Uncovering the hidden diversity of Paleogene sponge fauna of the East European Platform through reassessment of the record of isolated spicules

MAGDALENA ŁUKOWIAK, ANDRZEJ PISERA, and TETIANA STEFANSKA

Łukowiak, M., Pisera, A., and Stefanska, T. 2019. Uncovering the hidden diversity of Paleogene sponge fauna of the East European Platform through reassessment of the record of isolated spicules. Acta Palaeontologica Polonica 64 (4): 871–895.

Despite being reported from various localities and stratigraphic intervals, knowledge of the siliceous sponges from the Cenozoic of Eastern Europe remains surprisingly limited. Studies assessing their diversity are almost exclusively in Russian and rather hard to obtain. The most comprehensive elaboration of the sponge spicules from the Paleogene of the East European Platform was published in 2003 and deals with material from Ukraine, Russia, Belarus, and Lithuania. However, the classification in that paper is purely artificial and extremely difficult to interpret according to modern biological criteria. A reassessment of this material is carried out, with the aim of revising all morphotypes of spicules, and identifying them to the lowest possible taxonomic level. Results suggest that the assemblage is much more diverse than previously thought, including members of 24 demosponge families (class Demospongiae), one homoscleromorph (class Homoscleromorpha), and at least one hexactinellid (class Hexactinellida). Our improved understanding of the diversity of Paleogene sponge fauna of the East European Platform will have implications for the interpretation of the past and future ecological and paleobiogeographic studies.

Key words: Demospongiae, Homoscleromorpha, Hexactinellida, spicules, Ukraine, Russia, Eocene.

Magdalena Łukowiak [mlukowiak@twarda.pan.pl] and Andrzej Pisera [apis@twarda.pan.pl], Institute of Paleobiology, Polish Academy of Science, Twarda 51/55 00-818 Warszawa, Poland.

Tetiana Stefanska [t.stefanska@ukr.net], Institute of Geological Sciences, National Academy of Science of Ukraine, O. Gonchar St. 55-B 02054 Kiev, Ukraine.

Received 20 February 2019, accepted 26 July 2019, available online 15 November 2019.

Copyright © 2019 M. Łukowiak et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

Modern sponges are inherent components of marine benthic communities with notable ecological roles (Díaz and Rützler 2001; Bell 2008; de Goeij et al. 2013; Mueller et al. 2014; Łukowiak et al. 2018) and substantial share in terms of their biomass (Conway et al. 2001; Hooper et al. 2002; Pansini and Longo 2003; Samaai 2006; van Soest 2007; van Soest et al. 2012). As can be expected, the same is true for Paleogene and Neogene paleocenoses worldwide (Pisera 1999).

To infer the origins of Recent sponge associations, numerous studies have focused on Cenozoic assemblages which have proved to be of unexpectedly diverse and abundant character. These include, for example, rich sponge faunas from the Eocene of Australia and New Zealand (Hinde and Holmes 1892; Hinde 1910; Kelly and Buckeridge 2005; Buckeridge et al. 2013; Łukowiak 2015, 2016; Łukowiak and Pisera 2016) and the Eocene and Miocene of Europe (Pisera and Busquets 2002; Matteucci and Russo 2005; Pisera et al. 2006; Frisone et al. 2014, 2016).

Loose sponge spicules have been described from the Paleogene and Neogene of the Atlantic Ocean (Ivanik 1983; Palmer 1988) and current reports show spicule-rich deposits from the Paleogene of central Ukraine (e.g., Konenkova et al. 1996; Pisera 2000; Ivanova 2014; Stefanska 2014, 2015; Stefanska and Stefansky 2014). Neogene assemblages include spicules from the lower Miocene of the Vienna Basin (Łukowiak et al. 2014), middle Miocene of Poland (Hurcewicz 1991), Portugal (Pisera et al. 2006), Czech Republic (Pisera and Hladilová 2004), Bosnia and Herzegovina (Ivanik 2002), Croatia (Pezelj et al. 2016), and southern Ukraine (Ivanova and Olshtynska 2004).

The most comprehensive study of disassociated sponge spicules from the Paleogene of the East European Platform is that of Ivanik (2003). The study deals with sponge spicules from numerous outcrops and boreholes situated in Ukraine, Russia (the Volga region, Don River Basin, Kaliningrad region), Belarus, and Lithuania. Nevertheless, the morphotypes of spicules described in that study were assessed only artificially and classified within parataxonomic units that are based purely on geometrical characters of the spicules.

Despite the richness of the sponges studied by Ivanik (2003), the study remains virtually unknown and inaccessible as it was published in a book that is hard to obtain and, except for the summary, written in Russian. Moreover, Ivanik (2003) offers only very general and brief discussion of biological meaning of parataxonomically-described material.

