Dolocythere rara Mertens, 1956

Lord, Alan R., Cabral, M. Cristina & Danielopol, Dan L., 2020, Sieve-type normal pore canals in Jurassic ostracods: A review with description of a new genus, Acta Palaeontologica Polonica 65 (2), pp. 313-349 : 337-340

publication ID	https://doi.org/ 10.4202/app.00632.2019
persistent identifier	https://treatment.plazi.org/id/03C7A65F-C956-FFF7-FCF4-CD2A8F55F978
treatment provided by	Felipe
scientific name	Dolocythere rara Mertens, 1956
status

Treatment

Figs. 4A View Fig , 5A, 11B, 18, 19.

1956 Dolocythere rara sp. nov.; Mertens 1956: 192–193; pl. 10: 33–37;

pl. 13: 91–93.?1964 Dolocythere rara Mertens ; Kaye 1964: 322; pl. 55: 12, 14, 15.?2009 Dolocythere rara Mertens ; Slipper 2009: 335–336; pl. 3: 6.

Type material: Holotype BGR T.-K. 1298, C; paratypes: BGR T.-K. 1299, 1300, LV and RV female, respectively ( Figs. 4A View Fig , 5A, 18A, B).

Type locality: Borehole Lingen 196, 697– 704 m, Germany .

Type horizon: Lower Albian .

Material. —More than 250 C, V, juvenile, SMF collection, different localities and age.

Description of NPC.— Exterior: Minute NPC are visible on the ridges of the reticulated valve ( Fig. 18A View Fig ). Their apertures are less than 5 μm and can be differentiated from the larger alveolae belonging to the reticulum with diameters in the range of 6–8 μm ( Fig. 18A View Fig 3 View Fig , A 4 View Fig ). The solum of the alveolar reticulum display small round granules ( Fig. 18A View Fig 2 –A View Fig 4 View Fig ) while the punctae with a diameter of about 3 μm

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Height

Length (in mm)

Fig. 19. Length versus height plots for Dolocythere rara Mertens, 1956 (A) and Dolocythere amphistiela sp. nov. (B), comparison (C). A-1, A-2, estimated growth (moult) stages.

have a smooth bottom ( Fig. 18B View Fig 2 View Fig ). Simple normal pores have a size range of 1–2 μm ( Fig. 18C View Fig 3 View Fig ). Small StPC have diameter of about 3–4 μm with a large setal pore of about 1.5 μm ( Fig. 18C View Fig 2 View Fig ) and a reduced surrounding sieve plate represented by 1–2 rows of tubuli. In the figured example the StPC has a diameter of 1.8 μm and 5 tubuli with an inner diameter in the range of 0.3–0.4 μm. The SI for this latter StPC is 0.006 and the SeP-SI is 0.58, a value which is similar to those of Minyocythere species. Therefore, the small StPC of D. rara is in our opinion homologous to the StPC-m of Minyocythere species. The density of NPC visible on the external side of the valves is “low”. For the LV in Fig. 18C View Fig 1 View Fig we counted 30 entities, without making a distinction between the simple NPC and the StPC-m. Also, the number of pores could be slightly underestimated due to the difficulty in observing the apertures on the complicated reticular surface of

Collection, Hannover), female right valve in external view (B 1), ornamentation (B 2). C. SMF Xe 23756, male left valve in external view (C 1), small StPC (cf. StPC-m) (C 2), simple pore (C 3). D. SMF Xe 23757, male carapace in dorsal (D 1) and right (D 3) views, posterior zone (D 2), antero-dorsal area (D 4). E. SMF Xe 23758, female? left valve in external view, showing a form that may be a large D. rara or a different species. F. SMF Xe 23759, male right valve in external view, showing a form that may be a large D. amphistiela sp. nov. or a different species.

the valve. The DI ranges about 40 to 75 μm, pointing to the wide” dispersion of these pores on the surface of the valve.

Interior: Figure 11B View Fig 1 View Fig is the internal view of the valve in Fig. 18C View Fig 1 View Fig . We counted 32 small pores, and this difference to the number counted on the exterior is due to the better visibility of the apertures internally. Also, the total number of pores is slightly underestimated because the anterior peripheral area is not visible due to the inner lamella (the marginal infold of Yamada 2007). For one of the pore canals which probably relates to the outer StPC we measured a diameter of 4.4 μm (SI 0.009). An important observation is the stable position of several pore apertures around the central AMS. Figure 11B View Fig 2 View Fig is an enlargement of the central section marked on Fig. 11B View Fig 1 View Fig to show two apertures (black arrows, one above the AMS and one below the AMS). They can be recognized in Triebel’s material from Borehole Rodewald WA 6, 206 m Figs. 11B View Fig 1 View Fig and 18C View Fig 1 View Fig ) and also on the paratype of D. rara of Mertens (1956), Fig. 18A View Fig 5, A 6 here. In all these cases there are two apical pores which appear to be diagnostic for this species, because they do not appear in the same area of D. amphistiela sp. nov. (Figs. 5B 2 and 11D). Interestingly, if Fig. 18A View Fig 6 View Fig is enlarged for detail of the pore located posterior to the AMS of D. rara , inside the channel there is a sieve plate with 4–5 apertures, the largest having a diameter of 0.96 μm. The diameter of this pore from a specimen in the Mertens collection displays the same size as those measured on a valve from Triebel’s material, namely 4.4 μm. The DI for the pores visible on the valve interior display values similar to those for the external side, between 30 and 60 μm with an average of 42 μm. Therefore the values for density and dispersion of the pores on the interior match the data measured on the outer side of the same valve.

Remarks. —We figure here paratypic material from the Mertens collection and also specimens identified by Triebel SMF collections) as D. rara that we consider to be conspecific. The problem with the original figures of Mertens 1956) is partly shape of outline (due to photographs cut out and mounted on a black background) and lack of definition of the surface morphology and ornament.

D. rara of Slipper (2009: pl. 3: 6) from the British Aptian has an eyespot and may represent a different species, whereas our material lacks an eyespot and ocular sinus. Two valves we figure ( Fig. 18E, F View Fig ) are slightly larger, appear to show eye spots and are intermediate in shape between D. rara and D. amphistiela sp. nov. and may represent another species.

Stratigraphic and geographic range.—Aptian–Lower Albian, Lower Cretaceous; NW Europe.