[Mollusca • 2024] Cenonovaculina siamensis • Molecular phylogeny reveals Cenonovaculina gen. nov. (Adapedonta: Pharidae), A New freshwater razor clam Genus from Indochina

Cenonovaculina gen. nov. 
Cenonovaculina siamensis (Morlet, 1889), from Bang Pakong River, Prachin Buri, Thailand

in Jeratthitikul & Sutcharit, 2024. 

หอยเสียบน้ำจืดสยาม  ||  DOI: 10.1071/IS24024 

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photos: Kongkit Macharoenboon

Abstract  

The razor clam genus Novaculina is a secondary marine-derived freshwater taxa within the otherwise exclusively marine family Pharidae. Novaculina currently comprises four valid species that are distributed allopatrically across several drainages in Asia. We employed an integrated approach, combining morphology and molecular phylogenetic analyses to elucidate the taxonomic placement of members within this genus. The multi-locus phylogenetic trees based on cytochrome c oxidase subunit I (COI), 16S rRNA and 28S rRNA gene sequences demonstrate that Novaculina is polyphyletic. Specimens identified as N. siamensis form a distinct clade that is not sister group to other currently recognised congeners. Furthermore, morphological examination reveals distinct characteristics in ‘N. siamensis’, namely a fused, fringed siphon, in contrast to the separated, smooth siphons observed in other species. Based on these findings, we propose the establishment of a new genus, Cenonovaculina gen. nov., to accommodate ‘N. siamensis’. The new genus is distinguished from other genera in having a short shell, deep pallial sinus, elongate, oval to bean-shaped anterior adductor scar and long fused siphons surrounded by conical tentacles.

Keywords: freshwater razor clams, Indochina, marine-derived freshwater taxa, multi-locus phylogeny, new taxa, Pharidae, siphon anatomy, Thailand.

 

Ekgachai Jeratthitikul and Chirasak Sutcharit. 2024. Molecular phylogeny reveals Cenonovaculina gen. nov. (Adapedonta: Pharidae), A New freshwater razor clam Genus from Indochina. Invertebrate Systematics 38, IS24024. DOI: 10.1071/IS24024

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The taxonomic status of the freshwater razor clam Novaculina siamensis Morlet, 1889 is determined using molecular and morphological analyses. Phylogenetic analyses placed the species separately from other currently recognised Novaculina species. Additionally, N. siamensis also possesses distinct morphological characteristics including fused, fringed siphons instead of separated, smooth siphons, as found in the type species of Novaculina s.s. Therefore Cenonovaculina gen. nov. is proposed to accommodate ‘N. siamensis’. 

[Mollusca • 2023] Chamberlainia somsakpanhai • Discovery of A New Endangered Freshwater Mussel Species in the Genus Chamberlainia Simpson, 1900 (Bivalvia: Unionidae) from Mekong Basin

 

Chamberlainia somsakpanhai 

Kongim, Sutcharit & Jeratthitikul, 2023

Tropical Natural History. Supplement 7 

 tci-thaijo.org/index.php/TNH/

Abstract

Chamberlainia somsakpanhai sp. nov., the largest freshwater bivalve (Unionidae) in the Mekong Basin, is described using morphological characters and molecular analysis. The new species differs from its congeners by having an ovate shell outline and obtuse and distinct sub-biangulate posterior margin. A multi-locus phylogenetic tree (mitochondrial COI and 16S, and nuclear 28S genes) recognized the new species along with other two members of genus, namely C. hainesiana and C. duclerci. Average genetic divergence between the new species and its congeners is 13.8–14.1% by an uncorrected COI p-distance.

Keywords: conservation, endangered, pearl mussel, endemic, Thailand, Indochina

Holotype of Chamberlainia somsakpanhai sp. nov.

Chamberlainia somsakpanhai sp. nov.

 

Bangon Kongim, Chirasak Sutcharit and Ekgachai Jeratthitikul. 2023. Discovery of A New Endangered Freshwater Mussel Species in the Genus Chamberlainia Simpson, 1900 (Bivalvia: Unionidae) from Mekong Basin. Tropical Natural History. Supplement 7;242-250. 

 https://li01.tci-thaijo.org/index.php/TNH/article/view/257982

[Mollusca • 2021] Namkongnaia inkhavilayi & N. lemeslei • Molecular Phylogeny reveals A New Genus of Freshwater Mussels (Bivalvia: Unionidae) from the Mekong River Basin

Namkongnaia inkhavilayi gen. et sp. nov. 
Namkongnaia lemeslei (Morelet, 1875)

