1915. Streblosoma cochleatum, Caullery. Bull. Soc. Zool. France, t. xi, 1—3, p. 52.
1917. „ Bairdi, Hessle.. Zool. Bidr. Uppsala, Bd. v, p. 211.
Habitat.—Dredged in 80—90 fathoms in Busfca Voe, St. Magnus Bay, by Dr. Gwyn
Jeffreys in 1867 and 1868. Dredged at Station No. 6 (Atlantic) in the “ Porcupine ”
Expedition of 1870. Elsewhere it occurs in Sweden (Malingren, Malm).
The cephalic lobe is truncate in lateral view—a feature due tö the flattened arch of
the supra-oral fold, which in many Terebellids forms a spout- or hood-like projection.
The surface of the cephalic plate from which the tentacles arise is thus nearly vertical.
The dorsal collar presents no eye-specks in the preparations, and curves downward to
join the supra-oral fold externally and ventrally. The tentacles agree with those of
Thelepué, being well developed and" having a deep groove with frilled margins.
The general outline of the body agrees with that in Thelepus, though the details
differ. It is enlarged anteriorly and tapered posteriorly, no example, however, being
complete. The dorsal surface is rounded and smoother than in Thelepus, the ventral
surface flattened, and posteriorly slightly grooved. Anteriorly are ten to eleven glandular
ventral shields, which may be wrinkled in the preparations, and the outer edges of which
touch the rows óf hooks. A glandular belt accompanies the setigerous region, but it is
not so pronounced dorsally as to form anteriorly the definite edge as in Thelepus, though
posteriorly it is well defined. The ventral surface behind the shields is more thinly
coated with the glandular tissue, and a thickened median ridge continues for some
distance backward. The Norwegian examples appear to be smaller than the British.
Though Thelepus triserialis agrees with Streblosoma bairdi in having three pairs of
branchiae, yet their arrangement in connection with the bristle-tufts differs. In the
present form a branchial tuft of several filaments occurs on the anterior edge of the
second segment, but its attachment is above the line of the first setigerous process, which
is likewise on the second segment. Behind is a second tuft of branchiae with fewer
filaments, and which is in a line with the first setigerous process of the left side; whilst
on the right it is opposite the second setigerous process. The third is a prominent group
of about six filaments opposite the third bristle-tuft. The individual filaments are
similar to those of Thelepus, though in some they are longer; and the first set arise from
a transverse ridge, which, however, does not pass externally below the line of the bristles
as in Thelepus. On the whole the area covered by the branchiae is longer antero-
posteriorly than in Thelepus.
No more distinctive feature between Streblosoma and Thelepus exists than
the great size of the setigerous processes and the length of the bristles. The first
setigerous process occurs on the second segment, and it is slightly shorter than those
which follow, and in the region of the shields the processes form long lamellae with
slightly expanded tips set obliquely like the blades of a series of oars, the ventral edges
of which are curved and split for the. extended line of pale golden bristles. Moreover,
when the process is removed a distinct twist like the blade of a propeller occurs in all
the pencils of bristles—a condition closely connected with the functions of the bristle-
tufts. As in Thelepus the setigerous processes spring from the posterior part of each'
segment and are dorso-lateral in position. Two ranges of bristles occur in each tuft,
a longer and a shorter, the latter alternating with the former. The longer bristles (Plate
CXXVI, fig. 7) have nearly cylindrical shafts inserted deeply in the tissues, but thoy
taper from the cutieular surface distally so that when the narrow wings commence
considerable diminution has occurred, and they taper to very fine hair-like curved points.
The shorter forms are much more slender, but they also taper to hair-like points and
have narrow wings. The dorsal edge of each fascicle is bounded by three or four strong
bristles without the intervening shorter and more slender forms, whereas the ventral edge
has shorter and more slender bristles.
The number of bristle-tufts is about thirty-two, and the region behind has only
uncinigerous lamella. The posterior bristles are also inserted deeply in the tissues, are
stout and comparatively short and have considerably broader wings, but they likewise
taper to a fine hair-like point. They retain the same arrangement of the three or four
strong bristles without the intervening slender forms on the dorsal edge of the tuft. . As
the shorter, slender forms do not present traces of wings it is doubtful if they represent
reserve-bristles.
The first row of hooks commences opposite the fourth bristle-tuft, that is, in a
corresponding position to that of T. triserialis, though in the latter it is the third
setigerous process. The rows are somewhat shorter than in Thelepus, and they are sooner
elevated on ridges; indeed, at the eighth or ninth a distinct lamella is apparent, and at
the twenty-fifth it forms a fan-shaped flap with the single row of hooks in a curved line
on the anterior face of the edge. The hooks of the first are distinguished by the apparent
length of the base, but this is due to its narrowness. The typical hook (Plate CXXYI,
fig. 7 a) has two distinct teeth above the main fang, the crown above it being thus
elevated; the posterior outline is deeply indented, the anterior outline (below the main
fang) has a peculiar stud which leaves it at an obtuse angle, whilst the prow is continued
beyond it to end in a process for a ligament; the base is evenly convex inferiorly, and has
a process at the end of the posterior outline.
The tube is soft, rather thick, and composed of grey, muddy sand in fine grains. In
that dredged by the “ Porcupine ” the soft, translucent, yet fairly tough secretion had
minute grains of sand attached to it at intervals. Thus the tube is readily distinguished
as a rule from that of Thelepus cincinnatus.
Sars1 (1871), in the characters of the genus, gave the hooks only two teeth, but in the
British examples there are three.
Ehlers3 (1875) describes from the “ Porcupine ” Expedition a species termed Grymaea
brachiata, n.s., but the figures, for instance, of the hook are so indefinite that some doubt
remains as to its exact nature, for the slight differences noted by the author, such as the
occurrence of the hooks on the sixth segment, may yet be otherwise explained.
Genus CLIV.—Parathelkpus, Caullery, 1915.
Cephalic region with a frilled lobe around the mouth, the sides separated ventrally
and partially dorsally; an independent small lamella behind the mouth. Tentacles
1 ‘ Vidensk-Selsk. Forhandl. Christ./ p. 10.
? ‘Zeitsch. wiss. Zool./ Bd. xxv, p. 74, Taf. iv, figs. 24—27.