Unfortunately, Ivanik’s (2003) biological conclusions are only postulative, not demonstrative, i.e., he refers to numerous sponge taxa that supposedly existed in the study area during the Paleogene but does not illustrate the indicated spicule types, preventing independent evaluation. For example, Ivanik (2003) refers to the presence of “lychniscosans” (order Lychniscosida Schrammen, 1903) or Thrombus Sollas, 1886, but does not illustrate spicules that belong to these taxa. As such, the results of the study cannot be used directly to interpret sponge evolution, ecology, or paleobiogeography: while the work is comprehensive and rich, the utility of the publication is limited.

The aim of our study is to reassess Ivanik’s (2003) material in the light of currently accepted poriferan systematics by revising all spicule morphotypes and classifying them to the lowest possible taxonomic level. We also compare the spicules in Ivanik (2003) to their modern counterparts, allowing inferences of increased diversity to be made about the Paleogene sponges of the East European Platform. The study is expected to serve as a baseline for future ecological and paleobiogeographic reconstructions of ancient sponge fauna of this region.

Assignment of spicules to taxa

The plates published by Ivanik (2003: pls. 1–13) were reassessed following currently accepted systematics (see Boury-Esnault and Rützler 1997; Morrow and Cárdenas 2015) and rearranged to Figs. 1–10, with respect to their taxonomic affinities. The illustrations were slightly edited to improve their quality. Possible taxonomic affinities are summarized in Table 1. The most characteristic spicules are re-described, and their taxonomic position discussed in some detail, below. Additional spicule illustrations of Ivanik (2003: pls. 14–24) are not reproduced or re-illustrated as they are of poor quality, rendering the determination of spicule difficult. However, some of these are referred to in the text, and a reassessment of these spicules is presented briefly in Table 2.

Class Demospongiae Sollas, 1885

Subclass Heteroscleromorpha Cárdenas, Pérez, and Boury-Esnault, 2012

Order Tetractinellida Marshall, 1876

Suborder Astrophorina Sollas, 1887

Family Geodiidae Gray, 1867

Geodiidae indet.

Figs. 1C, E, J, N, 2Z.

Material.—Upper and middle Eocene, south-central Ukraine.

Remarks.—The bean-shaped to round massive microscleres with small projections tightly arranged on the spicule surface are considered to be sterrasters (Ivanik 2003: pl. 14: 1, 2, pl. 15: 1, 2; Fig. 1C, E, J, N ). They are found in two geodiid genera, Geodia Lamarck, 1815 and Caminus Schmidt, 1862 (compare Cárdenas et al. 2011 and van Soest et al. 2014: fig. 9). The spherical microsclere (Fig. 1B) may also belong to one of these genera (but affinity with Placospongia Gray, 1867 or even Tethyidae cannot be ruled out as well due to poor preservation). Likewise, the big, slender mesotriaenes with a characteristic shaft protruding from the both sides (Fig. 1K, I, V) are probably of geodiid affinity (compare Geo­dia garoupa in Carvalho et al. 2016 or G. praelonga in Sim-Smith and Kelly 2015). The same is true for characteristic tetraxial spicule with a long shaft and reduced two clads (Fig. 1W) that may belong to some Geodia (former Isops) species. Monaxonic spicules with bulb-shaped ending called exotyles (Fig. 5E) could be assigned to Geodia (Isops) but their vulcanellid, hadromerid, or raspailiid affinity is also possible (see Cárdenas et al. 2011). The same is true for some anatriaenes (Fig. 1L) and orthodichotriaenes (Ivanik 2003: pl. 22: 3; Fig. 1M, AB) which may belong to Geodiidae, Ancorinidae, or Pachastrellidae.

Amongst the illustrated spicules the plesiaster (Ivanik 2003: pl. 20: 2) most likely belongs to a geodiid sponge as well. However, more accurate taxonomic assignment is not possible due to the lack of characteristic features of this spicule.

Moreover, the short-shafted dichotriaene with flat, long leaf-shaped clads (Fig. 2Z) resembles triaenes of modern Penares Gray, 1867, especially those of P. sclerobesa Topsent, 1904 (compare Topsent 1904: pl. 10: 13). However, also some astrophorid lithistid demosponges are characterized by similar spicule types.

Genus Erylus Gray, 1867

Type species: Erylus mammillaris (Schmidt, 1862), Azores Canaries Madeira, Adriatic Sea, Recent.

Erylus sp.

Fig. 1A, G, H.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The flat, ellipsoidal spicules called aspidasters (Fig. 1A, G, H) are characteristic for geodiid Erylus Gray, 1867 (subfamily Erylinae Sollas, 1888; compare Adams and Hooper 2001: fig. 3I). Also other spicules (Fig. 5E, M) and some of the aspidasters (e.g., Fig. 1H), could belong to some other erylinin sponges e.g., Pachymatisma monaena Lendenfeld, 1907 (compare Lendenfeld 1907: pl. 35: 21–46). However, this assignment is highly speculative.

Family Ancorinidae Schmidt, 1870

Ancorinidae indet.

Figs. 1O, Z, 2E, H, K, R, U, V.

Material.—Lower, middle–upper Eocene, south-central Ukra­ine.

