Casearia devonica, Nose & Vodrážka & Fernández & Méndez-Bedia, 2014

Nose, Martin, Vodrážka, Radek, Fernández, Luis-Pedro & Méndez-Bedia, Isabel, 2014, First record of chambered hexactinellid sponges from the Palaeozoic, Acta Palaeontologica Polonica 59 (4), pp. 985-996 : 990-994

Casearia devonica sp. nov.

Figs. 5–8.

Etymology: After the report of Casearia in the Devonian. Type material: Holotype: BSPG 2012 I 46; from the holotype specimen three thin sections were prepared (Fig. 5A–C). Paratypes: BSPG 2012 I 47, BSPG 2012 I 48, BSPG 2012 I 49; two thin sections of each.

Type locality: Hillside immediately north of Colle , between Bonar and Sabero (road CL-626), NW Spain .

Type horizon: Upper Valporquero Formation , La Vid Group, Lower Emsian (= Sagüera Member, Esla Formation sensu Keller 1988) .

Diagnosis.—Cylindrical to conical, frequently branched multi-chambered sponge with axial spongocoel. Outer morphology reflecting internal segmentation. Stacked annular chambers variable in size and shape; some chambers fully encasing previous chamber.Cortex on dermal surface formed by single layer of hexactines with spherically-enlarged multiradiate nodes producing triangular meshes. Fused hexactines on gastral surface, within spongocoel, producing polygonal to rounded meshes, possibly representing exhalant canal openings. Chamber fillings characterized by dictyonal hexactine network with rectangular meshes.

Description.—Scattered sponge bodies occur within polymicritic mud mound limestone rocks. The sponges are usually preserved complete, although in some cases not in life position. The gross morphology of the sponges is characterized by successive addition of annular chambers. Chambers are highly variable in size and shape (Fig. 5A–C). There is a characteristic alternation of smaller, tabular annular chambers with larger, discoidal to crescent-shaped chambers (e.g., Fig. 5A 1); in some specimens the size of the chambers gradually increases from the base to the top ( Fig. 7 ). In a few instances, younger chambers may entirely enclose older chambers ( Fig. 6B ). Three of the four specimens are branched. Branches originate from basal chambers as well as from chambers higher up, in the middle part of the main branch. The total height of the sponge bodies reaches 3.5 cm. The height of the chambers ranges from 0.5 to 5 mm and their diameter varies between 6 and 12 mm. Up to 18 subsequent chambers may be developed.

The axial spongocoel is developed throughout the entire length of the sponge and measures approximately 1 mm in diameter at the base and up to 2.5 mm at the top. The gastral and dermal surfaces show strong diagenetic alteration in some of the thin-sections, with the outermost hexactine layer(s) sometimes lacking (e.g., Figs. 7 , 8A ). However, the dermal surface still exhibits annulations reflecting the internal chambered construction.

The cortex on the dermal surface, which is also represented by the wall between the individual chambers, is formed by a single layer of hexactines (e.g., Fig. 8A, B ) with spherically-enlarged multiradiate nodes producing triangular meshes (Figs. 5A 2, 6B). The distance between the centers

Fig. 5. Holotype of chambered hexactinellid sponge Casearia devonica sp. nov. from the Lower Emsian at Colle, Cantabrian Mountains, NW Spain; in → three serial thin sections ( A – C). Main branch sectioned almost parallel to axial spongocoel, exhibiting stacked annular chambers. Serial sections of branch in lower left, which although not parallel to the axial spongocoel, shows changing growth direction. Overgrowth by cementing bryozoans (e.g., fistuliporids). A. BSPG 2012 I 46a; A 2 , detail of A 1 , showing tangential section of wall between chambers (i.e., dermal cortex) formed by spherically-enlarged multiradiate nodes producing triangular meshes. B. BSPG 2012 I 46b; B 2 , detail of B 1 , focusing on two subsequent chambers and gastral surface within spongocoel; fused hexactines produce polygonal to rounded meshes (examples arrowed). C. BSPG 2012 I 46c.

of these multiradiate nodes varies between 0.18 and 0.38 mm. In the section tangential to the wall surface the nodes are circular and 0.12–0.22 mm in diameter, but irregularly elongated in the section perpendicular to the wall surface Fig. 8B ).

Within the individual chambers a dictyonal hexactine network with rectangular meshes is developed. Rectangular meshes are particularly recognizable in radial cross-sections ( Figs. 7 , 8A ), but is difficult to recognize in tangential cross-sections (e.g., Fig. 6A ), except for the framework directly below the cortex on the dermal surface ( Fig. 6C ). Rectangular meshes within the radial cross-sections are formed by beams extending parallel to the long axis of the sponge that are 0.19–0.44 mm long and by transverse beams 0.15– 0.34 mm long. Numerous spherically-enlarged nodes of hexactines reveal perforations resembling the pseudolychniscid structures typically developed in Casearia as it is described by Müller (1974) and Pisera (1997) ( Fig. 8A ).

