Sassenfjordia sassenfjordensis, Nakrem, 2017

Nakrem, Hans Arne, 2017, Gastropods from the Late Jurassic - Early Cretaceous seep deposits in Spitsbergen, Svalbard, Zootaxa 4329 (4), pp. 351-374 : 362

Sassenfjordia sassenfjordensis sp. nov.

( Fig. 7 )

2015 Gastropoda gen. et sp. indet. B; Hryniewicz et al. 2015a, table 1.

Diagnosis. Large multispiral protoconch ornamented with spiral bands. Naticiform teleoconch with stongly prosocline growth lines and deeply incised suture.

Holotype: PMO 217.512, H = 1.6 mm, W = 2.1 mm; one specimen only.

Type locality and age: Seep # 9 in Sassenfjorden area, Svalbard; late Berriasian, Early Cretaceous.

Description. Protoconch only partially preserved but large (1.1 mm in diameter) and ornamented by strong spiral bands. Demarcation between protoconch and teleoconch poorly preserved but seemingly expressed by a change in coiling geometry. Teleoconch naticiform with incised suture and strongly convex whorls. Shell flanks smooth apart from well expressed and strongly prosocline growth lines. Aperture and umbilical region not preserved.

Remarks. In spite of having only a single and imperfectly preserved specimen, we decided to describe a new genus and species, warranted by the unique set of characters, including a naticiform shell with strong, prosocline growth lines and a large protoconch ornamented by spiral bands. The most similar teleoconchs are observed in members of the Gyrodidae Wenz, 1938 , which are considered either as ampullospirids (Campaniloidea) by Kase & Ishikawa (2003) or naticoids by Bandel (1999) and Bandel & Dockery (2016). However, gyrodids posses entirely smooth protoconchs ( Dockery 1993; Bandel 1999). The only group having comparable large protoconch with spiral ornament we could trace is the naticoid subfamily Sininae . The protoconch of the Recent Sinum perspectivum ( Say, 1831) , illustrated by Bandel (1999), is large (1.5 mm of diameter) and strongly ornamented by spiral ribs. However, in contrast to S. sassenfjordensis the teloconch of Sinum also possesses a strong spiral ornament. Our identification of S. sassenfjordensis as Naticidae : Sininae remains, however, tentative, as according to Kase & Ishikawa (2003) the oldest confirmed Naticidae come from the Campanian (Late Cretaceous). A Berriasian (Early Cretaceous) age would be a large backward extension to the fossil record (approx. 60 myr) of this taxon.

Distribution. Type locality only.

Etymology. After its type area in Svalbard.

Figures

FIGURE 7. Sassenfjordia sassenfjordensis sp. nov., holotype (PMO 217.512), Seep deposit # 9, Sassenfjorden, Svalbard; late Berriasian (Early Cretaceous).