Remarks.—Spicules of ancorinid affinity are anatriaenes (Fig. 2H, K, U, V) and diaenes with wavy clads (Figs. 1Z, 2R). The latter ones resemble spicules of modern Tribrachium Weltner, 1882 (compare with van Soest 2017: fig. 51F). Also some of the pro- (Fig. 2E) and anatriaenes (Fig. 1O) could belong to ancorinids, e.g., Ecionemia Bowerbank, 1862 (compare van Soest and Beglinger 2009: fig. 7).

There are other spicules that could be assigned to Anco­ri­nidae, e.g., those from the Fig. 2Q (?Dercitus) and Fig. 10B (?Stryphnus; compare Sollas 1888: pls. 15, 6: 4–6); however, the later one can be also a dermal pentactine of Hexactinellida.

Genus Stelletta Schmidt, 1862

Type species: Stelletta grubii Schmidt, 1862 (type by subsequent desi­gnation), Adriatic Sea, Recent.

Stelletta spp.

Fig. 2A–D, F–J, L, P, T.

Material.—Cretaceous, lower Eocene, upper Eocene, lower Oligocene, south-central Ukraine.

Remarks.—Some of the big protriaenes (Fig. 2A, C), prodichotriaenes (Fig. 2I, L, P), and especially the protriaenes with massive shafts (Fig. 2B, D, G), resemble those of ancorinid Stelletta (compare Sim 1996: figs. 1–6). The same is true for incomplete anatriaenes (Fig. 2F, H, J, M) and orthodichotriaene (Fig. 2T) that resembles spicules of Stelletta (Myriastra) illustrated by Sollas (1888: pls. 12 and 14).

Family Pachastrellidae Carter, 1875

Pachastrellidae indet.

Figs. 3D, G–K, O–T, 7Y, 8L.

Material.—Lower Eocene, middle Eocene, upper Eocene, lower Oligocene, south-central Ukraine.

Remarks.—Pachastrellid affinity is apparent for numerous calthrops (Fig. 3T), mesotriaenes (Figs. 3D, I, K, O, P, 8L), mesodichotriaenes (Fig. 3J), and triods (Fig. 3Q, R) (compare Maldonado 2002; Łukowiak and Pisera 2016). A big plesiaster illustrated on the Fig. 3S may also be attributed to pachastrellids. It displays a great similarity to Characella pachastrelloides (Carter, 1876) (compare Lévi and Lévi 1989: fig. 33). The same is true for long club-shaped spicule (Fig. 7Y) whose morphology resembles that of the modern pachastrellid Ancorella paulini Lendenfeld, 1907 (compare with Lendenfeld 1907: pl. 12: 9). The pachastrellid affinity of some other spicules cannot be ruled out (e.g., Figs. 3A–C, F–H). However, these spicules might also belong to geodiids, calthropellids, ancorinids, or even tetillids.

Genus Triptolemma Laubenfels, 1955

Type species: Triptolemma cladosum (Sollas, 1888) (by original desi­gnation), Banda Sea, Recent.

Triptolemma sp.

Fig. 3M, N.

Material.—Lower and upper Eocene, south-central Ukraine.

Remarks.—The mesodichotriaenes with variously divided clads (Fig. 3M, N) are identical with spicules of pachastrellid genus Triptolemma. They show great resemblance especially to mesodichotriaenes of T. cladosum (Sollas, 1888) (compare Sollas 1888: pl. 35: 23).

Family Theneidae Carter, 1883

Theneidae indet.

Fig. 4A.

Material.—Middle Eocene, south-central Ukraine.

Remarks.—The long, thin protriaene (Fig. 4A) may be assigned to Theneidae. This type of spicules appear, e.g., in Thenea megaspina Lendenfeld, 1907 (Lendenfeld 1907: pl. 21: 20). The same applies for the diaenes (Fig. 1Y, AA) which resemble spicules of T. megaspina Lendenfeld, 1907 (compare Lendenfeld 1907: pl. 21: 21). However, geodiid affinity of the latter spicules cannot be ruled out either.

Family Thoosidae Cockerell, 1925

Genus Alectona Carter, 1879

Type species: Alectona millari Carter, 1879 (by monotypy), Celtic Sea, Recent.

Alectona spp.

Fig. 4I–K, O, P, R, T.

Material.—Middle–upper Eocene, south-central Ukraine.

Remarks.—The spiny triactines (also called acanthotriods) with long rays covered with spines regularly arranged in whirls (Ivanik 2003: pl. 21: 3, 4; Fig. 4I–K) resemble those of Alectona triradiata Lévi and Lévi, 1983 (compare Bavestrello et al. 1998: fig. 2a–c). However, the spicules of modern Alectona possess very well developed spines also on the ray tips while those from Ukraine lack the spines on the tips. Although, this difference in spines arrangement may be due to the poor preservation state of the fossil spicules.

