Opisthoporus Benson in Pfeiffer, 1851

Tongkerd, Piyoros, Tumpeesuwan, Sakboworn, Inkhavilay, Khamla, Prasankok, Pongpun, Jeratthitikul, Ekgachai, Panha, Somsak & Sutcharit, Chirasak, 2023, Systematic revision of the snorkel snail genus Rhiostoma Benson, 1860 (Gastropoda, Caenogastropoda, Cyclophoridae) with descriptions of new species, ZooKeys 1142, pp. 1-144 : 1

Genus Opisthoporus Benson in Pfeiffer, 1851

Cyclostoma sect. Opisthoporus Benson in Pfeiffer, 1851: 8.

Cyclotus (Opisthoporus) - Kobelt 1902: 213. Kobelt 1912: 834, 835. Egorov 2009: 26, 27.

Opisthoporus - Low and Tan 2017: 15, 16. Do et al. 2020a: 104.

Type species.

Cyclostoma taylorianum Pfeiffer, 1851. Type species by subsequent designation by Kobelt (1912: 834).

Diagnosis.

Shell small to medium, discoidal, spire varies from conical to nearly flattened. Shell colour uniformly yellowish to with brownish stripes; periostracum thin or thickened and hairy. Terminal part of last whorl attached to penultimate whorl or separated with short to long detached whorl. Peristome circular and double or sometimes with boundary inconspicuous; lip thick or thin and slightly to greatly expanded. Breathing device with tubular shape and located behind apertural lip; outer peristome slightly to broadly expanded; inner peristome inconspicuous or with a shallow incision. Umbilicus widely opened. Operculum calcareous, usually concave on both sides or plate-shaped, multispiral, and lateral fringe grooved.

Remarks.

This genus was nominated based on Cyclostoma taylorianum Pfeiffer, 1851 (which is a synonym of Opisthoporus biciliatus (Mousson, 1849)) as the type species. Recently, Do et al. (2020a) took Opisthoporus out of synonymy and raised it to full generic rank, provided quite comprehensive and clear diagnostic characters, and added new species to the genus, the first since Kobelt (1912). Nevertheless, the reliability and relationship of the Opisthoporus based on their conchology has not been thoroughly confirmed by other evidence, especially molecular analyses. Further research will undoubtedly be needed to clarify these systematic positions and affinities with other genera.