Dehmicystis ariasi, Zamora & Gutiérrez-Marco, 2023

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 : 188-190

Dehmicystis ariasi sp. nov.

Figs. 3 , 4 .

Zoobank LCID: urn:lsid:zoobank.org:act:88604815-85BD-4E73-8FA4-2381B337484C

Etymology: Dedicated to Francisco Arias Ferrero (Ponferrada, Spain) for collecting the only specimen known and making it available for study.

Holotype: MGM-208S-a (part) and MGM-208S-b (counterpart). Type locality: 340 m west of Poleares high (946 m), about 960 m northeast of O Castelo village in the Rubiá municipality, Ourense Province, Galicia, NW Spain. GPS coordinates: 42º27′22.5″ N, 6º51′57.1″ W .

Type horizon: Shale bed with a slight chloritoid content in the upper part of the Llagarinos Formation. Bed of a probably Gorstian (early Ludlow) age by lateral correlation with a nearby locality.

Material.— Holotype only.

Diagnosis. —A species of Dehmicystis with a globular theca, proxistele equal in length to the theca. Undifferentiated mesistele.

Description.—Thecal shape rounded, large (45 mm in length, 30 mm in width), nearly bilaterally symmetric with the left side more developed than the right. Theca widening posteriorly with an invagination for the insertion of the homoiostele. Narrow peripheral ring as a result of compression rather than originally biological. Plates very thin, superimposed integuments (taphonomic), polygonal and relatively large. Boundaries between plates are poorly preserved. Feeding appendage off the apex, on an integument with attachment to the theca on left side; relatively large with wider rectangular basal plates (flooring plates) and thinner, cover plates. Feeding appendage thinning distally, with food groove oriented to the substrate (see interpretation below). Small gonopore on a circular tiny plate, associated with some rugose plates interpreted as hydropore. Both separated one another. Periproct large, on the opposite side of the theca, close to the appendage insertion but on the right position. Proxistele very large, consisting of eleven tetramerous rings, two on each side. Posterior side of each ring with a depressed side for the articulation of adjacent rows distally. Distal stele only preserved proximally, composed of two dimeres. Theca slightly longer than the proxistele.

Remarks.—Comparison with the type species Dehmicystis globulus ( Dehm, 1934) from Germany ( Fig. 2 ), poses several problems; specially because German specimens are flattened and tectonically distorted, and also because none of the known specimens is totally complete ( Fig. 2 ). Holotype and individual 1 from Rahman and Linz (2012) have the anterior part of the theca incomplete, individual 2 preserves only the homoiostele and individual 3 preserves only the homoiostele and posterior part of the theca. Rahman and Linz (2012) indicated that the dimensions of the holotype are 70 × 67 mm, but based on new observations, this is unlikely (see Table 1 ). The length of the holotype is unknown because incomplete preservation of the anterior part and its width is about 40 mm. So dimensions of the holotype are comparable to D. ariasi . The other individuals seem relatively larger. Shape of the theca between both species seems different, being more elongate in the German taxon, but this difference can be also due to the strong tectonic distortion affecting the Hunsrück material. Another important difference is the relation between thecal and proxistele lengths. Spanish material seems to have a longer proxistele which is almost equal than the length of the theca. For contrast D. globulus has a shorter proxistele. Mesistele is well preserved in the individual 2 of Rahman and Linz (2012), but it is absent in the Spanish material, where transition from the proxistele to the dististele is more abrupt. Further comparison with the type species is not possible due to incomplete preservation of material from both Spain and Germany, and different preservation styles being German specimens more compressed.

Stratigraphic and geographic range.— Type horizon and locality only.

Figures

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.

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.