NEW INSIGHT ON ARCHITECTURE AND MICROSTRUCTURE … 40/18 RUSSO.pdf · OF ELLIPSACTINIA AND...

Geologica Romana 40 (2007), 215-225

NEW INSIGHT ON ARCHITECTURE AND MICROSTRUCTUREOF ELLIPSACTINIA AND SPHAERACTINIA (DEMOSPONGES)FROM THE GARGANO PROMONTORY (SOUTHERN ITALY)

Antonio Russo* & Michele Morsilli**

* Dipartimento del Museo di Paleobiologia e dell’Orto Botanico, Università di Modena e Reggio Emilia - [email protected]** Dipartimento di Scienze della Terra, Università di Ferrara

ABSTRACT - Ellipsactinia and Sphaeractinia are two groups of organisms which represent very importantstratigraphic markers, especially for the Jurassic and the Cretaceous, becoming the principal constituents of carbon-ate platform margins of these periods. Furthermore, because they lived exclusively in the Mesozoic Tethys sea, weconsider them as good palaeogeographic and palaeoclimatic fossils. They were very abundant in Late Jurassic andValanginian in the Adriatic and Apulian carbonate platforms.

The architecture and microstructure of these two groups are completely different. Ellipsactinia has a simplerarchitecture than Sphaeractinia, which exhibits an organization of lamellae and radial channels termed “dry-stonewall”, and the presence of astrorhizae-like structures. Also the microstructure is different. In Ellipsactinia there isa “water jet” (clinogonal) pattern of fibers, whereas in Sphaeractinia the fiber arrangement is spherulitic. In boththe genera, rare, isolated and scattered, monaxon spicules are present.

The skeletal organization and the types of microstructures allow us to ascribe these two genera toDemospongiae.

KEY WORDS: Ellipsactinia, Sphaeractinia, Demosponges, microstructure, Mesozoic, Apulia.

INTRODUCTION

Ellipsactinia and Sphaeractinia are two groups oforganisms very similar each to other, and they representvery important stratigraphic markers, mainly for theJurassic and the Cretaceous, periods when they becamethe principal builders of carbonate platforms.Furthermore, their distribution, limited to the MesozoicTethys, allow us to consider these organisms as excellentpaleoclimatic and paleogeographic fossils. In Italy theywere very abundant from Sicily to Friuli in Late Jurassicand Valanginian times.

Hill and Wells (in Moore, Treatise on InvertebratePaleontology, Part F, 1956) include, with some reserva-tions, the genus Ellipsactinia in the family HydractinidaeAgassiz, 1862, and the genus Sphaeractinia in the fami-ly Actinostromatidae Nicholson, 1886, order Stromato-poroidea.

From an architectural and microstructural point ofview, anyhow, these two groups, to which the two generahave been assigned, exhibit different peculiarities.

At present, the Hydractinidae are attributed to theCoelenterata, the gastric cavity of which makes four radi-al canals, the colonies are mainly incrusting with thecaulomes rising from a chitinous or calcareous mat oftangled hydrorhizae with periderm. The stromatoporoidson the contrary, previously ascribed to Hydrozoa, arenow considered, or at least a large part of them, as per-taining to the demosponges. Very interesting investiga-tions on Stromatoporoidea systematics have been madeby Stearn (1971, 1974); Wood (1987), Reitner (1992);and recently by Stock (2002) and Leinfelder et al.(2005), which include, tout court, Ellipsactinia andSphaeractinia in the stromatoporoid group.

The aim of this paper is to describe the micro-architecture and microstructure of Ellipsactinia andSphaeractinia in order to provide a more precise system-atic placement for these two genera.

Previous works

The genera Ellipsactinia and Sphaeractinia wereestablished in 1878 by G. Steinmann, and included bythe author in family Corynidae. This family comprisesother genera such as Hydractinia Van Beneden,Thalaminia Steinmann, Labechia Milne Edwards etHaime, Stromatopora Goldfuss, Loftusia Brady,Parkeria Carpenter, Cylindrohyphasma Steinmann, andPorosphaera Steinmann. The specimens described bySteinmann come from Stramberg (Moravia) and areTithonian in age.

