Occurrence and paleoecological significance of lyssacinosid sponges in the Upper Cretaceous deposits of southern Poland

Cretaceous lyssacinosid sponges (Hexactinellida) are rare and poorly recognized. This is the first description of lyssacinosid sponges from the Cretaceous of Poland. The sponges (including six species and three types of root tufts) come from the Upper Turonian–Lower Coniacian of the Opole Trough, Upper Campanian of the Miechów synclinorium, and Upper Campanian of the SE part of the border synclinorium. All localities lie southwards of the previous reports, widening thus the paleogeographic distribution of the group within the North European Province. Cretaceous lyssacinosids seem to be a useful tool in paleoecological interpretations. The presence of thin-walled lyssacinosids with root tufts indicates a soft substrate, slow rate of sedimentation, and calm and deeper water conditions.

Occasionally, lyssacinosids appear in Upper Cretaceous sponge assemblages of the North European Province, which consists mainly of other hexactinellids (Hexactinosida and Lychniscosida) and lithistids. Best known are Coniacian lyssacinosids from Bornholm (Mehl 1992;Brückner and Janussen 2005;Brückner 2006). However, single species of Lyssacinosida were also identified in the Cenomanian of Normandy (Moret 1926), Lower Cenomanian and Campanian of northwest Germany (Schrammen 1912;Salomon 1990), and from the Chalk of England (Bowerbank 1869; Reid 1968). Lyssacinosida have never been documented from the Upper Cretaceous of Poland.
Because the skeleton of lyssacinosid sponges is com posed of unfused, or only locally connected spicules, their fossilization potential is definitely lower than that of other siliceous sponges with a rigid skeleton (e.g., Krautter 2002). The poor preservational state of these sponges in the Upper Cretaceous is the reason for their poor taxonomic recognition. Root tufts of lyssacinosid sponges composed of long basal spicules, occurring in the Upper Cretaceous deposits of southern Poland, were mentioned in the liter ature as sea grasses (Rutkowski 1965) or plants (Roemer 1870, pl. 30, fig. 2;Kedzierski 1995). This paper aims to describe the lyssacinosid sponges from the Upper Turonian-Low er Coniacian of the Opole Trough, Upper Campanian of the Miechow synclinorium, and the SE part of the border synclinorium (Middle Vistula River section). In addition, their importance in paleoecological reconstructions is discussed.

M aterials and methods
The studied collection of lyssacinosid sponges comprises 98 specimens. The material was collected from three sec tions in the Miechow synclinorium (Rzezuśnia, Strzezów Jedrzejow), a single section in the SE part of the border synclinorium (Piotrawin), and a single section in the Opole Trough (Folwark quarry) (Fig. 1a-c). Details of the skel eton were analyzed under a stereoscope microscope at the Institute of Geological Sciences of the Jagiellonian Uni versity, Krakow. Thin-sections and rock samples were also analyzed under an optical microscope.
The studied specimens are hosted at the Institute of Geological Sciences of the Jagiellonian University, Krakow, collection no UJ220P, and in the Laboratory of Geology of the University of Lodz (collection no. ULXXIII).

Localities
In the extra-Carpathian Poland, Upper Cretaceous rocks crop out in the Southern Polish Uplands, in the Opole Trough, and in the Sudety M ountains (Fig. 1a). The so-called mid-Cretaceous eustatic transgression started in the middle Albian, covering rapidly most of its territory (Pozaryski 1960;Marcinowski 1974;Marcinowski andRadwanski 1983, 1989). The initial facies variability of the Albian and Cenomanian was quickly followed by a uni form facies during the Early Turonian. W ith the exception of the Sudetes, where siliciclastic sedimentation prevailed, the rest of the area is characterized by limestone-marly facies (Central Polish Uplands); limestones are restricted to the Krakow Swell area, while in other regions opoka (siliceous limestone)/marly facies dominate (Marcinowski 1970(Marcinowski , 1974W alaszczyk 1992;Voigt et al. 2008).

