Guettardiscyphia zitti sp. n. – a re mark able hexactinellid sponge from the Lower Turonian of the Bo he mian Cre ta ceous Ba sin
Radek VODRÁŽKA1, *
1 Czech Geo log i cal Sur vey, Klárov 3, 118 21 Prague 1, Czech Re pub lic
Vodrážka, R., 2017. Guettardiscyphia zitti sp. n. – a re mark able hexactinellid sponge from the Lower Turonian of the Bo he - mian Cre ta ceous Ba sin. Geo log i cal Quar terly, 61 (3): 632–640, doi: 10.7306/gq.1373
This pa per de scribes a new hexactinosidan hexactinellid Guettardiscyphia zitti sp. n. on the ba sis of a de tailed study of 279 spec i mens from 12 lo cal i ties in the south ern part of the Bo he mian Cre ta ceous Ba sin. All the stud ied ma te rial co mes from the basal Bílá Hora For ma tion (Lower Turonian). The ge ol ogy and palae on tol ogy of the sponge-bear ing strata at stud ied lo ca - tions ex hibit iden ti cal palaeoenvironmental set tings: 1 – transgressive char ac ter of sed i ments with low sed i men ta tion rates, 2 – pres ence of sub ma rine swells formed by crys tal line base ment, 3 – hemipelagic sed i men ta tion be low the storm-wave base, and 4 – the pres ence of pro lif er at ing di verse sponge fau nas with sub or di nate ac com pa ny ing macrofaunal re mains.
Key words: Up per Cre ta ceous, Turonian, hexactinellid sponge, Guettardiscyphia.
INTRODUCTION
The Lower Turonian transgressive sed i ments in the south - ern mar gin of the Bo he mian Cre ta ceous Ba sin (BCB) con tain abun dant si li ceous sponge fauna rep re sented mainly by hexactinellids and lithistid demosponges (e.g., Počta, 1883, 1884). Hexactinellids are rep re sented mainly by hexactino - sidan gen era Laocoetis Pomel, 1872, Hillendia Reid, 1964 and Guettardiscyphia de Fromentel, 1860; lychniscosidan hexa - ctinellids are less com mon (Žítt et al., 2006).
Cribrospongiids, which are char ac ter ized by a body with three stellate wings (lobes) and a dis tinct basidictyonal plate, are one of the most con spic u ous hexactinellids oc cur ring at these lo ca tions. Počta (1883) found these forms at Kamajka, Zbyslav and Velim and iden ti fied them as Guettardia trilobata Roemer (Fig. 1A). How ever, Pleuroguettardia trilobata (Roe - mer, 1864) ex hib its a dif fer ent ar range ment of ca nals in the choanosomal skel e ton and be longs to the fam ily Craticulariidae Rauff, 1893 (Fig. 1A, for de tails see the chap ter Sys tem atic Palae on tol ogy). Žítt et al. (2006, 2015) de picted this sponge from Chrtníky and Plaňany and iden ti fied it as Guettardiscyphia sp., be cause of its typ i cal cribrospongiid can a li za tion and sub - stan tial dif fer ences from all known spe cies of Guettardiscyphia.
This long-known rep re sen ta tive of Guettardiscyphia is de -
scribed herein as a new spe cies G. zitti. The de scrip tion of this new spe cies is based on the study of nu mer ous newly col lected spec i mens from the Bo he mian Cre ta ceous Ba sin, the vast ma - jor ity of which were ac quired by the au thor dur ing ex ten sive field work over the past 20 years.
MATERIAL AND METHODS
All spec i mens of G. zitti sp. n. come from 12 lo ca tions in the south ern part of the BCB (Fig. 2). The ex am ined ma te rial com - prises 279 spec i mens: 256 spec i mens rep re sent ma te rial newly col lected by the au thor and de pos ited in the col lec tions of the Czech Geo log i cal Sur vey (see the Ap pen dix 1*), 19 spec i mens come from the col lec tions of the Na tional Mu seum in Prague (for re pos i tory num bers see the Ap pen dix 1), and 4 spec i mens were stud ied in the col lec tions of the In sti tute of Ge ol ogy and Palae on tol ogy of the Fac ulty of Sci ence (Charles Uni ver sity in Prague).