Initially, the genera Ellipsactinia and Sphaeractiniawere monotypic, including only E. ellipsoidea and S.diceratina, but Zittel (1879), in his Handbuch derPaläontologie, ascribed Ellipsactinia to the familyStromatoporidae Nicholson et Murie; the Stromato-poridae together with the families Milleporidae Mosleyand Stylasteridae Gray constitute the suborderHydrocorallinae Mosley. In contrast, the generaHydractinia Van Beneden, Thalaminia Steinmann,Sphaeractinia Steinmann, Parkeria Carpenter, and, withsome doubs, Loftusia Brady, were included in the subor-der Tubularina Ehrenberg.

Also Portis (1881) ascribed the same genera listed bySteinmann to Hydrocorallinae Hydrozoa, including twonew species, Ellipsactinia fortisi and Sphaeractiniapedemontana, from the Upper Jurassic of Argentera,near the Stura Valley (Cuneo, Northern Italy).

Hoernes (1884) assigned the two named genera to the

family Stromatoporidae, suborder Hydrocorallinae,order Tubulariae. Nicholson (1886) listed Sphaeractiniaand Ellipsactinia among the Actinostromatidae, orderStromatoporoidea Nicholson and Murie, 1878.

Steinmann (1888) described a new species ofSphaeractinia without providing a specific name; thisspecies was later redescribed and named by Canavari(1893) as Sphaeractinia steinmanni.

The family Ellipsactinidae, order StromatoporoideaNicholson and Murie, class Hydroida has been estab-lished by Canavari (1890), who included in this familythe genera Ellipsactinia and Sphaeractinia. In the firstgenus Canavari (1890) included various species, amongwhich are some established by himself: E. ellipsoideaSteinmann, 1878, E. portisi Canavari, 1893, E. tyrrheni-ca Canavari, E. micropora Canavari, E. caprenseCanavari, E. africana Canavari, E. polypora Canavariand E. ramosa Canavari. In the second genus he includ-ed, besides the already known species S. diceratinaSteinmann, S. pedemontana Canavari, S. steinmanniCanavari, also the new species S. dicotoma Canavari.

Osimo (1910), ascribed the genera Ellipsactinia andSphaeractinia to Hydrozoa, particularly Tabularia group.

Kühn (1927, 1939) assigned the Sphaeractiniae tostromatoporids (at that time considered Hydrozoa),strictly related to Disjectoporidae, and established thenew order Sphaeractinoidea.

Steiner (1932), on the contrary, included the familyEllipsactinidae in the order Stromatoporoidea.

Lecompte (1951, 1952) included Ellipsactiniae andSphaeractiniae in the family Actinostromatidae, orderStromatoporoidea.

In 1956, Hill & Wells, in the “Treatise on InvertebratePaleontology”, included tentatively the genusEllipsactinia in the family Hydractiniidae Agassiz, 1862,order Hydrozoa, whereas the genus Sphaeractinia wasincluded, also doubtfully, in the family Actino-stromatidae Nicholson, 1886, order Stromatoporoidea.

Bachmayer & Flügel (1961) ascribed the generaEllipsactinia (type species E. ellipsoidea, Steinmann,1878) and Sphaeractinia (type species S. diceratinaSteinmann, 1878) to the family Sphaeractinidae Waagen& Wentzel 1887, order Sphaeractinoidea Kühn, 1927,class Hydrozoa Owen, 1843. Within this order theyincluded also the family Actinostromariidae Hudson,1955, now assigned to class Demospongiae Sollas, 1875,phylum Porifera Sollas, 1875.

Babayev (1973), as regards these two genera, followedthe classification of Steinmann.

Grubić (1959), besides listing all the sphaeractinidsknown at that time, established a new species,Sphaeractinia cylindrica, collected by himself in west-ern Serbia, Tithonian-Valanginian in age.

