Serpulidae, Rafinesque, 1815

Słowiński, Jakub, Vinn, Olev, Jäger, Manfred & Zatoń, Michał, 2022, Middle and Late Jurassic tube-dwelling polychaetes from the Polish Basin: diversity, palaeoecology and comparisons with other assemblages, Acta Palaeontologica Polonica 67 (4), pp. 827-864 : 852-859

Serpulidae sp. 4

Fig. 13C .

Material.— Six specimens (four partially preserved, attached to oyster shells and two specimens detached) from the lower Kimmeridgian ( Upper Jurassic ) of Małogoszcz , Mesozoic margin of the Holy Cross Mountains, Poland (see Table 1); GIUS 8-3747 .

Description.—Tubes large (up to 30 mm long, however, none of the specimens fully preserved), externally covered with prominent growth lines running perpendicularly to the tube long axis but showing no other ornamentation. Some thick, slightly curved tubes are attached to the substrate, but most specimens represent broken off anterior tube fragments. The cross-section is circular with the diameter up to 2 mm.

Remarks.—The specimens are superficially similar in general outline to Glomerula gordialis ( Schlotheim, 1820) apart from the perpendicular growth lines and much thicker tubes.

Discussion

Serpulid and sabellid diversity and distribution across palaeoenvironments.—The use of cluster analysis allowed us to group the investigated fossils into several clusters ( Fig. 14 ). The study shows that serpulids and sabellids are highly dependent on the habitat, especially the substrate they are cemented to, whereas the geological age or the stratigraphical distance between compared localities plays a minor role. This is in agreement with studies of other ancient serpulid and sabellid tubeworms. Although some morphotypes might have not been confined to certain substrates (e.g., Kočí et al. 2019), the nature and resultant physical properties of the substrate appear to have been among the most crucial factors inducing serpulid and sabellid colonization (see Ippolitov 2010). However, tube-dwelling polychaetes in general are also reliant upon factors other than substrate. Temperature, oxygen and salinity levels, as well as light availability might also influence larval settlement ( Kupriyanova et al. 2019).

The tube-dwelling polychaetes are preserved attached to a variety of available hard substrates (see Fig. 15 ). The highest similarity in serpulid and sabellid communities between certain localities is displayed between hiatus concretions and oncoids ( Fig. 14 ), both of which served as mobile substrates prone to physical disturbances (e.g., Wilson 1987; Zatoń et al. 2011a, 2012), differing, however, in the nature of encrusted surface, which had a quantitative and (to a lesser extent) qualitative impact on the communities. Relatively similar to them are hardgrounds sensu stricto, where all taxa present on mobile rockgrounds occur as well. Hardgrounds, hiatus concretions and oncoids evidently witnessed, albeit to a different degree, time-averaging, so that factor could have potentially played a role in composition of tubeworm assemblages. The serpulid and sabellid faunas at the hardground localities are among the most diverse.

Tubeworm faunas encrusting oyster shell beds and those encrusting bivalve shells derived from soft muddy substrates exhibit moderate similarity levels ( Fig. 14 ). Although the substrate available for tube dwelling polychaete colonization was similar, the prevailing conditions were quite different. Low taxonomic variability of serpulid and sabellid worm tubes encrusting parautochthonous oyster shells from the lower Kimmeridgian of Małogoszcz possibly was a result of impeded colonization in a relatively shallow marine environment affected by storm episodes ( Machalski 1998). On the other hand, oyster shells and their aggregations, together with belemnite rostra, provided isolated benthic islands (e.g., Zuschin et al. 1999; Taylor and Wilson 2003) on otherwise muddy seafloor in relatively calm (below storm wave-base) palaeoenvironments (Gedl et al. 2012). On a soft-bottom, they offered a sufficiently stable substrate for colonization and further establishment of populations. Such conditions led to the highest taxonomic variability among the all palaeoenvironments.

The community from the lower Oxfordian (Upper Jurassic) sponge bioherms of Zalas shows the highest taxonomic dis- tinctness ( Fig. 14 ). Biotic substrate provided by sponges led to domination by usually compact (e.g., Placostegus planorbiformis ) and fast-growing forms with minute diameters (e.g., Cementula spirolinites ) and possibly hampered colonization of larger, slowly growing serpulids.

