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| Metacyclops sakaeratensis Athibai, Wongkamhaeng & Boonyanusith, 2022 |
ABSTRACT
Metacyclops sakaeratensis sp. nov. and M. brancelji sp. nov. are described as being present in the mountainous areas of Northeastern and Southern Thailand, respectively. Two new species resemble M. woni in both sexes, but they are easily distinguished from their Cambodian relative by having: 1) transverse suture on the dorsal surface of the genital double-somite, 2) serrated hyaline frill on the posterior margin of third pedigerous somite, 3) different length / width ratio of caudal ramus, and 4) a row of spinule on caudal surface of intercoxal sclerite of the third swimming legs. The significant differences between M. sakaeratensis sp. nov. and M. brancelji sp. nov. are present in both sexes, including the body size, integumental ornamentation of the body surface, length / width ratio of caudal ramus, armature of the fifth swimming leg, and the male sixth swimming leg. In addition, an up-to-date key to the female of all fifteen species of Metacyclops recorded in Asia is provided.
Keywords: cave-dwelling copepod, karst, Sakaerat Environmental Research Station, Satun Province, Southeast Asia
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| Geographical location and details of the sampling sites. A. Map of Thailand and a location of Nakhon Ratchasima, Satun and Songkhla Provinces. B–C. Location (indicated by a black circle with no. 1) and sampling point of headwater stream in Nakhon Ratchasima Province. D. Locations of caves in Satun and Songkhla Provinces (indicated by black circles with nos 2, 3, 4). E–F. Sampling points in Phupha Phet Cave. G–H. Sampling points in Rakhang Thong Cave and Khao Nui Cave, respectively. |
Phylum Arthropoda von Siebold, 1848
Subphylum Crustacea Brünnich, 1772
Class Maxillopoda Dahl, 1956
Subclass Copepoda Milne-Edwards, 1840
Superorder Podoplea Giesbrecht, 1882
Order Cyclopoida Burmeister, 1834
Family Cyclopidae Rafinesque, 1815
Subfamily Cyclopinae Kiefer, 1927
Genus Metacyclops Kiefer, 1927
Metacyclops sakaeratensis sp. nov.
Diagnosis:
Female. Body size moderate (0.73–0.75 mm; n = 3), with shallow integumental pits. Posterior margin of second pedigerous somite undulated; those of third and fifth pedigerous somites with serrated hyaline frill. Genital double-somite dorsally with two sensilla and transverse suture, representing the remnant of ancestral articulation of the sixth thoracic somite and the first abdominal somite. Anal operculum developed, reaching insertion of caudal ramus; free margin smooth and straight. Caudal rami ca 2.1–2.3 × as long as wide, with few spinules at anterior third length on lateral surface and at base of seta II, combined with a row of strong spinules latero-ventrally at base of seta III. Seta VI slightly shorter than seta III. Setal and spine formulae of exp-2 of P1–P4 5.5.5.5 and 3.4.4.3, respectively. P4 exp-2 with single apical spine; spine slightly shorter than segment. Inner spine on free segment of P5 as long as segment; outer seta on P5 ca 4.5 × as long as inner spine.
Male. Body slenderer and smaller than female (0.62–0.67 mm; n = 3). Caudal rami ca 2.2–2.4 × as long as wide. P6 with two elements; outer (dorsal) seta about twice as long as inner (ventral) spine.
Etymology: The species name is a noun. The specific epithet was raised after the ʻSakaeratʼ Subdistrict, where the new species was encountered
Metacyclops brancelji sp. nov.
Diagnosis:
Female. Body size moderate (0.89–0.96 mm; n = 6), without integumental pits. Posterior margin of second pedigerous somite undulated, those of third and fifth pedigerous somite with serrated hyaline frill. Genital double-somite dorsally with two sensilla and transverse suture, representing the remnant of ancestral articulation of the sixth thoracic somite and the first abdominal somite. Anal operculum developed, reaching insertion of caudal ramus; free margin smooth and concave. Caudal rami ca 2.6–2.9 × as long as wide, ornamented with 3–4 spinules at anterior third length on lateral surface and few spinules at base of seta II, combined with a row of strong spinules latero-ventrally at base of seta III. Seta VI slightly shorter than seta III. Setal and spine formulae of exp-2 of P1–P4 5.5.5.5 and 3.4.4.3, respectively. P4 exp-2 with single apical spine; spine slightly shorter than segment. Inner spine of free segment of P5 longer than segment, ca 1.5 × as long as segment; outer seta on P5 ca 2.5 × as long as inner spine.
Male. Body length 0.71–0.76 mm (n = 3). Caudal rami ca 2.5–2.8 × as long as wide. P6 with two elements; inner (ventral) spine robust, slightly shorter than outer seta.
Etymology: The name is a masculine noun in genitive singular, raised after Professor Dr Anton Brancelj (National Institute of Biology, Ljubljana, Slovenia) in honor of his great contribution to the diversity of subterranean Copepoda in Thailand.
Sujeephon Athibai, Koraon Wongkamhaeng and Chaichat Boonyanusith. 2022. Two New Species of Metacyclops Kiefer, 1927 (Copepoda, Cyclopoida) from Thailand and An Up-to-date Key to the Species Recorded in Asia. European Journal of Taxonomy. 787(1); 146-181. DOI: 10.5852/ejt.2021.787.1621
