Research Article |
Corresponding author: Chaichat Boonyanusith ( chaichat.b@nrru.ac.th ) Academic editor: Kai Horst George
© 2021 Chaichat Boonyanusith, Sujeephon Athibai.
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:
Boonyanusith C, Athibai S (2021) A new species of Rangabradya (Copepoda, Harpacticoida, Ectinosomatidae) from a cave in Satun Province, southern Thailand. ZooKeys 1009: 45-66. https://doi.org/10.3897/zookeys.1009.54554
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A representative of the family Ectinosomatidae was discovered in a temporary pool in a cave in the Satun Province, southern Thailand. Based on the characteristics of the antennary exopod, armature of the female fifth leg, and configuration of the male sixth leg, a new species of the genus Rangabradya was identified, representing the first record of the genus in the continental waters of Thailand and in Southeast Asia. The new species can be distinguished from Rangabradya indica by the configurations of the fifth and the sixth legs in both sexes, the body ornamentation of the urosomite, and the armature of the mouthparts. These structures show a more primitive state in the new species. Accordingly, a new subgeneric rank in the genus Rangabradya, Siamorangabradya subgen. nov, was established to accommodate the Thai species and Rangabradya (Siamorangabradya) wongkamhaengae subgen. et sp. nov. was described. Also, the key to all 23 genera of the family was updated.
Anchialine caves, cave-dwelling copepods, Satun Geopark, Satun Province, Southeast Asia
Satun Province is located in southern Thailand and is part of the continental area of the Sunda Subregion (Fig.
The family Ectinosomatidae Sars, 1903 is speciose, encompassing 325 valid species from 23 genera (
Among the genera currently known as members of the family Ectinosomatidae, the genus Rangabradya Karanovic & Pesce, 2001 is a subterranean freshwater representative. The only known species of the genus is Rangabradya indica Karanovic & Pesce, 2001, previously described from a freshwater bore-well in India (Fig.
Five years ago, a representative of the family Ectinosomatidae was encountered in samples of cave-dwelling copepods from a cave in the La-Ngu District of Satun Province, southern Thailand. The morphology of body shape, maxilla, and swimming legs indicates the close relatedness of the Thai specimens and the genus Rangabradya, but a detailed examination revealed a more primitive state in the mouthparts, fifth and sixth swimming legs, and ornamentation of the urosomites. However, there is no apomorphic character to distinguish it as a new genus. For this reason, a new subgeneric rank was created within the genus Rangabradya, and the new cave-dwelling Harpacticoida from southern Thailand was named Rangabradya (Siamorangabradya) wongkamhaengae subgen. et sp. nov. In this paper, descriptions and illustrations of the new species are presented. Furthermore, an updated key to all 23 genera of the family is provided.
Samples were collected from a temporary pool in Khay Cave of Satun Province, southern Thailand, using a hand net with a mesh size of 60 µm, and stored in a solution of 4% formaldehyde. Specimens were sorted under a stereomicroscope and stored in 70% ethanol. Before the morphological examination, the specimens were placed in a mixture of glycerol and 70% ethanol (ratio ~1:10 v/v) for 30 minutes. They were subsequently completely dissected and mounted on slides in glycerol and covered with coverslips.
The examination of body parts and ornamentations was performed under a Nikon ECLIPSE E200 compound light microscope at 1000× magnification. The habitus and body appendages were drawn using a drawing tube attached to the compound microscope, and the final versions of the illustrations were prepared in Adobe Illustrator CC 2020. For a detailed examination, additional material was dehydrated in ethanol in a series of concentrations increasing from 70% to 100% and dried in a critical point dryer. Afterwards, they were mounted on stubs, coated with gold, and examined using a scanning electron microscope (Leo 1450VP).
Morphological descriptions were made following the terminology used in
Endp endopod;
Exp exopod;
Endp/Exp-1 (2, 3) proximal (middle, distal) segment of endopod and exopod;
ae aesthetasc;
I spine;
P1–P6 swimming legs 1–6.
