Diagnosis: Borings with one entrance or embedment structure, pouch-shaped, created by a U-shaped gallery. More complex structures can result from multiple lobes of similar structure. The individual limbs of the gallery can be clearly visible along their total length, they can be connected by the vane, or they can be fused in an oval or flattened pouch shape without the vane. The distal end has at least double the width of the apertural end. The cross-section is variably flat-oval, elliptical, constricted, or dumbbell-shaped. Symmetrical, radially organized grooves or deep pits can be developed near the aperture n some cases (normally 2 to 4 in number). The aperture may have similar form to the proximal cross-section or it may be modified by the development of superficial branches, grooves, and/or holes (Bromley and d’Alessandro, 1983).

Unbranched, U-shaped

Category of architectural design: 2.61. U-shaped borings.

Macroboring; substrate calcareous; tracemaker invertebrate

Emended diagnosis.—Borings with one entrance or embedment structure, pouch-shaped, created by a U-shaped gallery. More complex structures can result from multiple lobes of similar structure. The individual limbs of the gallery can be clearly visible along their total length. They can be connected by the vane, or they can be fused in an oval or flattened pouch shape without the vane. The distal end has at least double the width of the apertural end. The cross section is variably flat oval, elliptical, constricted, or dumbbell-shaped. Symmetrical, radially organized grooves or deep pits can be developed near the aperture in some cases. The aperture may have a similar form to the proximal cross section, or it may be modified by the development of superficial branches, grooves, and/or holes (modified after Bromley and D’Alessandro 1983, with some modifications by Pokorný and Štofik 2017).

Remarks.—Information about the number of grooves branching from the aperture “(normally 2 to 4 in number)” is removed from the diagnosis of Bromley and D’Alessandro (1983: 286) because the new ichnospecies of Caulostrepsis described below has much more grooves. Caulostrepsis is a boring produced mostly by species of the spionid polychaete Polydora Bosc, 1802 (Boekschoten 1966), foremost P. ciliata (Johnston, 1838) (Radwański, 1969), and the eunicid polychaete Lysidice ninetta Audouin and Milne-Edwards, 1833 (Bromley 1978, 2004). Caulostrepsis ranges from the Devonian to the present (Clarke 1908; Bromley 2004). It occurs mainly in the infralittoral Plio-Pleistocene and the recent Mediterranean coasts (Bromley and D’Alessandro 1990), but mostly in the lower intertidal and subtidal zones, rarely deeper, and very rarely on the continental slope and the abyssal zone (Ekdale et al. 1984: 127).