Dehmicystis Caster, 1968

Zamora, Samuel & Gutiérrez-Marco, Juan Carlos, 2023, Filling the Silurian gap of solutan echinoderms with the description of new species of Dehmicystis from Spain, Acta Palaeontologica Polonica 68 (2), pp. 185-192 : 187

Genus Dehmicystis Caster, 1968

Type species: Dendrocystites ( Dendrocystoides ?) globulus Dehm, 1934 , Lower Devonian of western Germany ( Fig. 2 ).

Emended diagnosis.—Solutan with a rounded flattened theca composed of polygonal plates. Medium-size feeding appendage on one of the thecal surfaces, with the hydropore and gonopore on same surface but separated one from each other. Periproct on the opposite face of the theca than the feeding appendage, consisting of a terminal anal pyramid, right to the homoiostele insertion. Large tetramerous proxistele and long dististele composed of paired ossicles.

Remarks.—From all characters listed by Rahman and Lintz (2012) for the genus Dehmicystis the most important is the presence of a feeding appendage (arm) and anus “on the same face of the theca” ( Rahman and Lintz 2012: 62). The position of the anal pyramid in Dehmicystis is problematic due in part to the poorly preservation of the material and also because the limited number of specimens available for study. Rahman and Lintz (2012) considered that both structures are on the same face of the theca based on a new studied specimen ( Fig. 2B : individual 1). This contradicts the position of the anus in the holotype ( Fig. 2A ) which appears in the right side and opposite to the face where the feeding appendage is located. Specimens from Germany are extremely flattened and distorted resulting in the superimposition of both faces of the theca. Rahman and Lintz (2012) proposed three hypotheses explaining such position of the anus. The first of them considers this was a result of preservation, in which thecal plates have been displaced to partly reveal the opposing thecal surface where the anus is located, so that it appears to be on the opposite side of the theca. The second as a result of a “situs inversus” where structures located on one side of the theca are transposed to the opposite side, presumably as a result of developmental abnormalities. Finally, they choose a favored scenario in which flattening trajectories during burial affected the position of the anus. Our new material from Spain is less f lattened than German specimens because different preservation in a coarser rock. The single specimen shows the arm and anus in the same face ( Fig. 3A ), but close observations of the anal pyramid ( Fig. 3A 4 ) suggest that it is preserved in a different plane than the feeding appendage. This supports the first scenario suggested by Rahman and Lintz (2012) in which some plates have been displaced revealing the opposite side of the theca where the anus was located. We thus consider that in Dehmicystis the arm and anus are on opposite faces. Other solutans (i.e., Dendrocystites Barrande, 1887 , Coleicarpus Daley, 1996 and Maennilia Rozhnov and Jefferies, 1996 ) also have the arm and anus on opposite extremities; or have a terminal arm and the anus on one of the integuments ( Girvanicystis ) ( Noailles et al. 2014). An undescribed Ordovician species from Hope Shale Formation in Shropshire shows the arm and stele on the same thecal face, and the anus on opposite face. A similar situation occurs in “Solutan indet., gen. et sp. nov.”, from the Middle Ordovician of Bohemia ( Lefebvre et al. 2012). For contrast Dehmicystis has a terminal homoiostele, offset arm on one of the integuments and anus on the opposite side, right to the homoiostele insertion. Kolata et al. (1977) also consider that Belemnocystites wetherbyi Miller and Gurley, 1894 , had the arm located some distance away from the margin. Minervaecystis (see Ubaghs 1970), Pahvanticystis see Lefebvre and Lerosey-Aubril 2018) and Plasiacystis see Lefebvre et al. 2012) also have an offset position of the arm.

Figures

Fig. 2. Solutan echinoderm Dehmicystis globulus (Dehm, 1934) from the the Lower Devonian Hunsrück Slate, Germany. A. Holotype (SMF-HS 432), almost complete specimen showing the theca and posterior appendage. Note anus in on right side. B. SMF-HS 969, slab containing three individuals. Note that individual 1 has the anus on “left” position.Repository number assigned to a replica of the newly prepared slab.Photographs courtesy of Ulrich Jansen.

Fig. 3. Solutan echinoderm Dehmicystis ariasi sp. nov. from the Llagarinos Formation, Ludlow, Silurian, northern Central Iberian Zone, Spain. A. MGM- 208S.A1, complete specimen in dorsal aspect preserving proxistele and feeding appendage above the body. A2, counterpart of same specimen.A3, detail of feeding appendage consisting on biserial floor plates and cover plates. Gonopore on single plate, and a possible hydropore close to the feeding appendage attachment. A4, detail of the periproct on right position. Note that the periproct is visible from the inside and was located on dorsal right part of the theca.A5, detail of the appendage preserving the complete proxistele and proximal dististele. Photographs are from latex casts whitened with ammonium chloride sublimated.

Fig. 4. Camera lucida drawings of solutan echinoderm Dehmicystis ariasi sp. nov. from the Llagarinos Formation, Ludlow, Silurian, northern Central Iberian Zone, Spain; with interpretation of main anatomical parts.