Sea Fir

Sea-Fir, or SERTULARIA ABIETINA (Linn.), is a species of zoophytes belonging to the family of Sertularidae and the order Hydroidea (q.v.). As it is one of the commonest members of this group, the popular name is sometimes extended to include them all, such as the Sea-tamarisk (Diphasia tamarisca, Linn.), the Sea-pine Coralline (D. pinaster, Ell. and Sol.), the Podded Coralline (Aglaophenia pluma, Linn.), etc. The group are all marine, and are plant-like in form. The skeleton is horny or chitinous, repeatedly branched, and is attached to rocks and shells. The zoophyte is colonial, many different polypites or individuals uniting to form a fixed colony or hydrosoma. This is composed of a chitinous or horny crust known as the perisarc, which surrounds and protects the softer tissues. Each polypite is protected by an expansion of the perisarc forming a cup or hydrotheca. The polypites are of two types of structure; they are modified to serve either for nutrition (the hydranths), while another set (the gonothecae) serve for reproduction. The skeleton consists of two parts: the basal hydrorhiza by which it is fixed, and the hydrocaulus, or the erect, branching stem; the two form the hydrophyton. In some genera, otherwise resembling the Sertularians, there are no hydrothecae to protect the polypites; these form the order Athecata, while the Sertularians belong to the order Thecaphora. The Campanularians are familiar representatives of the former. The Sea-firs and their immediate allies are marine.