In 1961, Grubić revised the Sphaeractiniae, splittingthem into Triassic, Liassic and Paleogene.

The Triassic listed species are:Lithopora koehneni Tornquist, 1900, a species that

subsequently Dehorne (1920) and Steiner (1932)assigned to the genus Ellipsactinia Steinmann

Stromactinia triassica Vinassa de Regny, 1901Circopora sp. (following Grubić it is a synonym of C.

caucasica)Circopora caucasica Moiseew, 1944Sphaeractinia rothpletzi Leuchs, 1931Sphaeractinia kinzigensis Leuchs, 1931According to Grubić, these last species show morpho-

logic features and microstructures that are quite differentfrom true Sphaeractiniae; again, a restudy of the typematerial appears necessary. Nevertheless Ellipsactiniabonomi Vialli is considered as strikingly different fromall the other fossil Hydrozoa, so it belongs to Anthozoa,close to Alcyonaria, Stolonifera.

In the Liassic group, Grubić included: Ellipsactiniaellipsoidea Steinmann, Ellipsactinia caprense Canavari,Ellipsactinia tyrrhenica Canavari, Ellipsactinia africanaCanavari, and Ellipsactinia bonomi Vialli, 1938. In thisgroup G. Meneghini (1884) and Canavari (1893) includ-ed taxa found in Tunisia, such as Ellipsactinia ellip-soidea Steinmann, E. caprense Canavari, E. tyrrhenicaCanavari, and E. africana Canavari.

Among the Paleogene sphaeractinids, Capeder (1898)described Ellipsactinia gassino (from the Calcare diGassino - Gassino Limestone), Ellipsactinia ponzone(from the Calcare di Ponzone - Ponzone Limestone) andEllipsactinia prasco (from the Calcare di Prasco - PrascoLimestone), considering them as the last anomalous taxaof the Sphaeractiniae family. The aspect of these threeforms should be the same of the Sphaeractinia, neverobserved in Ellipsactinia. Nevertheless Capeder’sSphaeractinia species show characters not seen in anySphaeractiniae known until that time.

In 1959, Grubić established a new Sphaeractiniaspecies: Sphaeractinia poljaki; this species was revisedlater by him (Grubić, 1983a). This taxon was recordedfor the first time by J. Poljak in 1938 as Sphaeractinia sp.

In the same paper Grubić (1959) points out the preva-lence of these forms in Tithonian-Valanginian depositsand debates the origin of these two genera from a com-mon ancestor in the stromatoporoids. Furthermore, theauthor divides the Ellipsactiniae and the Sphaeractiniaeon the basis of different morphologic features.

Geological and stratigraphical setting

The study fauna comes from samples collected in theMonte Sacro limestone: a stratigraphical unit of UpperJurassic-Berriasian age cropping out in the GarganoPromontory (Apulia, southern Italy) (Fig. 1).

The Gargano Promontory, mainly consists of carbon-ate rocks, belongs to the Apulia Carbonate Platform, amajor Mesozoic paleogeographic element southern mar-gin of the Tethys Ocean (Bernoulli, 1972; D’Argenio,1976; Bosellini et al., 1999).

Structurally it is a part of the foreland of the Apenninechain, broadly deformed into a gentle anticline with aWNW-ESE axis (Martinis, 1965). This area is alsoaffected by numerous faults with various trends andkinematics (Funiciello et al., 1992; Bertotti et al., 1999;

RUSSO & MORSILLI216 Geologica Romana 40 (2007), 215-225

Brankman & Aydin, 2004). The most prominent featureis the Mattinata fault, a regional E-W shear zone thatcrosses the entire Gargano area.

The Gargano area, together with the MaiellaMountain, is the only place where the transition betweenplatform and slope-to-basin facies crops out (Bosellini etal., 1999). In other areas, the eastern margin of this plat-form lies offshore under the Adriatic Sea, about 20 to 30km from the present coastline (De Dominicis &Mazzoldi, 1989).

