Bryocyclops muscicola (Menzel, 1926)

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

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Bryocyclops muscicola (Menzel, 1926)


Bryocyclops muscicola (Menzel, 1926)  Figs 9, 10, 11

Material examined.

One dissected adult female and male mounted separately on one slide from each (seven) caves: Pha Pu Cave (NPU 2018-004-005), Na-Or Subdistrict, Muang District, Loei Province, 17°33'21"N; 101°43'39"E, altitude: 247 m, collected on 18 August 2014; Chang Phueak Cave (NPU 2018-006-007), Banna Subdistrict, Muang District, Chumphon Province, 10°26'46"N; 99°02'06"E, altitude: 104 m, collected on 10 August 2015; Mae Nang Songsi Cave (NPU 2018-008-009), Hin Tok Subdistrict, Ron Phibun District, Nakhon Si Thammarat Province, 08°14'45"N; 99°52'01"E, altitude: 45 m collected on 23 October 2015; Khao Tiphon Cave (NPU 2018-010-011), Thung Wa Subdistrict, Thung Wa District, Satun Province, 07°05'10"N; 99°47'53"E, altitude: 46 m collected on 24 October 2015; Khao Jean Cave (NPU 2018-012-013), Khlong Khut Subdistrict, Muang District, Satun Province, 06°38'32"N; 100°05'77"E, altitude: 38 m collected on 25 October 2015; Kaew Cave (NPU 2018-014-015), Laem Thong Subdistrict, Phakdi Chumphon District, Chaiyaphum Province, 15°58'27"N; 101°24'36"E, altitude: 394 m, collected on 19 September 2016; Khao Maka Cave (NPU 2018-016-017), Sala Lamduan Subdistrict, Muang District, Sa Kaeo Province, 13°47'10"N; 101°56'51"E, altitude: 121 m, collected on 5 November 2017. Four adult males and four adult females from Chang Phueak Cave mounted on one stub for SEM analysis (NPU 2018-018). All specimens collected by author.

Description of adult female.

Body length (n = 5) excluding caudal setae, 481-491 μm (mean 486 μm), width 154-156 μm (mean 155 μm), body length/width ratio approximately 3.0 (Figs 9A, 11A). Prosome length 290-293 μm (mean 292 μm), urosome length 208-213 μm (mean 210 μm); prosome/urosome length ratio 1.4. Body surface with refractile points from cephalothorax to genital double-somite. Cephalothorax with dorsally incorporated scar, pair of dorsolateral body pits. Prosomites with smooth posterior dorsal margins; pedigers I-IV with serrated lines above posterior margins; pedigers I and II with dorsolateral body pits. Urosomites with dorsally serrated posterior margins; finely serrated on pediger V; urosomites coarsely serrate both dorsally and ventrally (Fig. 9B, C, E). Genital double-somite (Fig. 9 B–D) symmetrical, 1.6 times as long as wide. Pair of sclerotized structures dorsolaterally, single copulatory pore midventrally. Urosomite 3-4 (Figure 9E) with body pits on dorsolateral surface. Anal somite (Fig. 9 E–F) with strong spinules along entire posterior margin; pair of long sensilla above base of anal operculum. Anal operculum ovate, coarsely serrated and reaches over three-fourths of caudal ramus.

Caudal rami (Fig. 9 E–F) parallel. Ramus 1.6 times as long as wide; with well-developed dorsal keel. Each ramus with four (seta II–V) pinnate setae and two (seta VI–VII) bare setae: posterolateral (III), outer terminal (IV) and dorsal (VII) setae with spinules above its insertion; setae IV and V (inner terminal seta) with breaking plane.

P1-P4 (Fig. 11 B–E) biramous with two-segmented Exp and Enp but P4 with one-segmented Enp. Intercoxal sclerites with acute projections on distal margin. P2-P3Exp-2 with two blunt-tipped setae (apical and inner seta) (Figure 11C). P1-P3Enp-1 with spiniform process on outer distal corner. P4Enp with spiniform process on mid-outer margin. 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 (Figure 9G) completely fused to pediger V, represented by three pinnate setae: dorsal seta longest, on small prominence; two ventral setae completely fused with pediger, inner seta shortest.

P6 (Figure 9H) located on genital double-somite at 1/2 length, dorsolaterally; represented by one short pinnate seta and two tiny spinules on small plate.

Adult females with pair of egg sacs (Figure 12B), each with two eggs, with a mean diameter of 50 μm (n = 8).

Spermatophore (Figure 9C) bean-shaped, paired, visible on genital double-somite mid-posteroventrally.

Description of adult male.

Body length (Figs 10, 11 F–H) smaller than female with total body lengths of 432-440 μm (mean 436 μm), prosome/urosome length ratio 1.3 (n = 5). Body ornamentation, armature of P1-P2, P3-P4Exp-2, and P5 similar to those of females. P3 (Figure 11I) with two-segmented Enp, Enp-1 with inner pinnate seta and spiniform process on outer distal margin. Enp-2 with three inner setae (distalmost seta bare, two others pinnate), transformed apical spine and outer pinnate seta. Transformed spine with medial-produced, semi-circular shape with spinules on swollen portion; with long distance between swollen portion and its tip; tip acute. P4 (Figure 11J) with two-segmented Enp; Enp-1 with inner pinnate seta and spiniform process on outer and inner distal margins; spiniform process strong and well-expressed on inner margin. Enp-2 with apical spine and three long pinnate setae, apical and inner seta subequal in length, 2.5 times as long as spine, outer seta shortest, 1.5 times longer than spine. P6 (Figure 11F, H) reduced to simple plate, represented by three unequal pinnate setae.

Geographical distribution.

Bryocyclops muscicola  is the most widely distributed species within the genus Bryocyclops  , which is mainly found in Southeast Asia with one record finding from North America (Florida, Reid 1999). To date, the species has been found in Indonesia (Java, Sumatra) and Thailand, including the north eastern region (Loei and Chaiyaphum provinces), the eastern region (Sa Kaeo Province), the southern region (Chumphon, Nakhon Si Thammarat, and Satun provinces) ( Menzel 1926; present study, see Figure 1).


Bryocyclops muscicola  belongs to Bryocyclops  group II sensu Lindberg (1953) ( Dussart and Defaye 2006). All specimens of B. muscicola  collected from caves in Thailand are consistent in terms of the details of their legs, anal operculum, and body ornamentation as observed by Menzel (1926) and Reid (1999). Some differences are noted on caudal rami and prosome: (1) the caudal ramus of Thailand’s specimens have tiny spinules at the insertion of the dorsal seta (VII) instead of the lateral seta (III) in both sexes, and the males have an obviously longitudinal keel on their rami that is absent in the Florida’s specimens; (2) the cephalothorax and pedigers II-IV of Thailand’s specimens have serrated dorsal frills above their posterior margins, a frill only present on pedigers II-IV in the Florida specimens.