For the majority of localities and settings, moderate Simpson Index of Diversity (1-D) and Dominance (D) values indicate intermediate polychaete variability, with no species highly dominating (see Table 2). Such diversity and dominance values are confined to locations with intermediate levels of hydrodynamic and physical disturbances (e.g., Wilson 1987). Highest biodiversity has been noted on upper Bathonian–lower Callovian and Callovian hardgrounds (Bolęcin and Zalas, respectively) and upper Bajocian– lower Bathonian oncoids (Ogrodzieniec-Świertowiec) (see Table 2);it may attest to time-averaging of deposits with lowered sedimentation rates (hardgrounds) and particularly favourable conditions (oncoids). Slightly lower, but still among the highest diversity levels of Simpson and Dominance indices, are serpulid and sabellid communities derived from middle Bathonian skeletal remains from Gnaszyn Dolny, serving as benthic islands on the soft sediment (see Table 2). Such quiet water conditions may have fitted best with the feeding strategy of most tube-dwelling polychaete species. Based on the values of Shannon index (H), polychaetes from these substrates, together with hardgrounds, are also among the most diverse, followed by oncoids (see Table 2). Evenness values point to moderate (in the case of oncoids from Ogrodzieniec-Świertowiec and lower Kimmeridgian oyster shell beds from Małogoszcz, as well as a part of hiatus concretion localities, e.g., Ogrodzieniec, upper Bathonian), or even low biodiversity (in the case of a part of hiatus concretion localities, e.g., Krzyworzeka, upper Bathonian, and the Callovian hardground of Zalas) (see Table 2), which is an effect of similar proportions of different species’ representatives within these assemblages. The lowest evenness level in the case of the middle Bathonian (Middle Jurassic) of Gnaszyn Dolny (see Table 2) testifies to the highest species richness and abundance of both species and individuals at this locality, indicating highly advantageous palaeoenvironmental conditions (see Table 1).

Mobile rockgrounds.—Both fossil (e.g., Wilson 1985; Lee et al. 1997; Zatoń et al. 2011a) and Recent (e.g., Osman 1977; Sousa 1979; Maughan and Barnes 2000; Kuklinski 2009) encrusting biotas inhabiting mobile lithic substrates are strongly affected and restrained by physical disruptions within marine environments, which strongly influences the ecology of substrate-dwellers. Generally, an increase in physical en- ergy in the environment leading to frequent overturning of loose lithic substrates such as hiatus concretions and oncoids causes an increase in diversity of the fauna and hampers single species prevalence (Wilson 1987; Barnes and Kuklinski 2005). On the other hand, too high levels of physical disturbance, where the cobble and pebble overturning is continuous and frequent, may be destructive, leading to a lethal outcome even for the most opportunistic, robust, and scour-resilient serpulids, highly impeding any ecological succession.

Sediments from which the concretions were derived are interpreted to have been deposited in calm conditions, usually located below storm wave-base (e.g., Leonowicz 2013). Hiatus concretions ( Majewski 2000; Zatoń et al. 2006, 2011a) and such sedimentological fabrics, as e.g., trace fossil associations, alternating laminated and bioturbated intervals, or biodeformational structures ( Leonowicz 2015a) within the Middle Jurassic siliciclastic sediments of the Polish Jura indicate episodic storm events causing distinct sedimentation breaks and seafloor erosion. Rather rare episodic overturning of the mobile substrates resulted in relatively low diversity (in total five species, Table 1) leading to a predominance of robust, thick-walled species of Propomatoceros and ubiquitous Glomerula gordialis .

The shape and regularity of the concretions’ surfaces is another important factor strongly influencing the quantity and distribution of serpulids and sabellids (Wilson 1987). Larger and more rounded hiatus concretions (as well as oncoids; see below) were less resilient to hydrodynamic events and overturning on the sea bottom, compared to wider and more flattened ones. While resting on the seafloor, only the upper sides of these substrates were available for serpulid and sabellid colonization, while lower surfaces facing the sediment were inaccessible. It is possible that even such relatively stable concretions did not offer full stability against overturning. Minor differences in the encrustation pattern between certain localities seem to reflect slight disparities in the general concretions’ outlook which in turn presumably resulted from the frequency of episodic hydrodynamic activities, depth of concretions’ burial or biological activity of animals inhabiting firmgrounds (Zatoń et al. 2011a). The differences in concretions’ bioerosional patterns between the localities, likewise, reflect the position of the certain setting (proximal/distal) and thus the intensity and the frequency of palaeoenvironmental currents ( Sadlok and Zatoń 2020). Organisms burrowing in the ambient sediment might have also loosened it enhancing exhumation of the concretions ( Hesselbo and Palmer 1992).