Jeratthitikul, Sutcharit, Ngor & Prasankok, 2021

DOI: 10.5852/ejt.2021.775.1553

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ABSTRACT

A new genus of freshwater mussels (Bivalvia: Unionidae) is described from the Mekong River Basin as Namkongnaia gen. nov. The validity of the new genus is supported by its unique conchological characteristics, namely the lack of hinge dentition and elongated shells, together with its evolutionary distinctiveness as estimated by multi-locus phylogenetic analyses (mitochondrial COI and 16S, and nuclear 28S genes). The new genus includes two lineages with deep divergence, shown by 5.10% uncorrected COI p-distance. One lineage is a type species described herein as Namkongnaia inkhavilayi gen. et sp. nov. The other is a recognized species under the name ‘Pilsbryoconcha lemeslei (Morelet, 1875)’. Molecular phylogenetic analysis further shows that the new genus belongs to the tribe Pseudodontini, and evolutionarily is closely related to the genus Monodontina Conrad, 1853. However, its conchology is similar to the genus Pilsbryoconcha Simpson, 1900. Time-calibrated phylogeny suggests that the main radiation events of the tribe Pseudodontini occurred during the Late Cretaceous to the Eocene, with the divergence between the new genus and Monodontina placed in the Miocene. The discovery of new freshwater mussel taxa in this study highlights the importance of the Mekong River Basin as one of the world’s biodiversity hotspots for freshwater fauna.

Keywords: Indochina, freshwater mussels, multi-locus phylogeny, new taxa, time-calibrated phylogeny

Family Unionidae Rafinesque, 1820

Subfamily Gonideinae Ortmann, 1916

Tribe Pseudodontini Frierson, 1927

Subtribe Pilsbryoconchina Bolotov et al., 2017

Genus Namkongnaia gen. nov.

Differential diagnosis: The new genus is distinguished from other genera in Pseudodontini by having a narrow, elongated, and less inflated shell. It is also represented as a distinct clade in multi-locus phylogenetic analyses.

Description: Shell Medium-sized, thin, narrow and elongated, rather compressed, very in equilateral; anteriorly round; posteriorly round or somewhat pointed; umbonal area not elevated and usually eroded. Ligament very narrow. Hinge without dentition, posterior end of the hinge structure with V-shaped fossette. Anterior adductor muscle scar shallow, ovate, and fused with pedal retractor muscle scars; posterior adductor muscle scar very shallow. Excurrent aperture smooth, shorter than incurrent; incurrent with 1-2 rows of conical papillae. Gills elongated and slightly ribbed; anterior margin of inner gills slightly longer and wider than outer gills.

Etymology: The generic name “Namkongnaia” is from the word “Namkong”, a name for the Mekong River used by Thai and Lao peoples, and Greek word “naiad” meaning freshwater mussels. The name of this genus thus means “freshwater mussels from Mekong River”.

Distribution: Mekong River and its tributaries in Laos, Cambodia, and Thailand (Fig. 3; Brandt 1974; Ng et al. 2020). The distribution range may include the Mae Klong River Basin in Thailand (Brandt 1974), although the taxonomic status of the specimens recorded in Brandt (1974) needs to be confirmed.

Map showing distribution localities of Namkongnaia gen. nov. Boundaries of river basins follow Abell et al. (2008).

Namkongnaia inkhavilayi gen. et sp. nov.

Pilsbryoconcha lemeslei – Brandt 1974: 263, pl. 18 fig. 22 (in part, only records from “Nang Rong (Prov. Burirum)”, Thailand) [non Anodonta lemeslei Morelet, 1875].

Etymology: This new species is dedicated to our colleague and distinguished malacologist, Dr Khamla Inkhavilay, from the National University of Laos

Namkongnaia lemeslei (Morelet, 1875) gen. et comb. nov.

Distribution: This species is restricted to Tonle Sap Lake and its tributaries in Cambodia. Its distribution probably reaches the headwater of Tonle Sap basin in eastern Thailand (Brandt 1974).

Habitat: This species was recorded in mud substrate in still sections of rivers or in lentic habitat, i.e., ponds and lakes (Morelet 1875; Morlet 1889; Brandt 1974).

Distribution: This new species appears to occur in the Lower Mekong watershed. In Laos, it was recorded from several locations near Vientiane, Kammoune, and Champasak Provinces. In Thailand, it is known from the Songkram and Mun river basins in the northeast region (Brandt 1974).

