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| Pilsbryoconcha mekongiana Jeratthitikul & Prasankok, P. hoikaab Jeratthitikul & Prasankok, P. acuta Jeratthitikul & Prasankok, & P. kittitati Jeratthitikul & Prasankok in Jeratthitikul, Paphatmethin, Sutcharit, Ngor, Inkhavilay & Prasankok, 2022 |
Abstract
The body of knowledge regarding the classification and evolution of freshwater mussels in the family Unionidae (Bivalvia) in Indochina has recently increased. However, the taxonomic revision of all extant taxa in the region is still ongoing. In this study, the genus Pilsbryoconcha was revised based on an integrative analysis of shell morphology, biogeography, and molecular data. Multi-locus phylogeny indicated the availability of eight species within the genus. Four previously recognized species are P. exilis (Lea, 1838), P. schomburgki (Martens, 1860) stat. rev., P. linguaeformis (Morelet, 1875), and P. carinifera (Conrad, 1837), while four other species are described herein as P. acuta sp. nov., P. mekongiana sp. nov., P. kittitati sp. nov., and P. hoikaab sp. nov. In addition, the neotype of P. carinifera is also designated to clarify its long taxonomic ambiguity. Divergent time estimation and historical biogeography analysis revealed that Pilsbryoconcha originated in the area now called the Khorat Plateau around the middle of the Eocene (mean age = 43.12 Mya), before its range was expanded across Indochina through a series of complex geomorphological changes of river systems, which also led to diversification of the genus.
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| Shells of Pilsbryoconcha species. (a,b) P. exilis, (a) syntype USNM 86726, Java, (b) specimen MUMNH-UNI2792, Sa Kaeo, Thailand; (c,d) P. schomburgki, (c) holotype NHMUK 1859.5.23.8, Siam, (d) specimen MUMNH-UNI 2810, Nakhon Ratchasima, Thailand; (e,f) P. carinifera, (e) specimen ANSP 56519, ‘India’, (f) neotype MUMNH-UNI2823, Sa Kaeo, Thailand; (g,h) P. linguaeformis, (g) holotype NHMUK 1893.2.4.614, Battambang, Cambodia, (h) specimen MUMNH-UNI2636, Pursat, Cambodia; (i) P. mekongiana sp. nov. holotype MUMNH-UNI0843, Bueng Kan Thailand; (j) P. hoikaab sp. nov. holotype MUMNH-UNI0305, Nakhon Phanom, Thailand; (k) P. acuta sp. nov. holotype MUMNH-UNI1510, Ubon Ratchathani, Thailand; (l) P. kittitati sp. nov. holotype MUMNH-UNI0372, Udon Thani, Thailand. Scale bar = 10 mm. Image: USNM collection database [a], D. Graf and K Cummings, https://mussel-project.uwsp.edu [c]; P. Callomon [e], and NHMUK collection database under a CC0 1.0 license [g]. |
Pilsbryoconcha schomburgki (Martens, 1860)
Type locality: Siam [Thailand].
Anodonta (Lamproscapha) schomburgki Martens, 1860: 1522.
Pilsbryoconcha carinifera (Conrad, 1837)
Pilsbryoconcha linguaeformis (Morelet, 1875)
Type locality: Cambodje [Cambodia].
Anodonta linguaeformis Morelet, 1875: 329, pl. 14, Fig. 523.
Pilsbryoconcha expressa (Martens, 1900)
Type locality: See Danau-Baru, Indragiri, Sumatra.
Anodonta expressa Martens, 1900: 12–1347.
Pilsbryoconcha mekongiana Jeratthitikul & Prasankok sp. nov.
Type materials: Holotype: MUMNH-UNI0843 (length 106.2 mm, height 52.5 mm, width 18.8 mm); THAILAND: Tributary of Mekong River at Khok Kong Mueang District, Bueng Kan Province; 18°20′17.4"N, 103°45′44.7"E. Paratypes: 4 shells, MUMNH-UNI0840, UNI0841, UNI0842 and UNI0844; THAILAND: same collection data as for holotype.
Etymology: The specific name is from its type locality, the Mekong River.
Diagnosis: The new species is most similar to P. hoikaab sp. nov. but can be distinguished by having a longer shell, and a more rounded posterior end. It also bears a set of unique fixed nucleotide substitutions in COI gene fragment (Table 2).
Distribution: Tributaries of Mekong River in Sakon Nakhon Basin, Thailand (Fig. 4).
Pilsbryoconcha hoikaab Jeratthitikul & Prasankok sp. nov.
Type materials: Holotype: MUMNH-UNI0305 (length 92.3 mm, 47.3 height mm, width 15.3 mm); THAILAND: Kam River at Na Khu, Na Kae District, Nakhon Phanom Province; 16°57′29.2"N, 104°30′16.3"E. Paratype: 1 shell, MUMNH-UNI0306; THAILAND: same collection data as for holotype.
Etymology: The specific name ‘hoikaab - หอยกาบ’ means ‘unionids or freshwater mussels’ in the Thai language.