The type material has been deposited at the Princess Maha Chakri Sirindhorn Natural History Museum, Prince of Songkla University, Songkhla, Thailand (
Order Harpacticoida Sars, 1903
Family Ectinosomatidae Sars, 1903
Genus Rangabradya Karanovic & Pesce, 2001
Ectinosomatidae, with fusiform habitus. Urosomite with spinule ornamentation. Antennule six-segmented in both male and female; third segment longest. Distal segment of antennary Exp elongate, with two apical setae; longest seta normally developed; shortest one as long as segment bearing it. Mandible with additional spine at dorsal site of pars incisiva. Coxa of maxillule free. Maxilla straight, with three setae on distal endite of syncoxa and allobasis with two medial setae. Maxilliped three-segmented, with four setae on Endp. Armature formula of Exp-3, from P1–P4: 5.6.6.6. Female P5 Exp partly fused with baseoendopod, with three marginal setae; endopodal lobe of baseoendopod with two apical elements. Female P6 reduced to small protuberance with one apical seta on peduncle. Male P5 Exp completely fused to baseoendopod, with two apical setae on endopodal lobe. Male P6 reduced to simple plate and unarmed.
Rangabradya (Siamorangabradya) wongkamhaengae subgen. et sp. nov.
The subgenus is named after Siam, Thailand’s former name, prefixed to the existing generic name Rangabradya. The name is a feminine noun in the nominative singular.
Holotype : Thailand • 1 ♀ (adult), 485 μm long; Satun Province, Khay Cave; 6°53'40"N, 99°46'44"E, 17 m a.s.l.; 17 Dec. 2014; C. Boonyanusith leg.; hand net; completely dissected and mounted on a slide in glycerol and sealed with nail polish; PSUZC-PK2005-01. Allotype: Thailand • 1 ♂ (adult), 428 μm long, collection data as for holotype; PSUZC-PK2005-02. Paratypes: Thailand • 1 ♀ (adult) and 1 ♂ (adult); same data as for holotype; PSUZC-PK2005-03 and PSUZC-PK2005-04, respectively.
Thailand • 3 ♂♂ (adult), 1 ♀ (adult), 3 copepodids; same data as for holotype; preserved in 70% ethanol; retained in collection of the first author (CB).
Khay Cave in La-Ngu District, Satun Province, Thailand. The cave’s geography and morphology have previously been described in
Total body length, excluding caudal setae, 485–489 µm (mean = 487; N = 3). Preserved specimens colourless. Habitus fusiform, gradually tapering posteriorly, with maximum width at posterior margin of cephalothorax (Figs
Urosome comprising fifth pedigerous somite, genital double-somite, and three free abdominal somites (Fig.
Caudal rami (Figs
Antennule (Figs
Antenna (Figs
Labrum (Fig.
Mandible (Figs
Maxillule (Figs
Maxilla (Figs
Maxilliped (Fig.
P1–P4 with three-segmented Exp and Endp. Endp always longer than Exp. Segments with rows of strong spinules on outer margins and without ornamentations on inner margins. Armature formula as follows (legend: inner-outer element; inner-apical-outer; Arabic numerals representing setae; Roman numerals representing spines):
Legs | Basis | Exopod | Endopod | ||||
---|---|---|---|---|---|---|---|
1 | 2 | 3 | 1 | 2 | 3 | ||
P1 | I-1 | 0-I | 1-I | 1-II-II | 1-0 | 1-0 | 2-II-I |
P2 | 0-1 | 1-I | 1-I | 2-II-II | 1-0 | 1-0 | 2-II-I |
P3 | 0-1 | 1-I | 1-I | 2-II-II | 1-0 | 1-0 | 2-II-I |
P4 | 0-1 | 1-I | 1-I | 2-II-II | 1-0 | 1-0 | 2-II-I |
P1 (Fig.
P2–P4 (Fig.
P5 (Figs
P6 (Fig.