The most important serpulid and sabellid adaptive strategies for persistence on mobile lithic grounds (Wilson 1987) were: (i) the morphological resistance to abrasion which was possible by hard and solid tubes; (ii) cavity dwelling; hazard- ous impact of repeated substrate overturning in highly energetic environments might have entailed attempts of withdrawal, whenever an opportunity had arisen. Tube-dwelling polychaetes often resolve to cryptic lifestyle ( Kobluk 1988) hiding in places such as empty borings and concavities (e.g., Palmer and Fürsich 1974; Wilson and Palmer 1990; Palmer and Wilson 1990; Wilson 1998; Taylor and Wilson 2003; Mallela 2007; Schlögl et al. 2008). Such a solution facilitates also retreating from competition with dominating species. Anyhow, in spite of the presence of borings, some of the tubes encrust the surface of the concretions. A possible explanation is that such cavities have already been occupied by boring bivalves, which made the unavailable for nestling by tubeworms, thus of necessity colonizing the outer surface (see also Zatoń et al. 2011a).

Concretions from Mokrsko, Bugaj, Ogrodzieniec, Krzyworzeka, and Żarki experienced high taphonomic loss as the vast majority of encrusters inhabiting the surface of the concretions were prone to abrasion/corrasion, what is evidenced by many poorly preserved fossils, presumably representing various ecological successions.

Although serpulids and sabellids inhabiting large oncoids are only slightly more taxonomically diverse than that from hiatus concretions, attaining one species more (in total six species, Table 1), their abundance is much higher. Tube-dwelling polychaetes thrived inhabiting these coated grains in spite of the fact, that cryptic places were highly limited by the lack of borings, which were common on the hiatus concretions. Intense colonization and further flourishment of serpulids and sabellids must have been enhanced by the photic conditions, where cyanobacterial mats covering oncoids could develop (Zatoń et al. 2012; Słowiński 2019). A high availability of food supply, especially composed of mixed algae species, significantly induced larval development and subsequent growth ( Leone 1970; Kupriyanova et al. 2001; Gosselin and Sewell 2013). Although algal mats covering substrates may hamper epibionts’ development ( McKinney 1996; Kuklinski 2009; Zatoń et al. 2011b), they may also facilitate it (Wieczorek and Todd 1998; Kupriyanova et al. 2019). Additionally, in contrast to the tubeworms encrusting hiatus concretions, tubeworms colonizing oncoids were able to settle on the not yet lithified substrate during the formation of possibly still mucous biofilm forming on the oncoids Taylor and Wilson 2003). Another advantage of oncoids over hiatus concretions (serving as a substrate for colonization) is that their stability might have been enhanced during growth. The formation of subsequent cortex layers increased the volume and thus reduced the susceptibility to overturning on the sea bottom.

Hardgrounds.—Serpulids and sabellids from hardgrounds are derived from two localities (Zalas and Bolęcin) of slightly different in palaeoecological conditions. Limited supply of sediment and resulting time-averaging ( Giżejewska and Wieczorek 1977; Tarkowski et al. 1994; Mangold et al. 1996; Taylor 2008; Zatoń et al. 2011b) strongly influenced encrustation patterns of both communities. The species richness of tube-dwelling polychaetes in these localities could have resulted from favorable palaeoenvironmental conditions and long-term exposure of the hard substrates; however, some time-averaging responsible for the final assemblage preserved is not excluded (Taylor 2008; Zatoń et al. 2011b).

The Zalas deposits are characterized by a much more abundant and more taxonomically diverse sessile polychaete fauna (in total nine species, see Table 1) as compared to Bolęcin (in total six species, see Table 1). Such differences presumably resulted from more favourable conditions for the settlers, such as a relatively steady salinity level, a calm, sublittoral environment located within a dysphotic zone (Zatoń et al. 2011b), and a slow sedimentation rate at Zalas ( Giżejewska and Wieczorek 1977). The total number of tube-dwelling polychaetes from Bolęcin, the deposits of which may be an equivalent of the uppermost Bathonian– lowermost Callovian Balin Oolite (e.g., Tarkowski et al. 1994; Mangold et al. 1996; Taylor 2008), is not among the lowest. However, the investigated number of substrate-serv- ing fossils was ample. Therefore, the percentage of inhabiting sessile polychaetes is low, possibly due to higher abrasion levels and Quaternary periglacial events, which may have reworked the sediments ( Mangold et al. 1996), affecting the preservation of the fossils.

