Research Article |
Corresponding author: Chaichat Boonyanusith ( chaichat.b@nrru.ac.th ) Academic editor: Danielle Defaye
© 2020 Chaichat Boonyanusith, Koraon Wongkamhaeng, 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, Wongkamhaeng K, Athibai S (2020) A new species of Boholina (Crustacea, Copepoda, Calanoida) and a first record for stygobiotic calanoid fauna from a cave in Thailand. ZooKeys 904: 1-22. https://doi.org/10.3897/zookeys.904.37609
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A new species of Calanoida belonging to the genus Boholina Fosshagen & Iliffe, 1989 was found in a freshwater pool within a cave of the Satun province, South Thailand. It is the first record of the genus and of a stygobiotic representative of calanoid fauna in this country. The new species is most similar to B. crassicephala Fosshagen & Iliffe, 1989, based on position of genital pores, structures of P4 and P5 in both sexes, relative length of subapical spine vestige on the male right P5, and shape of the male left P5 endopods. However, this new species is distinguished from its known congeners by: (1) relatively longer distal outer spines on the male right P5 exopods, (2) smaller endopods of the male left P5 and (3) elongated apical spines on the distal exopodal segment of the female P4 and P5. Furthermore, the distinctive characteristic of the Thai Boholina is the presence of inner minute seta on the distal segment of the male right P5 exopod. Detailed descriptions of the new species and a key to all six known species of the genus Boholina is provided.
anchialine cave, cave-dwelling copepod, Pseudocyclopidae, Satun Province, Southeast Asia
The study of the Copepoda diversity in Southeast Asia is progressing rapidly due to an intensive program coordinated by Prof. La-orsri Sanoamuang and her colleagues. During 12 years of intensive sampling of cave-dwelling copepods in Thailand and Vietnam, many new Cyclopoida and Harpacticoida have been presented to science (
Various calanoid copepods showing plesiomorphic features, belonging to the families Boholinidae, Ridgewayiidae (now both synonyms of the family Pseudocyclopidae) and Epacteriscidae were discovered from several anchialine environments in tropical and subtropical waters around the world (e.g.,
During the investigation of cave-dwelling Copepoda in the Satun province, South Thailand, a representative of Calanoida was collected from a freshwater pool within a cave. Based on the unique characteristic of a grasping organ on the males’ left P5, the cuticular pointed projection on the caudal rami (
According to
In Thailand, six specimens of Boholina were collected from a freshwater pool within a cave. This type locality is in an area that has recently been designated as a UNESCO global geopark.
Samples were collected from a pool in Khay Cave of Satun province, South Thailand (Fig.
Endp endopod;
Exp exopod;
Endp/Exp-1 (2, 3) proximal (middle, distal) segment of rami;
ae aesthetasc;
I spine;
P1–P5 swimming legs 1–5.
Type material has been deposited at the Princess Maha Chakri Sirindhorn National History Museum, Prince of Songkla University, Songkhla, Thailand (
Holotype : THAILAND • ♀ (adult), 0.73 mm long; Satun Province, Khay Cave; 6°53'40"N, 99°46'44"E, 17 m a.s.l.; 17 December 2014; C. Boonyanusith leg.; hand net; completely dissected and mounted on two slides in glycerol and sealed with nail vanish; PSUZC-PK2004-01–02. Allotype: THAILAND • ♂ (adult), 0.67 mm long, collection data as for holotype; PSUZC-PK2004-03. Paratypes: THAILAND • 1 ♀ (adult) and 1 ♂ (adult); same data as for holotype; PSUZC-PK2004-04–05.
THAILAND • 2 ♂♂ (adult); same data as for holotype; preserved in 70% ethanol; retained in collection of the first author (CB).
The species is named after Prof. Dr. La-orsri Sanoamuang (Khon Kaen University) in honour of her great and invaluable contribution on the knowledge of the planktonic fauna in Thailand. The name of species is a feminine noun in genitive singular.
The Khay Cave is in La-Ngu district, Satun province, ca. 760 km south of Bangkok (Thailand) (Fig.