Body slightly smaller than in female, fusiform. Total body length, excluding caudal setae, 427–431 µm (mean = 429; N = 3). Preserved specimens colourless. Prosome ca 1.5× as long as urosome (Fig.
Urosome (Figs
Antennule (Fig.
Rostrum, antenna, mouthparts and P1–P4 (not figured) as in female.
P5 (Fig.
P6 (Fig.
No variability was observed in the female. In one male, on the right P3 Endp were two segments only. The terminal segment short, armed with one lateral spine and two apical setae, unequal in length (Fig.
The species name is a feminine noun in the genitive singular case, named after Dr Koraon Wongkamhaeng (Kasetsart University) in honour of her contribution to the research into the diversity of cave-dwelling copepods in Satun and Songkhla provinces.
The species is known only from the type locality.
As previously mentioned in the descriptions of Boholina laorsriae (
Rangabradya (Siamorangabradya) wongkamhaengae subgen. et sp. nov. Scanning electron microscope photographs A female habitus, ventral view B cephalothorax, ventrolateral view C antennule D distal segment of antenna E maxillule F maxilla G P5. The arrows and the triangular in figure B indicate the sensilla and integumental pore, respectively. The asterisk in figure E indicates coxa of the maxillule.
Two characters commonly used in assessing phylogenetic relationships of the family Ectinosomatidae are: 1) the shapes of the cephalothorax and habitus and 2) the orientation of the maxillary allobasis.
The recently known genera of the family can be divided into three groups, according to the shapes of the cephalothorax and habitus. The first includes six genera with a rectangular cephalothorax and a cylindrical body shape. They are comprised of: Arenosetella Wilson, 1932; Ectinosomoides Nicholls, 1945; Glabrotelson Huys in Kihara & Huys, 2009; Noodtiella Wells, 1965; Oikopus Wells, 1967; and Tetanopsis Brady, 1910. The second group includes 15 genera with a cephalothorax tapering anteriorly and a fusiform body shape: Bradya Boeck, 1873; Bradyellopsis Brian, 1925; Chaulionyx Kihara & Huys, 2009; Ectinosoma Boeck, 1865; Ectinosomella Sars, 1910; Halophytophilus Brian, 1919; Halectinosoma Vervoort, 1962; Klieosoma Hicks & Schriever, 1985; Microsetella Brady & Robertson, 1873; Parahalectinosoma George & Schwabe, 2019; Parabradya Lang, 1944; Pseudectinosoma Kunz, 1935; Pseudobradya Sars, 1904; Rangabradya Karanovic & Pesce, 2001 (including Siamorangabradya, subgen. nov.); and Sigmatidium Giesbrecht, 1881. The third group comprises genera with a cephalothorax clearly wider than the urosome and a dorsoventrally depressed prosome, including Peltobradya Médioni & Soyer, 1968 and Pontobradya Apostolov, 2011. Of the above-mentioned genera, Halectinosoma is most speciose with 69 valid species (
The orientation of the maxillary allobasis is another significant taxonomic character, which can be divided into two types: prehensile and non-prehensile. The maxilla of most Ectinosomatidae is geniculated, with the allobasis considerably bending medially to form a prehensile appendage. In the other genera, as well as in the new species, the maxilla is not geniculate and an allobasis bends slightly, forming a slight angle between the syncoxa and the allobasis. A third group represented by the genus Parahalectinosoma has a maxilla that is strongly atrophied (
Among the genera with a fusiform body, most characters of the Thai specimens match well the characteristics of Rangabradya. The shared characters are as follows:
Of the nine shared characters, the combination of characters 6) and 7) confirms the close phylogenetic relationships between the new species from Thailand and the Indian species within the genus Rangabradya.
The female P5 in the new species is similar to that of Ectinosoma in that it has subdivided Exp and lacks a surface seta on the segment. However, the former has only three setae on Exp compared to the four reported for Ectinosoma. Three spiniform setae have also been observed in the female P5 Exp in Halectinosoma, but its representatives have a surface seta on this segment.