In turn, the long, bent oxeas that are rather irregularly covered by minute spines (Fig. 4P) show great resemblance to spicules of modern Alectona primitiva Topsent, 1932 (compare Vacelet and Vesseur 1971: fig. 22).

The smaller acanthoxeas (Fig. 4O, R, T) are less bent in the middle of its shaft and regularly covered with minute spines. They are almost identical with the spicules of modern Alectona millari Carter, 1879 (compare Carter 1879: pl. 17: 3). The acanthorhabds (Fig. 4S), in turn, might be of alectonid affinity because similar spicules (diactines) have been described by Bavestrello et al. (1998) and assigned to Alectona sp. (see Bavestrello et al. 1998: fig. 7). Still, these spicules also resemble sanidasters of Crellastrina alecto Topsent, 1898 and spicules of some species of Halicnemia Bowerbank, 1864 (Stelligeridae; van Soest 2017: fig. 34).

Family Theonellidae Lendenfeld, 1903

Theonellidae indet.

Fig. 9A, D–H, L, O, P, R, U, X, Z.

Material.—Lower Eocene, middle–upper Eocene, Upper Creta­ceous, Paleocene, south-central Ukraine.

Remarks.—The most common lithistid spicules reported by Ivanik (2003) seem to belong to the family Theonellidae. These are mostly ectosomal phyllotriaenes (Fig. 9A, E, H, U), as well as discotriaenes (Fig. 9D, F, G). Such spicules are characteristic for Discodermia du Bocage, 1869 (discotriaenes) and Theonella Gray, 1868 (phyllotriaenes) and closely related genera. Presence of one or more of these genera is also supported by occurrence of rare fragmentary preserved tetraclone desmas (Fig. 9S, X, Z) that are characteristic for this family.

The ectosomal phyllotriaenes with complex morphology of the cladome (Fig. 9L, O, P) resemble those found in an undescribed theonellid sponge taxon from the Salomon Islands (AP unpublished material).

Family Pleromidae Sollas, 1888

Pleromidae indet.

Fig. 9J, K, N, Q, S–W, Y.

Material.—Lower Eocene, Upper Cretaceous, south-central Ukraine.

Remarks.—Pleromidae are commonly represented by smooth megaclones. Despite that some of the illustrated megaclones (Fig. 9J, K, N, Q, T–W, Y) are Late Cretaceous, the same type of spicules was also found in the Paleogene deposits (e.g., Fig. 9S, see figure caption).

Suborder Spirophorina Bergquist and Hogg, 1969

Family Samidae Sollas, 1888

Genus Samus Gray, 1867

Type species: Samus anonymus Gray, 1867; by monotypy.

Samus anonymus Gray, 1867

Fig. 4E, G, H.

Material.—Middle–upper Eocene, upper Eocene, south-­central Ukraine.

Remarks.—The spicules illustrated on the Fig. 4E and the partially preserved spicules on the Fig. 4G, H are amphitriaenes. These highly diagnostic spicules are almost identical in size (clads about 50 µm long) and shape with spicules of modern spirophorid sponge Samus anonymus Gray, 1867 (compare van Soest and Hooper 2002: fig. 1). The broken amphitriaene from the Fig. 4F seems to belong to Samus as well.

Family Tetillidae Sollas, 1886

Tetillidae indet.

Fig. 4D.

Material.—Middle and upper Eocene, south-central Ukraine.

Remarks.—The stout centrotylote oxea of about 230 µm of length (Fig. 4D) is of great morphological resemblance, and the same size, as the spicules of tetillids (compare e.g., Acanthotetilla gorgonosclera, van Soest 1977: fig. 4e). However, similar spicules can be found in geodiids (van Soest 2017: fig. 55d) and thoosids (e.g., Carballo et al. 2004: fig. 21d). The long thin anatriaenes (Fig. 4B, C) and acanthoxea (Fig. 6N) could belong to tetillids as well. The acanthoxeas of similar morphology are found, e.g., in Acanthotetilla walteri Peixinho, Fernandez, Oliveira, Caires, and Hajdu, 2007 (Peixinho et al. 2007: fig. 7c), but their coelosphaerid affinity is more likely.

Order Agelasida Hartman, 1980

Family Agelasidae Verrill, 1907

Genus Agelas Duchassaing and Michelotti, 1864

Type species: Agelas dispar Duchassaing and Michelotti, 1864 (by subsequent designation; Burton and Rao 1932), Eastern Caribbean, Recent.

Agelas spp.

Fig. 4L–N.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The long verticillate oxeas illustrated on Fig. 4L, M belong to Agelas. These spicules are equipped with 18 whorls of short tubercles regularly arranged along the spicule. They are similar with acanthoxeas of modern species of Agelas, especially A. axifera Hentschel, 1911 and A. sansibarica Perino and Pronzato in Manconi et al., 2016. These two species have in their skeletons verticillated oxeas of almost identical morphology (compare Hentschel 1911: fig. 54 and Manconi et al. 2016: fig. 3). The spicules illustrated by Ivanik (2003) seem to exhibit a greater resemblance to spicules of A. sansibarica as they are of comparable length and possess a similar number of whorls.