Any reciprocal interactions (see Taylor 2016) were very rare, or even absent in Bolęcin; therefore, most of them might have simply resulted from random settling of worms in close proximity and are not an evidence of spatial competition Zatoń et al. 2011b; Taylor 2016). Most often, tube-dwelling polychaetes are overgrown by bryozoans and other polychaetes, both of the same and different genera, sup-

porting an explanation of random and post-mortem overgrowth on a small surface of substrate (Taylor and Wilson 2003). Anyhow, a scarce number of mutual (reciprocal) overgrowths and intraspecific stand-offs (“when growth of both interacting individuals is halted at their junction”; see Taylor 2016) may suggest that at least some sclerobionts, notably serpulids, were actively competing for available substrate. Some individuals tended to grow towards the deflections between Ctenostreon proboscideum (Sowerby and Sowerby, 1820) shell ribs or on the underside of lower valves indicating the preferences of inhabiting cryptic niches.

Oyster shell beds.—In the shell beds with Actinostreon gregareum (Sowerby, 1815) within lower Kimmeridgian (Upper Jurassic) deposits of Małogoszcz quarry, many oyster shells which served as substrate for serpulids and sabellids are disarticulated. The oysters set up parautoch- tonous accumulations, resulting from storm events in a relatively shallow-marine environment (Seilacher et al. 1985; Machalski 1998; Zatoń and Machalski 2013). In spite of the high substrate availability for these polychaetes, their colonization was there impeded by mode of life of the oysters. These bivalves displayed different kinds of ecophenotypic adjustments, such as mud-sticker mode of life populating the sediment in a vertical position, sometimes cementing to other individuals; and recliners, which lay flat on the sediment and might have cemented to various hard objects, as e.g., fragmented rocks, shells or oncoids ( Machalski 1998). While the flat-lying shells provided convenient settling conditions and relatively much space, in the vertically arranged ones, it was highly limited, especially when only an anteriormost part of the shell protruded from the sediment.

Possibly, a part of the shells forming small clusters of cemented valves, which displayed a three-dimensional shape might have been occasionally overturned. Such a situation occurred in slightly younger shell beds with Nanogyra nana (Sowerby, 1822) from the lower Kimmeridgian (Upper Jurassic) of Małogoszcz, which contributed to the formation of ostreoliths (Zatoń and Machalski 2013). Such large, spherical objects were prone to overturning due to hydrodynamic and biological agents (Zatoń and Machalski 2013). However, even isolated shells or shell clusters exhibiting rather flat morphology presumably might have been occasionally overturned due to their smaller sizes and a relatively shallow marine palaeoenvironment with episodic storm events ( Machalski 1998; Radwańska and Radwański 2003).

The diversity of serpulid and sabellid fauna from these deposits is among the lowest of all the sites investigated (in total four species, Table 1). On the ostreoliths mentioned above, Zatoń and Machalski (2013) noted only two sessile polychaete species. Interestingly, similarily low sessile polychaete diversity was noted on lower Kimmeridgian carbonate cobbles from nearby Sobków locality by Krajewski et al. (2017). Presumably, such low diversity might have been governed by salinity fluctuations in shallow water settings, as evidenced by stable isotopes ( Krajewski et al. 2017).

Nonetheless, oysters provided a range of places to be colonized, offering many cryptic and upward-facing habitats, what may reveal encrusters’ polarization. Although the slight majority of tube-dwelling polychaetes inhabited the exterior surfaces of the valves (Szewczuk 2010), many of them settled on the interiors, evidencing that encrustation of the oyster shells also took place post-mortem (e.g., McKinney 1995; Fagerstrom et al. 2000). Clustered oyster valves also could have acted as a good cryptic habitat due to an increased accessibility of fissures and crevices (e.g., Kidwell 1986; Zuschin et al. 1999; Coen and Grizzle 2007; Zatoń and Machalski 2013).

Soft muddy substrates.—Serpulids and sabellids derived from the middle Bathonian (Middle Jurassic) of Gnaszyn Dolny and lower Bathonian (Middle Jurassic) of Kawodrza Górna inhabited mainly oyster shells and belemnite rostra, as well as wood-falls (see Kaim 2011), scattered over the soft muddy seafloor. Thus, biogenic substrates suitable for sclerobiont colonization were very patchy. Tube-dwelling polychaetes on such benthic islands frequently occur crowded, forming dense aggregations, and exhibit the highest diversity among the all studied sites (in total eleven species, see Table 1).