The Jurassic to Eocene successions of the Garganowere divided into different second-order stratigraphic

sequences, bounded by unconformities of different typesand origins, that represents various depositional envi-ronments (Bosellini et al., 1993; Morsilli & Bosellini,1997; Bosellini et al., 1999; Bracco Gartner et al., 2002;Conti et al., 2005).

For the purpose of present paper we consider only thelowest sequence called Monte Sacro Sequence (Fig. 2,Morsilli & Bosellini, 1997) spanning in age from theCallovian p.p. to the Valanginian p.p., and particularlythe Monte Sacro Limestones, which corresponds to thebioconstructed margin of the Apulia Carbonate Platform.This unit, Oxfordian p.p. to Berriasian in age, crops out

NEW INSIGHT ON ARCHITECTURE AND MICROSTRUCTURE ... 217Geologica Romana 40 (2007), 215-225

Fig. 1 - Facies distribution of the Gargano Promontory during the Early Cretaceous. Symbols: 1) inner platform facies; 2) oolitic shoals; 3)Ellipsactinia margin (Monte Sacro Limestones); 4) slope to basin facies (slightly modified after Morsilli & Bosellini, 1997).

Fig. 2 - Schematic depositional profile and facies belts. From left to right listed the facies association from F1 to F8. Samples collected mainly inthe F5 (modified after Morsilli & Bosellini 1997).

in a narrow and arcuate belt from M. d'Elio to Mattinata(Fig. 1).

Monte Sacro Limestones consists of massive wacke-stones with Ellipsactinia, Sphaeractinia and, in someareas, stromatactis-like features. The outcropping thick-ness can be estimated to be about 300 m (the base is notexposed). This formation has been referred to a “bankreef” (Mattavelli & Pavan, 1965; Martinis &Pavan,1967; Cremonini et al., 1971). The same facieshas been interpreted as an “external margin” on theCapri Island (Barattolo & Pugliese, 1987) and as repre-senting a “slope environment” in the Marsica area(Colacicchi & Praturlon, 1965; Colacicchi, 1967).

Morsilli & Bosellini (1997) in a sedimentologicalstudy divided the Monte Sacro Sequence in 8 faciesassociations, where Monte Sacro Limestones corre-sponds mainly to the Facies Associations n. 5 (Fig. 2).F5 was divided in four main lithofacies with a variableareal distribution.

The lithofacies are:F5A: massive wackestone with Ellipsactinia,

Sphaeractinia, stromatoporoids, Tubiphytes sp. Stroma-tactis are common in some areas.

F5B: poorly stratified rudstone with stromatoporoidsand some branching and single corals, Ellipsactinia israre. The matrix consists of skeletal grainstone.

F5C: massive grainstone with fragments of stromato-poroids, Ellipsactinia, corals, gastropods (Nerinea sp.)and crinoid ossicles. Stromatactis are very abundant.

F5D: small lenses of skeletal grainstone (2-4 m wideand 30-40 cm thick), frequently laminated (low angleconcave-convex lamination) and interbedded with F5Aand F5C.

This facies association was interpreted as indicative ofan external gently dipping margin (5-10°), below fair-weather wave base at a depth between 10 and 50 m(Bosellini & Morsilli, 1994). F5D is probably the resultof storm wave action. F5C is related to wave action orsmall storms in the shallowest zone of this facies associ-ation (Morsilli & Bosellini, 1997).

Architectural and microstructural organizationof the genus Ellipsactinia

In spite of the name, which indicates an ellipticalshape, this morphology is quite rare. More usually, onthe contrary, they have cylindrical, subconical, more orless slender shapes, which sometimes show incipient bi-or trifurcation. In some cases the shape is more irregular.The sizes of the body ranges from few centimetres tomore than 15 centimeters high. Very often the body mayenvelope small clasts, upon which the colony grows upasymmetrically mainly following a preferential direction(Fig. 3).