The larg est num ber of spec i mens was col lected in the Chrtníky ac tive quarry near Heřmanův Městec (e.g., Zágoršek et al., 2009; Žítt et al., 2006, 2014). The sec ond most pro duc tive lo ca tion for the stud ied spe cies was an other ac tive quarry at Plaňany near Kolín (e.g., Žítt and Vodrážka, 2013; Žítt et al., 2015). The Velim, Nová Ves, Radim, Zbyslav, Kamajka and Žehušice lo ca tions were al ready fa mil iar for pi o neer Bo he mian re search ers (e.g., Frič, 1869, 1911; Počta, 1883, 1884, 1885).
Other newly col lected ma te rial is rep re sented by spec i mens from Nákle, Lipoltice and Markovice (Žítt and Nekvasilová, 1991, 1992) and from the re cently de scribed Kolín-Peklo lo ca - tion (Žítt et al., 2013). The ge ol ogy and age of these sponge -
* E-mail: radek.vodrazka@geology.cz
Received: January 30, 2017; accepted: June 1, 2017; first published online: August 17, 2017
* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1373
-bear ing strata ex hibit iden ti cal lithological char ac ter is tics, fa - cies, age, and ac com pa ny ing macrofauna (see the ref er ences above). All the stud ied ma te rial co mes from the basal Bílá Hora For ma tion (Lower Turonian, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones – see, e.g., Žítt et al., 2006, 2015). Lower Turonian siltstones at these lo ca tions trans - gress over the rem nants of the Up per Cenomanian sed i ments or di rectly over the meta mor phic base ment.
Newly col lected ma te rial was pre pared me chan i cally and chem i cally. Var i ous meth ods of chem i cal prep a ra tion were em - ployed, in clud ing the use of so dium car bon ate (Bolli, 1952) and 38% sulphuric acid (Vodrážka, 2009). Si lici fied sponge skel e - tons were treated by etch ing in 3–10% ace tic (Reid, 1958) or hy dro chlo ric acid in or der to ob tain ma te rial for SEM-stud ies. Si - lici fied skel e tons were stud ied us ing stan dard tech niques of SEM mi cros copy (Phillips XL-20, Pol ish Acad emy of Sci ences, War saw; JEOL JSM-6380LV, Charles Uni ver sity, Prague).
The sponge clas si fi ca tion used in this pa per fol lows Systema Porifera (Krautter, 2002; Reiswig, 2002), a rec og nized au thor i ta tive ref er ence for sponge tax on omy.
SYSTEMATIC PALAEONTOLOGY
Phy lum Porifera Grant, 1836 Class Hexactinellida Schmidt, 1870 Or der Hexactinosida Schrammen, 1903
Fam ily Cribrospongiidae Roemer, 1864 Ge nus Guettardiscyphia de Fromentel, 1860 Fig. 1A – orig i nal il lus tra tion of Počta (1883: p. 23, text, fig. 9) of
Guettardia trilobata (Roemer) from Zbyslav (Lower Turonian, Czech Re pub lic) with ca nals ar ranged in quincunx; B – orig i nal il lus tra tion of Roemer (1864: tab. 5, fig. 8) of Pleurostoma trilobatum Roemer = Pleuroguettardia trilobata (Roemer) from Gehrden (Lower Campanian, Ger many) with ca nals ar ranged in quadrunx
Fig. 2. Geo log i cal sketch map show ing Up per Cre ta ceous sed i ments of the Bo he mian Cre ta ceous Ba sin with the lo cal i ties yield ing Guettardiscyphia zitti sp. n. in di cated (mod i fied af ter Košïák et al., 2010)
S y n o n y m s . – ?Badinskia Pomel, 1872; Pseudo gu - ettardia Moret, 1925; Koleostoma Regnard, 1926.
E m e n d e d d i a g n o s i s. – Cribrospongiid sponges with wall folded lon gi tu di nally above a tu bu lar stalk to form ra di - ate and bi lat er ally com pressed wings or hol low flanges of typ i - cally tri an gu lar form, which re main con nected ax i ally; ra dial flanges some times sep a rate ax i ally, ei ther sin gly or in pairs, to form blade-like branches; rounded, el lip ti cal or horse shoe -sha - ped pa ri etal oscula along nar row mar gins of flanges; flan ges freely open at the top, partly closed by trans verse bridges of sec ond ary skel e tal mesh work, or closed around a sin gle ax ial osculum.