 

Ekgachai Jeratthitikul, Chirasak Sutcharit, Peng Bun Ngor and Pongpun Prasankok. 2021. Molecular Phylogeny reveals A New Genus of Freshwater Mussels from the Mekong River Basin (Bivalvia: Unionidae). European Journal of Taxonomy. 775(1), 119-142. DOI: 10.5852/ejt.2021.775.1553

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[Mollusca • 2020] Hemiplecta ligorica & H. thailandica • Reassessment and Systematic Position of the Sinistral Snails of Genus Hemiplecta from Thailand (Eupulmonata: Ariophantidae), with Description of Two New Species

  

Hemiplecta ligorica & H. thailandica

Sutcharit & Panha, 

in Sutcharit, Jeratthitikul, Tongkerd & Panha, 2021.

DOI: 10.1163/18759866-BJA10016 

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Abstract

Indochina land snails of the family Ariophantidae are in need of thorough systematic revision. Here we comprehensively revise the systematics of the large-shelled, sinistral (counterclockwise) coiling snails from Thailand and Peninsular Malaysia. Molecular phylogeny based on mitochondrial (coi and 16S) and nuclear (28S) gene sequences demonstrates that these sinistral snails are not members of Dyakiidae as previously thought, but instead are more closely related to the genus Hemiplecta in the family Ariophantidae. Comparative morphology also reveals similarity of reproductive organ features (globular gametolytic organ, well-developed dart apparatus, and lack of amatorial organ complex). Based on this evidence, we propose to transfer these sinistral snails to the genus Hemiplecta. Molecular phylogenetic analyses further strongly support the monophyly of this sinistral lineage with respect to other members of Hemiplecta. This monophyletic clade consists of five members including three species that were previously classified as “Dyakia”, H. lahatensis, H. retrorsa and H. salangana, and two new species described herein, Hemiplecta ligorica n. sp. and H. thailandica n. sp. This study also suggests that the anatomy of the gametolytic organ in the genus Hemiplecta corresponds well with the phylogenetic relationships and appears to be a taxonomically informative character, while the penial verge has little utility for generic recognition.

Keywords: Pulmonata; Dyakiidae; sinistral; endemic species; Indochina

Family Ariophantidae Godwin-Austen, 1888

Genus Hemiplecta Albers, 1850

1. Hemiplecta retrorsa (Gould, 1843)

2. Hemiplecta salangana (Martens, 1883)

3. Hemiplecta lahatensis (Morgan, 1885)

Shell characters.
A. Hemiplecta lahatensis, specimen cumz 5259/2.
B, C, Hemiplecta thailandica n. sp., (B) holotype cumz 5095/1 and (C) specimen cumz 5098 from Chanthaburi Province.
D, E. Hemiplecta ligorica n. sp., (D) holotype cumz 5093/1 and (E) paratype cumz 5087 from the type locality.

4. Hemiplecta thailandica Sutcharit and Panha, n. sp.

Etymology. The species name “thailandica” refers to the type locality of this new species in Chanthaburi Province, Thailand.

Diagnosis. Large and low conic shell with brown to brownish yellow shell color, rounded last whorl with narrow dark brown spiral band on periphery. Penial sculpture with small penial papillae arranged over nearly entire penis length.

 

5. Hemiplecta ligorica Sutcharit and Panha, n. sp.

Etymology. For the historical name of Nakhon Si Thammarat Province, where the type locality is situated.

Diagnosis. Small, sinistral helicoild shell with whitish color, rounded last whorl with dark brown to brownish spiral band on periphery and upper shell surface. Penial sculpture with small papillae arranged over about half of penis length.

Conclusion: 

Based on phylogenetic results and morphological information in the present study, we have transferred the sinistral species previously and incorrectly assigned to Dyakia (family Dyakiidae) to the genus Hemiplecta (family Ariophantidae). Two previously unrecognised species are described based on consistent differentiation in molecular, shell, and genitalia characters. Our data also provide further support for three other sinistral Hemiplecta species, which are also re-described herein. The results also suggest the synonymization of the formerly recognized as (sub)genus Koratia under the Hemiplecta. Finally, the results indicate the evolutionary instability of shell traits that are often used for land snail classification, while genital characters are highlighted as reliable taxonomic markers for delimiting species and at least some higher taxa. The integration of multiple independent characters including molecular evidence is crucial for delimiting higher systematic levels.

  Chirasak Sutcharit, Ekgachai Jeratthitikul, Piyoros Tongkerd and Somsak Panha. 2021. Reassessment and Systematic Position of the Sinistral Snails of Genus Hemiplecta from Thailand (Eupulmonata: Ariophantidae), with Description of Two New Species. Contributions to Zoology. 90(2); 183–215. 

DOI: 10.1163/18759866-BJA10016

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