Bryocyclops asetus, Watiroyram, Santi, 2018

Watiroyram, Santi, 2018, Bryocyclopsasetus sp. n. and the presence of Bryocyclopsmuscicola (Menzel, 1926) from Thailand (Crustacea, Copepoda, Cyclopoida, Cyclopidae), ZooKeys 793, pp. 29-51 : 29

Bryocyclops asetus sp. n. Figs 2, 3, 4, 5, 6, 7, 8

Type locality.

A rimstone pool in Sai Cave, Khao Daeng Subdistrict, Kui Buri District, Prachuap Khiri Khan Province, western Thailand; 12°10'46"N; 100°00'26"E, altitude: 107 m above sea level.

Material examined.

Holotype: one adult male, NHMUK 2018.1043, dissected and mounted on one slide; allotype: one adult female, NHMUK 2018.1044, dissected and mounted in one slide; paratypes: one ovigerous female, two adult females and three adult males, NHMUK 2018.1045-1050, preserved in 70% ethanol in 1.5 ml microtube and three adult females and three adult males, NPU 2018-003, preserved in 70% ethanol in 1.5 ml microtube; all specimens collected on 1 December 2016 by author.

Differential diagnosis.

Anal operculum ovate and serrate. P1-P4 with acute projections on distal margin of intercoxal sclerite; no inner coxal seta. Basis of P1 with inner spine. P1-P4 with two-segmented Exp and Enp. Setal and spine formula of P1-P4Exp-2 as follows: 5.5.5.4; 3.3.3.3; with no blunt-tipped setae; P1-P4Enp-2 as 3.4.5.3 and 1.1.1.1. Male P3Enp-2 with six elements, including one transformed spine and seta: transformed spine with acute tip; slightly swollen in medians part, armed with strong spinules; transformed seta bare, strong.

Description of adult female.

Preserved specimens colourless. Nauplius eye and refractile points on integument absent. Body length (Figs 2A, 3A) (n = 5) measured from anterior margin of rostrum to posterior margin of caudal rami 398-415 μm (mean 406 μm, n = 5); greatest width at distal part of cephalothorax 156-169 μm (mean 164 μm, n = 5); body length/width ratio 2.5. Cephalothorax completely fused to pediger I, without dorsal scar. Prosome length 245-248 μm (mean 246 μm, n = 5), urosome length 165-169 μm (mean 167 μm, n = 5); prosome/urosome length ratio 1.5. Prosomites with posterior dorsal margins smooth; urosomites serrated; pediger V finely serrated, and genital double-somite and two later urosomites coarsely serrated, both dorsally and ventrally (Fig. 3B, D). Genital double-somite (Figs 2 A–C, 3F) symmetrical; length 73-76 μm (mean 75 μm, n = 5), width 98-100 μm (mean 99 μm, n = 5); 1.3 times wider than broad. Pair of sclerotized structures dorsolaterally, remnant of ancestral segment both dorsally and ventrolaterally; copulatory pore situated midventrally. Anal somite (Figs 2 A–C, 3 D–E) with strong spinules along entire posterior margin; pair of long sensilla above base of anal operculum. Anal operculum ovate, coarsely serrated, extending over three-fourths of caudal ramus length.

Caudal rami (Figs 2 A–C, 3 D–E) divergent, slightly tapering on distal half, 1.5 times as long as wide. Each ramus with six setae (seta II–VII): anterolateral (II) seta bare, slightly shorter than ramus; posterolateral (III) seta pinnate, 1.3 times as long as ramus, with strong spinules near venterolateral insertion; outer terminal (IV) and inner terminal (V) setae longest, pinnate, with fracture plane; terminal accessory (VI) seta shortest, bare, 0.5 times as long as ramus; dorsal (VII) seta located on distal margin of dorsal keel, bare, 2.2 times as long as ramus, with articulate insertion.

Antennule (Figure 2D) 11-segmented do not reach posterior margin of cephalothorax. Armature formula: 1(6S), 2(2S), 3(5S), 4(2S), 5(0), 6(1S), 7(3S), 8(2S), 9(2S), 10(2S), 11(7S+1A).

Antenna (Figure 4A) uniramous, consisting of coxobasis, and three-segmented Enp. Coxobasis with one smooth seta on distal inner corner. Enp-1-3 with 1, 5, and 7 setae respectively; with row of spinules on outer margin.

Mandible (Figure 4B) with six strongly chitinized teeth; dorsal seta on gnathobase. Palp reduced to single seta.

Maxillule (Figure 4C) with four strongly chitinized teeth on precoxal arthrite; inner margin with four bare setae and one plumose seta. Palp two-segmented: proximal segment with distal plumose seta; two bare setae distally; one bare seta dorsally; distal segment with three bare setae.

Maxilla (Figure 4D) with precoxal endite with two pinnate setae. Coxa with two endites: proximal endite with one bare seta; distal endite with one pinnate, and one bare setae. Basis with two strong claw-like expansions, bare seta close to its base. Two-segmented Enp, Enp-1 with unipinnate seta; Enp-2 with one unipinnate seta, two bare setae.

