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Journal of Paleontology 91(4):672–684
in V. ubaghsi); (2) the extension of ambulacra (short and restricted to the summit of the vaulted oral area in F. luckae); (3) the morphology of the oral surface (strongly vaulted in Felbabkacystis, almost flat in Vyscystis); (4) the extension of the tessellate part of the body wall (restricted to the apical part of the test in V. ubaghsi, more extensive and forming the upper two-thirds of the lateral walls in F. luckae); (5) the morphology of tessellate thecal plates (they are large, granu- lated, star-shaped, with incurved edges in F. luckae, but small, polygonal, smooth, and flat in V. ubaghsi); (6) the morphology of epispires (elongate and V-shaped in F. luckae, consistently small and roundish in Vyscystis at all growth stages); and (7) the extension of the imbricate, stalk-like appendage (long and cylindrical in Felbabkacystis, apparently short and wide in Vyscystis).
Felbabkacystis differs from Lepidocystis by having thinner
brachioles, larger plates, and wider epispires in a more extended tessellate region and narrower ornamented plates in the imbricate region (Fig. 2.2; Table 1; Foerste, 1938; Sprinkle, 1973). Comparison with Kinzercystis shows that Felbabkacystis has larger epispires over a more contracted oral area, and a fusiform tessellate plating area (Fig. 2.1; Table 1; Sprinkle, 1973). Felbabkacystis contrasts with the coeval eocrinoids (Akadocrinus Prokop, 1962; Lichenoides Barrande, 1846) in its bipartite body wall and the imbricate plating of its aboral cup and the stalk-like appendage, and the possession of thin, large star-shaped adjacent plates (Table 1; Fig. 6). It resembles some co-occurring gogiid eocrinoids by possessing elongate elliptical epispires (as in Lichenoides) and short isotomous ambulacra (as in Akadocrinus). The absence of identified gonopore in Felbabkacystis does
not allow documenting the degree of maturity of observed specimens. All Felbabkacystis specimens are homogeneous in size and in the relative proportions of the tessellate and imbricate regions of the body wall. This suggests that all specimens were probably at similar ontogenetic stage.
Evolutionary implications
Phylogenetic results.—The peculiar morphology of Felbabka- cystis n. gen. allows interpreting the relationships and the evolutionary history within the early blastozoan genera (lepidocystoids, coeval eocrinids, and later eocrinoids), using Stromatocystites Pompeckj, 1896 as an outgroup (Appendix, Supplementary Data S1). Primary homologies have been iden- tified independently among the three morphological modules (aboral region, body wall, and feeding system; Table 1, Appendix), whereas mechanistic homologies were used to describe the organization of each module, independently from any terminological influence (David et al., 2000; Nardin et al., 2009; Zamora et al., 2012; Zamora and Rahman, 2014). Phylogenetic analysis of the 13 characters scored for 13
taxa found nine equally parsimonious cladograms (see Appendix for further details). The majority-rule consensus of these trees places Felbakbacystis n. gen. near the base of the blastozoans, more derived than the lepidocystoids and as a sister-group of the two crownward clades: the gogiids and the later eocrinoids (Fig. 7). Among the blastozoans, the basal lepidocystoids are characterized by the plesiomorphic features
Table 1. Comparison of the morphological characters of selected lepidocystoids and eocrinids genera with Felbabkacystis n. gen. Refer to the Supplementary Data S1 for the sources of the description. Akadocrinus
Brachioles
Location of the ambulacral flooring plates
Branching of the ambulacral ray
Extension of the tessellate region
Epispires
Shape of the stalk-like appendage
Length of the ambulacra short, restricted to the periostomial area
straight
most likely embedded in the oral disc
Shape of the oral zone
Shape of the adjacent plates
isotomy flat
forming the entire body wall
small, irregularly pentagonal to hexagonal
Location of the periproct unknown
Plating of the stalk-like appendage
tessellate
small, roundish to ellipsoidal
sub- to holomeric column
Felbabkacystis straight
Gogia
most likely embedded in the oral disc
isotomy strongly vaulted
forming the oral zone and part of the lateral body wall
medium-sized to large, star-shaped
elongate and V-shaped
adoral third of the lateral body wall
imbricate
probably very short, restricted to the peristomial area
straight embedded in the oral disc embedded in the oral disc no flooring plates embedded in the oral disc embedded in the oral disc
short, restricted to the periostomial area
isotomy flat to slightly domed
forming the entire body wall
small, polygonal small and roundish
homeomorphic long peduncle heteromorphic relatively short stalk
tessellate
aboral third to half of the lateral body wall
relatively long extending over the oral disc
holotomy flat
small, polygonal
long, reaching the lateral circlet
heterotomy flat
restricted to the oral disc forming the entire body wal
small and roundish oral disc
homeomorphic long peduncle
imbricate
elongate and V-shaped
unknown
atrophied basal disc of platelets
tessellate
relatively long extending over the oral disc
holotomy flat
large, subhexagonal medium-sized, subhexagonal
small, roundish to ellipsoidal
oral disc
homeomorphic long peduncle
imbricate
relatively long extending over the oral disc
exotomy flat
restricted to the oral disc restricted to the oral disc
medium-sized and polygonal
small and roundish oral disc
homeomorphic cup imbricate
Lepidocystis straigth
Lichenoides straight
Kinzercystis straight
Vyscystis coiled
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