Distinctive characters between Siamorangabradya subgen. nov. and the nominative subgenus Rangabradya.
Characters | Siamorangabradya subgen. nov. | Rangabradya |
---|---|---|
Ornamentation of urosomite | present | absent/reduced |
Number of setae on caudal ramus | 7 | 6 |
Number of segments of antennule | 6 | 5 |
Spine between pars incisiva and lacinia on mandibular gnathobase | present | absent |
Number of setae on mandibular Endp | 8 | 5 |
Basal seta on praecoxal arthrite | present | absent |
Setal formula of maxillary syncoxal endite from proximal to distal ones | 3.2.3 | 4.1.2 |
Number of setae on maxillipedal Endp | 4 | 3 |
Exp and baseoendopod of female P5 | subdivided | fused |
Number of setae on female P6 | 1 | absent |
Number of setae on endopodal lobe of the male P5 | 2 | 1 |
After
1 | Body cylindrical with cephalothorax rectangular in dorsal aspect; body approximately the same width throughout its length | 2 |
– | Body fusiform with cephalothorax sub-triangular in dorsal aspect; greatest body width usually at posterior margin of cephalothorax; urosome gradually tapering towards the posterior end | 7 |
– | Body with dorsoventrally depressed prosome, clearly wider than urosome | 20 |
2 | Exp of antenna two-segmented; maxilla prehensile, with major articulation between elongate syncoxa and elongate allobasis | Noodtiella Wells, 1965 |
– | Exp of antenna one- or three-segmented; maxilla not prehensile, with at most a slight angle between syncoxa and allobasis | 3 |
3 | P2–P4 Endp two-segmented | Ectinosomoides Nicholls, 1945 |
– | P2–P4 Endp three-segmented | 4 |
4 | Anal somite with dorsal armature of claws, lappets or spiniform processes around anal opening; P5 Exp with three marginal and one surface seta | Arenosetella Wilson, 1932 |
– | Anal somite without such ornamentation | 5 |
5 | Exp of antenna one-segmented | Tetanopsis Brady, 1910 |
– | Exp of antenna three-segmented | 6 |
6 | Female P5 Exp and baseoendopod with foliaceous setae, Exp with three marginal and no surface setae; male P5 Exp with four normal marginal setae | Oikopus Wells, 1967 |
– | P5 Exp and baseoendopod with normal setae in both sexes, Exp with three marginal and typically a surface seta [absent in Glabrotelson soyeri (Bodin, 1979)] | Glabrotelson Huys in Kihara & Huys, 2009 |
7 | P1–P4 Endp two-segmented | Pseudectinosoma Kunz, 1935 |
– | P1 Endp two- or three-segmented, P2–P4 Endp three-segmented | 8 |
8 | P1 Endp prehensile | 9 |
– | P1 Endp not prehensile | 12 |
9 | P1 Endp two-segmented | 10 |
– | P1 Endp three-segmented | Klieosoma Hicks & Schriever, 1985 |
10 | P1–P2 Exp-3 with two outer elements | 11 |
– | P1–P2 Exp-3 with three outer elements | Halophytophilus Brian, 1919 |
11 | Antennule with large spine on second segment (and often first and third segments); Exp of antenna rudimentary, with one to three small setae; P1 Endp-2 with four elements (one to two pinnate and claw-like) | Bradyellopsis Brian, 1925 |
– | Armature elements on first to third antennulary segments setiform; Exp of antenna well developed and three-segmented; P1 Endp-2 with six elements (outer one bifid and claw-like) | Chaulionyx Kihara & Huys, 2009 |
12 | Maxilla prehensile, with syncoxa and allobasis forming right angle; P5 Exp poorly developed, short, fused to baseoendopod in female and distinct in male, with three marginal and no surface setae; body very small (< 300 μm) | Sigmatidium Giesbrecht, 1881 |
– | These characters not combined | 13 |
13 | Female P5 Exp and baseoendopod fused, forming a single plate in both sexes, or partly discrete; male P6 forming a single plate or absent | 14 |
– | Female P5 Exp and baseoendopod at least partly discrete; male P6 with armature element | 15 |
