Blackites minusculus Steurbaut & Nolf, 2021, n. sp.
Creators: name: Steurbaut, Etienne
name: Nolf, Dirk
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Chromista
Haptophyta
Prymnesiophyceae
Coccosphaerales
Coccolithaceae
Blackites
Blackites minusculus

description: Blackites minusculus n. sp.
(Fig. 18 S-V)
urn:lsid:zoobank.org:act: 9B705E57-195D-405F-A8C0-51A169BE9B57
Blackites perlongus – King et al. 2013: 187 (non B. perlongus Deflandre in Grassé, 1952).
HOLOTYPE. — Fig. 18V (IRSNB b7114) (negative stored in the collections of the RBINS).
PARATYPES. — 3 figured specimens (l = 7.2-8.8 µm, w = 1.0 µm) from the Brussel Sand Formation, 1 from the Mont-des-Récollets (Unit B1) (Fig. 18S) (IRSNB b7111) and 2 from Vossem (Unit B3) (Fig. 18 T-U) (IRSNB b7112, b7113).
DIAGNOSIS. — Tiny rhabdoliths, without a basal enlargement or collar, including a tapering stem wirh irregular surface surmounting a thin basal plate.
DERIVATIO NOMINIS. — Refers to the thin and delicate rhabdoliths,which are minuscule compared to most of the other representatives of the genus.
LOCUS TYPICUS. — Vossem:otolith sample taken in middle of the quarry by D. Nolf in 1974, about 1.50 m beneath a conspicuous sandstone (map 32/1, x = 164.175, y = 169.290; 50°50’01.96”N, 4°34’08.96”E).
STRATUM TYPICUM. — Brussel Sand Formation, middle of Unit B 3; lower middle part of NP14.
DIMENSIONS. — Length = 7.5 to 10.4 µm; Maximum width of stem = 1.0 to 1.1 µm; Maximum width of basal plate = 1.7 to 2.1 µm (holotype: l = 8.6 µm, wm = 1.1 µm, wbp = 1.8 µm).
DISTRIBUTION. — At the Mont-des-Récollets B. minusculus n. sp. ranges from the top of the Aalter Formation (upper part of Unit A4) up to the upper part of the Brussel Sand Formation (top Unit B3), although inconsistently and in low numbers. It has not been recorded in Unit B4, and rarely in the overlying Lede Sand Formation at this locality. It occurs in many outcrops of the Brussel Sand Formation in its type-area (Vossem, Neerijse, St-Lambrechts-Woluwe, Nederokkerzeel, etc.), essentially in Unit B3 and is known from Unit B 4 in the Vlakte van de Raan BH (Steurbaut unpublished). This species is consistenly present in the ‘Chaumont-en-Vexin sands’ of the Paris Basin, attributable to the base of NP14. Hence, its range in the North Sea Basin seems to be restricted to NP14 and the lower part of NP15, with a major influx in the lower middle part of NP14 (Unit B3). B. minusculus n. sp. has been encountered in west Kazakhstan, also in low numbers, but appearing at a slightly lower position (middle of NP13) (King et al. 2013).
DESCRIPTION
The rhabdoliths of this new taxon are tiny, ranging from 7.5 to 10.4 µm in length. They consist of a slender tapering stem, without a collar, surmounting a thin basal plate. The stem is slightly inflated in its upper part, reaching its maximum thickness at about 1/5 of its length, measured from the rounded distal tip. Its surface is rugose. The basal plate consists of 1 layer of radially oriented elements.
DISCUSSION
The presence of an elongated stem, rising vertically from a rather small and thin basal plate, and its optical characteristics (typical vertical extinction line and interference colours of the stem) allow this taxon to be attributed to the genus Blackites. It is distinct from all other described Blackites taxa by its tiny rhabdoliths (generally around 8.5 µm in length, maximum width c. 1 µm). Its silhouette resembles that of B. perlongus, although the latter is twice as long (17- 18 µm for holotype, see Deflandre & Fert 1954: pl. XII, figs 34-35, text fig. 86) and has its maximum thickness in a more central position (c. at the middle of the stem) (see also Bown 2005: pl. 24).
description: Published as part of Steurbaut, Etienne & Nolf, Dirk, 2021, The Mont-des-Récollets section (N France): a key site for the Ypresian-Lutetian transition at mid-latitudes - reassessment of the boundary criterion for the base- Lutetian GSSP, pp. 311-363 in Geodiversitas 43 (11) on pages 348-350, DOI: 10.5252/geodiversitas2021v43a11, http://zenodo.org/record/4891107