Thelyssina

Helwerda, Renate Ariane, Wesselingh, Frank Pieter & Williams, Suzanne T., 2014, On some Vetigastropoda (Mollusca, Gastropoda) from the Plio-Pleistocene of the Philippines with descriptions of three new species, Zootaxa 3755 (2), pp. 101-135 : 114

Thelyssina ? spec. 1

( Figures 20–22 )

Material. Anda 2 (5); AndaDeVos (2).

Characterization. Shell minute, H 0.8 mm, W 0.7 mm; P 1.1 whorls, with fine anastomosing sculpture, DN 0.08 mm; P/T boundary rounded varix; second varix at 1.6 whorls; T whorls with a sharp keel; microsculpture granulate; body whorl with two sharp spiral ribs; aperture rounded; umbilicus narrow; umbilical ridge weak.

Remarks. This seguenzioid skeneimorph species is provisionally placed in Thelyssina , based on the presence of dendritic teleoconch sculpture and a keeled shoulder. At the highest magnifications available, we observed very brilliantly shiny shell material at the inner side of the outer lip that we interpret as nacre. The small protoconch is also similar to the protoconch of the type species for the genus, T. sterrha Marshall, 1983 , in the anastomosing sculpture and characteristic shape. However, this assignment is uncertain, because the fossil species is relatively tall and more strongly granulate and keeled. Thelyssina ? spec. 1 also resembles Conotalopia minima ( Golikov, 1967) , a Recent trochid species from Japan, in general shape, but it has a smaller protoconch relative to the first teleoconch whorl, a dendritic granulate sculpture on the teleoconch and a narrower umbilicus.

Figures

FIGURES 18 – 25. Seguenziidae. 18. Calliobasis lapulapui Poppe, Tagaro & Dekker, 2006. RGM 608.251. Locality Anda 1. (a) rear view, (b) apertural view, (c) side view, (d) basal view, (e) apical view. 19. Calliobasis lapulapui Poppe, Tagaro & Dekker, 2006. RGM 608.252. Locality Anda 3. (a) SEM, side view, (b) SEM detail of protoconch. 20. Thelyssina? spec. 1. RGM 608.263. Locality Anda 2. (a) rear view, (b) apertural view, (c) basal view, (d) apical view. 21. Thelyssina? spec. 1. RGM 608.264. Locality Anda 2. (a) SEM detail of protoconch, (b) SEM, side view. 22. Thelyssina? spec. 1. RGM 608.265. Locality Anda 2. SEM, basal view. 23. Thelyssina? spec. 2. RGM 608.268. Locality AndaDeVos. (a) rear view, (b) apertural view, (c) basal view, (d) apical view. 24. Thelyssina? spec. 2. RGM 608.269. Locality AndaDeVos. SEM detail of protoconch. 25. Thelyssina? spec. 2. RGM 608.270 Locality AndaDeVos. SEM, basal view.