Corresponding author: Koraon Wongkamhaeng (
Academic editor: Tin-Yam Chan
Thermosbaenaceans are subterranean crustaceans, widespread and occur in freshwater, oligohaline or anchialine caves or thermal springs. Currently, four families, seven genera,and 45 species are recognised worldwide. During our studies of the isolated karst, Tham Loko (Loko Cave) in Khao Chiason District, Phatthalung Province, we found an undescribed thermosbanacean species in the genus
Thermosbaenaceans are generally recognised by their small size (< 5 mm), roughly cylindrical body, short carapace, biramous pereopods, blindness, lack of pigment and the female broods her eggs (
In the Oriental Region, only
Here, we present a third species of the genus
Specimens were discovered in the dark zone of an isolated limestone of Tham Loko (Loko Cave), Khao Chiason District, Phatthalung Province (Fig.
Abbreviations used in the description are:
A- antenna; GN- gnathopod; MX- maxilla; MP- maxilliped, P- pereopod; PL- pleopod; T- telson and UR- uropod
NHM-PSU = Princess Maha Chakri Sirindhorn Natural History Museum, Prince of Songkla University, Songkhla, Thailand.
Antenna 1 (Fig.
The new species was found swimming and walking on the clay substrate of the pool in the dark zone of the Cave. The physical factors in the pool were as follows: Temperature (25.1–25.70C); conductivity (217–282 µS); total dissolved solids (146–182 ppm); salinity (108–137 ppm); dissolved oxygen (6.0–8.2 mgO2/l); pH (7.98–8.22); turbidity (8–12 FAU); water hardness (99–150 mg/l CaCO3); and CaCO3 (70.20–85.40 mg/l). The new species co-occurs with stygobiotic isopod
The researchers herein propose
1 | Uropod endopod with elongate plumose macrosetae shorter than exopod, lateral edge margined with small spiniform macrosetae and two filiform plumose setae at mid-length |
|
– | Uropod endopod with elongate plumose macrosetae subequal to exopod, lateral edge is margined with a row of scaliform macrosetae |
|
2 | Telson entire |
|
– | Telson apically emarginate |
|
This work is supported by the Thailand Research Fund (TRG5880189) and the Biodiversity-Based Economy Development Office (Public Organization) for Sopark Jantarit. We would like to thank Phannee Sa-ardrit for the water quality measurement. We thank all the PSU-speleological team for assistance in the field. Thanks also to the local authority, Khao Chaison Subdistrict Administration Organization, for permitting us to collect the specimens in the areas.
Distribution of
Diagnostic morphological characters of known
|
|
|
|
Flagellum on antenna 1 | 29 | 25 | 19 |
Accessory flagellum | 14 | 13 | 10 |
Ocular scales | evenly arcuate and rounded | more transverse, with the widest point being just medial to the centre-line of the structure. | evenly arcuate and rounded |
|
|||
Palp segment | 1:2:1 | 1:2:3 | 1:2:1 |
Setae | 8 plumidenticulate macrosetae | 6 microsetae | 6 plumose macrosetae |
Corpus mandibula | L- 6 dentate, R-4 dentate | N/A | L- 6 dentate, R-5 dentate |
subequal | twice | four times | |
Maxillopodal exopod | 1.5 times its basal width | greatly reduced, as long as width and the point of articulation is not clear; fused | twice as long as basal width |
|
|||
shape | subrectangular | subtriangular, widest apically | subrectangular |
membranous macrosetae | present (3) | absent | present (3) |
dorsoapical ungual spine | absent | present | present |
ventroapical setal tuft | absent | present | present |
distal margin | widened and somewhat flattened | convex | convex |
distomedial angle | N/A | a row of short setae | inerm |
unguis | three arced (modified) serrulate macrosetae (type IIB1) with a prominent membrane ventrally. | single curved spine at the distolateral corner. | three curved spines at the distolateral corner. |
|
|||
coxa | not pronounced | pronounced | not pronounced |
Exopod: endopod | N/A | 0.8 | 0.8 |
Basal segment | N/A | rectangular, with a spine at distolateral corner | suboval, inerm. |
Penial lobe | subcylindrical and slightly bent | straight and fusiform | simple, naked, tall, almost straight |
|
present | absent | absent |
|
|||
Endopod | Oval, distal segment bearing elongate plumose macrosetae subequal to endopod, lateral edge is |
Oval, distal segment bearing elongate plumose macrosetae shorter than exopod, lateral edge margined with small spiniform macrosetae and two filiform plumose setae at mid-length. | Suboval, distal segment bearing elongate plumose macrosetae subequal to exopod, lateral edge is |
Exdopod | Distal segment subovate, lateral margin with elongate plumose macrosetae, medial edge without spines; segment apex with single elongate spine 0.8x the length of the segment. | Distal segment subovate, lateral margin with elongate, plumose macrosetae; medial edge margined with spines; segment apex with single elongate spine 0.8x length of |
Distal segment subovate, lateral margin with elongate, plumose macrosetae; medial edge margined with stout |
|
entire | emarginate | emarginate |
Telson length/width ratio | 0.8 | 1.2 | 1.8 |
Telson apex | apical region margined with macrosetae, apex entire. | apex lobes have curved, rigid spines that arc medially towards the medial cleft | apex lobes have curved, rigid spines that arc medially towards the medial cleft |