Bristle Worm - Floriprotis sabiuraensis

Tanjung Lampy, Lembeh.

Quoting a few facts from this article (https://www.researchgate.net/publication/257649459_Occurrence_Formation_and_Function_of_Organic_Sheets_in_the_Mineral_Tube_Structures_of_Serpulidae_Polychaeta_Annelida):
Serpulids are marine polychaete tubeworms that dwell in all latitudinal and depth zones of the ocean. They are the only polychaete tubeworms with exclusively calcareous tubes. Serpulids are important calcifiers, especially in the
temperate seas where they construct small reefs. They are vulnerable to the ongoing modern ocean acidification.
These worms have the most advanced biomineralization system among the annelids. Serpulids can build tubes of aragonite, calcite or a mixture of both of these minerals. Their skeletal microstructures are similar to those found in a variety of invertebrate phyla and are comparable to those of cnidarians and arthropods in diversity.
Serpulid tubes contain both soluble (in EDTA) and insoluble organic matrices. The major components of the soluble
organic matrix are carboxylated and sulfated polysaccharides. Minority components of the soluble organic matrix are various amino acids, such as aspartic acid, glutamic acid, glycine and proline. Tanur et al. Their organic sheet structures may also contain polysaccharides. Sulfated and carboxylated polysaccharides have been found to influence the process of biomineralization.