Architecture and tube structure of Sabellaria spinulosa (Leuckart, 1849): Comparison with the Mediterranean S. alveolata congener

Abstract

The Atlantic-Mediterranean polychaete Sabellaria spinulosa (Leuckart, 1849) lives in agglutinated tubes forming discrete reef-like bioconstructions on shallow-water bottoms beaten by waves where sediment particles are constantly resuspended.Tubes are built with sand grains glued by a proteinaceous cement. Analyses of a S. spinulosa reef sample of this worm collected off the Casarza coast (central Adriatic Sea) allowed the description of its tube architecture and gluing modality. The tube consists of three layers of agglutinated sand: (a) a thin inner layer with sandy particles arranged side by side with a flat side facing the tube lumen (b) a thick middle layer with larger isodiametric and squat grains with empty pores in between; and (c) a thin discontinuous outer layer of heterometric clasts, prevalently large and flat, diverging towards the opening. This fits the general tube construction known for S. alveolata and in general for tubes of the sabellariidae family, but compared to Sabellaria alveolata, S. spinulosa possesses a smaller tube with a wall about 1/3 thick; the agglutinated sandy elements are finer, and some number of muddy particles participates in the tube construction. Morphological and epifluorescence observations revealed that biocement portions are irregularly and haphazardly distributed compared with those of S. alveolata that consist of drops and strips of glue carefully placed. Adjacent tubes leave empty interspaces in between them only locally filled by loose sand, extremely reduced to absent in S. alveolata.

New records of rarely reported species in the Mediterranean Sea (July 2023)

“…Of the two species present in the Mediterranean Sea, Sabellaria alveolata (Linnaeus, 1767) and Sabellaria spinulosa (Leuckart 1849), the first is known for building large banks; however, there are increasing records of large bioconstructions also for the latter (Gravina et al, 2017). Data about S. spinulosa are scattered along the Italian and Croatian coasts (Mikac, 2015;Lisco et al, 2021, Sanfilippo et al, 2022. In public databases, S. spinulosa is reported in the Aegean Sea (Greece), Egypt, and the Gulf of Trieste (Italy; OBIS, 2023).…”