There is also one verticillate style (Fig. 4N) with regular whorls of tubercles that could be assigned to one of the Agelas species (compare spicules of Agelas ceylonica Dendy, 1905, illustrated by Manconi et al. 2016: fig. 11e).

Order Tethyida Morrow and Cárdenas, 2015

Tethyida indet.

Fig. 5Y, AE, AF, AG.

Material.—Middle Eocene, upper Eocene, Upper Creta­ceous, south-central Ukraine.

Remarks.—The oxyaster shown on the Fig. 5AF clearly belongs to Thetyida. This spherical spicule with divided ray tips is about 150 µm in diameter and might belong to some species of Timea Gray, 1867 (Timeidae; Timea diplasterina Rützler, Piantoni, van Soest, and Díaz, 2014: fig. 125c). However, it could also belong to Tethya Lamarck, 1815 (Tethyidae; compare Sarà 2002: fig. 9e). Also, various asters (~60–150 µm in diameter) might belong to Tethya (Figs. 1B, 5Y, AE, AG).

Order Axinellida Lévi, 1953

Family Axinellidae Carter, 1875

Axinellidae indet.

Fig. 5Q–T.

Material.—Middle–upper Eocene, south-central Ukraine.

Remarks.—Among the illustrated spicules, the 200–480 µm long flexuous oxeas (Fig. 5Q–T) may show axinellid affinities. However, flexuous oxeas are also characteristic for the heteroscleromorph family Bubaridae (compare Alvarez and van Soest 2002). Still, owing to the general shape and thickness of the discussed spicules, their attribution to Axinellidae is more likely.

Family Raspailiidae Nardo, 1833

Genus Plocamione Topsent, 1927

Type species: Plocamione dirrhopalina Topsent, 1927 (by monotypy), Azores, Canaries, Madeira (geounit), Recent.

Plocamione spp.

Fig. 5F–K.

Material.—Middle–upper Eocene, south-central Ukraine.

Remarks.—The spicules illustrated on the Fig. 5J, K and in Ivanik (2003: pl. 19: 3) are identical with spicules of the two raspailiid species, Plocamione carteri (Ridley and Duncan, 1881) and P. dirrhopalina Topsent, 1927. The skeleton of these two species possesses choanosomal acanthostrongyles (compare Hooper 2002: fig. 20d) of comparable size (50 µm in living and 34 and 45 µm in fossil representatives; Ridley and Duncan 1881: pl. 23: 19). The morphologies of the other choanosomal acanthostrongyles, illustrated on the same figure are very similar too (Fig. 5F–I). The style from the Fig. 3Q may belong to some Plocamione species as well (compare Hooper 2002: fig. 20a). Nevertheless, its vulcanellid affinity cannot be ruled out either.

The same is true for the long acanthostyle illustrated on the Fig. 5M which resembles the spicules belonging to the recent taxon Plocamione pachysclera (Lévi and Lévi, 1983) (compare Raspailia pachysclera Lévi and Lévi, 1983: fig. 12.2; Hooper 2002: fig. 20j). They are identical in terms of their morphology and size. Still, similar spicules also appear in erylinid Pachymatisma monaena Lendenfeld, 1907 (Lendenfeld 1907: pl. 35: 35).

The spicules illustrated on the Fig. 5E, L, N may belong to Plocamione as their morphology and size is comparable with some spicules of this extant genus (compare with Hooper 2002: fig. 20d).

Genus Janulum Laubenfels, 1936

Type species: Janulum spinispiculum (Carter, 1876) (type by original designation), South European Atlantic Shelf, Recent.

Janulum sp.

Fig. 5B–D.

Material.—Middle Eocene, south-central Ukraine.

Remarks.—The strongyles (Fig. 5B–D) are similar in size (165–250 µm) and morphology to acanthostrongyles of the modern raspailiid genus Janulum (compare Kelly et al. 2015: figs. 2, 3). The fossil spicules seem to have some signs of erosion in places where the spines in the modern spicules originate.

Order Haplosclerida Topsent, 1928

Family Petrosiidae van Soest, 1980

Petrosiidae indet.

Fig. 5V–X.

Material.—Middle–upper Eocene, south-central Ukraine

Remarks.—The strongyles (Fig. 5V–X) may belong to one of the species of Petrosia Vosmaer, 1885 (compare Petrosia davilai Alcolado, 1979, Silva and Zea 2017: fig. 2) or Xesto­spongia Laubenfels, 1932 (X. deweerdtae, Silva and Zea 2017: fig. 5).

Order Clionaida Morrow and Cárdenas, 2015

Family Clionaidae d’Orbigny, 1851

Genus Dotona Carter, 1880

Type species: Dotona pulchella Carter, 1880 (type by monotypy), South India and Sri Lanka.

Dotona sp.

