Serradonta omagariensis, Kaim & Jenkins & Hikida, 2009

Kaim, Andrzej, Jenkins, Robert G. & Hikida, Yoshinori, 2009, Gastropods from Late Cretaceous Omagari and Yasukawa hydrocarbon seep deposits in the Nakagawa area, Hokkaido, Japan, Acta Palaeontologica Polonica 54 (3), pp. 463-490 : 469-470

publication ID	https://doi.org/ 10.4202/app.2009.0042
persistent identifier	https://treatment.plazi.org/id/03FBF625-FFD5-2138-7EBD-90A3FD0A2537
treatment provided by	Felipe
scientific name	Serradonta omagariensis
status	sp. nov.

Treatment

Serradonta omagariensis sp. nov.

Fig. 3 View Fig .

2003 Serradonta cf. vestimentifericola Okutani, Tsuchida, and Fujikura, 1992 View in CoL ; Hikida et al. 2003: 338, fig. 10: 4, 5.

2007 Serradonta cf. vestimentifericola Okutani, Tsuchida, and Fujikura, 1992 View in CoL ; Jenkins et al. 2007a: 371, fig. 2A.

2007 Serradonta sp. ; Jenkins et al. 2007b: 134, fig. 5.1.

Etymology: After the type locality.

Holotype: UMUT MM29351 View Materials ( Fig. 3A View Fig ), almost complete shell lacking protoconch.

Type locality: Omagari site, Nakagawa area , Northern Hokkaido, Japan. Coordinates 44 ° 39’ 26’’ N, 144 ° 2’ 25’’ E GoogleMaps .

Type horizon: Fossil hydrocarbon seep deposits of Omagari Formation, Campanian, Upper Cretaceous.

Material.— 431 moderately to well preserved specimens from Omagari. 371 specimens at UMUT and 60 at NMM. Seven specimens from Yasukawa (all housed at UMUT). The specimen illustrated by Jenkins et al. (2007a) on fig. 2A was mislabeled as collected from Yasukawa; actually the specimen UMUT MM29351 View Materials (designated here as holotype) came from Omagari ( Fig. 3A View Fig herein) .

Dimensions.—The average shell length is 4.0 mm ± Ơ 0.63, shell width 1.8 mm ± Ơ 0.25, and shell height 2.3 mm ± Ơ 0.50 in the material of 41 specimens measured from Omagari site.

Diagnosis.— Serradonta − type shells with strongly compressed shell and uneven aperture with neither concentric nor radial ornamentation on any portion of the shell. S. vestimentifericola Okutani, Tsuchida, and Fujikura, 1992 is ornamented throughout the ontogeny and S. kanesunosensis Sasaki, Okutani, and Fujikura, 2003 is ornamented only on the juvenile shell. Serradonta omagariensis is usually higher than wide while the Recent species are wider than high.

Description.—The shell is patelliform with elliptical aperture. The shell width ranges 34–64% (average 46 ± Ơ 5.7, n = 41) of shell length. The apex is situated slightly subcentral anteriorly (at 36–50% of shell length, average 44 ± Ơ 4.5). There is no ornamentation apart from concentric growth lines. The protoconch and inner surface of teleoconch are unknown. The microstructure is obliterated by diagenesis in the examined specimens but it seems to be composed of at least one inner (possibly cross lamellar) layer and two (possibly prismatic) outer layers ( Fig. 3D 3 View Fig , D 4 View Fig ).

Discussion.—The shell shape of Serradonta is heavily influenced by its way of life on the worm tubes. It seems that the shell shape variation depends on the shape and size of the tubes. A preliminary survey of 41 specimens from the Omagari site shows a rather wide range of shell dimensions. In spite of that the shells of S. omagariensis differs from other species of the genus in being higher than wide. Moreover, all specimens are of small size similarly to S. kanesunosensis (that is, however, slightly wider than S. omagariensis ) while S. vestimentifericola achieves a much larger size (Okutani et al. 1992). The size, however, may be determined by the smaller size of the worm tubes for S. omagariensis and S. kanesunosensis . An independent character differentiating the species is the timing of the appearance of ornamentation during the ontogeny (see diagnosis). S. omagariensis is the sole species of Serradonta known from the fossil record. The species is relatively common at the Omagari hydrocarbon seep where great abundances of worm tubes are reported, whereas it is relatively rare at the Yasukawa hydrocarbon seep where worm tubes are uncommon ( Jenkins et al. 2007a, b; see also Table 2).

Stratigraphic and geographic range.—Omagari and Yasukawa hydrocarbon seeps in Nakagawa area of northern Hokkaido, Japan. Campanian, Upper Cretaceous.

UMUT	University Museum, University of Tokyo

Copyright notice

No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.

Taxonomy

Kingdom	Animalia
Phylum	Mollusca
Class	Gastropoda
Family	Pectinodontidae
Genus	Serradonta