Opole Trough
The Cretaceous succession of the Opole Trough spans the Cenomanian to M iddle Coniacian time interval (W alaszczyk 1992).
Rare lyssacinosid sponges occur in the Upper Marl Unit. All specimens are strongly pyritized with only single sili ceous spicules preserved.
The Jedrzejow section was a temporary road cut in the northern part of the city of Jedrzejow. The succession is composed of opokas and marls of the ''Inoceramus'' inkermanensis Zone to ''Inoceramus'' costaecus-''Inoce ramus '' redbirdensis Zone (Jurkowska, in prep.). The ''I ''. inkermanensis Zone is very fossiliferous, with abundant inoceramids, pectinids, belemnites, and echinoids. In the ''I" . costaecus and ''I ''. redbirdensis Zones, echinoids and inoceramids become rare and big gastropods occur. Hexactinosid and lychniscosid sponges are numerous in the lower part of the succession but less common in the upper part where massive lithistids appear. Lyssacinosids are most numerous in the ''I ''. inkermanensis Zone, while in the ''I ''. redbirdensis Zone they are absent.
M icrofacially, opokas from the studied sections repre sent packstone (Fig. 2b -e) with planktonic foraminifera and spicules of the siliceous sponges (mainly non-lithistid demosponges). In Rzezuśnia, dispersed spicules of hexactinellid sponges also occur ( Fig. 2c). In some thin-sections from Strzezow, current alignment of spicules can be observed. Organic components also comprise fragments of bivalves and rare echinoids. An admixture of detritic material and glauconite was detected in Jedrzejow and Strzezow; in Rzezuśnia it is, however, insignificant.
All collected specimens of lyssacinosids are strongly limonitized. Rare, short fragments of siliceous or calcitized spicules have been found only in some specimens from Jedrzejow and Strzez ow. In all sections, root tufts type 1 are dominant. Large, fairly complete root tufts are pre served in life position while separated bundles of basal spicules lie horizontally.

SE part of the border synclinorium
In the SE part of the border synclinorium, the Upper Cretaceous succession is best exposed in the Middle Vistula River section (Pozaryski 1938;Marcinowski and Radwanski 1983;Voigt et al. 2008) (Fig. 1a).
The Piotrawin section is an inactive quarry with a monotonous, poorly bedded succession of Upper Campa nian opoka (Fig. 1c), which belongs to a local lithostratigraphic unit of Piotrawin Opoka (W alaszczyk 2004). Based on ammonites, Błaszkiewicz (1980) assigned the succes sion from this section to the Nostoceras pozaryskii Zone (=Nostoceras hyatti Zone according to Kennedy et al. 1992). W alaszczyk (2004) included its lower part into the ''Inoceramus'' altus Zone, whereas its middle and upper parts belong to the ''Inoceramus'' inkermanensis Zone.
Microfacially, these opokas represent packstone ( Fig. 2f) with foraminifera and spicules of siliceous spon ges (mainly non-lithistid demosponges). Other bioclasts are fragments of bivalves, echinoderms, and rare bryozoans. Locally, in the upper part of the succession, current-aligned spicules are observed. Admixture of quartz and glauconitic grains is insignificant.
The lyssacinosid sponges are represented mainly by isolated root tufts. Bodily preserved sponges are much less numerous. Moreover, they are poorly preserved. All spec imens are strongly limonitized and often only single spic ules are visible. Fragments of siliceous spicules occur sporadically.

Lyssacinosid sponges from the studied sections
The studied material is dominated by isolated root tufts composed of basal spicules (spicules which protruded from the dermal surface and anchored sponges in the sediment).
Bodily preserved sponges are less numerous and, moreover, they are strongly deformed by compaction. They are usually incomplete, occasionally strongly fragmented with poorly visible single spicules. Better preserved spec imens (described below) often possess only large spicules of the main (choanosomal) skeleton. Other taxonomically important spicules, such as autodermalia (megascleres supporting the dermal membrane directly), hypodermalia (megascleres lying under autodermalia), and supradermalia (megascleres protruding from the sponges surface), are rare. Microscleres, critical for the taxonomy of Recent taxa, have not been found. Due to their poor preservation, the taxonomic position of most of the sponges is uncertain.
Different types of spicules were recognized in studied specimens: monactines (one-rayed spicules), diactines (two-rayed spicules with rays aligned on the same axis), hexactines (spicules with six rays), and pentactines (hexactines with reduction of one ray) with four rays par allel to the body surface (tangential rays) intersecting at angles of 90° (ortotropal pentactines) or intersecting at angles other than 90° (paratropal pentactines).

Description
The better preserved specimen is roundish, 35 mm in diameter (Fig. 3a). The round osculum on its top is 13 mm in diameter. The height of the sponge is unknown, as the specimen was compressed almost parallel to its axis. The dense choanosomal skeleton is composed of variably ori ented diactines and diactine bundles, up to 6 -7 mm long (Fig. 3b). Small, 1-2-mm-long, hypodermal diactines are arranged parallel to the wall surface (Fig. 3c). Single auto dermal hexactines, supradermal orthotropal pentactines, paratropal pentactines (Fig. 3c), and fragments of few basal spicules occur (Fig. 3a).