On the gastral surface, within the spongocoel, the fused hexactines occur in the form of polygonal to rounded meshes (Fig. 5B 2), possibly representing exhalant canal openings. These openings, each 0.20–0.48 mm in diameter, are slightly larger than the rectangular meshes within the chambers and are randomly arranged. The size and position of the putative canal openings in radial section (e.g., Fig. 7 ) suggest the existence of radially arranged canals that extended outwards, but lacked skeletal expressions within the chambers.

Remarks and comparisons.— Mehl (1992) synonymized Casearia depressa Kolb, 1910 (Upper Jurrasic), Casearia eurygaster Zittel, 1878 (Upper Jurrasic), Innaecoelia pamirica Boiko, 1990 (Upper Triassic) and Innaecoelia kurtekia Boiko, 1990 (Upper Triassic) with Casearia articulata ( Schmidel, 1780) (Upper Jurrassic–Upper Triassic). Following Pisera (1997) and Senowbari-Daryan and Zankl (2010), we do not accept the synonymy list of Mehl (1992) and treat all above-mentioned taxa as a separate species of Casearia . Other valid species of the genus Casearia include the Late Triassic C. oblata ( Wu, 1990) , C. decursiva ( Wu, 1990) , C. alpina Senowbari-Daryan and Zankl, 2010 , C. iranica Senowbari-Daryan and Amirhassankhani, 2012 , C. vezvanensis Senowbari-Daryan and Amirhassankhani, 2012 , and C. delijanensis Senowbari-Daryan and Amirhassankhani, 2012 .

The Early Devonian taxon C. devonica sp. nov. described in this paper differs from the all other species asigned to Casearia in the following features: (i) stacked annular chambers that are highly variable in size and shape, and (ii) a cortex on the dermal surface that is formed by a single layer of hexactines with spherically-enlarged multiradiate nodes occurring in the form of triangular meshes.

Moreover, in comparison with the type species C. articulata there is also an absence of a paratangential network formed by fused stauractines on the dermal and gastral skeletal surfaces (e.g., Müller 1974). The gastral surface of C. devonica sp. nov., which is formed by a dense network of polygonal to rounded meshes that might represent the openings of shallow exhalant canals, is also unique in comparison to the other species of Casearia . The presence of this relatively “primitive” type of canalization in C. devonica sp. nov. is a remarkable feature since the geologically younger representatives of the genus are characterized by a sophisticated canalization system that includes a skeletal expression of the canals within the wall.

Stratigraphic and geographic range.—Upper Valporquero Formation, La Vid Group, Lower Emsian; Hillside north of Colle, between Bonar and Sabero, NW Spain.

Figures

Fig. 7. Three-armed branched individual of chambered hexactinellid sponge Casearia devonica sp. nov., BSPG 2012 I 47a (paratype) from the Lower Emsian at Colle, Cantabrian Mountains, NW Spain. Central branch exhibiting almost longitudinal section with chambers gradually increasing in size from base to top, and axial spongocoel. Irregular gastral surface within spongocoel, showing possible openings of exhalant canals (arrows). Sponge encrusted by fistuliporid bryozoans, at least some of which colonized surface of sponge post mortem, see, e.g., bryozoan fully overgrowing the osculum.

Fig. 6. Chambered hexactinellid sponge Casearia devonica sp. nov., BSPG 2012 I 46c (holotype) from the Lower Emsian at Colle, Cantabrian Mountains, NW Spain. A. Detail of Fig. 5C; branch with irregularly-chambered structure, sectioned roughly parallel to growth direction and tangentially to dermal cortex. Upper chambers exhibiting seemingly irregular hexactinellid framework, which shows regular rectangular meshes in radial cross-sections (compare with Figs. 7 and 8A). B. Detail of A, showing tangentially-sectioned dermal cortex of small chamber (indicated by arrow), completely enclosed by considerably larger subsequent chamber. Triangular meshes of dermal cortex resulting from interconnecting, spherically-enlarged multiradiate nodes. C. Detail of lowermost chamber in A; tangential section showing enlarged nodes forming dermal cortex and producing triangular meshes (arrowed), and regular rectangular meshes directly below dermal cortex.

Fig. 8. Chambered hexactinellid sponge Casearia devonica sp. nov. A. BSPG 2012 I 46b (holotype); regular rectangular meshes of hexactinosidan skeleton in radial cross section. Note paragaster in lower right of image and dissolved centres of several thickened spicule nodes (arrowed) which seem to be identical with those forming pseudolychniscid structures similar to that described, e.g., by Müller (1974). B. BSPG 2012 I 47a (paratype); dermal cortex between two chambers, constructed of single thickened hexactine layer with spherically-enlarged nodes. Nodes often irregularly elongated perpendicular to surface of wall (arrow).