig. 2F ): four-segmented, composed of syncoxa, basis and two-segmented Endp. Syncoxa with a group of spinules on lateral margin, distal endite with two pinnate setae, unequal in length. Basis with row of long spinules on proximal medial margin, group of spinules at distal outer corner, two setae along medial margin unequal in length. Endp-1 with one long, strong pinnate seta. Endp-2 with three setae, one pinnate, two smooth.

Intercoxal sclerites in P1–P4 ( Fig. 3 A–D): unornamented, distal margin broadly concave, minute rounded projections only slightly overreaching distal margin of sclerite. Coxa rectangular, cuticular pore present anteriorly, close to medial margin. Long plumose seta present at inner distal angle of P1–P3 coxa, corresponding seta absent in P4. Basis with plumose seta laterally. Exp and Endp two-segmented. Basis triangular, with rounded tips. Exp-2 and Endp-2 of P2–P4 with cuticular pore anteriorly, near insertion of subapical and apical spine, respectively. Exp-2 spine and seta formula: 3.3.3.3 and 5.5.5.4, respectively. Endp-2 spine and seta formula: 1.1.1.1 and 4.5.5.4. Complete armament of P1–P4 is shown in Table 2.

P 1 ( Fig. 3A ): basis with strong medial spine reaching middle of Endp-2. Exp-1 and Exp-2 as long as wide. Spine on Exp-1 blunt. Endp-2 about 1.5 times as long as wide, apical spine as long as segment bearing it.

P2 ( Fig. 3B ): Exp-1 as long as wide, Exp-2 about 1.3 times as long as wide. Endp-1 slightly shorter than its width, Endp-2 1.8 times as long as wide; apical spine as long as segment bearing it.

P3 ( Fig. 3C ): Exp and Endp identical to P 2 in shape, armament and proportions. Apical spine on Endp-2 shorter than segment, blunt and slightly curved.

P4 ( Fig. 3D ): Exp and Endp similar to P2 and P 3 in shape and proportions; apical spine on Endp-2 slightly longer than segment, straight.

P5 ( Fig. 1D ): reduced to cuticular lobe completely fused to Pd5; two setae present apically, equal in length; dorsal seta uni-pinnate, ventral seta smooth and spiniform.

P6 ( Fig. 1D ): small, simple cuticular plate positioned laterodorsally on genital double-somite, with two minute spines.

Male ( Fig. 4 ): total body length, measured from tip of rostrum to posterior margin of caudal rami, 796–880 µm (mean: 859 µm; n = 3). Habitus slender than in female ( Fig. 4A ). Body length/width ratio about 3.1, prosome/urosome ratio about 1.5 (including caudal rami), naupliar eye not discernible. Prosome with numerous sensilla, in bilaterally symmetrical pattern along body axis. Rostrum as in female.

Cephalothorax anteriorly oval, as long as wide, representing 33% of body length, with greatest width at posterior end. Posterior margins of all pedigerous somites smooth. Genital somite barrel-shaped ( Fig. 4A, B ), about 21% of length of urosome (including caudal rami). Genital somite and three subsequent somites with hyaline fringes with irregular serration both ventrally and dorsally. Anal somite and anal operculum as in female.

Caudal rami slightly shorter than in female, about 4.1 times as long as wide. Armament and ornamentation similar to those in female. Length ratio of caudal setae II–VII to ramus length (excluding reduced seta IV): 0.2, 0.4, 6.0, 0.1, and 0.8, respectively. Length ratio of caudal setae II –VII (excluding reduced seta IV): 1.0: 2.0: 28: 0.5: 3.7.

Antennule ( Fig. 4C ): 15-segmented, geniculate. Armature formula as follows (however, number of elements on some segments couldn’t be verified): 7+3ae.4.2.2+ae.2.2.0.2.0.2 +ae.1+I.2+ae.1.2.11+ae. All aesthetascs except aesthetasc on segment 15 very long. Terminal segment with acrothek.

Antenna, mouthparts, P1−P5 similar to those in female, but P4 Endp-2 bearing two inner setae only. P4 Endp-2 twice as long as wide, apical spine slightly longer than segment.

P6 ( Fig. 4B ): trapezoidal plate, with two sub-equal spiniform setae inserted laterally.