Female : Pseudocyclopidae. Fourth and fifth pedigerous somites completely fused. Postero-lateral corners of cephalosome and first three pedigerous somite rounded. Genital double-somite barrel-shaped, ornamented with hyaline membrane all around the posterior margin; hyaline membrane with large medial notch ventrally. Genital pores paired, located ventrolaterally. Hyaline membrane of preanal somite expanded dorso-medially to form trapezoidal double-pointed flap. Caudal ramus with triangular pointed projection on distal margin. Antennule relative short, not reaching beyond distal margin of prosome. Apical spine on female P4 Exp-3 elongated, ca. 3 × as long as outer terminal spine. Apical spine on female P5 Exp-3 ca. 1.8 × as long as outer terminal spine. Male: The left P5 Exp-3 highly transformed, bearing three irregular lobes; Endp oval-shaped, much shorter than right P5 Endp, ca. 1.6 × as long as wide. The male right P5 Exp with minute inner spiniform seta; distal outer spine elongated, ca. 3.4 × as long as proximal outer one and ca. 2.7 × as long as apical spine; subapical spine vestige ca. 0.7 × as long as apical spine.
Body (Fig.
Caudal rami (Fig.
Rostrum (Fig.
Antennule (Fig.
Antenna (Fig.
Mandible (Fig.
Maxillule (Fig.
Maxilla (Fig.
Maxilliped (Fig.
P1–P4 (Fig.
Armament of female thoracic legs P1–P5 in Boholina laorsriae sp. nov. (Roman numerals represent number of spines; Arabic numerals represent number of setae).
Swimming leg | Coxa | Basis | Exopod | Endopod |
---|---|---|---|---|
P1 | 0-1 | 1-1 | I-0; I-1; II, I, 4 | 0-1; 0-1; 0, I+1, 3 |
P2 | 0-1 | 0-0 | I-1; I-1; II, I, 5 | 0-1; 0-2; 2, 2, 4 |
P3 | 0-1 | 1-0 | I-1; I-1; III, I, 5 | 0-1; 0-2; 2, 2, 4 |
P4 | 0-1 | 1-0 | I-1; I-1; III, I, 5 | 0-1; 0-2; 2, 2, 3 |
P5 | 0-1 | 1-0 | I-0; I-1; III, I, 3 | 0-1; 2, 2, 3 |
P5 (Fig.
Body with a total length of 0.65 and 0.67 mm (measured from anterior margin of cephalosome to tip of the projection of caudal rami; mean: 0.66 mm; N = 2). Habitus smaller and slenderer than in female (Fig.
Caudal rami (Fig.
Antennule (Fig.
Antenna, mandible, maxillula, maxilla, maxilliped, and P1−P4 as in female.
P5 (Fig.
The new species was confidently identified to the genus Boholina based on the combination of the following characteristics mentioned by
(1) fourth and fifth pedigerous somites fused,
(2) rostrum with a rounded tip,
(3) genital pores paired and separate,
(4) caudal rami with cuticular pointed projection distally,
(5) distal outer corner of all endopodal segments of P1 forming a triangular pointed projection,
(6) P1 Endp-3 without outer seta,
(7) P4 Exp-3 with modified apical spine,
(8) female P5 with a 2-segmented Endp,
(9) male left P5 Exp-3 modified to unique characteristic grasping organ, and
(10) female and male with 4- and 5-segmented urosome, respectively; anal somite very short and sometimes concealed within the preceding somite.
Examination of the structure of the genital double-somite, of P4 and P5 in both males and females, the relative length of subapical spine vestige on the male right P5 and the shape of the male left P5 Endp revealed that the new species is most similar to B. crassicephala, which had previously been described from a pool in a cave of Bohol Island, the Philippines. Several characters are shared by both species, especially the structure of the male P5. However, there are also remarkable differences (Table
Morphological comparison of the six species of genus Boholina. Abbreviations: GDS, genital double-somite; CR, caudal rami; A2, antenna; Mb, mandible; Mx, maxillule (*measured from figures of the original description).