In contrast to other kinds of substrates, oyster shells provided here a sufficiently stable habitat for the encrusters. The sediments are interpreted to have been deposited in a relatively deep, calm, oxygenated environment below the storm-wave base ( Marynowski et al. 2007; Zatoń et al. 2009; Gedl and Kaim 2012; Gedl et al. 2012). However, colonization might have been intermittent as presumably a bulk of larvae did not even have a chance to settle on a convenient hard substrate. In the case of successful colonization, subsequent larvae possibly had a greater chance to be recruited in the direct vicinity because of available adjacent space. Even though serpulid larvae exhibit either lecithotrophic or planktotrophic larval development strategies ( Kupriyanova et al. 2001; Rouse and Pleijel 2001), many serpulids settle non-randomly ( Kupriyanova et al. 2019), which may result in a relatively distant dispersal ( Andrews and Anderson 1962; Dirnberger 1993; Kupriyanova et al. 2001). The larvae may develop into dense monospecific assemblages with regard to attached individuals of their own species ( Scheltema et al. 1981). To encourage gregarious settling, chemical signals associated with living adults may be used ( Pawlik 1992; Toonen and Pawlik 1996; Bryan et al. 1997). On the other hand, the absence of a mature source population in close proximity to an accessible hard substrate will highly reduce the chance of recruitment (see Taylor and Wilson 2003).

Restriction of the surface may have resulted in occa- sional competitive interactions. Despite difficulties in a clear designation between syn vivo and post-mortem interactions (see Fagerstrom et al. 2000), possibly at least a part of overgrowths between epibionts did not result from overgrowing dead skeletons. Although clear reciprocal overgrowths are absent, a part of intraspecific interactions resulted in stand-offs (see Taylor 2016). Such an outcome may support the interpretation that encounters of the same species acted syn vivo (Taylor 2016). It is evident that some sclerobionts colonized the interiors of bivalve valves, being a proof of post-mortem colonization (e.g., McKinney 1995; Fagerstrom et al. 2000). Some tubes of Propomatoceros lumbricalis also acted as hosts for in vivo bioclaustrating hydroids; however, such interactions were extremely rare (Słowiński et al. 2020).

Large, flat-lying oyster valves were highly resilient against physical agents, especially in calm settings as in the present case, offering a stable substrate, where irregularly, slowly growing, large Propomatoceros lumbricalis constituted the basis of the community. Smaller, compact and faster-growing tube-dwellers were outcompeted. Nonetheless, because sclerobionts were substrate-restricted in settlement and colonization, they were forced to settle together with more opportunistic and thus dominating polychaetes, sometimes displaying cryptic behavior, encrusting e.g., the deflections between the oyster shell ribs. A different situation occurred on the substrate provided by belemnite rostra. Regardless of the calm palaeoenvironment, they were less stable on the seabed, being much more susceptible to any disturbances. Despite scarce exceptions, robust, slowly growing species were unable to successfully colonize the rostra, whereas smaller species like species of Nogrobs showed higher plasticity enabling them to adjust to such small, conical/cylindrical substrates. Yet another ecological adjustment was performed by flat, free-living Nogrobs aff. tetragona , which was favored by a slow sedimentation rate. Possibly, juvenile representative first encrusted a small surface of any hard substrate available, subsequently detaching, and terminating as a free-lying on the soft sediment ( Sanfilippo 2009). Rare, curved tube portions may have resulted from shifting due to a response to a temporary instability within a sediment, showing an attempt to avoid ecologically unpleasant conditions (Fig. 9H; see also Sanfilippo 2009: fig. 6A, C, L). Alternatively, they may have lived embedded within the sediment with only their apertures protruding and lying upon the sea floor, as do the Recent soft bottom-inhabiting species Ditrupa arietina ( Hove and Smith 1990; Vinn et al. 2008b).

Due to a stable palaeoenvironment with low hydrody- namics (Gedl et al. 2012), most encrusters were not intensively abraded, which attests that negative taphonomic processes affecting the fossil assemblages were insignificant.

Sponge build-ups.—The substrate for the tube-dwelling polychaetes from the Oxfordian (Upper Jurassic) of Zalas was provided by lithistid sponges (Trammer 1982), that formed biohermal structures (Trammer 1982, 1985; Ostrowski 2005; Matyszkiewicz et al. 2012). Such sponge mounds provided “live” substratum for sclerozoans. With respect to taxonomic composition (in total five species, Table 1), sessile polychaetes are here completely different from the all other sites, as the species composition was presumably strongly influenced by substrate-specific preferences (see Kupriyanova et al. 2001, 2019; Ippolitov 2010).