Fig. 5U.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The verticillate cylindrical acanthostrongyle (Ivanik 2003: pls. 18: 5, 19: 1; Fig. 5U) covered with spirally coiled rows of tubercles and with microspined heads can be found in the modern clionaid Dotona pulchella Carter, 1880 (compare Calcinai et al. 2001: fig. 2a, b). However, the spicules of Dotona do not exceed 100 µm in length, while the spicules described by Ivanik (2003) are twice as long (200 µm). This type of spicules resembles also acanthostrongyles of acarnid Zyzzya (compare Z. fuliginosa [Carter, 1879], van Soest et al. 1994: figs. 19, 20).

Family Placospongiidae Gray, 1867

Genus Placospongia Gray, 1867

Type species: Placospongia melobesioides Gray, 1867 (by original desi­gnation), geounit Palawan/North Borneo, Recent.

Placospongia spp.

Fig. 1D, F.

Material.—Middle Eocene, south-central Ukraine

Remarks.—The bean-shaped to round, massive, 70–85 µm long microsclere spicules with polygonal plates between the grooves arranged on the spicule surface (Fig. 1D, F) are selenasters. This type of spicules is characteristic for clionaid genus Placospongia.

The nearly spherical spicule (Fig. 5AH) might also belong to this genus, except that it is considerably bigger than the spherasters typically found in Placospongia. As such, this assignment should be treated with caution.

Family Spirastrellidae Ridley and Dendy, 1886

Spirastrellidae indet.

Fig. 6X.

Material.—Middle Eocene, south-central Ukraine.

Remarks.—The anthasters (Fig. 6X); that is, spherasters with complex ray tips, are similar to the spicules characterizing modern spirastrellid Diplastrella megastellata Hechtel, 1965 (compare Rützler et al. 2014: fig. 19b).

Order Polymastida Morrow and Cárdenas, 2015

Family Polymastiidae Gray, 1867

Genus Sphaerotylus Topsent, 1898

Type species: Polymastia capitatus Vosmaer, 1885 (by original designation), geounit Northern Norway and Finnmark, Recent.

Sphaerotylus spp.

Fig. 6A–C.

Material.—Middle Eocene, middle-upper Eocene, south-­central Ukraine.

Remarks.—The club-shaped spicules (Fig. 6A, B) resemble exotyles of Recent Sphaerotylus, especially those of S. vanhoeffeni Hentschel, 1914 (Plotkin et al. 2017: fig. 29d). Also, the tylostyles (Fig. 6C, ?D) and a fragment of the club-shaped spicule (Fig. 6G) could be part of an exotyle and assigned to one of the Sphaerotylus species (compare Plotkin et al. 2017: fig. 18).

Order Poecilosclerida Topsent, 1928

Family Mycalidae Lundbeck, 1905

Genus Mycale Gray, 1867

Type species: Hymeniacidon lingua Bowerbank, 1866 (by subsequent designation; Thiele 1903), Celtic Seas, Recent.

Mycale spp.

Fig. 6H.

Material.—Middle Eocene, south-central Ukraine.

Remarks.—The nail-shaped spicule (Fig. 6H), even if incomplete and lacking a central button on its top, strongly resembles those of modern Mycale (Rhaphidotheca) loricata (Topsent, 1896) (compare van Soest and Hajdu 2002: fig. 13a, b). A club-like spicule (Fig. 6G) is similar to those in Mycale (R.) arctica Fristedt, 1887 (compare Koltun 1959: pl. 70: 25) and could be attributed to Mycale as well.

Family Coelosphaeridae Dendy, 1922

Genus Histodermella Lundbeck, 1910

Type species: Histodermella ingolfi Lundbeck, 1910 (by subsequent designation; Laubenfels 1936), South and West Iceland, Recent.

Histodermella spp.

Fig. 6N, O, Y, Z.

Material.—Middle Eocene, middle-upper Eocene, south-­central Ukraine.

Remarks.—The long oxeas that are spined along their whole length except for their tips (Ivanik 2003: pls. 20: 8, 9, 21: 1; Fig. 6N, O) could probably be assigned to Histodermella. This genus includes 4 extant species (van Soest et al. 2018). Three of those species (Histodermella kagigunensis Lehnert, Stone, and Heimler, 2013, H. natalenisis [Kirkpatrick, 1903], and H. inglofi Lundbeck, 1910) possess this type of spicules (compare Kirkpatrick 1903: pl. 6: 18; Lehrnert et al. 2013: fig. 1; Lundbeck 1910: pl. 4: 4).

In addition, the fusiform tylotes (Fig. 6Y, Z) can be found in H. natalensis as well (compare Kirkpatrick 1903: pl. 7: 18a). However, a coelosphaerid or myxillid (see below) affinity of that spicule (compare Coelosphaera [Coelosphaera] tubifex Thomson, 1873, Boury-Esnault et al. 1994: fig. 80a) cannot be ruled out either but is less possible.

Family Myxillidae Dendy, 1922

Genus Myxilla Schmidt, 1862

Type species: Myxilla (Myxilla) rosacea (Lieberkühn, 1859), Adriatic Sea, Recent.