14 | Armature formula of P1–P4 Exp-3: 5, 6, 6, 6; male P6 absent or unarmed | 21 |
– | Armature formula of P1–P4 Exp-3: 6, 7, 8, 8; male P6 with two setae; body of female large (≥ 1200 μm); marine, usually deepwater | Parabradya Lang, 1944 |
15 | Integument of somites with distinctive sub-rectangular pores; P5 Exp with four marginal setae | Ectinosoma Boeck, 1865 |
– | Integument of somites without distinctive sub-rectangular pores; P5 Exp with three marginal setae and one seta on anterior surface | 16 |
16 | Mandible with rudimentary gnathobase, elongate basis and filiform rami, each terminating in two to three setae; Exp of antenna without lateral spines | Ectinosomella Sars, 1910 |
– | These characters not combined | 17 |
17 | Third segment of female antennule 3× as long as wide; Endp of mandible with one strong seta laterally; P1–P4 Exp-3 with two outer spines; planktonic (occasionally in sediment) | Microsetella Brady & Robertson, 1873 |
– | These characters not combined | 18 |
18 | Body comparatively robust with prosome–urosome separation usually distinct (exception: Bradya kurtschminkei Seifried & Martínez Arbizu, 2008 with dorsoventrally flattened habitus); antenna with two setae on Exp-1 and one seta on Endp-1; Exp of mandible with at least five setae; maxilliped robust with short Endp usually fused at an angle with basis and bearing four conspicuous setae | Bradya Boeck, 1873 |
– | Body comparatively slender with no sharp separation between prosome and urosome; antenna with less than two setae on Exp-1 (except Pseudobradya ambigua Sars, 1920 with two) and no seta on Endp-1; Exp of mandible generally with less than five setae; maxilliped usually slender and straight with discrete Endp bearing one small and four conspicuous setae | 19 |
19 | Antennule with or without dark pigment spot within the proximal three segments; maxilla prehensile, allobasis usually truncate distally and carrying three-segmented Endp (although Endp sometimes very small and segmentation difficult to discern; reduced to a narrow three-segmented cylinder in P. leptognatha Sars, 1920); maxilliped short and robust | Pseudobradya Sars, 1904 |
– | Antennule without pigment spot; maxilla with at most a slight angle between syncoxa and allobasis, the latter generally tapering distally, Endp three-segmented but always small, its morphology not clearly discernible; maxilliped generally slender | Halectinosoma Vervoort, 1962 |
20 | P1 Endp three-segmented; female P5 Exp with four marginal elements | Pontobradya Apostolov, 2011 |
– | P1 Endp two-segmented; female P5 Exp with three marginal elements and one surface seta | Peltobradya Médioni & Soyer, 1968 |
21 | Exp of antenna three-segmented; maxillule and maxilla normally developed; maxilliped three-segmented; continental groundwater | Rangabradya Karanovic & Pesce, 2001 |
– | Exp of antenna one-segmented; maxillule and maxilla strongly atrophied; maxilliped two-segmented; symbiosis in echiuran coelom | Parahalectinosoma George & Schwabe, 2019 |
22 | Female P5 Exp fused to baseoendopod; male P5 with one seta on baseoendopodal lobe | Rangabradya (Rangabradya) Karanovic & Pesce, 2001 |
– | Female P5 Exp and baseoendopod partly discrete; male P5 with two setae on baseoendopodal lobe | Rangabradya (Siamorangabradya) subgen. nov. |
This paper is a result of research project supported by a grant from the Office of the Higher Education Commission, Thailand (2558A13562002) and was funded by the Research and Academic Affairs Promotion Fund (RAAPF), Faculty of Science, Khon Kaen University, the Fiscal year 2017. The authors sincerely thank Dr Kai Horst George, Dr Anton Brancelj, and B.A. Venmathi Maran for their valuable revision of the manuscript.