R e m a r k s. – Reid (1963) sep a rated the spe cies for merly re ferred to as Guettardia Michelin, 1844 into two dif fer ent but homeomorphic gen era based on ca nal or ga ni za tion. One is Guettardiscyphia de Fromentel, 1860 (= Guettardia Michelin, 1844, non Nardo, 1833), with ca nals ar ranged in a quincuncial (cribrospongiid) pat tern, and be longs to the Cribrospongiidae Roemer, 1864; the sec ond ge nus – Pleuroguettardia Reid, 1963 – is char ac ter ized by ca nals ar ranged in a qua dran gu lar (craticulariid) pat tern and be longs to the Craticulariidae Rauff, 1893. It is note wor thy that Reid (2004) con sid ered Pleuro - guettardia to be a ju nior syn onym of Ptychocoetis Pomel, 1872.
How ever, Ptychocoetis Pomel, 1872 is nomen nudum and nomen oblitum, whereas Pleuroguettardia Reid, 1963 is con - sid ered a valid ge nus (e.g., Pisera and Besquets, 2002).
Synonymization of Badinskia Pomel, 1872 with Guettar - discy phia de Fromentel, 1860 was pro posed by Pisera and Besquets (2002). The ge nus Badinskia Pomel, 1872 was pre vi - ously synonymized with Aphrocallistes by Moissette et al.
(1984) and Brimaud and Vachard (1986). Pisera and Besquets (2002) in ter preted tu bu lar out growths fig ured by Pomel (1872:
tab. II bis, figs. 8 and 9) not as tu bu lar branches, as did Moissette et al. (1984) and Brimaud and Vachard (1986), but as prob a ble roots com mon in Guettardiscyphia. The il lus tra tions and de scrip tion of Pomel (1872: p. 85) leave no doubt that the tu bu lar out growths can not be in ter preted as roots of Guettardiscyphia or any other sponge; the sur face of the out - growths (Pomel, 1872: tab. II bis, figs. 8 and 9) ex hib its well-de - vel oped reg u lar can a li za tion with quincunx ar range ment, which is ev i dence that the out growths rep re sent tu bu lar branches formed by choanosomal skel e ton. More over, Pomel (1872: tab.
II bis, figs. 8 and 9) fig ured and de scribed trans verse sec tions of tu bu lar out growths with a reg u lar ra dial ar range ment of ca nals of the same type as in his fig. 6, tab. II bis. Synonymization of Badinskia with Guettardiscyphia, as pro posed by Pisera and Besquets (2002), is fol lowed with a ques tion mark, be cause Pomel´s de scrip tion (1872) of the gen eral shape of Badinskia lobata re sem bles rep re sen ta tives of Guettardiscyphia and Hillendia. The pres ence of pa ri etal oscula (Pomel, 1872: p. 85) and quincuncially ar ranged ca nals (Pomel, 1872: p. 85, 86) are also char ac ter is tic for both gen era. Im por tant tax o nom i cal char - ac ter is tics, such as the ar range ment of aporhyses, or de scrip - tion of the whole shape of the com plete spec i men, are lack ing in Pomel´s (1872) de scrip tion. The above ar gu ments make the synonymization of Badinskia with Guettardiscyphia doubt ful.
T y p e s p e c i e s. – Guettardia stellata Michelin, 1844, p. 121, 122, pl. 30, figs. 1–11.
Guettardiscyphia zitti sp. n.
(Figs. 3–5)
1883 Guettardia trilobata Roem. – Počta, p. 23, text. fig. 9 1911 Guettardia trilobata Röm. – Frič, p. 79, fig. 328 1997 Guettardia trilobata Roem. – Žítt et al., pl. 2, fig. 2
2006 Guettardiscyphia sp. – Žítt et al., fig. 12G, H, K 2015 Guettardiscyphia sp. – Žítt et al., fig. 9I, J
H o l o t y p e. – Spec i men RV347-PG49 (Fig. 3A). Housed in the Col lec tions of the Czech Geo log i cal Sur vey, Prague, Czech Re pub lic.
P a r a t y p e s. – Spec i mens RV363-PG65 (Fig. 3B), RV402-NG20 (Fig. 3C), RV391-NG9 (Fig. 3E), RV225-CHG76 (Fig. 3F), RV245-CHG96 (Fig. 4C). Paratypes are housed in the Col lec tions of the Czech Geo log i cal Sur vey, Prague, Czech Re pub lic.