Maxilliped (Figure 4E) syncoxal endite with two strong spiniform setae, and row of spinules on anterior surface. Basis with spiniform seta, two rows of spinules on anterior surface. Two-segmented Enp; Enp-1 with one pinnate seta; Enp-2 with two bare setae.

P1-P4 (Fig. 5 A–D) biramous, with two-segmented Exp and Enp. Intercoxal sclerites with no ornamentation, with acute projections on distal margin. P1 with group of tiny spinules at insertion of inner spine. All setae on P1-P4Exp-2 with normal tips. P1-P4Enp-1 with spiniform process on outer distal corner. Outer seta and inner proximal seta on P1Enp-2 as long as spine, shorter than inner distal seta. Outer seta and inner proximal seta on P2Enp-2 as long as spine, shorter than two inner distal setae. Proximal inner seta on P3Enp-2 as long as spine, shorter than the rest of segment; outer seta slightly longer than spine, followed by two inner medial setae and apical seta. Apical seta on P4Enp-2 longest, 2.5 times as long as spine, followed by inner and outer seta. Spine and setal formula of P1-P4 as follows (seta in Arabic numerals, spine in Roman numerals for outer-inner or outer-apical-inner seta/spine):

P5 (Figs 3G, 4F) fused to pediger, represented by three pinnate setae on small prominence: dorsal seta longer than two ventral setae; outer seta longer than inner one.

P6 (Figs 2 A–B, 3F) situated laterodorsally next to heavily sclerotized structure on genital double-somite: with one short pinnate seta dorsally; two tiny spinules next to it ventrally element on small plate.

Adult females with pair of egg sacs (Figure 12A), each with two eggs, with a mean diameter of 64 μm (n = 8).

Description of adult male.

Body length (Figs 6A, 7A) measured from anterior margin of rostrum to posterior margin of caudal rami 369-373 μm (mean 371 μm, n = 5); smaller than female. General segmentation and ornamentation (Figs 6 A–C, 7 A–C) similar to female, with five-segmented urosome. Anal operculum (Figure 7C) more finely serrated than in female. Antennae, mouthparts, P1-P2, P3Exp-2, and P5 (Figs 7G, 8 A–C) similar to those of female, except P2Enp-2 with longer inner medial seta.

Antennule (Figs 6D, 7F) 16-segmented, geniculate. Armature formula as follows: 1(7S+2A), 2(3S), 3(1S), 4(2S+1A), 5(2S), 6(1S), 7(2S), 8(1A), 9(1S), 10(2S), 11(1Sp), 12(0), 13(2S+1A+1Sp), 14(1S), 15(3S), 16(7S+1A).

P3 (Figure 8C) intercoxal sclerite with acute projections on distal margin. Enp-1 with inner pinnate seta. Enp-2 with outer pinnate seta; transformed apical spine with hook-like tip, thin pinnate seta; inner strong bare seta, two inner pinnate setae. Transformed apical spine with several spinules at 2/3 length of it; less-produced medial portion; with short, acute tip.

P4 (Figure 8D) intercoxal sclerite with acute projections on distal margin. Coxa without inner seta. Basis and Exp-1 with outer seta and spine, respectively. Exp-2 with three outer spines and two pinnate apical and inner setae. Enp-1 with inner pinnate seta and spiniform process on inner and outer distal margins. Enp-2 with apical spine and three long pinnate setae: apical and inner setae equal in length, 3.0 times as long as spine; outer seta 1.5 times longer than spine.

P6 (Figs 6B, C, 7D) reduced to simple plate, represented by three subequal pinnate setae.

Variability.

Two out of five examined females have round rather than acute distal margins on intercoxal sclerite of P1.

Etymology.

The specific name asetus refers to the one of the primary characteristic that discriminates the new species from other species of group I sensu Lindberg (1953) by the first swimming leg without an inner coxal seta.

Geographical distribution.

This species is currently known only from Sai Cave, Khao Daeng Subdistrict, Kui Buri District, Prachuap Khiri Khan Province, Thailand.

Remarks.

The new species is most similar to B. maewaensis , found in caves in northern and western Thailand. They share the same morphological characteristics, such as the free margin of anal operculum ovate and serrate, the same setae and spines formula on P1-P4Exp-2 (setae: 5.5.5.4; spines: 3.3.3.3) and the same setae formula on P1-P4Enp-2 (3.4.5.3) in both sexes, except the male P3Enp-2 of B. asetus sp. n. which has five instead of four setae. The new species is clearly differentiated from B. maewaensis by its typical divergent caudal rami, the absence of a coxal seta on P1 and the absence of blunt-tipped setae on P2-P3Exp-2. Female P4Enp-1 of B. asetus sp. n. is larger than Enp-2 and has no spiniform process on the inner distal margin, which is present in B. maewaensis . Female P4Enp-2 of the new species has three long slender setae which are longer than the apical spine on the same segment, but B. maewaensis has robust and short setae that are approximately as long as spine. Male P3Enp-2 of the new species has a different transformed spine compared to B. maewaensis : the expansion is less expressed and is armed with strong spinules in the new species, but B. maewaensis has a well-expressed expansion and no ornamented surface.