In general, the Sabellæ inhabit tubes which are not calcareous or
shelly; they are composed of a soft flexible substance somewhat
resembling wet parchment, made of a secretion from the animal’s
body, in which the impalpable muddy sediment which the waves agitate,
consisting of decomposed organic matter for the most part, is
interwoven. The tissue so made is sufficiently tough and enduring,
retaining its form long after the animal has died out of it.
In our dredge-hauls we find a pretty little kind[146] common enough,
which lives in association, the tubes apparently from half-an-inch
to an inch in length, forming dense masses on stones and shells, and
projecting in every direction. A dozen or more may be in one group, and
when all are alive, one or another protruding or retiring every moment,
it makes a pretty object.
The gill-filaments are nine to eleven in each row, of a yellowish
white, occasionally patched with dead-white, or red-brown: delicately
and densely pinnate. The filaments, in the act of protruding, are
closed together like a straight bundle of rods which suddenly fall open
at the ends. In this moment of unfolding, their tips are seen to be
a little hooked inwards. The tube is about as large as a crow-quill;
under a lens it appears speckled, as if the inorganic matter imbedded
in it were grains of the finest sand. On carefully removing all the
surrounding tubes and other objects so as to isolate one, we see that
it is truly about three inches in length, but that two-thirds of the
whole are prostrate and adherent; this basal portion is horny and
pellucid, no mud entering into its texture. The animal when extracted
is an inch in length, of which the gill-tufts form one-third.
Mingled with these there are one or two specimens of a much more
imposing species, the Hook-plumed Sabella.[147] It grows to a large
size, the crown of gill-filaments sometimes attaining a height of an
inch, and the same diameter. The two rows are incurved in regular
spirals of half a turn, each consisting of about eighteen filaments,
which are rather stout, the whole crown sometimes taking the form of a
funnel, sometimes that of a cup, often arching inward at the tip. Their
pinnæ are long and close, the two rows forming a groove, but nearly
parallel. Each primary stem is set along the back with twelve pairs of
feather-like processes, hooked downwards;--a very remarkable character,
and one by which this species may be in a moment distinguished. Their
colour is pale red-brown, mottled irregularly with deep brownish purple
and with white; there is a pair of brown specks at the origin of
each pair of hooks. The base of the crown is always concealed in the
mouth of the tube, but it springs from a narrow frilled membrane of
pure white. The body is destitute of a thoracic shield, or conspicuous
collar. The tube is largely composed of soft homogeneous mud, usually
of a pale purplish hue, of about the thickness of the shelly tube of
_S. tubularia_.