S t u d i e d m a t e r i a l. – 279 spec i mens from the Bo - he mian Cre ta ceous Ba sin: 12 spec i mens from the Kamajka lo - ca tion, 3 spec i mens from Zbyslav, 128 spec i mens from Chrt - níky, 11 spec i mens from Velim, 8 spec i mens from Nová Ves, 1 spec i men from Lipoltice, 1 spec i men from Radim, 6 spec i mens from Markovice, 2 spec i mens from Žehušice, 84 spec i mens from Plaňany, 25 spec i mens from Nákle, 3 spec i mens from Kolín-Peklo. The spec i men from Zbyslav fig ured by Počta (1883) and Frič (1911) (spec i men NM-O3278, see Ap pen dix 1).
Spec i mens from Velim, Chrtníky and Plaňany, fig ured by Žítt et al., 1997, 2006, 2015 (see syn on ymy list), have also been ex - am ined. For the age and ge ol ogy of the lo cal i ties see the chap - ter Ma te rial and Meth ods, for their lo ca tion see Fig ure 2. For the re pos i to ries of the spec i mens see the Ap pen dix 1.
L o c u s t y p i c u s. – Plaňany Quarry near Kolín, Czech Re pub lic.
S t r a t u m t y p i c u m. – Up per Cre ta ceous, Early Turonian, Mytiloides labiatus Zone. Lower part of the Bílá Hora For ma tion (sensu Čech et al., 1980).
E t y m o l o g y. – In hon our of Jiří Žítt (In sti tute of Ge ol ogy of CAS, Prague), a great per son age and out stand ing re search worker, who pub lished ma jor works on ge ol ogy and palae on tol - ogy of the nearshore fa cies of the Bo he mian Cre ta ceous Ba sin.
D i a g n o s i s. – The sponge forms typ i cally three stellate wings in its up per part. In its lower part, the sponge skel e ton is ir reg u larly lobate or el lip ti cal in cross sec tion and forms a basi - dictyonal plate on its basal part with oc ca sional root-like out - growths (sec ond ary de po si tion of the reg u lar dictyonal frame - work). Rounded to el lip ti cal pa ri etal oscula oc cur along the edges of the wings, as well as along the lobate por tion of the lower part of the sponge. Epirhyses (i.e. in hal ant ca nals) show a reg u lar quincuncial ar range ment of ca nal open ings on the der - mal sur face; their num ber var ies be tween 96 and 304 per square centi metre. Aporhyses (i.e. exhalant ca nals) are in the same ar range ment as epirhyses (quincunx), but the gastral side may ex hibit twice as many ap er tures, of which only half are true aporhyses, and the sec ond half are epirhyses ex tend ing from the der mal sur face.
D e s c r i p t i o n. – In cross-sec tion, the sponge is stellate in its up per part (e.g., Figs. 3A and 4F) and lobate to el lip ti cal (resp. cir cu lar) in its lower part. The up per, stellate por tion is com posed of three (96.5% of spec i mens), rarely of two (2.2% of spec i mens; Fig. 4A) or four (1.3% of spec i mens) lat er ally com - pressed wings that orig i nate by ra dial fold ing of the walls. These wings are star con nected and 3 mm (ju ve niles) to 13 mm (gerontic) thick. Two par al lel walls form ing a wing are sep a rated by a nar row space. The wall form ing a wing has a thick ness of 1.3–4.6 mm. In the lower part of the plicated por tion, the nar row space be tween wings is usu ally filled in by a sec ond ary dictyonal skel e ton (Figs. 3A and 4E–G)
Rounded to eliptical pa ri etal oscula oc cur along the edges of these wings, as well as along the lobate por tion of the lower part of the sponge (e.g., Fig. 4A, C, D). Pa ri etal oscula are 0.8 x 0.8 to 10.3 x 8.4 mm in di am e ter (see the Ap pen dix 1) with spac ing of 3.5–19 mm; spec i mens with larger pariatal oscula
Fig. 3. Guettardiscyphia zitti sp. n.
A – holotype RV347-PG49, Plaňany, note two Spondylus sp. valves ce mented near the basidictyonal plate; B – paratype RV363-PG65, Plaňany, note the bi valve Atreta sp. ce mented on the at tach ment sur face of the basidyctional plate; C – paratype RV402-NG20 with large pa ri etal oscula along the edges of the wings, Nákle; D – spec i men RV224-CHG75 with seem ingly ir reg u lar dis tri bu tion of ca nals due to thick ened cor ti cal layer, Chrtníky; E – paratype RV391-NG9, gerontic spec i men with rhizobasidyctional plate, Nákle; F – paratype RV225-CHG76, Chrtníky
Fig. 4. Guettardiscyphia zitti sp. n.
