Fig. 183.—A group of tubes of Serpula vermicularis L., from the mouths of two of which the animals are protruding, that on the right being seen from above. br, The gill plume; m, thoracic membrane; op, operculum; op1, corresponding gill filament of the opposite side; t, tube. (From Cuvier's Règne Animal.) Nat. size.
Filigrana implexa Berkeley is a small worm, but the slender white tubes intertwine and adhere together in masses 3 or 4 inches high, occurring at low tide and down to 18 fathoms in the North Sea and Mediterranean. The animal has only eight gill filaments on each side, one of which on each side is slightly expanded to serve as an operculum. The worm multiplies by transverse division.
Spirorbis borealis Daudin is a still smaller worm, the tube of which is coiled in a flat spiral about 1⁄16 to ⅛ inch across; it is common, adhering to Fucus, shells, and other objects. It is represented by fossils in the Palaeozoic rocks. Cosmopolitan.
Protula (Psygmobranchus) tubularia Mont. is a Serpulid without an operculum; it forms a straight or slightly and irregularly curved tube. Atlantic and Mediterranean. Salmacina dysteri Huxley has no operculum; it is a small worm incrusting seaweeds, or forming masses like Filigrana.
Sub-Order 2. Hermelliformia.
The single family Hermellidae is represented by two species—Sabellaria alveolata L., which is littoral, and S. spinulosa Leuck., occurring in 10 to 30 fathoms.
S. alveolata[[396]] is about an inch long; the thorax is purple, the abdomen yellow to red. The narrow caudal region is bent sharply forwards, so that the anus, situated at its tip, comes to lie at the orifice of the tube, which is irregular and sandy. Great numbers of the animals live together, so that the masses of their tubes may be 2 or 3 feet thick and several feet long. They are well seen on the shore, at Paignton, near Torquay, and on Hilbre Island, off the Cheshire coast. North Sea, Atlantic, Mediterranean.
Fig. 184.—Spirorbis. A, the shell, enlarged. B, the animal, × 50. c, Peristomial collar; e, eggs in the brood pouch at the end of the operculum; g, gills; m, thoracic membrane (characteristic of Serpulidae); n, the single pair of thoracic nephridia opening by a median dorsal pore beneath the collar (common to all Sabelliformia); o, ova in the anterior abdominal segments; op, operculum; s, spermatozoa in the hinder abdominal segments; st, stomach. (From Claparède.)
Order III. Myzostomaria.[[397]]