Cyclotus Swainson, 1840

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 Cyclotus Swainson, 1840

Cyclostoma (Cyclotus) Swainson, 1840: 186, 336.

Cyclotus - Kobelt 1902: 188, 189. Kobelt 1911: 773, 793. Egorov 2009: 26.

Type species.

Cyclotus variegatus Swainson, 1840 by subsequent designation by Pfeiffer (1852: 16).

Diagnosis.

Shell small to large, low conical to flattened. Shell colour uniformly brownish or with irregular brownish stripes; periostracum thin or thick corneous. Terminal part of last whorl usually attached to penultimate whorl, and rarely with short separation. Peristome circular and double or multi-layered; lip thick or thin and expanded and reflexed. Breathing device sometimes absent; if present at upper junction of peristome with wing-like projections, canal or completely tubular structure located in suture behind apertural lip. Umbilicus wide. Operculum calcareous, somewhat flattened, or plate-shaped, lateral fringe deeply grooved, slightly concave externally, anticlockwise multispiral, nucleus central.

Remarks.

This is one of the most speciose genera among the tribe Cyclotini . The authenticated specimen of the type species (Fig. 5 , said to be “Type” ex. Cuming coll. from Palawan) is figured herein for detailed comparison. Traditionally, the genus was divided into six subgenera but has been subject to revision since Kobelt (1902, 1911). The genus comprises more than 100 nominal species ( MolluscaBase 2022), which have wide distribution ranging from southern China to Japan, Southeast Asia, and New Guinea ( Kobelt 1902). Since the last compilation in Kobelt (1902, 1911-1914), no comprehensive revision has been carried out, only the descriptions of new species. Therefore, systematic research based on morphology and molecular data from its range is essential and urgent to reveal its systematics.

Figures

Figure 5. Comparison of breathing device and operculum characteristics among the five genera that closely resemble Rhiostoma. The specimens and opercula represented herein are the type specimen or topotype of the respective type species of each genus; Pterocyclos: P. rupestris Benson, 1832 (lectotype UMZC I. 102070, no locality data), Spiraculum: S. hispidum Pearson, 1833 (specimen NHMUK 1906.4.4.72, from Khasi, Teria Ghat), Rhiostoma: R. haughtoni Benson, 1860 (syntype UMZC I. 103445, from Moulmein), Cyclotus: C. variegatus Pearson, 1833 (specimen NHMUK 1896.6.7.34 - 35, from Palawan), Opisthoporus: Cyclostoma taylorianum Pfeiffer, 1851 = junior synonym of Pterocyclos biciliatum Mousson, 1849 (specimen NHMUK 20210200 for shell, from Basan, Sarawak) and Pterocyclos tener Menke, 1856 (NHMUK ex. Cuming collection for operculum, from Cochin China), and Ptychopoma: Cyclophorus chinensis Moellendorff, 1875 (lectotype SMF 39415, from Lushan bei Kiukiang, China). Red arrows indicate the expansion of outer lip at upper junction of the peristome. Blue arrows indicate breathing tubes (apertural tube in Rhiostoma and sutural tubes in Spiraculum and Opisthoporus).