Remarks
The basal spicules are fragmentary, and the anchors typical of the genus Rossella Carter, 1872 (see Tabachnick 2002c) are not preserved. The species has been so far reported from the Coniacian of Bornholm (Brückner 2006).

Description
The sponges are probably cup-like (Fig. 3d) and more than 80 mm in height. All skeletons are strongly disintegrated. The spicules are scattered and their primary arrangement is occasionally unclear. The choanosomal skeleton is composed of isolated diactines (3-4 mm in length), diactine bundles (4-5 mm in length), and large hexactines (4-10 mm in size) (Fig. 3f). Supradermal pentacines are rare. Small autodermal hexactines (0.5-0.9 mm in size), found in a well-preserved fragment, form a dense and quite regular lattice (Fig. 3e). Numerous autodermal hexactines and few choanosomal hexactines (probably derived from the lower part of the body) were also observed between basal spicules. Straight or wavy basal spicules are thin, with an average thickness of ca. 0.1 mm. They comprise a dense, broad root tuft (Fig. 3d). Some of the basal pen tactines are preserved with toothed anchors (Fig. 3g).

Remarks
All specimens are very poorly preserved with m ost of the spicules lost. Composition and size of the preserved spic ules corresponds well to the diagnosis of R. bromlei from the Coniacian of Bornholm (compare Brückner and Janussen 2005; Brückner 2006). Chaunoplectella sp. Figure 4a, b Material Three specimens from Strzezow and 2 specimens from Jedrzejow.

Description
The fragments are derived from thin-walled, probably cup like sponges. The largest fragment, with a partly damaged wall, measures 160 mm. These sponges are characterized by an irregular choanosomal skeleton (Fig. 4 a, b) and are composed mainly of giant hexactines, with thick rays (0.2-0.25 mm), and up to 16 mm long. The rays of some hexactines are curved (Fig. 4a). Variably orientated diactines, 0.1 mm thick and 4-8 mm long, are less common (Fig. 4b). Locally small autodermal hexactines, with rays up to 1 mm in length, are preserved (Fig. 4b).

Remarks
In contrast to Recent thick-walled representatives of the genus Chaunoplectella Ijima, 1896 , the specimens are characterized by a thin wall, similar to Chaunoplectella macrospiculata Brückner, 2006, from the Coniacian of Bornholm. The choanosomal hexactines of the specimens are distinctly larger than hexactines in Ch. macrospiculata where rays are up to 8 mm long (Brückner 2006). Recent representatives of Chaunoplec tella are basiphytous with a short stalk. Bases in the studied specimens were not preserved. Figure 4c, d Material Five specimens from Jedrzejow and 1 specimen from Strzez ow.

Description
The fragments are derived from thin-walled (ca. 1 mm thick) tube-and cup-like sponges, up to 50-90 mm in diameter and over 150 mm in height. Occasionally they are preserved with broken single basal spicules or small frag ments of dense root tuft. The characteristic feature of these sponges is their choanosomal skeleton, composed of diactine bundles and isolated diactines, which run parallel and diagonal in growth direction (Fig. 4c). The diactine bun dles are large, 20-30 mm long. Isolated diactines are smaller, 10-15 mm long on average. The hexactines, also occurring in the choanosomal skeleton, are 2-8 mm in size (Fig. 4d). Dermal spicules are absent.

Description
This is a small, ca. 40-mm-high, thin-walled, cup-like sponge, with round to oval wall openings, 1-2 mm in diameter (Fig. 4e). The moderately dense skeletal lattice of this sponge is formed by long, thick (0.5-0.8 mm) diactine bundles, iso lated diactines (0.1 mm thick and up to 3 mm in long) and rare hexactines, up to 2 mm in size (Fig. 4f). The diactine bundles run mostly in growth direction. Other spicules are not visible.

Remarks
The lack of dermal spicules does not allow a precise tax onomic identification.

Material
Three specimens from Folwark.

Description
These are wall fragments (up to 3 cm in size), derived from cup-like sponges. The wall is thin (up to 1 mm) with irregu larly distributed rounded or oval wall openings, 0.8-2 mm in diameter. The dense choanosomal skeleton consists of diactines, pointing in all directions, and of single hexactines. These spicules are poorly visible in a pyritized mass. The fragment of broad root tuft, preserved in the lower part of one of the specimen, is composed of thin (ca. 0.1 mm), straight spicules with a broken terminal part. Others spicules were not observed.