Fig. 3 - Field picture of Ellipsactinia showing the elongate shape ofspecimen, the “first lamella” (on the left of figure) and the differentialerosion of lamellae (eroded and black) and interlaminar spaces (whiteand filled by calcite). Road from Foresta Umbra to Carpino. x 1.

Fig. 4 - The SEM microphotograph shows the “first lamella” piercedby pores, and the eroded lamellae showing the small sticks which cor-respond to radial channels, filled by calcite, crossing the lamellae. Theinterlamellar spaces are in relief because filled by calcitic cement.Ellipsactinia specimen.

Fig. 5 - Thin section of Ellipsactinia specimen. Particular of “firstlamella” with pores, and some following lamellae (larger and dark)separated by interlamellar spaces (narrow and white). x 7.

Architectural organization

The calcareous skeletal structure consists of superim-posed lamellae, more or less thick and spaced, linked bycalcareous vertical pillars, similar to the stromatoporoidbauplan. These superimposed lamellae, deeply arcuatedin the central part, converge towards the periphery,where they tend to blend. Sometimes the lamellae aredeformed by small foreign bodies (Fig. 4).

In Ellipsactinia, generally, the lamellae are thickerthan the interlamellar spaces.

In longitudinal section the lamellae show two kinds ofpores (Fig. 5): larger, and smaller, with a diameter larg-er half part of previous ones, which represent the endingof radial channels. Also the first lamina or “parent lamel-la” (sensu Poljak, 1936) shows pores large about 100-160 µm (Fig. 6), and others larger about 50-70 µm. Thebasal part of the coenosteum, which includes the first 5-6 lamellae, shows the interlamellar spaces larger thanthose of the upper part of colony (Fig. 7).

The natural transversal cross section shows, on surfaceof half part of specimens, because of a differential ero-sion, the interlamellar spaces filled by a calcite fibro-lamellar cement, to be protrusive. The lamellae, on thecontrary, in origin probably made up of aragonitic fibres,are eroded and appear as empty spaces (Figs. 3, 8). Thesespaces show calcitic interconnections (very similar tointerlamellar pillars, as interpreted by previous authorssuch as Meneghini and Oppenheim), but they representon the contrary the radial channels (Figs. 4, 8). Thesesmall channels cross perpendicularly the lamellae, andare generally filled by diagenetic calcite.

As pointed out by Canavari (1893), the original emptyspaces (interlaminar empty spaces and channels) noware filled by diagenetic calcite and appear white, on thecontrary the lamellae, probably constituted by fibrous-lamellar aragonite, now, because of the erosion, appearas empty spaces on surface. All the specimens studied inthe present paper from the Gargano area show this typeof differential erosion (Fig. 3). Canavari (1893)described, for specimens collected from Rocca Calascio,near Monte Camarda, southern part of Gran Sassod’Italia, a reverse situation: i.e., the laminae are not erod-ed, and then are protruding, whereas the interlaminae

spaces are not filled, and then appear as empty spaces.The true pillars (Fig. 9), in Ellipsactinia, generally

connect two lamellae; sometimes they may be superim-posed on each other connecting several lamellae (Fig.10). In this case they may simulate the tubuli. In theEllipsactinia the pillars are fairly rare.

In longitudinal section, and/or in SEM observations,linear pseudotubuli (Fig. 11) crossing several lamellaeare present. They appear, in thin section, as white struc-tures, 0.18 mm large and up to 3.5 mm long. They areproduced by superposition on each other of some radialchannels. Observed at the SEM, on the contrary, theyappear filled by calcite, and they seem in relief.

Microstructure

As observed above, the skeleton of Ellipsactinia isentirely recrystallized in calcite. Neverthless it is possi-


Fig. 6 - Tangential thin section of “first lamella” and following lamel-lae to show the pore types in Ellipsactinia. x 6.

Fig. 7- Detail of “apical” part of Ellipsactinia showing “first lamella”,following lamellae and interlamellar spaces. On the left are visible few“radial channels”. SEM photograph.

