Nardin et al.—Transitional blastozoan from the middle Cambrian of the Czech Republic
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Figure 5. (1, 2) Photographs of two specimens of Felbabkacystis luckae n. gen. n. sp. (Jince Formation, Příbram-Jince Basin, Czech Republic). (1) Internal view showing the location of the periproct in the lateral body wall in the paratype SZ343; (2) details on the subvective system restricted in the narrow oral area of the holotype SZ349. (3) Enlargement on the oral surface of the small specimen NML28665 of Vyscystis ubaghsi Fatka and Kordule, 1990 (Jince Formation, Příbram-Jince Basin, Czech Republic) showing the periproct border laterally to the oral disc and the relatively long embedded ambulacrum bearing brachiole facets. Colors indicate the different skeleton regions according to the extraxial-axial theory framework (Mooi and David, 1998; Nardin et al., 2009; Lefebvre et al., 2015). Latex casts have been whitened with ammonium chloride. Scale bars = 1mm.
conical, expanding in diameter from the stalk to its lower part (Figs. 3.2, 3.3, 4.2); width regularly increasing from the base to the upper part of the test. Adoral tessellate part (L = 8.2– 22.2mm, W = 5.8–8.1mm) ~1.8 times length and ~1.3 times width of imbricate one (L = 5.8–10.0mm, W = 4.5–6.7 mm). All specimens showing approximately the same proportions for the two regions. Imbricate part of the test with length 1.5 times width, composed of numerous, scalar plates, slightly over- lapping adorally (about 60% exposed), small and squamous, longer than high, thin (0.08mm on average), constant in size from the base to the top of that part; organized in circlets (Fig. 3.3); slightly domed, without any respiratory structures, smooth on their exterior and interior surfaces. Connection between the two parts of the body wall consisting of one or two circlets of straightened-up imbricate-type plates without epis- pires (Figs. 3.2, 4.4). Tessellate part of the body wall region with length 1.5 to 2.1 times width, constituted by numerous large adjacent plates, polygonal in shape, possibly organized into poorly defined circlets aborally and with no apparent organiza- tion in the oral region (Figs. 4.3, 5.1, 5.2). Interior surface of the plates smooth; exterior surface slightly granular. Adjacent plates twice as thick as imbricate ones (0.15mm), flat to slightly domed, depending on the number of epispires. One to three simple epispires occurring on each plate side; deeply excavated into adjacent plates, forming elongate peripores (Fig. 4.1); elliptical and large only at the suture margins, probably uncovered. Periporal edges thin and short. Periproct opening in the first adoral third of the tessellate part of the body wall (Fig. 3.1). Oral surface relatively narrow, composed of few adjacent
plates, each bearing only a few small epispires (Fig. 3.2). Plates irregularly pentagonal to hexagonal in shape. Oral area not sufficiently well preserved to show complete ambulacral system. Straight and thin (0.7mm in diameter) brachioles
probably originating at the border of peristomial area, at least six in number, being mounted on two large, domed plates with no epispires, interpreted as ambulacral flooring plates (Fig. 5.1, 5.2). Brachiolar plates pentagonal, unornamented, domed, and alternating in a biserial pattern. Few plates covering brachiolar food grooves proximally observed; their presence over the entire length of the brachioles being highly probable, due to the presence of two slits occurring on interior edge of brachiolar plates. At present, no hydropore and gonopore observed in any specimen.
Etymology.—From Lucka, daughter of the third author.
Material.—Holotype, SZ349, complete body wall and articu- lated brachioles. Best paratype, MI2, complete body wall and long stalk. Other figured paratypes SZ343 (slab with several specimens), SZ346-347, SZ349, LK1, and LK2 (slab with one specimen of Vyscystis); five additional unfigured partial speci- mens, some with preserved stalk attached to the body wall and proximal parts of brachioles.
Remarks.—Felbabkacystis n. gen. differs from all lepido- cystoids and gogiid eocrinoids described so far. The occurrence of the lepidocystoid Vyscystis in the same level and same locality as Felbabkacystis could question the validity of the new genus and suggest that putative differences in morphology may simply result from differences in ontogeny and/or in preserva- tion: individuals assigned to these two taxa are sometimes found associated, on a same slab (Fig. 4.5). However, in recent years, the discovery of several new, well-preserved specimens of Vyscystis shows that their morphology is clearly distinct from that of Felbabkacystis (Table 1; Figs. 2.3, 2.4, 4.5, 5). Main differences between the two genera concern: (1) the morphology of the brachioles (straight in F. luckae, spiraled
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