Relatively calm environment, quite low sedimentation rates, and high nutrient availability ( Matyszkiewicz et al. 2012) probably escalated spatial and resource competition ( Palmer and Fürsich 1981). Faster calcification rates seem to have been favored in the environment of the reefal substrate, which promoted polychaetes, which were easily adaptable to the prevailing conditions by a higher ecophenotypic plasticity. It may explain the absence of any species of Propomatoceros within sponge build-ups of Zalas. Conspicuous in this population is also the relative scarcity of Glomerula gordialis . Being rather easy-adjustable to different conditions (e.g., Parsch 1956; Ippolitov 2010; Vinn and Wilson 2010; Breton et al. 2020), this sabellid is here dominated by much more abundant and possibly more opportunistic Cementula spirolinites , which tended to occur in the advantageous conspecific aggregations (e.g., Palmer and Palmer 1977; Palmer and Fürsich 1981; Schlögl et al. 2008).

Tube-dwelling polychaetes from Zalas were attached to both sides of the sponges, being slightly more numerous on the exterior (33% compared to 22% on the interior, as calculated from Kuziomko-Szewczuk 2010). Such a polarization of space occupation could have arisen from relatively equal preferences towards certain sides. Anyway, it appears that more serpulids and sabellids inhabited the external sides of sponges. With their often irregular shapes, these principal frame-builders provided a variety of microhabitats where tubeworms might have led a cryptic mode of life ( Riding 2002). Outwardly projected growth of sponges, laterally widening to the top possibly provided shaded, cryptic niches on the undersides of the mushroom-shaped sponge skeleton Palmer and Fürsich 1981; Wilson et al. 2008).

Many sponges are fragmented, limiting an insight into actual shape of the entire organism. Such fragments possibly constituted a biohermal talus. Nevertheless, the differences in the level of tube-dwelling polychaete encrustation on both sides seem to be small. Presumably, they were able to settle on any available hard substrate provided by sponges surrounded by soft sediment (see Trammer 1982, 1989).

Remarks on serpulid and sabellid evolution during the Middle and Late Jurassic.—Following the radiation that commenced in the aftermath of the Triassic/Jurassic mass extinction, significant diversification of tube-dwelling polychaetes occurred during the Early and Middle Jurassic, when the total number of known morphotypes increased greatly. However, the Middle Jurassic was also a time of a relative stagnation within the already established clades, such as e.g., the sabellid Glomerula and serpulids Filograna , three-keeled Metavermilia , or Propomatoceros see Ippolitov et al. 2014, for a review). Among the new evolutionary clades that appeared is Metavermilia striatissima ( Fürsich et al. 1994) , regarded as a possibly separate minor lineage within the genus Metavermilia , and

Genicularia ( Quenstedt 1856: 589) , a genus which has not been reported in the Polish Basin.

Biostratigraphy of serpulids is highly constrained (but see Macellari 1984; Tapaswi 1988) and specific morphotypes most often do not correspond to certain stratigraphic intervals. It is further complicated by slow intrageneric radiation during the Middle Jurassic and an increase in tube disparity within particular species, which possibly may be an outcome of the evolution of the group, but also a result of some local, ecophenotypic adjustments. These make taxonomic attribution of many Jurassic serpulids and sabellids problematic, and there is still no widely acknowledged current scheme of species and morphological or stratigraphical borders between species in most of these clades.

The serpulid fauna became more diversified with the emergence of sponge and microbial facies. The advent of some new forms occurred during Oxfordian (Late Jurassic), when such build-ups became widespread in Europe (e.g., Goldfuss 1831; Parsch 1956; Trammer 1982; Pisera 1991; Radwańska 2004; Matyszkiewicz et al. 2012), and locally being present even in the Bathonian (Middle Jurassic; Palmer and Fürsich 1981). Such new forms include here “ Serpula cingulata ”, Cementula spirolinites , Placostegus planorbiformis , and Filogranula spongiophila sp. nov. However, tube-dwelling polychaete faunas during the Oxfordian and Kimmeridgian beyond these reefal deposits still remained rather “old-fashioned” (e.g., Wignall 1990; this study). Such distribution supports an explanation for high substrate-de- pendent serpulid and sabellid settlement ( Ippolitov 2010).

Apart from the serpulid genera of clade BII represented by monophyletic Spirorbinae , members of all the informally established clades (see Kupriyanova et al. 2009) are present in our material. Some of them, like e.g., Filogranula , which possibly is a polyphyletic taxon (see Ippolitov et al. 2014; Kočí and Jäger 2015a) need further investigation. However, such considerations, although essential, are beyond the scope of the present study.