Variability. In one male specimen, the proximal most medial seta on the terminal endopodal segment of P1 was missing on the left side, but it was observed to be normally developed on the right side. Other differences were not observed, except for some minor variations in size, shape, and number of spinules ornamenting the limbs and somites. Etymology. The specific epithet alludes to very long aesthetascs located on the male antennules. It is used as a noun in apposition.

Remarks. Pseudograeteriella longiaesthetascus , new species, shares some characters with P. longifurcata ( Tran & Chang, 2013) , which was described from the same cave in Central Vietnam. The characters that distinguish the new species from P. longifurcata are, as follows: i) in P. longiaesthetascus , new species, the outer terminal caudal seta (seta IV) is completely reduced ( Fig. 1D, F ); however, in P. longifurcata , seta IV is present and appears as a stout spine slightly shorter than the posterolateral seta (III) ( Tran & Chang, 2013: fig. 1E, F); ii) in P. longiaesthetascus , new species, the anterolateral seta (II) is inserted laterally at 3/4 length of the ramus ( Fig. 1G ); however, in P. longifurcata , it is “inserted dorsally at about the middle of the caudal ramus” ( Tran & Chang, 2013: fig. 1E); iii) in P. longiaesthetascus , new species, the ventral spiniform seta of P5 is robust and slightly longer than dorsal seta ( Fig. 1D, E ); however, it is slim and equal to the dorsal seta in P. longifurcata ( Tran & Chang, 2013: fig. 1C, D); iv) there are eight setae on Endp-2 of antenna in P. longiaesthetascus , new species ( Fig. 2B ), but five in P. longifurcata ( Tran & Chang, 2013: fig. 2B); v) aesthetascs on the first and fourth segments of the male antennule overreach the geniculate section in P. longiaesthetascus , new species ( Fig. 4C ), whereas they are much shorter in P. longifurcata ( Tran & Chang, 2013: fig. 4C); vi) the apical spines on the terminal endopodal segments of P1, P2, and P4 are as long as corresponding segments in P. longiaesthetascus , new species ( Fig. 3A, B, D ), but they are distinctly shorter in P. longifurcata ( Tran & Chang, 2013: fig. 3A, B, D); vii) prominences on the intercoxal sclerites are minute in P. longiaesthetascus , new species ( Fig. 3 A–D), but conspicuous in P. longifurcata ( Tran & Chang, 2013: fig. 3A–D).

Both species were collected in different habitats. P. longifurcata was collected in a syphon lake located about 1,200 m from the tourist entrance, and P. longiaesthetascus , new species was collected in a pool filled with drip water located approximately 400 m from the tourist entrance. Although physical and chemical parameters in these two habitats were not measured at the time of specimen collection, records from locations in Europe indicate significant differences between the two habitats ( Brancelj, 2002). It is possible that populations, both in the syphon lake and in the pools, represent “a sink population” that is washed by dripping water from the epikarst zone, with each drip point acting as an “island” due to very limited lateral communication between and among adjacent drip points ( Brancelj, 2006). Coexistence of two closely related species within a small geographical area indicates that sympatric speciation might occur within ancestral populations. The reduction in outer apical caudal seta (seta IV) and the remarkably elongated aesthetascs on the male antennule in P. longiaesthetascus , new species, suggests a more specialised and older lineage in both of these subterranean dwellers.

Figures

Fig. 1. Pseudograeteriella longiaesthetascus new genus, new species, female. A, habitus, dorsal view; B, rostrum, frontal view; C, genital double-somite, dorsal view; D, urosome, ventral view; E, genital double-somite, lateral view; F, caudal rami, dorsal view; G, caudal ramus, lateral view. Scale bars: A, 250 μm; B, 50 μm; C–G, 100 μm.

Fig. 2. Pseudograeteriella longiaesthetascus new genus, new species, female. A, antennule (arrow indicates the aesthetasc); B, antenna; C, mandible; D, maxillule; E, maxilla; F, maxilliped. Scale bars: 100 μm.

Fig. 3. Pseudograeteriella longiaesthetascus new genus, new species, female. A, P1; B, P2; C, P3; D, P4. Scale bars: 100 μm.

Fig. 4. Pseudograeteriella longiaesthetascus new genus, new species, male. A, habitus, dorsal view; B, genital somite, ventral view; C, antennule; D, Endp-2 of P4. Scale bars: A, 250 μm; B–D, 100 μm.