Character | B. ganghwaensis | B. parapurgata | B. munaensis | B. purgata | B. crassicephala | B. laorsriae sp. nov. |
Female | ||||||
Body length (mm) | 1.03–1.29 | 0.93–1.11 | 0.70–0.77 | 0.73–0.79 | 0.75–0.85 | 0.68–0.73 |
Posterior lateral corner of second and third pedigerous somites | Pointed | Pointed | Rounded | Pointed | Rounded | Rounded |
Genital pores on GDS | Either side of ventralmidline | Either side of ventralmidline | Ventrolaterally | Either side of ventralmidline | Ventrolaterally | Ventrolaterally |
Hook–like process on genital pore plate | Yes | No | No | No | No | No |
Length/width ratio of CR | 1.6 | 1.5 | 1.5 | 1.6* | 1.8* | 1.8 |
Distal two segments of A2 Exp | Separated | Separated | Separated | Fused | Fused? | Separated |
Number of setae on distal endopodal segment of Mb | 11 | 10 | 10 | 10 | 10 | 10 |
Setal formula of Mb Exp | 1,1,1,1,2 | 0.1,1,1,2 | 0,1,1,1,2 | 1,1,1,1,2 | 1,1,1,1,2 | 1,1,1,1,2 |
Basis and first endopodal segment of Mx | Partly fused | Fused | Fused | Fused | Fused | Separated |
Length ratio of apical and outer terminal spines of P4 Exp–3 | 1.6* | 1.5 | 1.9 | 1.5 | 2.5 | 3.0 |
Length/width ratio of distal endopodal segment of P5 | 2.5 | 2.6 | 2.6 | 1.8* | 1.6* | 2.6 |
Length ratio of apical and outer terminal spine of P5 Exp–3 | 1.0 | 0.8 | 1.4 | 0.8* | 1.2* | 1.8 |
Length ratio of apical spineand P5 Exp–3 | 0.9 | 0.9 | 0.8 | 0.8* | 1.0* | 1.2 |
Male | ||||||
Body length (mm) | 0.87–0.93 | 0.66–0.71 | 0.68 | 0.64–0.73 | 0.70–0.77 | 0.65–0.67 |
Length ratio of left and right Endp of P5 | 1.1* | 0.8* | 0.5 | 0.7* | 0.8* | 0.45 |
Length/width ratio of right P5 Endp | 3.2 | 3.6 | 3.5* | 2.6* | 2.7* | 3.0 |
Right P5 Endp with large inner spiniform process | No | No | Yes | No | No | No |
Right P5 Endp armature | 2 slender spines | 2 sigmoid spines | Absent | 2 slender spines | 2 slender spines | 2 slender spines |
Length ratio of two outer exopodal spines on right P5 | 1.5 | 1.8 | 1.3 | 1.7* | 1.7* | 3.4 |
Relative length of subapical spine compared to apical spine on left P5 Exp | Less than 0.5 × | Less than 0.5 × | More than 0.5 × | Less than 0.5 × | More than 0.5 × | More than 0.5 × |
i) Apical spine of the female P5 Exp-3 is ca. 1.8 × as long as outer terminal spine in the new species, but it is sub-equal to the outer terminal spine found in B. crassicephala.
ii) Exopodal segment of the male right P5 has medial minute seta in the new species; however, it is absent in B. crassicephala.
iii) Distal outer spine on exopodal segment of the male right P5 is relatively long, and the distal outer spine is ca. 2.9 × as long as the proximal one; however, in B. crassicephala, the spine on exopodal segment of the male right P5 is relative shorter and the distal outer spine is ca. 1.9 × as long as the proximal one.
iv) The male left P5 Endp is relatively smaller in the new species than that of B. crassicephala.
The Thai Boholina can be easily distinguished from B. purgata, B. parapurgata, and B. ganghwaensis by the characteristics of the widely separated genital pores, relatively longer subapical spine vestige on the male right P5 when compared to the length of apical spine, the higher length ratio of the apical spine to the outer terminal spine in the female P5 Exp-3 and the elongated apical spine of the female P4 Exp (Table
Only six specimens were collected from a pool and the new species was not encountered in the other eight caves visited in this research project. Freshwater Cyclopoida belonging to the genera Thermocyclops, Metacyclops, and Mesocyclops, as well as harpacticoids of the genus Schizopera and of the family Ectosomatidae were also collected from the type locality.
