Rhiostoma ebenozostera Tongkerd & Panha, 2023

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

11. Rhiostoma ebenozostera Tongkerd & Panha sp. nov.

Figs 18 , 29 , 32D

Type material.

Holotype CUMZ 4703 (cW 19.4 mm, cH 11.1 mm, dL 13.7 mm; Fig. 29A ). Paratypes CUMZ 3887 (228 shells), CUMZ 3889 (53 adults + 25 juveniles; Fig. 29C ), CUMZ 4704 (2 shells; Figs 29B , 32D ), CUMZ 4766 (99 adults + 24 juveniles), NHMUK 20220439 (5 shells), and SMF 368674 (5 shells). All paratypes are from the type locality.

Type locality.

Tham Pha Poo, Muang District, Loei Province, Thailand (17°34'45.1"N, 101°42'36.2"E). Dry dipterocarp forest on limestone hill.

Other material examined.

Thailand: Wat Tham Pha Ban, Chiangkan, Loei: CUMZ 4444. Phu Pha Lom, Muang, Loei: CUMZ 10013. Wat Tham Phu Pha Lom, Muang, Loei: CUMZ 4443. Tham Khuha Waree, Wang Sapung, Loei: CUMZ 3925, 3946. Tham Pha Fang, Wang Sapung, Loei: CUMZ 10155. Khao Wangpha, Na Wang, Nongboa Lumphu: CUMZ 3935. Tham Suwannakhuha, Na Wang, Nongboa Lumphu: CUMZ 4765 (Fig. 29E ). Wat Paphaya, Suwannakhuha, Nongboa Lumphu: CUMZ 10031. Wat Suwannakhuha, Ban Nasi, Suwannakhuha, Nongboa Lumphu: CUMZ 3889, 3933, 10021. Wat Phu Poon, Lomkao, Phetchabun: CUMZ 10211 (Fig. 29D ). Tham Poo Loup, Chum Phae, Khon Kaen: CUMZ 3931. Tham Nennoi, Chum Phae, Khon Kaen: CUMZ 10015. Tham Phayanakarat, Chum Phae, Khon Kaen: CUMZ 10025. Phu Wiang, Wiang Kao, Khon Kaen: CUMZ 10166/1, 10166/2 (Fig. 29F ) .

Diagnosis.

Shell medium, thick and depressed. Detached whorl medium in length, curved, and slightly descending. Breathing device tubular. Broad dark brown spiral band on periphery present.

Differential diagnosis.

Rhiostoma ebenozostera sp. nov. can be distinguished from all other recognised Rhiostoma species by having a prominent wide dark brown to black peripheral band. This colour pattern persists in all populations recognised for this species. Regardless of the peripheral band, this new species can be distinguished from R. housei in having straight and slender tubular breathing device, and relatively longer detached whorl. In contrast, R. housei has a stout and curved tubular breathing device and relatively shorter detached whorl.

Description.

Shell. Shell medium, cW 17.7-22.6 mm, cH 9.4-12.1 mm, thick, and sub-discoidal to discoidal shape; detached-whorl length 8.5-14.5 mm. Apex acute; spire nearly flat to elevated. Whorls 4 to 5, convex, increasing regularly; suture wide and shallow; last whorl rounded and stout. Detached whorl medium in length, approximately the same length as apertural width, curved and descending. Shell surface with fine growth lines. Periostracum thin, corneous, and transparent. Shell colour uniformly brownish or with pattern of dark brown blotches, and faded on ventral shell surface; dark spiral band on periphery always present and broad. Peristome circular and double; lip thickened, expanded and multi-layered. Aperture opened sub-ventrally. Breathing device tubular, perpendicular to detached whorl and its tip attached to preceding whorl; outer lip forming long and closed tube and located just behind apertural lip; inner lip with deep incision or small hole inside aperture. Umbilicus widely opened and deep. Operculum calcareous, cup-shaped, and multispiral (Fig. 29 ).

Radula. Teeth arrangement and shape are similar to those of R. housei . Central tooth with large central cup and two lateral cusps on each side. Lateral teeth composed of three cusps; central cusp large, with convex tip, and flanked by small pointed tips of one outer cusp and one inner cusp. Marginal teeth each consisting of three pointed cusps (Fig. 32D ).

Etymology.

The specific name ebenozostera is derived from the two Greek words ebenos meaning black colour, and zoste meaning girdle or belt. This name refers to the prominence of a dark, wide, peripheral band, which is the distinguishing character of this species.

Distribution.

This new species has narrow distribution; it is known from several limestone outcrops in dry deciduous forests of Loei, Nong Bua Lam Phu, and Khonkaen provinces (Fig. 18 ).

Remarks.

The specimens from Nong Bua Lam Phu possess a stout shell, slightly shorter detached whorl, and paler shell colour (Fig. 29E ) than the typical population. However, a prominent broad, dark, peripheral band suggests that they are conspecific.

Figures

Figure 18. Distribution map of Rhiostoma housei - species group.

Figure 29. Shell of Rhiostoma ebenozostera sp. nov. A holotype CUMZ 4703 from Tham Pha Poo, Loei B, C paratypes from type locality B paratype CUMZ 4704 and C paratype CUMZ 3889 D specimen CUMZ 10211 from Lom Kao, Phetchabun E specimen CUMZ 4765 from Suwannakhuha, Nongboa Lumphu F specimen CUMZ 10166 / 2 from Phu Wiang, Khon Kaen.

Figure 32. Radula morphology A Rhiostoma housei specimen CUMZ 3982 from Wat Tham Srivilai, Saraburi B Rhiostoma hainesi specimen from Chanthaburi C Rhiostoma jalorensis specimen CUMZ 3994 from Wat Tham Sua, Krabi D Rhiostoma ebenozostera sp. nov. paratype CUMZ 4704 from Tham Pha Poo, Loei E Rhiostoma lannaense sp. nov. paratype CUMZ 4701 from Chiang Dao, Chiang Mai F Rhiostoma tigrina sp. nov. paratype CUMZ 4497 / 2 from Mae Sai, Chiang Rai.