Myxilla spp.

Fig. 6I, K, U, V.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—Several spicules of different morphology may be assigned to the family Myxillidae, or even to the genus Myxilla. These are the acanthostyles (Fig. 6I, K), and anisochelae (Fig. 6U, V). However, this attribution is not unambiguous and their referral to mycalids is also possible. Still, the slender fusiform tylotes (Fig. 6Y, Z), that were here ascribed to Histodermella, might be also of myxillid affinity.

Family Microcionidae Carter, 1875

Microcionidae indet.

Fig. 6E, F, J, M.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The acanthostyles with massively sculptured heads (Fig. 6E, F), as well as other acanthostyles illustrated on the same figure (Fig. 6J, M), could be assigned to some of the microcionid genera. For instance, the former resemble the acanthostyles present in modern Clathria (Thalysias) zeai van Soest, 2017 (compare van Soest 2017: fig. 95b, e). Similar spicules also appear in Discorhabdella Dendy, 1924 (compare Boury-Esnault et al. 1994: fig. 83a).

Order Merliida Vacelet, 1979

Family Merliidae Kirkpatrick, 1908

Genus Merlia Kirkpatrick, 1908

Type species: Merlia normani Kirkpatrick, 1908 (type by original designation), Azores, Canaries, Madeira, Recent.

Merlia sp.

Fig. 6L.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The small oval, ring-shaped spicule called clavidisc shown on Fig. 6L can be assigned to one of the species of Merlia. Four recent species of Merlia are distinguished and three of them, M. normani Kirkpatrick, 1908, M. tenuis Hoshino, 1990, and M. deficiens Vacelet, 1980, possess clavidiscs. The spicule that is illustrated here can be assigned to one of these species or its close relatives. It is worth noting that Merlia is characterized by basal calcareous skeleton that was not found in these deposits. Similar calvidiscs, not associated with basal calcareous skeleton, are known since the Early Jurassic (Wiedenmayer 1994).

Family Acarnidae Dendy, 1922

Genus Zyzzya Laubenfels, 1936

Type species: Zyzzya fuliginosa (Carter, 1879) (type by original designation), Torres Strait Northern Great Barrier Reef, Recent.

Zyzzya sp.

Fig. 6P–R.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The verticillate acanthostrogyles (Fig. 6Q, R) and acanthostrongyle (Fig. 6P) can be assigned to one of the species of Zyzzya. Five species are currently distinguished within this genus (van Soest et al. 2018). Amongst them, Z. fuliginosa (Carter, 1879) is characterized by presence of both these spicule types (compare van Soest et al. 1994: figs. 19, 20). The length of the acanthostrongyles found in modern Z. fuliginosa is up to 250 µm (see van Soest et al. 1994: table 2), while the fossil spicule is 165 µm long, thus falling within the range observable in that taxon. There are also some other spicules of similar morphology (Fig. 5U). However, contrary to the verticillate acanthostrongyles of Zyzzya, these spicules are strongly sculptured also at the tips. Such morphology makes their attribution to Acarnidae less likely.

Family Crellidae Dendy, 1922

Crellidae indet.

Fig. 4S.

Material.—Upper Eocene, south-central Ukraine.

Remarks.—The long acanthorhabd with slightly spirally twisted rhabd and long spines along the whole spicule (Fig. 4S) may belong to some sponges of the family Crellidae. Today, there is a single species known in this family, Crellastrina alecto which is characterized by similar, though smaller (up to 120 µm long), curved acanthoxeas (compare Topsent 1904: pl. 15: 16). Besides, the acanthoxeas present in this species are characterized by rugose spine tips which distinguishes them from the fossil spicules described by Ivanik (2003). Thus, the fossil spicule that is illustrated here may belong to unknown species of Crellastrina.

Other demosponge spicules

Material.—Lower Eocene, middle–upper Eocene, upper Eocene, Upper Cretaceous, south-central Ukraine.

Remarks.—The long bent oxeas (Fig. 2N, O) might belong to sponges of the suborder Astrophorina.

Pinakid spicules (Fig. 2W–Y); that is, flat oval discs with peripherally arranged gaps (that can be marginally open), are difficult to assign to a family level taxon as no such spicules are known in living sponges. They probably belong to some demosponges related to the geodiid Erylus, e.g., E. monticularis Kirkpatrick, 1900. This species possesses aspidasters that resemble the pinakids. Pinakids are quite common in the fossil record (Carter 1871; Mostler 1986: fig. 35.12–15, Schrammen 1924: pl. 7.43).

Some of the spicules illustrated by Ivanik (2003), such as those on Fig. 5O, P, resemble ophirhabds present in bubarid sponges. However, the general morphology of these spicules make their assignment difficult.

The desma illustrated on Fig. 9L is also difficult to be attributed to a taxon with certainty. Still, its morphology resembles the triders of Phymaraphinidae. The lithistid ectosomal irregular phyllo/dichotriaene (Fig. 9C) cannot be easily attributed to any lower taxon as well. On the contrary, the object (Fig. 8Q) illustrated by Ivanik (2003), attributed by him to the category of discoidal spicules, is actually a fragment of a diatom.