Fig. 8 - Detail of Ellipsactinia to show the radial channels (simulating“false pillars”) of eroded lamella and interlamellar spaces filled by cal-cite (in relief).

ble to distinguish the original microstructure with anorganization of fibers following a “water jet” (clinogo-nal) pattern (Fig. 13). These fibers start from a basalpoint and diverge going up to form a penicillate or“water jet” arrangement. Generally each lamella consistsof two superimposed layers of such fibers disposition.Interbedded with the lamellae there are the interspacesfilled by an ortho-fibrous calcitic cement (Fig. 12). Also


Fig. 12 - SEM microphotograph. Particular of an interlamellar spacefilled by ortho-fibrous cement. Ellipsactinia specimen.

Fig. 13 - SEM microphotograph. Particular of lamella microstructureshowing the “water jet” (orthogonal) disposition of fibers. Ellipsacti-nia specimen.

Fig. 14 - SEM microphotograph. Particular of a monaxon spicule inEllipsactinia.

Fig. 9 - Detail of thin section of Ellipsactinia showing the pillars. x 17.

Fig. 10 - Detail of thin section of Ellipsactinia showing the pillars laidone upon the other to form a “pseudotubulus”. x 12.

Fig. 11 - Detail of thin section of Ellipsactinia showing two “pseudo-tubuli”. x 13.

in this case this filling is made up of two superimposedlayers separated by a thin discontinuity surface. Thereare present rare monaxon spicules, which lie on the tis-sue, without being immerged into the skeletal tissue, giv-ing the idea that they are fallen in (Fig. 14).

Architectural and microstructural organizationof the genus Sphaeractinia

As in Ellipsactinia, the generic name, Sphaeractinia isrelated to the shape, but this is not always true. In fact themorphology varies from globular to elliptical, cylindri-cal, and sometimes shows incipient of bi- or trifurcation.The size of colonies is variables, but generally they aresmaller than Ellipsactinia. Very often the colony canenvelope small clasts, upon which the colony grows up(Fig. 15).

Architectural organization

The superimposed lamellae, dark in colour, are thinnerin the “marginal zone” (sensu Grubić 1983), and theirtickness is about 0.18-0.20 mm, whereas the interlami-nar spaces may have the same tickness or be thicker,more than 0.30 mm.

The first lamella or “parent lamella” is pierced bynumerous pores with diameters large about 0.30-0.50µm (Fig. 16). The lamellae have a regular trend, some-times arched and convergent towards the astrorhizae-likeorganized radial tubuli. They show numerous largepores, and, sometimes, in tangential thin section it ispossible to observe a meandriform skeletal tissue (Fig.17).

As in Ellipsactinia, the lamellae, on surface, are erod-ed for some millimetres, and appear as empty spaces,whereas the interspaces are filled by calcitic cement andare in relief. On the longitudinal surface, these emptyspaces, corresponding to original eroded lamellae, showinterconnections representing the radial channels (Fig.18). These small channels cross perpendicularly the


Fig. 15 - Field photograph of Sphaeractinia, in which are clearly visible the lamellae course, the radial channels and, on lower middle part of pic-ture, the “radial tubuli” arranged like astrorhizae pattern. Road from Foresta Umbra to Carpino.

Fig. 16 - Thin section of Sphaeractinia showing the “first lamella”pierced by two type of pores (smaller and larger), the lamellae deeplyperfored, and, on the upper left, the pillars laid one upon the other toform a “pseudotubulus”. x 7.

Fig. 17 - Tangential thin section of Sphaeractinia showing themeandriform tissue of lamellae and the pseudotubuli (lower part ofpicture). x 5.

lamellae, and generally are filled by diagenetic calcite.The pillars (Fig. 19), on the contrary, connect two

lamellae, and are much more numerous compared withEllipsactinia. They are well ordered and superimposed

to each other like a “dry-stone wall”. Also in Sphae-ractinia pseudotubuli (Fig. 19) are present, but, unlikeEllipsactinia, there are also bundles of tubuli convergenttowards the exterior, near the periphery, which have aspecial pattern simulating the astrorhizae of stromato-porids. The internal wall of these tubuli is lined by a darkfilm. These structures, typical only of Sphaeractinia,have been already observed by Canavari (1893), and arecalled radial tubuli (Figs. 20, 21).

