Research Article |
Corresponding author: Santi Watiroyram ( santi.watiroyram@npu.ac.th ) Academic editor: Fabio Stoch
© 2024 Santi Watiroyram, Kamonwan Koompoot.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Watiroyram S, Koompoot K (2024) Siamcyclops isanus sp. nov. (Copepoda, Cyclopoida, Cyclopidae), a new cave-dwelling species from northeastern Thailand. Subterranean Biology 49: 185-200. https://doi.org/10.3897/subtbiol.49.135303
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Siamcyclops isanus sp. nov. has been found from a cave in northeastern Thailand. It differs from the other member of its genus by having: 1) smooth free margin of anal operculum, 2) a different armature on the second endopod of the first and fourth legs, 3) the armature of the second endopod of the male third leg, and 4) the shape of spermatophore. The discovery of the second species from the genus Siamcyclops thus leads to the proposal for the generic diagnosis. The morphological differences between the genus Siamcyclops and other closely related genera is added.
Groundwater, Indo-Burma region, limestone cave, taxonomy, unsaturated zone
Thailand is a part of the Indo-Burma region, a hotspot for biodiversity in Asia (
The genus Siamcyclops Boonyanusith, Sanoamuang & Brancelj, 2018, a monospecific genus, was described from Ratchaburi and Prachuap Khiri Khan provinces and its distribution appears to be restricted to the central part of Thailand (
The Maholarn cave is located in Nonghin subdistrict, Nonghin district, Loei province, northeastern Thailand (Fig.
Map of the sampling site of Siamcyclops isanus sp. nov. A map of Thailand [triangle = location of the Moholarn Cave] B location of Loei Province [triangle = location of the Moholarn Cave; square = capital city nearby] C, D photo of the sampling site [white arrow indicates small pool at the entrance].
The samples were collected from a small pool near the entrance and a large rimstone pool in the innermost part of the cave (Fig.
Type specimens were deposited at the Thailand Natural History Museum in Pathum Thani, Thailand (THNHM) and at the Faculty of Science in Nakhon Phanom University, Thailand (NPU).
The morphological terminology follows
Order Cyclopoida Burmeister, 1834
Family Cyclopidae Rafinesque, 1815
Siamcyclops cavernicolus Boonyanusith, Sanoamuang & Brancelj, 2018
Siamcyclops isanus sp. nov.
Body cyclopiform, small size, with the greatest width at the cephalothorax. Pseudosegment present anterior to the genital double somite. Genital double-somite enlarged laterally, shorter than wide. Genital pore located near middle of somite length. Seminal receptacle small; anterior expansion longer and wider than posterior part. Anal operculum well developed or not, with a smooth or serrated distal margin. Antennule 11-segmented in female, 15-segmented in male. Antenna without Exp. Mandibular palp reduced, represented by three setae. P1–P3 coxa with inner seta but absent on P4. P1–P4 intercoxal sclerite with round prominences. P1 basis with inner seta. P1–P4 with 2-segmented Exp and Enp, subequal in size; setal and spines formula of Exp-2 as 5.5.5.4–5 and 3.3.3.2, respectively. P5 fused to pediger 5, with lateral seta and two ventral setae on small lobe. P6 of female with slender seta and two spiniform setae, located dorso-laterally on the simple plate of the genital double-somite; three slender setae in male. P3 Enp-2 of male with a transformed apical spine and inner subterminal seta.
The Maholarn cave, Nonghin Subdistrict, Nonghin District, Loei Province, northeastern Thailand: 17°06'23.04"N, 101°52'48.54"E, 315 m altitude. Sample collected from a rimstone pool in the innermost zone, filled with dripping water.
Siamcyclops isanus sp. nov. is named after ‘Isan’, the local name for northeastern Thailand. The species epithet is a masculine, singular adjective.
Holotype • one adult female dissected and mounted on one slide, THNHM-IV-20465. Allotype • one adult male dissected and mounted on one slide, THNHM-IV-20466. Paratypes • one adult female and male dissected and mounted on two separate slides, (NPU 2024-01–02) • four adult females and nine adult males stored in a 1.5 ml microtube with 70% ethanol, (NPU 2024-01–02) • one adult female and male dissected and mounted on two separate slides, NPU 2020-003 • one adult male dissected and mounted on one slide, THNHM-IV-20467. All samples were collected by the first author on 5 July 2013.
(holotype). Habitus (Fig.
Antennule (Fig.
Antenna (Fig.
Mandible (Fig.
Maxillule (Fig.
Maxilla (Fig.
Maxilliped (Fig.
P1–P4 (Fig.
