Maeandropolydora Voigt, 1965

Gaaloul, Nadia, Uchman, Alfred, Ali, Syrine Ben, Janiszewska, Katarzyna, Stolarski, Jarosław, Kołodziej, Bogusław & Riahi, Sami, 2023, In vivo and post-mortem bioerosion traces in solitary corals from the upper Pliocene deposits of Tunisia, Acta Palaeontologica Polonica 68 (4), pp. 659-681 : 669-671

Ichnogenus Maeandropolydora Voigt, 1965

Type ichnospecies: Maeandropolydora decipiens Voigt, 1965 , Kunrader Member of the Maastricht Formation , upper Maastrichtian, Kunrade, the Netherlands .

Diagnosis. —Long cylindrical galleries having two or more apertures, running through the substrate sinuously or in irregular contortions. Galleries may run parallel in contact with each other in pairs, with or without fusion. Loose or tight loops may occur; the limbs of these may be connected by a vane or form a pouch (cited from Bromley and D’Alessandro 1983).

Remarks.— Maeandropolydora Voigt, 1965 , is a boring of suspension-feeding spionid polychaete (e.g., Bromley and D’Alessandro 1983). It occurs since the Triassic and Palaeozoic occurrences are uncertain ( Bromley 2004).

Maeandropolydora elegans Bromley and D’Alessandro, 1983

Figs. 5G , 9A 4 , 10 , 11A , 10B , 13B 2 , SOM 2.

Material.— INGUJ 265P150, 151, 153–155, 159, 163, 170, 171, 184, 188, 192; branched, flat galeries on the surface of coralla; the El Melah stream section, the upper part of the Argiles de Sidi Barka Formation (upper Pliocene) of Tunisia.

Diagnosis. —System composed of cylindrical galleries of constant diameter, irregularly sinuous, tending to run in paired fashion, the limbs touching but normally not fused. Numerous apertures (cited from Bromley and D’Alessandro 1983).

Description. —Surface groves or subsurface branched galleries running in pairs, mostly parallel, within the corallum wall. Some stretches of the subsurface galleries capped by a thin roof commonly transit into surface grooves ( Fig. 10D ). Most of the surface grooves show overhanging side margins. These pairs are 0.5–1 mm wide, with a very narrow, usually indistinct, vane between the galleries/grooves or without a vane. The observed length may exceed 10 mm. Branches at an acute or normal angle. The plane of the borings is usually more or less parallel to the corallum, but some segments are perpendicular. The boring is concentrated in the corallum wall (SOM 2).

Remarks. —The surface galleries are usually a part of subsurface galleries, where the roof was broken or collapsed. So far, Maeandropolydora elegans is known from bivalve and brachiopod shells.

Stratigraphic and geographic range.—Middle Triassic

( Knaust 2007)–Recent; the Atlantic and the Mediterranean regions.

Maeandropolydora sulcans Voigt, 1965

Figs. 5F , 11B , SOM 3.

Material.— INGUJ 265P152, 166, 169, 181, and thin section 5/29 from INGUJ 265P136; cylindrical, contorted tunnels in coralla; El Melah stream section, the upper part of the Argiles de Sidi Barka Formation (upper Pliocene) of Tunisia.

Diagnosis. —Cylindrical gallery having at least two apertures, irregularly contorted, commonly bent to loops, never showing fusion where walls are in mutual contact; vane absent (cited from Bromley and D’Alessandro 1983).

Description. —Loosely contorted cylindrical tunnels spreading through the whole volume of the corallum, 1.3–2 mm in diameter (SOM 3). They show a few oval openings that are oblique or perpendicular to the surface of the corallum.

Remarks.— Maeandropolydora sulcans is usually described from diverse skeletal elements, mostly shells, and rarely the rocky substrates (e.g., Łaska et al. 2021).

Stratigraphic and geographic range.— C ommon in the Cretaceous and the Cenozoic, foremost in the Atlantic and the Mediterranean regions; the Paleozoic occurrences are rare and problematic ( Bromley 2004).