Very rare and sparse monaxon spicules are presentalso in Sphaeractinia.

Microstructure

As in Ellipsactinia, also the skeleton of Sphaeractiniais entirely recrystallized to calcite. Neverthless it is pos-sible to distinguish the original microstructure with anorganization of fibers following a “spherulitic” pattern(Figs. 22, 23). These fibers start from a central point andradiate all over the directions to form a spheruliticarrangement. Interbedded with the lamellae there are theinterspaces filled by a “dog-tooth” calcitic cement (Fig.24). There are present rare monaxon spicules, which lieon the tissue, without being immerged in the skeletal tis-sue, giving the idea that they are fallen in.

CONCLUSIONS

The classification of fossil sponges is based on themineralogical composition and shape of the spicularskeleton, and therefore the lack of a spicular skeleton inmost sponges makes their “natural” classification diffi-cult.

Even with these restrictions, it is possible to includeEllipsactinia and Sphaeractinia in the class Demo-spongiae, phylum Porifera, because of their microstruc-ture and skeletal organization. The systematic position at


Fig. 21 - Thin section of Sphaeractinia. Particular of radial tubuli (likeastrorhizae pattern). x 17.

Fig. 20 -Thin section in Sphaeractinia. In the lower part of picture isclearly visible the radial tubuli arranged like astrorhizae. x 7.

Fig. 18 - SEM microphotograph. Detail of two interlamellar spaces(white and in relief) with an intercalated lamella showing the sticks ofradial channels pointed out by differential erosion in Sphaeractinia.

Fig. 19 - Longitudinal thin section in Sphaeractinia showing numer-ous deeply perforated lamellae, pillars and pseudotubuli. x 7.5.

lower level, on the contrary, must be better defined.There are, in fact, differences in the microstructurebetween these two genera. Ellipsactinia has a “water jet”(clinogonal) fiber arrangement, whereas Sphaeractiniashows a spherulitic microstructure.

The genus Ellipsactinia Steinmann includes formswith peculiar features: laminae larger than the interlam-inar spaces, few pillars with an irregular arrangement

and finally, tubuli (pseudotubuli), very long but not inastrorhizae arrangement.

The genus Sphaeractinia Steinmann, instead, is char-acterized by laminae usually narrower than the interlam-inar spaces, “dry-stone wall” pattern of the laminae,which may exhibit meandriform structures, large num-ber of pillars also placed upon, numerous pseudotubuliand, near the periphery, radial tubuli with astrorhizaearrangement. Radial canals and spiculae are commonfeatures in both genera.

According to our preliminary research, it seems thatSphaeractinia is more abundant than Ellipsactinia in theGargano. Further research is necessary to establishwhether these two genera inhabited the same environ-ment.

Our interpretations are preliminary and should stimu-late further studies.

ACKNOWLEDGEMENTS - We thank Dr. Paolo Serventiand Claudio Gentilini for technical support. A particular thankto Prof. J. Pignatti, Università “La Sapienza”, Roma, forEnglish improvement and useful suggestions.

Contribution to MIUR PRIN project 2004045107 (Palaeo-climatic forcing on building organism communities, carbonateproductivity and depositional systems of some Italian Meso-Cenozoic shelf deposits). Bosellini A., coordinator.


Fig. 22 - SEM microphotograph. Sphaerulitic microstructure ofSphaeractinia lamella.

Fig. 23 - SEM microphotograph. Sphaerulitic organization of fibersmaking a sphaerulitic pattern.

Fig. 24 - SEM microphotograph. In the central part of picture thelamella tissue sandwiched by “dog-tooth” calcitic cement in aSphaeractinia specimen.

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