A – spec i men RV226-CHG77 with a small at tach ment scar hav ing only two de vel oped wings, Chrtníky; B – spec i men RV199-CHG50, root-like out growths of the basal plate over grow ing lithistid demosponge Chonella sp., Chrtníky; C – paratype RV245-CHG96, car bon - ate dis solved in acid, Chrtníky; D – spec i men RV236-CHG87 over grown (in the left part) by hexactinellid Cyrtobolia morchella (Reuss), Chrtníky; E – spec i men RV178-CHG29, cross-sec tion of a wing in the lower part infilled with a sec ond ary skel e ton and closely spaced ca nals, Chrtníky; F – spec i men RV364-PG66 ex pos ing both the gastral sur face and the der mal sur face of the wall, Plaňany; G – spec i - men RV155-CHG6, trans verse sec tion of the wing show ing the pri mary choanosomal skel e ton pierced by epirhyses and aporhyses (left and right part) and wing in te rior infilled by an ir reg u lar sec ond ary frame work pierced by smaller and larger ca nals (cen tral part), car - bon ate dis solved in acid, Chrtníky
also ex hibit wider interspaces (cf. Fig. 3A, C). Pa ri etal oscula are rounded to el lip ti cal; they usu ally show par al lel elon ga tion with a gen eral di rec tion of sponge growth ex cept in 0.5% of the spec i mens un der study (see the Ap pen dix 1). Close to the basal part of the sponge, the pa ri etal oscula are usu ally filled in by ac cre tions of an ir reg u lar sec ond ary skel e ton.
The stud ied spec i mens at tach to hard and semi-hard sub - strates mainly by a broad basidictyonal plate (basiphytous mode of at tach ment; Figs. 3A, B, F and 4A). The basidictyonal plate is formed by a reg u lar sec ond ary dictyonal skel e ton, ex - hib it ing straight dictyonal strands. In ad di tion to a var i ously shaped basidictyonal plate, some spec i mens ex hibit the pres - ence of root-like out growths emit ted from the cen tres of the sec - ond ary skel e ton de po si tion (rhizobasiphytous mode of at tach - ment; Figs. 3E, F and 4B).
In hal ant ca nal open ings, sit u ated on the der mal sur face of the choanosomal skel e ton, are rounded to el lip ti cal. The di rec - tion of elon ga tion of in hal ant ca nal open ings cor re sponds to the gen eral di rec tion of growth. The cor tex on the der mal sur face of the chonaosomal skel e ton is well-de vel oped (Fig. 5A). In hal ant ca nal open ings are ar ranged in a quincunx pat tern (Fig. 5A) and are well-ex posed typ i cally on the wall sur faces in de pres sions be tween the wings (Fig. 4A, B, D). Ca nal open ings on the der mal sur face may be seem ingly ab sent in places where they are veiled by a thin layer of sec ond ary dictyonal skel e ton, es pe cially close to the edges of the wings as well as close to the basidictyonal plate (Fig. 5E, F). In hal ant ca nal open ings may also ex hibit an ap par ently ir reg u lar dis tri bu tion pat tern caused by the pres ence of a thick ened layer of reg u lar sec ond ary dictyonal skel e ton (Figs. 3D and 5E). The length of the in hal ant ca nal open ings (in the di rec tion of growth of the wall) is 0.22–0.43 mm and the width equals 0.18–0.42 mm. In hal ant ca nal open ings are sep a rated by skel e tal bands, 0.34–0.83 in width.
The re sults of 119 mea sure ments (see the Ap pen dix 1) show that the num ber of epirhyses per square is highly vari able – there are 96–304 ca nal open ings per square centi metre with a me dian value of 175 per cm2. The low est den sity of epirhyses (96–128 per cm2) was counted ex clu sively on the dis tal parts of the wall (e.g., Fig. 3A). In con trast, the high est den sity counts (240–304 per cm2) are lo cated on the walls close to the basi - dictyonal plate or on ju ve nile spec i mens.
Ca nals in side the chonaosomal skel e ton are rounded (Fig.