Comparisons with other Middle and Upper Jurassic tube-dwelling polychaete assemblages.—The great majority of all known Middle and Late Jurassic tube-dwelling polychaete communities are described from Europe, including the European part of Russia (among more recent publica- tions e.g., Pugaczewska 1970; Jäger et al. 2001; Radwańska 2004; Ippolitov 2007a, b; Kočí et al. 2019; Breton et al. 2020). Except of some clearly outdated studies (e.g., Parsch 1956), the majority of these reports dealt with assemblages coming from single stratigraphic intervals (e.g. Ippolitov 2007a, b), or with assemblages which were not the main objective of the investigation (e.g., Zatoń et al. 2011a). Thus, this research dealing with fossil material spanning the upper Bajocian to lower Kimmeridgian, representing a variety of palaeoenvironments, may serve as a potential reference point for future investigations.

Relatively little data is available on Jurassic serpulids and sabellids settling on mobile rockgrounds. Investigations by Kaźmierczak (1974), Chudzikiewicz and Wieczorek (1985), Fürsich et al. (1992), Zatoń et al. (2011a), and Krajewski et al. (2014, 2017) did not deal with tube-dwelling polychaete assemblages as the major scope. The total number of the taxa reported in above mentioned studies was rather low, comprising two, or three species compared to five noted during the present study. Despite different stratigraphic intervals, the taxonomic composition of the assemblages indicated above was very similar to the hiatus concretions described here, dominated by the genera Glomerula and Propomatoceros . The quantitative data also seem to be comparable, with polychaetes being at least not abundant.

In comparison to hiatus concretions, oncoids are significantly more heavily encrusted. Tube-dwelling polychaetes preserved on this kind of substrate have been mentioned from, e.g., the Bajocian (Middle Jurassic) of England ( Gatrall et al. 1972; Palmer and Wilson 1990) and France ( Palmer and Wilson 1990), Bathonian (Middle Jurassic) of Poland (Zatoń and Taylor 2009a; Zatoń et al. 2012), or Oxfordian (Upper Jurassic) of Switzerland (Védrine et al. 2007). The record of serpulid and sabellid taxa present on the oncoids in the current study (six taxa) is comparable to those in the studies listed above, reaching seven ( Palmer and Wilson 1990) to nine species (Zatoń et al. 2012). These assemblages are dominated by species of Glomerula , followed by those of Propomatoceros . It has to be noted that Zatoń et al. (2011a) and Zatoń et al. (2012) used most of the same research material as in the current study revealing eight and nine tubeworm species, respectively. However, presumably due to overinter- pretations of certain morphotypes, which rather represented ecophenotypic variations of the same species, the number of serpulid and sabellid species is lower, comparable to the present study. Although the species richness is not significantly higher as compared to hiatus concretions, the overall number of polychaete tubes is substantially larger. In spite of the fact that at least a part of the investigations listed above (e.g., Gatrall et al. 1972; Védrine et al. 2007) might have not been sufficiently focused on serpulids and sabellids, their abundance has usually been noted.

In comparison to various mobile rockgrounds, more is known about tube-dwelling polychaetes from metazoan build-ups and a variety of hardgrounds. Serpulids and sabellids preserved on Jurassic reefal structures extending across Europe have been mentioned many times (e.g., Goldfuss 1831; Parsch 1956; Flügel and Steiger 1981; Palmer and Fürsich 1981; Pisera 1991; Radwańska 2004; Matyszkiewicz et al. 2012; PleŞ et al. 2013). However, more recent investigations focusing on sessile polychaetes in more detail have been performed only by Radwańska (2004) and to a lesser extent by Palmer and Fürsich (1981). Compared to only five species from the Oxfordian (Upper Jurassic) of Zalas, Radwańska (2004) reported 14 polychaete taxa occurring in Kimmeridgian sponge buildups of Wapienno/Bielawy in Kuyavia region (see also Loba and Radwańska 2022). In spite of striking differences in species numbers, the serpulid and sabellid fauna from Zalas appears to be more abundant than that of Kuyavia ( Radwańska 2004). The Wapienno/ Bielawy quarries ( Radwańska 2004) contain the majority of the taxa found in Zalas, including Glomerula gordialis , Cementula spirolinites , and the genera Placostegus and Filogranula . They are also present in the Oxfordian (Upper Jurassic) sponge facies of southern Germany ( Parsch 1956). Upper Bathonian (Middle Jurassic) tube-dwelling polychaetes described by Palmer and Fürsich (1981) consist of seven species. However, “ Spirorbula sp. ”, which has been described as the most abundant tubeworm within the upper Bathonian sclerobiont assemblage ( Palmer and Fürsich 1981), has been proven to actually represent a microconchid (Vinn and Taylor 2007). Other species may also require systematic reinvestigation, although the genera Glomerula , Propomatoceros and Cementula are likely to be represented.