Figures

Fig. 5. Structural features of the caryophylliid coral Ceratotrochus (Edwardsotrochus) duodecimcostatus (Goldfuss, 1826) coralla from upper Pliocene deposits in a tributary valley of the El Melah stream, north-east of Hammamet town, Tunisia. A. Virtual sections of INGUJ265P153 in lower (A1) and in more distal part (A2) of corallum. B. Thin-section 3/76 of INGUJ265P139 that shows nearly completely developed 5 cycles of septa. Positions of 10 S1 septa marked with black dots. C. Thin section 2/118 of INGUJ265P138, enlarged region of transversely sectioned corallum to show diverse pat- terns of mid-septal zone development (from zig-zag in S1, S2 septa to straight in S4 septa). D. Thin sections of INGUJ265P137, transverse (D1, thin section T1/8) and longitudinal (D2, thin section T1/9) sections to show some variability of septal cycle development (D1), and development of tabular dissepiments (D2). E. INGUJ265P188, distal (E1) and lateral (E2) views of specimen with major structural features indicated. F. Longitudinal thin section 5/29 of INGUJ265P136 with the boring Maeandropolydora sulcans Voigt, 1965. G. Virtual longitudinal section of INGUJ265P188 with the boring Maeandropolydora elegans Bromley and D’Alessandro, 1983.

Fig. 9. Snapshots from micro-CT images of Caulostrepsis in the skeleton of caryophylliid coral Ceratotrochus (Edwardsotrochus) duodecimcostatus Goldfuss, 1826) (INGUJ265P153), from the El Melah stream section, the upper part of theArgiles de Sidi Barka Formation (upper Pliocene) of Tunisia. A. The surface with indications of bioerosion traces, with partial transparency, and without corallum, A1–A4, respectively; Ct, Caulostrepsis taeniola Clarke, 1908; Me, Maeandropolydora elegans Bromley and D’Alessandro, 1983. B. View from the other side, B1–B4, respectively; Ca, Caulostrepsis avipes Bromley and D’Alessandro, 1983.

Fig.4. Exposures of the El Melah stream the section, upper part of theArgiles de Sidi Barka Formation (upper Pliocene) of Tunisia.A. Coral level III.General view (A1), close view of the sampling area (A2). B. The coral level II/coral level III boundary.C. Coral level II. General view (C1), close view of the sampling area (C2). D. General view of coral level I. Quadrangles indicate sampling areas.

Fig. 10. Maeandropolydora elegans Bromley and D’Alessandro, 1983, a dominichnion produced by polychates, in the skeleton of caryophylliid coral Ceratotrochus (Edwardsotrochus) duodecimcostatus (Goldfuss, 1826), from the El Melah stream section, the upper part of the Argiles de Sidi Barka Formation (upper Pliocene) of Tunisia. A. INGUJ265P171. B. INGUJ265P155. C. INGUJ265P159. D. INGUJ265P163.

Fig. 11. Micro-CT images of the skeletons of caryophylliid coral Ceratotrochus (Edwardsotrochus) duodecimcostatus (Goldfuss, 1826) with domichnia Maeandropolydora elegans Bromley and D’Alessandro, 1983, INGUJ265P150 (A) and Maeandropolydora sulcans Voigt, 1965, INGUJ265P152 (B) from the El Melah stream section, the upper part of the Argiles de Sidi Barka Formation (upper Pliocene) of Tunisia; surface view (A1, B1), surface view with indication of bioerosion structures (A2, B2), partial transparency (A3, B3), and without corallum (A4, B4).

Fig. 13. Sulcichnus sigillum Martinell and Domènech, 2009, a fixichnion produced by commensal polychaetes in the skeleton of caryophylliid coral Ceratotrochus (Edwardsotrochus) duodecimcostatus (Goldfuss, 1826), from the El Melah stream section, the upper part of the Argiles de Sidi Barka Formation (upper Pliocene) of Tunisia. A. INGUJ265P173. B. INGUJ265P170 in different side views (B1, B2). C. INGUJ265P175 in different side views (C1, C2). Abbreviation: Me, Maeandropolydora elegans.

Fig.2. Lithostratigraphy and subdivision of the Neogene and Quaternary series of northern (A) and north-eastern Tunisia (B) (Burollet 1951; Colleuil 1976).