Coxa | Basis | Exp | Enp | |
P1 | 0-1 | 1-I | I-0; III-2-3 | 0-1; 1-I-2 |
P2 | 0-1 | 1-0 | I-0; III-2-3 | 0-1; 1-I+1-2 |
P3 | 0-1 | 1-0 | I-0; III-2-3 | 0-1; 1-I+1-3 |
P4 | 0-0 | 1-0 | I-0; II-2-2 | 0-1; 0-I+1-2 |
P1 (Fig.
P2 (Fig.
P3 (Fig.
P4 (Fig.
P5 (Fig.
P6 (Fig.
Egg sac (Fig.
Spermatophore (Fig.
(allotype). Body length (Fig.
Antennule (Fig.
Antenna, mouthparts, P1, P2 and P5 similar to female.
P3 (Fig.
P4 (Fig.
P6 (Fig.
One of female (out of five) has P6 with two elements.
Known only from the type locality.
The new species is similar to S. cavernicolus Boonyanusith, Sanoamuang & Brnacelj, 2018 in the following characteristics: 1) mandibular palp with three setae; 2) Exp and Enp of P1–P4 are subequal; 3) spine formula of P1–P4 Exp-2 is 3.3.3.2; 4) P4 lacks coxal seta; 5) P4 intercoxal sclerite with round distal margin; 6) P5 fused to pediger 5, remaining small unsegmented lobe; 7) P6 with three elements (see Table
The SEM photos of P5 show the degree of reduction in Siamcyclops and Bryocyclops species. The distal segment of P5 is reduced to a small lobe on pediger 5 in Siamcyclops (Fig.
1 | Anal operculum well-developed, with serrated free margin; P4 Exp-2 with five setae; the female P1 Enp-2 with five elements; the male P1 & P3 with five elements each | S. cavernicolus |
2 | Anal operculum short, with smooth free margin; P4 Exp-2 with four setae; the female P1–Enp-2 with four elements; the male P1 & P3 Enp-2 with four and six elements, respectively | S. isanus sp. nov. |
In terms of oligomerization, many characters were used for species and generic determination which are apomorphic traits developed for living in semiterrestrial and subterranean habitats (
The genus Siamcyclops has a transformed apical spine on P3 Enp-2 in the male, coxal seta on P4 and P5 segment absent in both sexes, indicating that it closely resembles the genus Palaeocyclops Monchenko, 1972 [Bryocyclops (Palaeocyclops) jankowskajae Monchenko, 1972 is an alternative name used by
Morphological differences between the genus Siamcyclops and the closely related genera.
Genera characteristics | Bryocyclops | Thalamocyclops | Palaeocyclops | Siamcyclops |
---|---|---|---|---|
Both sexes | ||||
Mandibular palp | With 1 seta | With 1 seta | Unknown | With 3 setae |
Annal operculum | Well-developed | Well-developed | Well-developed | Normal – Well-developed |
Size of Exp versus Enp on P1–P4 | Larger | Larger | Subequal | Subequal |
Spine formula of P1–P4 Exp-2 | 3.3.3.3(4) | 3.3.3.3 | 2.3.3.3 | 3.3.3.2 |
Setal formula of P1–P4 Exp-2 | 5(4).5.5.4 | 5.5.5.4 | 5.5.5.4 | 5.5.5.5(4) |
Coxal seta of P1–P4 | 1(0).0.0.0 | 1.0.0.0 | 1.1.1.0 | 1.1.1.0 |
Intercoxal sclerite of P4 | Acute | Acute | Acute | Round |
P5 segment | Absent –prominence (shape a) | Large lobe (shape c) | Absent (shape a) | Small lobe (shape b) |
Female | ||||
Number of segments on P4 Enp-2 | 1 or 2 | 1 | 2 | 2 |
Number of setae and spines on P4 Enp-2 | 4 | 4 | 5 | 5 |
Male | ||||
Number of setae and spines on P6 | 3 | 3 | 2 | 3 |
In the Bryocyclops group sensu
Our findings indicate that the genus Siamcyclops is endemic to Thailand, with two species having a well separated distribution area: S. cavernicolus in the central part and the new species in the northeastern part of the country. Regarding copepod samples taken by the first author, S. cavernicolus is also distributed southwards to Prachuap Khiri Khan province (
The study was supported by the National Science, Research and Innovation Fund (NSRF) (Fundamental Fund: grant No. SRI-27/2023: proposal No. 66A134000008). We would like to thank and express our appreciation to Prof. Anton Brancelj and Prof. Fabio Stoch for their corrections and suggestions regarding the article’s accuracy and adherence to taxonomic standards.