Serpulid and sabellid communities inhabiting lithic substrates (e.g., hardgrounds) and carbonate skeletal remains of various organisms seem to be more diverse due to a wider range of substrate types and prevailing conditions (up to eleven taxa in the present study). Breton et al. (2020) described tube-dwelling polychaetes among other sclerobionts from the Bajocian (Middle Jurassic) ferruginous oolithic facies of France. They are mostly preserved on mollusk shells, with diversity reaching nine species, where Glomerula gordialis and Propomatoceros lumbricalis dominate. Krajewski et al. (2017) mentioned only one serpulid species, Tetraserpula sp. (possibly representing Nogrobs ); and two sabellid species represented by Cycloserpula sp. and Glomerula gordialis (presumably representing a single species) from the Kimmeridgian (Upper Jurassic) carbonate cobbles from the Mesozoic margin of the Holy Cross Mountains.

Serpulid and sabellid assemblages preserved on marl nodules and invertebrate skeletons from the Callovian (Middle Jurassic) of Russia described by Ippolitov (2007a, b) are represented by eight species. Interestingly, in contrast to the majority of reports, sabellids (e.g., Glomerula ) are a minor component there, with a predominance of Propomatoceros lumbricalis constituting hundreds of specimens.

Outside of Europe, Middle Jurassic serpulid and sabellid fauna has also been described from the Matmor Formation in Israel, being the closest to the equator assemblage during the Middle Jurassic (Vinn and Wilson 2010). It differs in the high dominance of the species of sabellid genus Glomerula and the presence of the genus Vermiliopsis , which seems to be uniformly absent in the Jurassic of Europe. Such differences might have resulted from a domination of the species of opportunistic Glomerula ; however, Vermiliopsis might have originated in the warm equatorial, shallow seas be- fore its further dispersal towards higher latitudes (Vinn and Wilson 2010).

Kočí et al. (2019) described nine serpulid and sabellid species from the Oxfordian (Upper Jurassic) of the Czech Republic, mainly encrusting brachiopod shells and sponge remains. However, all the taxa are represented by only a few individuals limiting an insight into the community. Even though the species composition differs from site to site, diversity remains relatively similar, often displaying a pattern of biodiversity increase through time (see Ippolitov 2010). Moreover, tube-dwelling polychaete assemblages are frequently dominated by a single, possibly most opportunistic species. Finally and crucially, true sabellid and serpulid diversity was likely higher in all studied Jurassic sites. This is because the taxonomy of fossil tube-dwelling polychaetes is based exclusively on the morphology of their tubes, while many different modern serpulid species produce similar or identical tubes ( Hove and Kupriyanova 2009).

Figures

Fig.13. Serpulid polychaetes from the Jurassic of Poland.A. Unattached Serpulidae sp.2 from the middle Bathonian of Gnaszyn Dolny (GIUS 8-3730/27). B. Dense aggregation of closely spaced Serpulidae sp. 3 encrusting a fragment of a belemnite rostrum from the middle Bathonian of Gnaszyn Dolny GIUS 8-3730/28). C. Serpulidae sp. 4 from the lower Kimmeridgian of Małogoszcz (GIUS 8-3747/3).

Fig. 14. Dendrogram showing clustering of substrates sharing similar taxa of tube-dwelling polychaetes from the Polish Basin.

Fig. 15. Representative hard substrates colonized by the Middle and Upper Jurassic tube-dwelling polychaetes from the Polish Basin. A. Upper Bathonian hiatus concretion from Ogrodzieniec; sabellid Glomerula gordialis (Schlotheim, 1820) (GIUS 8-3751), indicated by arrows. B. Bajocian–Bathonian oncoid from Ogrodzieniec-Świertowiec; the entire oncoid is intensively encrusted by serpulids and sabellids (GIUS 8-3750). C. Callovian bivalve Ctenostreon proboscideum (Sowerby, 1820) from hardground of Zalas; black arrow indicates sabellid Glomerula gordialis, white arrow indicates juvenile serpulid Propomatoceros lumbricalis (GIUS 8-3589). D. Lower Kimmeridgian oyster from oyster shell beds of Małogoszcz; an arrow indicates sabellid Glomerula gordialis (Schlotheim, 1820) (GIUS 8-3747).E. Middle Bathonian oyster from soft muddy substrates of Gnaszyn Dolny; serpulid Propomatoceros lumbricalis (Schlotheim, 1820) is exemplified by arrows (black and white). White arrows point the specimens infested by the hydroid Protulophila gestroi (Rovereto, 1901) (GIUS 8-3730). F. Oxfordian sponge from Zalas; an arrow indicates serpulid Filogranula spongiophila sp. nov. (GIUS 8-3746). Scale bars 10 mm.