Limacina tanzaniaensis, Cotton & Janssen & Pearson & Driel, 2017

Cotton, Laura J., Janssen, Arie W., Pearson, Paul N. & Driel, Rens van, 2017, Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Eocene / Oligocene boundary interval of three cored boreholes in southern coastal Tanzania and their response to the global cooling event, Palaeontologia Electronica 20 (3), pp. 1-21 : 10

Limacina tanzaniaensis sp. nov.

Figures 7.1-4 , 8

zoobank.org/ 8C1AB54C-4643-4D30-9455-97C37B793992

Type material. Holotype ( Figure 7.1 ) RGM 777428 b; paratype 1 ( Figure 7.2 ), RGM 777438 ; paratypes 2 and 3 ( Figure 7.3-4 ) RGM 777416 b-c. Kilwa Group, Pande Formation (Eocene, Priabonian, biozones P 18 and NP 21 ).

Additional specimens. Fourteen specimens from TDP 17 ( Table 3), all from the Priabonian part of the section. Most specimens poorly preserved as pyritic internal moulds.

Type locality. Stakishari ( Tanzania, Kilwa region), cored borehole TDP 17, sample 38.2, 22-29 cm, 111.12-111.19 m below surface = 123.12-123.19 m composite depth .

Diagnosis. Spherical limacinid of almost four whorls, apex flattened. Last whorl inflated, 95% of total shell height, aperture c. 75% of total shell height, margin simple, base of shell umbilicate.

Description. Limacinid of spherical shape, measurements of holotype H = 0.92, W = 1.00 mm, consisting of 3.75 moderately convex whorls with convex tangent. First two whorls flattened, last whorl very large, inflated, occupying 95% of total shell height. Aperture large, about 75% of total shell height, attaching on (holotype, Figure 7.1 ) or slightly below (paratype 1, Figure 7.2 ) periphery of penultimate whorl. Apertural margin simple, semicircular, inner margin and columella invisible as all specimens are in pyritic internal mould preservation. Base of shell regularly rounded, umbilicus present, 20-25% of shell diameter.

Discussion. The available specimens demonstrate variability in height of the apex, in some the initial flattening continues to the third whorl, resulting in an only slightly raised apical shell part. There is some resemblance to the Ypresian species Limacina heatherae Hodgkinson in Hodgkinson et al. (1992, p. 17, pl. 2, figures 15-18). In that species, however, the whorls attach higher on the foregoing whorl, the aperture is narrower and its umbilicus smaller.

Figures

FIGURE 7. Limacina tanzaniaensis sp. nov. 1: Holotype, apertural view, RGM 777428b, TDP 17.38.2, 22-29 cm; 2: paratype 1, apertural view, RGM 777438, TDP 17.36.2, 80-95 cm; 3: paratype 2, umbilical view, RGM 777416b, TDP 17.36.1, 10-25 cm; 4: paratype 3, apical view, RGM 777416c, same data as 3. Bar equals 100 μm.

FIGURE 8. Limacina tanzaniaensis sp. nov.; holotype, apertural view, RGM 777428b, 3dPDF. For animation see: http://palaeo-electronica.org/content/2017/2024- pteropoda-from-tanzania.