Saturday, March 31, 2018

[Gastropoda • 2018] Aenigmatoconcha sumonthai • A New Helicarionid Land Snail (Helicarionidae: Durgellinae) from Chumphon Province, Southern Thailand

 Aenigmatoconcha sumonthai
C. Tumpeesuwan & S. Tumpeesuwan, 2018


 Aenigmatoconcha sumonthai, new species, is described from Tham Chang Phueak, a limestone range in Chumphon province, southern Thailand. The external morphology of the shell and soft parts, the genital system, and radula morphology were examined and compared with the type species of the genus, A. clivicola C. Tumpeesuwan & S. Tumpeesuwan, 2017 from northeastern Thailand. Externally the new species differs from A. clivicola in having a smaller shell, presence of black bands from the base of the long tentacles to the mantle edge, and both mantle shell lobes have numerous tiny white spots and irregular black marbling. The radula comprises approximately 22–35 transverse v-shaped rows of teeth, with each row having 11–150 unicuspid spatulated teeth. In the genital system, the penis is longer than the epiphallus and the base of the gametolytic sac is longer than the middle part. 

Key words. Aenigmatoconcha, mantle shell lobes, radula, karst, endemic taxa, disjunct distribution 

Fig. 2. Aenigmatoconcha sumonthai, new species, in natural habitat at the type locality; photographs taken on June 2017. A, two snails with the dorsal shell surface complately covered by the mantle shell lobes; B, two snails with mantle shell lobes retracted. (Photograph courtesy of Mr. Montri Sumontha).

Superfamily Helicarionoidea Bourguignat, 1877
Family Helicarionidae Bourguignat, 1877
Subfamily Durgellinae Godwin-Austen, 1888
Tribe Durgellini Godwin-Austen, 1888

Genus Aenigmatoconcha C. Tumpeesuwan & S. Tumpeesuwan, 2017
Type species. Aenigmatoconcha clivicola C. Tumpeesuwan & S. Tumpeesuwan, 2017

Aenigmatoconcha sumonthai, new species

Etymology. The species is named after the collector Montri Sumontha; the specific epithet “sumonthai” is from the family name “Sumontha”.

Diagnosis. The characters distinguishing Aenigmatoconcha sumonthai, new species, from A. clivicola are the colour patterns on mantle shell lobes and body, as well as morphology of radula and genital organs. Mantle shell lobes bear irregular black marbling pattern and numerous tiny white spots (Fig. 2A). Two black bands, each running from the base of a long tentacle (eyestalk) to mantle edge, are present (Fig. 2A). Central teeth of radula have a globose unicuspid cusp, with their size smaller than the 1st lateral teeth and only the distal halves of the globose cusps emerge from the 1st lateral teeth (Fig. 4C). The epiphallus is shorter than penis, and the middle part of the gametolytic sac in the new species is shorter than in A. clivicola (Fig. 5).

Chanidaporn Tumpeesuwan and Sakboworn Tumpeesuwan. 2018. Aenigmatoconcha sumonthai, A New Helicarionid Land Snail from Chumphon Province, Southern Thailand (Helicarionidae: Durgellinae). RAFFLES BULLETIN OF ZOOLOGY. 66; 170–176. 

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