1 | Female genital double-somite globular-shaped, as long as wide; male right P5 Endp unarmed, with large inner spinous process | B. munaensis Boxshall & Jaume, 2012 |
– | Female genital double-somite barrel-shaped, longer than wide; male right P5 Endp armed with 2 elements, without large inner spinous process | 2 |
2 | Female genital pores located ventrolaterally; postero-lateral corners of second and third pedigerous somites rounded in both sexes; male right P5 Exp with relatively large spine vestige; spine vestige longer than half length of apical spine | 3 |
– | Female genital pores located close together on either side of body midline; postero-lateral corners of second and third pedigerous somites pointed in both sexes; male right P5 Exp with relatively small spine vestige; spine vestige shorter than half length of apical spine | 4 |
3 | Apical spines on female P5 sub-equal in length; male right P5 Exp without inner spiniform seta; male left P5 Enp large, as long as right P5 Endp | B. crassicephala Fosshagen & Illife, 1989 |
– | Inner apical spines on female P5 ca. 1.6 × as long as outer one; male right P5 Exp with inner spiniform seta; male left P5 Enp small, much shorter than right P5 Endp | B. laorsriae sp. nov. |
4 | Apical spine on female P5 Exp-3 longer than outer terminal spine; gonoporal plate without small hook-like process | 5 |
– | Apical spine on female P5 Exp-3 slightly shorter than outer terminal spine (0.96 x); gonoporal plate with small hook-like process | B. ganghwaensis Moon & Ho, 2014 |
5 | Male right P5 Endp ca. 2.6 × as long as wide, bearing two slender spines; distal endopodal segment of female P5 Endp ca. 1.8 × as long as wide; outer terminal spine on female P5 Exp-3 shorter than segment bearing it | B. purgata Fosshagen & Illife, 1989 |
– | Male right P5 Endp ca. 3.6 × as long as wide, bearing two sigmoid spines; distal endopodal segment of female P5 Endp ca. 2.6 × as long as wide; outer terminal spine on female P5 Exp-3 longer than segment bearing it | B. parapurgata Boxshall & Jaume, 2012 |
Calanoid copepods are ubiquitous in marine, brackish, and fresh waters, comprising 44 families and approximately 330 genera (
The genus Boholina clearly shows affinities to the families Ridgewayiidae and Pseudocyclopidae, by the presence of several plesiomorphic characters in the antennule, antenna, mouthparts, and swimming legs. Nearly all species of Boholina were collected from anchialine caves: this habitat is different from a benthic environment in shallow water where the two families have frequently been found (
The geographical distribution of the new species is slightly different from those of all other species of Boholina, as it was collected from a freshwater pool within a cave located very far from the sea (ca. 6.5 km) compared with those of B. crassicephala and B. purgata (200 m), B. parapurgata and B. munaensis (700 m), and B. ganghwaensis (inter-tidal mudflat). The occurrence of the new species in a cave located so far from the coast is the same as that of Stygoridgewayia, which were collected from bores/wells located up to 450 km inland from the coast in the Cape Range Peninsula and Pilbara region, Western Australia (
Based on structure (i.e., degree of modification) of mouthparts, especially with respect to the mandible, maxilla, and maxilliped, feeding habits were suggested for several taxa of the families Epacteriscidae, Ridgewayiidae, and Pseudocyclopidae (e.g.,
Even if many calanoid taxa in the superfamily Pseudocyclopoidea Giesbrecht, 1893 were collected from anchialine caves, it is likely that there is no specific adaption/modification in relation to the cave habitat in this family. Such a morphological adaptation or modification generally corresponds to the zones of the water column in which the copepod lives. Based on the relative length of the antennule, we suggest that the genus Boholina is a hyperbenthic form, because it has relatively short antennules (not extending beyond prosome) as in most epacteriscids. In the genera Exumellina and Stargatia, which were collected in the water column of anchialine caves, the antennules extend beyond the prosome (Fosshagen and Iliffe, 1998, 2003). In our opinion, only the reductions of the eyes and outer seta on P1 Endp are adaptations of Boholina corresponding with life in caves, as
This research was supported by a grant from the Office of the Higher Education Commission, Thailand (2558A13562002) and was funded by the Government of Thailand’s Grants to Khon Kaen University (KKU) (Project code 561302). The authors gratefully thank Dr. Danielle Defaye, Dr. Anton Brancelj, and an anonymous reviewer for their useful comments on the manuscript.