Microglyphis angulata

Helwerda, Renate A., 2015, Acteonidae, Bullinidae and Ringiculidae (Gastropoda: Heterobranchia) from the Plio-Pleistocene of the Philippines, Zootaxa 3990 (2), pp. 197-220 : 217

publication ID	https://doi.org/ 10.11646/zootaxa.3990.2.2
publication LSID	lsid:zoobank.org:pub:BDF1BC11-4848-4858-99DC-0336A5FBEE2B
DOI	https://doi.org/10.5281/zenodo.6116558
persistent identifier	https://treatment.plazi.org/id/03FA878C-9504-FE5E-FF26-E5E30106CF17
treatment provided by	Plazi
scientific name	Microglyphis angulata
status

Treatment

Microglyphis angulata View in CoL nov. spec.

( Figure 39–40 View FIGURE 34 – 40. 34 )

Type material. Holotype RGM 961.759 (Type locality), paratype RGM 961.833 (Tiep2)

Other material. Anda1 (2) RGM 961.839, Anda3 (6) RGM 961.840, Anda4 (8) RGM 961.841, Roxas (36) RGM 961. 842, Tiep2 (124) RGM 961.843, Tiep3 (46) RGM 961.814, Tiep4 (6) RGM 961.844, Tiep5 (107) RGM 961.845.

Type locality. Roxas.

Derivatio nominis. Angular, adjective. Named after the strong subsutural shoulder of the shell.

Diagnosis. Shell small, slightly turreted; H 2.15 mm, W 1.29 mm; protoconch simple, 1.3 whorl, DP 0.21–0.22 mm; nucleus small, DN 0.07–0.08 mm; teleoconch with shouldered subsutural ridge above broad groove; narrow grooves on rest of whorl; aperture narrow.

Description. Shell small for its genus, squarely shouldered. Largest specimen has a total of 5.2 whorls, including a protoconch of 1.3 whorl. Protoconch small, smooth, slightly inclined. Teleoconch sculpted with spiral grooves, which are very weak on the first teleoconch whorl, but become distinct after that. A rounded subsutural shoulder is present, becoming stronger along the whorls. It develops a light creamy brown colour, distinct from the rest of the shell, which is milky white. A very broad spiral groove is present below the subsutural shoulder. There are 13 more spiral grooves on the body whorl. Their interspaces become narrower towards the base. Weakly sigmoid growth lines are visible within spiral grooves. Whorls weakly convex to nearly straight-sided. Suture canaliculate. Body whorl shows a subtle change in coiling direction. Aperture not thickened. Parietal area and columella covered with a thin, translucent callus. Columella bears two smooth folds, with the upper one weaker than the lower one. Outer lip thin, slightly sigmoid. Anterior and posterior sinus rather shallow.

Differentiation. Eight species of Microglyphis are known to date. Four of them, M. curtula ( Dall, 1889) , M. brevicula ( Dall, 1902) , M. estuarina ( Dall, 1908) and M. mazatlantica ( Dall, 1908) , are from American coasts, M. perconica ( Dall, 1889) is from the Galapagos and two of them, M. globularis ( Smith, 1875) and M. japonica ( Habe, 1952) , are from Japan. These species are all Recent, whereas the last species, M. mirandus Lozouet, 1999 , is from the Oligocene of France. All of these species are much more rounded than M. angulata nov. spec. and also larger, 3 mm or more in height, except for M. mirandus Lozouet, 1999 , which is approximately the same size. None of them have a strong shoulder as in M. angulata nov. spec.. Its shape is unusual for a Microglyphis , but the lack of a thickened outer lip in “adults”, combined with the observations that all of the numerous larger “adult” specimens show their determinate growth characters with a subtle change in coiling direction and reach exactly the same size, places this species in genus Microglyphis .