5D), rarely slightly el lip ti cal with elon ga tion par al lel to the growth di rec tion. They have a di am e ter of 0.16–0.36 mm and dis - tances be tween their cen tres equal to 0.35–0.63 mm.
Exhalant ca nal open ings, sit u ated on the gastral sur face of the choanosomal skel e ton, may be in the same ar range ment as the in hal ant ca nal open ings (Fig. 5D), or the gastral side ex hib - its twice as many ap er tures, of which only half rep re sent aporhyses and the sec ond half are epirhyses ex tend ing from the der mal sur face (Fig. 4F).
The cor tex is not de vel oped on the gastral sur face (Fig. 5C, D). The gastral sur face within the wings is partly or en tirely filled with an ir reg u lar sec ond ary dictyonal frame work (Fig. 5F).
These sec ond ary frame work de pos its within the wings show the ab sence of dictyonal strands and are pen e trated by ir reg u - lar smaller and larger ca nals (Fig. 4E, G) that un doubt edly in ter - con nect the gastral sur face with pa ri etal oscula.
The pri mary (choanosomal) skel e ton of the wall ex hib its a reg u lar dictyonal frame work with dis tinct dictyonal strands (Fig.
5B, D, F). The frames formed by in ter con nected hexactines are squared to rect an gu lar, 0.10–0.27 mm (in the di rec tion of growth) x 0.09–0.19 mm in size. The sur face of the spicules is smooth (Fig. 5B), rarely show ing fine gran u la tion es pe cially close to the cor tex (Fig. 5C). Fine gran u la tion was also ob - served on hexactines form ing the cor ti cal layer.
DISCUSSION
The skel e tal can a li za tion of Guettardiscyphia was first de - scribed from Guettardiscyphia (=Koleostoma) godeti (Regnard, 1926: p. 473, 474, pl. XVIII, fig. 1). Moret (1926) es tab lished the pres ence of the same type of struc ture in the type spe cies G.
stellata (Michelin). The per fo rat ing char ac ter of many epirhyses is a spe cial de vel op ment and sug gests that in hal ant ca nals ex - tended to the subgastral stra tum of the trabecular net work (Reid, 1962). Guettardiscyphia stellata (Michelin), Guettardi scy phia go - deti (Regnard in Moret), Guettardiscyphia ra di ans (Hinde) and Guettardiscyphia bisalata (Schrammen) are spe cies that ex hibit per fo rat ing char ac ter of the epirhyses. The epirhyses of Guettardi scyphia thiolati (d´Archiac), in con trast, end blindly un - der the gastral sur face of the choanosomal skel e ton (Pisera and Besquets, 2002). Guettardiscyphia zitti sp. n., com pared with the above-men tioned Guettardiscyphia spe cies, show both per fo rat - ing and non-per fo rat ing char ac ter of epirhyses.
Guettardiscyphia thiolati (d´Archiac) dif fers from Guettardi - scyphia zitti sp. n. sig nif i cantly by skel e tal ex pres sion of epirhy - ses and aporhyses in side the choanosomal skel e ton. In side the wall of G. thiolati, epirhyses and aporhyses run in one large skel e tal space, oval in cross-sec tion, whereas G. zitti sp. n. al - ways shows sep a rate in hal ant and exhalant ca nals (cf. Fig. 5D;
Pisera and Besquets, 2002: tab. 12, fig. 3). These two spe cies, how ever, show sim i lar skel e tal char ac ter is tics of the wing “in fill - ing” by a sec ond ary skel e ton with in ter con nect ing ca nals (cf.
Fig. 4E; Pisera and Besquets, 2002: tab. 7, fig. 8).
Guettardiscyphia zitti sp. n. dif fers from all the above-men - tioned Guettardiscyphia spe cies in typ i cally pos sess ing 3 wings, whereas other rep re sen ta tives of the ge nus usu ally bear 4–6 wings. The wings of the newly de scribed spe cies are al - ways united, which is not true for most Guettardiscyphia spe - cies (e.g., Guettardiscyphia stellata), which emit sep a rated hol - low flanges in the up per part of wings.
Guettardiscyphia zitti sp. n. shows the for ma tion of a dis tinc - tive basidictyonal/rhizobasidictyonal plate formed by a reg u lar sec ond ary dictyonal frame work. Such prom i nent at tach ment struc tures were not de scribed or fig ured by pre vi ous au thors in Guettardiscyphia. How ever, the tax o nom i cal im por tance of these struc tures re mains ques tion able, as they might be a re - sponse to spe cific palaeoenvironmental con di tions (sub strate) at stud ied lo ca tions.