Remarks
Because of their poor preservation, the specimens are left in open nomenclature.
Root tufts type 1 Figure 5a-d Material Nine specimens from Folwark, 35 from Rzezuśnia, three from Strzez ow, five from Jedrzejow, and four from Piotrawin.

Description
The specimens are moderately dense, broad root tufts (Fig. 5a) composed of straight or slightly curved, thick (0.2-0.3 mm) spicules (Fig. 5d). The terminal parts of the spicules are not visible, but usually broken. The best-pre served specimens from Rzezuśnia are very large, up to 250 mm long, and 160 mm wide (Fig. 5a). In the lower part of the root tufts, the spicules are loosely packed, the distance between them being up to 5-7 mm (Fig. 5b). A few specimens from M iechow synclinorium are repre sented by narrow (5-10 mm wide), separated bundles composed of few or several long spicules (Fig. 5c).

Remarks
Terminal parts of spicules forming these root tufts are not visible; thus a precise determination is impossible.
Root tufts type 2 Figure 5e, f Material One specimen from Piotrawin and 2 specimens from Rzez uśnia.

Description
The specimens are composed of thin (0.05 mm thick), nonanchorate basal spicules which form narrow, separate, wavy tufts. The specimen from Piotrawin is composed of a fragment of the body and five separate tufts (up to 55 mm long and 2.5-3.5 mm wide) (Fig. 5f). The root tufts from Rzezuśnia are broken and dispersed (Fig. 5e).

Remarks
The basalia gathered in several tufts are characteristic of some Recent genera of lyssacinosids of the family Euplectellidae Gray, 1867 (e.g., genus Chaunangium Schulze, 1904) and Rossellidae Schulze, 1885(e.g., Lophocalyx Schulze, 1887 (Tabachnick 2002a, c). Numerous separate tufts are also typical of the genus Pheronema Leidy, 1868 (subclass Amphidiscophora Schulze, 1886), but basal spicules of the specimen do not have anchores typical of Pheronema (compare Tabachnick and M enshenina 2002b). Moreover, in the strongly dam aged body fragment preserved with root tuft from Piotrawin, single diactines were recognized. These spicules are uncommon in Pheronema. b Fig. 5 a- Root tufts type 3 Figure 5g Material One specimen from Folwark and two specimens from Piotrawin.
In the lower part of root tufts, the spicules are slightly dispersed. The best-preserved root tuft from Folwark is over 65 mm long, 5 mm wide in the upper part, and ca. 8 mm wide in the lower part. Specimens from Piotrawin are large, over 90 mm in length and 15 mm wide. Terminal parts of all specimens are broken.