Diagnosis: This species resembles P. mekongiana sp. nov., but it can be distinguished by its shorter shell and more truncated posterior margin with a somewhat pointed posterior end. It can also be distinguished from the congeners by fixed nucleotide substitutions in the COI gene fragment (Table 2).
Distribution: Songkhram River and tributaries of the middle Mekong River in Thailand and Laos (Fig. 4).
Pilsbryoconcha acuta Jeratthitikul & Prasankok sp. nov.
Type materials: Holotype: MUMNH-UNI1510 (length 83.6 mm, height 39.1 mm, width 16.1 mm); THAILAND: Dom Yai River at Pho Sai, Phibun Mangsahan District, Ubon Ratchathani Province; 15°13′51.9"N, 105°09′25.4"E. Paratype: 1 shell, MUMNH-UNI1509; THAILAND: same collection data as for holotype.
Etymology: The specific name ‘acuta’ is from the Latin word meaning ‘sharp or pointed’, which refers to the pointed posterior end, the diagnostic character of this new species.
Diagnosis: Shell elongated, pointed posterior end and yellowish periostracum. It can also be distinguished from the others by fixed nucleotide substitutions in the COI gene fragment (Table 2).
Distribution: Mun River in Thailand, tributaries of Mekong River in southern Laos (Fig. 4), and probably Vietnam7.
Remarks: Specimens from Vietnam identified as ‘Pilsbryoconcha lemeslei’ in Bolotov et al. (2020) are phylogenetically placed in this new species.
Pilsbryoconcha kittitati Jeratthitikul & Prasankok sp. nov.
Type materials: Holotype: MUMNH-UNI0372 (length 90.7 mm, height 40.4 mm, width 21.3 mm); THAILAND: Unnamed pond near Nong Ya Sai, Wang Sam Mo District, Udon Thani Province; 16°58′47.4"N, 103°20′13.4"E. Paratype: 1 shell, MUMNH-UNI0374; THAILAND: same collection data as for holotype.
Etymology: This species name is dedicated to our colleague, Mr. Kittitat Wisittikoson, who collected these specimens.
Diagnosis: More elongated shell outline, more laterally inflated, and dorsal margin almost parallel with ventral margin. It is also unique in its fixed nucleotide substitutions in the COI gene fragment (Table 2).
Distribution: Known only from the type locality.
Ekgachai Jeratthitikul, Siwanon Paphatmethin, Chirasak Sutcharit, Peng Bun Ngor, Khamla Inkhavilay and Pongpun Prasankok. 2022. Phylogeny and Biogeography of Indochinese Freshwater Mussels in the Genus Pilsbryoconcha Simpson, 1900 (Bivalvia: Unionidae) with Descriptions of Four New Species. Scientific Reports. 12: 20458. DOI: 10.1038/s41598-022-24844-9
เปเปอร์หอบกาบชนิดใหม่ของปีนี้ เป็นความร่วมมือจากนักวิจัยจากหลายสถาบันและหลายประเทศ Streptaxis LA Unidentata Siwanon Paphatmethin ศึกษาหอยกาบสกุล Pilsbryoconcha (ชื่อสกุล แปลว่า เปลือกหอยของ Pilsbry- มากจาก ชื่อคน Henry Augustus Pilsbry นักสังขวิทยาชาวอเมริกา +concha แปลว่า shell หรือ เปลือกหอย) หอยกาบสกุลนี้พบได้ทั่วไปในเกือบทุกแหล่งน้ำ ทั้งแม่น้ำ หรือบ่อน้ำที่มนุษย์ขุดขึ้นมา การจำแนกด้วยสัณฐานของเปลือกแบ่งออกเป็น 4 ชนิด แต่จากการใช้ DNA มาช่วยจัดจำแนก พบทั้งหมด 8 ชนิด ในภูมิภาคอินโดจีน ในจำนวนนี้ เป็นชนิดใหม่ 4 ชนิด ดังนี้ 1. P. mekongiana พบตามลำน้ำที่เชื่อมกับแม่น้ำโขงตอนกลาง 2. P. hoikaab พบในลุ่มแม่น้ำสงคราม 3. P. acuta (acuta แปลว่า แหลม หรือ ยื่น ตั้งตามลักษณะของส่วนปลายเปลือกที่ยื่นออกแหลม) พบทั่วไปในลุ่มน้ำมูล น้ำชี และ 4. P. kittitati (ตั้งชื่อเพื่อเป็นเกียรติแก่คุณ กิตติทัต Kittitat Wisittikoson ผุู้เก็บตัวอย่างหอยชนิดนี้) พบเพียงที่เดียวบริเวณต้นน้ำของแม่น้ำปาว นอกจากนี้ยังยุบชนิด P. compressa ไปอยู่ใต้ชนิด P. exilis และตั้ง Neotype ของ P. carinifera อีกด้วย งานศึกษานี้พิมพ์ในวารสาร Scientific Report.