Class Homoscleromorpha Bergquist, 1978

Order Homosclerophorida Dendy, 1905

Family Plakinidae Schulze, 1880

Genus Placinolopha Topsent, 1897

Type species: Placinolopha bedoti Topsent, 1897 (by original designation), Banda Sea, Recent.

Placinolopha spp.

Fig. 8F–K, O.

Material.—Lower, middle, upper Eocene, south-central Ukraine.

Remarks.—Many spicules display features characteristic for the sponges of the smallest modern sponge class, Homoscleromorpha. They are characterized by the lophate actine tips. There are several 500–600 µm long lophodiactines (Fig. 8F–H, O) that resemble amphiclads of the Recent species Placinolopha sarai Lévi and Lévi, 1989 (compare Lévi and Lévi 1989: fig. 13). In turn, some lophoclathrops (Fig. 8I, J, possibly K) with long lophate clads characterize modern Placinolopha moncharmonti Sarà, 1960 (compare Sarà 1960: fig. 1).

Class Hexactinellida Schmidt, 1870

Hexactinellida indet.

Figs. 8B–E, 10A, B, D, E–G, I–L.

Material.—Middle, middle–upper Eocene, south-central Ukraine.

Remarks.—The hexactines illustrated on Fig. 10C, E, F, I, H are most probably dermal spicules of rosselid sponges (compare Tabachnick 2002b: figs. 18, 19). However, similar spicules can be found also in other hexactinellid groups, e.g., Euretidae Zittel, 1877 (order Sceptrulophora), Aphro­callistidae Gray, 1867 (order Hexactinosida), or even in the amphidiscosid family Pheronematidae Gray, 1870 (see Reiswig 2002a; Reiswig and Wheeler 2002; Tabachnick and Menshenina 2002b). Yet, their rossellid affinity seems most likely because another spicule illustrated on the same figure (Fig. 10J), called dermal triactine, is also noted in the rossellid sponges (compare Tabachnick 2002b: fig. 40d). Besides, a fragment of the sparsely tuberculated pentactine (Fig. 10A) can be attributed to rossellids as well. It resembles especially the hypodermal pentactines of Crateromorpha (Neopsacas) Tabachnick, 2002b (see Menshenina et al. 2007: figs. 2k, 7h; as well as Tabachnick 2002b: fig. 18e).

In turn, the hexactine with a rough, weakly tuberous surface, slightly bent rays, and one ray fusing with a fragment of another spicule (Fig. 10K) seems to be a part of dictyonal framework of hexasterophorid sponges (see Reiswig 2002b: figs. 2b, 3c; 2002c: fig. 2b–d; Reiswig and Wheeler 2002: fig. 8B).

Some anchorate basalia (Fig. 10J) may belong to phero­nematid sponges (compare Lévi and Lévi 1989: fig. 2).

Some pentactines (Figs. 8B, 10B) and stauractines (Fig. 10M) resemble dermalia of Symplectella Dendy, 1924 (Lys­sa­cinosida, Euplectellidae) (see Tabachnick 2002a: fig. 27f–h).

The oxyhexactines (Figs. 8C, 10L) show some affinity to choanosomal spicules of Hyalonema Gray, 1832 (Amphi­discosida, Hyalonematidae) (see Tabachnick and Menshenina 2002a: fig. 1l). Amongst the spicules of unquestionable hexactinellid affinity are also those illustrated on Figs. 8B, D, E, 10K, but their more accurate attribution is impossible.

Concluding remarks

A reassessment of the disassociated Paleogene sponge spicules from the southwestern of the East European Platform studied by Ivanik (2003) revealed a diverse sponge fauna. The fauna appears to be dominated by Demospongiae (at least 24 families) while Hexactinellida were relatively rare but diverse. The majority of spicules attributable to hexactinellids appear to be dermal pentactines and their derivatives, most likely representing the family Rossellidae. Potentially, a single genus of Homoscleromorpha was recognized as well.

This reassessment, together with a new as yet unpublished material (MŁ, AP, and TS, unpublished data), will serve as a baseline for further taxonomic, ecological, and biogeographic studies of the poorly known Paleogene sponge fauna of this region.

Acknowledgements

We would like to thank Viviana Frisone (Museo di Archeologia e Scienze Naturali “G. Zannato”, Vicenza, Italy) , Michelle Kelly (NIWA, Wellington, New Zealand), and an anonymous reviewers whose suggestions helped to considerably improve this manuscript. We would like to thank Daniel Madzia (Institute of Paleobiology, PAS, Warsaw, Poland) for linguistic help. This study was financially supported by National Science Centre Grant No. 2016/21/B/ST10/02332 to AP.

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Acta Palaeontol. Pol. 64 (4): 871–895, 2019

https://doi.org/10.4202/app.00612.2019