Remarks
Similar root tufts appear in several Recent lyssacinosids and in hyalonematid sponges (non-rigid hexactinellid sponges of the subclass Amphidiscophora Schulze, 1886). Sponges with stalk-like root tufts and some isolated stalk like root tufts from the Upper Cretaceous of Germany were described as the sole fossil representatives of the genus Hyalonema Gray, 1835 (Mehl andHauschke 1995). Basal spicules of living hyalonematid sponges usually have 4-8 teeth (Tabachnick and M enshenina 2002a). Due to the lack of the characteristic toothed anchors of basal spicules, the attribution of the specimen to Hyalonema is uncertain.
The distribution of ancient hexactinellids shows that they were more common in the neritic zone than their Recent counterparts. Development of hexactinellid sponges in the Late Cretaceous was correlated with high sea levels (Pisera 1999). It is also likely that the occurrence of lyssacinosids and other hexactinellids in Cretaceous European epicontinental seas, was related to the upwelling zones of the Tethys Ocean (see e.g., Mehl and Niebuhr 1995). The studied sections are located clearly southward of the for merly reported occurrences of lyssacinosids; the Tethyan influence could have been significantly higher.
The morphology and life function of lyssacinosids suggest that they were adapted to a low sedimentation rate and low turbulence, therefore they are located almost invariably in deeper shelf areas (e.g., W endt et al. 1989;Pisera and Busquets 2002;Beresi 2003). Only some thickwalled sponges from the Triassic might have lived below the fair-weather wave-base but above the storm wave-base (Pisera and Bodzioch 1991;Bodzioch 1994). In all of the studied sections, lyssacinosids are represented by thinwalled forms, similar to deep-water forms known from the Coniacian of Bornholm (Brückner 2006). Recent thinwalled (<5 mm) lyssacinosid sponges occur at depth of ca. 100 m or deeper (up to 7,000 m) (Tabachnick 2002a, c).
Some modern lyssacinosid sponges live on a hard sub strate, attached by a basal plate. Although basal plates occur in some fossil species (Pisera and Bodzioch 1991;Bodzioch 1994), they were not found in the studied spon ges, suggesting their adaptation to soft-bottom conditions. Such adaptation is also suggested by the occurrence of lophophytal sponges (with root tufts) and numerous iso lated long root tufts in the material studied (compare Brückner et al. 2003;Brückner 2006). The presence of lophophytal lyssacinosid sponges was used as an indicator of soft bottom conditions by Reid ( 1962) for the English Chalk Rock. Soft-bottom conditions in the studied suc cessions is also suggested by the presence of rhizoidal lychniscosid and hexactinosid sponges (see also Tarkowski 1991;Swierczewska-Gładysz 2006), infaunal echinoids (Maczynska 1968;Olszewska-Nejbert 2007), and some bivalves (Abdel-Gawad 1986).
The inferred life conditions of the studied sponges are also supported by other paleontological and sedimentological data. Packstone with foraminifera and spicules suggest calm water condition with periodic activity of weak currents. W eak currents favor the development of Recent hexactinellids (Leys et al. 2004;W hitney et al. 2005) and, consequently, are also inferred for the Creta ceous lyssacinosids.
Thin-walled lyssacinosid sponges can only be preserved intact when quickly buried (Bruckner et al. 2003;Brückner 2006). M ost of the specimens studied herein have been partly destroyed due to a prolonged residence time on the sea floor, suggesting a slow rate of sedimentation in all of the successions. Quite often, only the root tufts that were buried in the sediment during the sponges' lifetime have been preserved (Leys et al. 2007). The isolated root tufts of lyssacinosids and other non-rigid hexactinellid sponges were often described from other assemblages of fossil sponges, e.g., from Eocene of Catalonia (Pisera and Busquets 2002) or Permian of Texas (Rigby et al. 2007). The lack of well-preserved specimens and occurrence of dis persed spicules in the Campanian deposits result most likely from a slow rate of sedimentation and periodic weak bottom currents, which prevented the accumulation of the sediment and favored destruction of skeletons of dead sponges. Small specimens are more complete and may have been buried relatively quickly.
The significance of Lyssacinosida for bathymetric interpretation is confirmed by their distribution in the Cretaceous of the Opole Trough. Their occurrence in the Upper Marl Unit and absence from the underlying Marly Limestone Unit suggest deepening of the Opole Basin during the latest Turonian and Early Coniacian. This agrees well with the current bathymetric interpretation of the succession based on ichnofabrics (Kedzierski and Uchman 2001) and analysis of shark assemblages (Niedzwiedzki and Kalina 2003).
During the Campanian, the present-day M iddle Vistula Valley area and M iechow area were situated in the Danish-Polish trough (Hakenberg and Swidrowska 1998). According to bathymetric interpretations based on non cephalopoda molluscs from the M iddle Vistula River sec tion, Upper Campanian Piotrawin opokas were deposited in a mid to outer shelf setting (Abdel-Gawad 1986).
In the uppermost Campanian ( "I" . costaecus-"I". redbirdensis zones) of the Jedrzejow section (Miechow area) Lyssacinosida are not observed, suggesting shallower water conditions. This is confirmed by the replacement of hexactinellid sponges by lithistids in these zones (e.g., Reid 1968;Ulbrich 1974). In the stratigraphically equivalent deposits of the M iddle Vistula River section, where lychniscosid and hexactinosid sponges are less common, Lyssacinosida have not been noted (Swierczewska-Gładysz, 2012 and Chaunoplectella sp were recognized. The taxo nomic position of three other species is impossible to determine, because the specimens are poorly preserved without diagnostic spicules. Due to the lack of rigid skeletons, most of the specimens are strongly disinte grated, and occasionally only root tufts, composed of thick, long spicules, are preserved. In the studied section, three types of root tufts were recognized. 3. Cretaceous Lyssacinosids can be used as paleoenvironmental tools. The presence of thin-walled forms with root tufts indicates a soft bottom, slow rate of sedimentation, and calm and comparatively deep water conditions.