The num ber of in hal ant ca nal open ings per cm2 (rep re sent - ing also the num ber of epirhyses), which used to be con sid ered an im por tant tax o nom i cal char ac ter is tic at the spe cies level (e.g., Schrammen, 1912; Mehl, 1992, was found to be very vari - able for G. zitti sp. n.; 94–304 per cm2). More over, based on 119 mea sure ments (see the Ap pen dix 1), it can be con cluded that the den sity of ca nal open ings of G. zitti strongly de pends on the part of the sponge in which the den sity count was car ried out.
There fore, the sin gle num ber counts of epirhyses per area are not con sid ered a prin ci pal tax o nom i cal char ac ter is tic for the Guettardiscyphia.
The ge ol ogy and palae on tol ogy of the sponge-bear ing strata at stud ied lo ca tions ex hibit iden ti cal palaeoenvironmental set tings:
– transgressive char ac ter of sed i ments with low sed i men - ta tion rates,
– pres ence of sub ma rine swells formed by the crys tal line base ment,
– hemipelagic sed i men ta tion be low the storm-wave base, – pres ence of pro lif er at ing di verse sponge fau nas with
sub or di nate ac com pa ny ing macrofaunal re mains.
Fig. 5. Guettardiscyphia zitti sp. n., SEM mi cro pho to graphs of a si li ceous skel e ton, Chrtníky
A – der mal sur face of the wall with quincuncially ar ranged epirhyses, frag ment of RV261-CHG112; B – pri mary choanosomal skel e ton in a trans verse sec tion of the wall, frag ment of RV261-CHG112; C – gastral sur face of the wall with gran u lated spicules and quadratically ar ranged epirhyses and aporhyses, frag ment of RV235-CHG86; D – gastral sur face of the wall with tan gen tial sec tion through the cen tral part of the wall (lower half of the fig ure), frag ment of RV235-CHG86; E – der mal sur face of the wall veiled by a 0.5-mm thick layer of a sec - ond ary frame work, which was re moved in the up per third of the pic ture, frag ment of RV259-CHG110; F – trans verse sec tion of the wing, show ing the out er most thin layer of a reg u lar sec ond ary frame work, wall formed by a reg u lar dictyonal skel e ton and the in te rior of the wing partly infilled by an ir reg u lar sec ond ary mesh work, frag ment of RV155-CHG6
This is in con for mity with nu mer ous mod ern stud ies re port - ing Late Cre ta ceous hexactinellid fau nas typ i cally linked to transgressive cy cles, low sed i men ta tion rates, and depths be - low the storm-wave base (see e.g., Schnei der et al., 2011, 2013; Vodrážka and Crame, 2011 and ref er ences therein).
CONCLUSIONS
All the stud ied spec i mens (279 spec i mens from 12 lo ca - tions) of G. zitti sp. n. come from the basal Bílá Hora For ma tion in the Bo he mian Cre ta ceous Ba sin (Lower Turonian). This is a very re mark able sponge, known to Czech sci en tists since the 19th cen tury (Počta, 1883), but was only rec og nized as a new spe cies af ter more than a hun dred years. It is con cluded that some vari able tax o nom i cal char ac ter is tics of Guettardiscyphia,
such as the den sity of epirhyses per area, are of lim ited tax o - nom i cal im por tance.
Ac knowl edge ments. This re search was funded by the Grant Agency of the Czech Re pub lic (No. GP14-31662P). In the first place, I would like to thank A. Pisera (Pol ish Acad emy of Sci ences) for his kind tu tor ing of my ini tial re search on si li ceous sponges from the BCB. J. Žítt (Czech Acad emy of Sci ences), M. Košïák (Charles Uni ver sity in Prague) and S. Čech (Czech Geo log i cal Sur vey) are thanked for in valu able dis cus sions on the ge ol ogy and palae on tol ogy of the stud ied lo ca tions. Thanks go also to J. Sklenář (Na tional Mu seum in Prague) for ac cess to the Na tional Mu seum col lec tions and for his as sis tance dur ing nu mer ous joint field trips. I also wish to thank E. Świerczewska - -Gładysz, F. Wiese, T. Peryt and Anon y mous Re viewer, whose sug ges tions and crit i cal re marks helped to im prove the manu - script.
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