Pillai: Serpulid polychaetes from the Australian Kimberleys 
175 
Spirobranchus paumotanus (Chamberlin, 1919) 
Figs 54A-F, 55A-K 
Pomatoceros paumotanus Chamberlin, 1919: 479, pi. 78, 
figs 6-9. 
Spirobranchus paumotanus (Chamberlin) 1919.—Nishi & 
Asakura (1996: 51-54). 
Spirobranchus giganteus .— Gibbs (1971: 203, in part). 
Material examined. BMNH 1970.855, numerous specimens, including a 
tiny juvenile, 5; Solomon Islands, separated in Royal Society Expedition 
to the Solomon Islands, coll, and presented by P. Gibbs. Identified as S. 
giganteus (Pallas, 1766), according to label on the jar. 
Description 
Measurements. Maximum width of tube figured (Fig. 54A), 
including its lateral flanges: 10.0 mm; in comparison with 
latter, length of second spine also 10.0 mm and width at its 
base, 5.0 mm; diameter of tube aperture itself is only 2.5 
mm, approximately equal to diameter of opercular plate. 
Total lengths of two of the largest specimens, 35.0 mm & 
31.5 mm; thoracic widths, 2.2 mm and 2.5 mm; lengths 
of operculum and peduncle 5.0 mm & 4.0 mm, heights of 
longest opercular horn (mid-ventral one) 1.5 mm and 1.0 
mm; diameters of opercular plate 2.2 mm and 2.3 mm; 
numbers of radioles: numerous; spirally arranged. Number 
of spirals on each side: 4 and 4, and 4 and 4. In a third, 
somewhat contracted specimen, there are 5 spirals on each 
side. Lengths of abdomen: 24.0 mm and 22.0 mm; numbers 
of abdominal segments: 88 and 91. 
Tube. White; mutually bonded and aggregated into clumps, 
their shape quite characteristic, when unhindered in their 
formation by competing individuals in the same clump. Each 
tube has an obtusely triangular cross-sectional appearance, 
and initially only a low median longitudinal ridge (Fig. 54A), 
then abruptly develops 1 to about 4 or 5 massive forwardly 
directed teeth (the one figured has two); most anterior tooth 
projects conspicuously over the aperture. A very wide 
lateral flange present on each side. Tooth-like processes at 
the anterior ends of tubes may be hindered from developing 
or may be obliterated by tubes of competing individuals 
growing over them. Apparently, once a competing individual 
grows over the aperture of another tube, the latter continues 
to grow underneath the former without developing any more 
such processes. Consequently, the tube growing underneath 
may only bear 1 to a few such processes posterior to where 
the competing tube grows over it. Shapes of such processes 
and the direction in which they point are also variable. 
The most anterior process, for instance, may be pointed, 
somewhat flattened, or shaped like a cobra’s hood, and 
directed forward or laterally. Tube surface frequently pitted 
with irregularly shaped foramina (Figs 54A, 55G), evidently 
caused by a boring sponge; some tubes lack them. 
Worm. The following description is based on examination 
of 8 adult specimens. Operculum on the left, no rudimentary 
operculum on right; opercula of 4 above specimens 
damaged; hence description based remaining 3, while a 
partly damaged operculum is also described from another. 
Opercular plate in all specimens circular, somewhat 
concave, and bears three horns which arise from a short 
stout stem (Figs 54B-F, 55A-D). Two of the horns are 
dorsolateral, the third ventral. As seen in the figures, the 
dorsolateral horns are quite horn-like and curved outwards 
and ventrally. Each dorsolateral horn characteristically 
bears along its lateral edge, what is apparently a groove, 
but is actually covered by a brownish chitinous layer; it 
may sometimes also bear a small knob dorsomedially at its 
base, (Fig. 54B-D). The ventral horn is also characteristic. 
Viewed laterally, it is the tallest of the three, projecting 
conspicuously anteroventrally, then curved anteriorly, 
and ending distally in two main outwardly curved 
branches(Figs 54B,F, 55B). Each of the latter may, in turn, 
be dichotomously branched once or twice towards its tip 
to give rise to short processes, which are outwardly curved 
(Figs 54B-F, 55A-D). An operculum with the tip of the left 
dorsolateral horn damaged is shown in Fig. 54D,E. 
Peduncular wings: unfringed (Figs 54B,C,E,F, 55A-D). 
Radioles numerous, arranged spirally on each side; number 
of whorls in each spiral mostly 4 on either side; 5 on either 
side in one specimen. Prostomial ocelli are not discernible. 
On the ventral side of the thorax, distances between 
corresponding pairs of uncinal tori decrease posteriorly 
leaving an inverted triangular area between them; the last 
pair of tori meeting mid-ventrally in worms fixed within their 
tubes; not seen in juvenile (Fig. 55H,I). An apron is present. 
Maximum number of abdominal segments counted, 91. Anal 
segment bears a pair of small rounded swellings in juvenile 
(Fig. 55K), lacking in adults. 
Chaetae. Special collar chaetae bayonet-shaped, boss not 
squarish in side view, curved smoothly from shaft to the base 
of the blade (Fig. 55E); blade is considerably narrower than 
shaft; approximately equal in length to that of serrated distal 
end of chaetal shaft. Remaining collar chaetae: similar to 
special collar chaetae, but considerably narrower. Thoracic 
uncini: saw-shaped with 12-14 teeth in a row; anterior 
abdominal uncini similar, with about 12 teeth in a row; both 
in addition to the anterior gouge. Abdominal neurochaetae 
with long shafts projecting from the body wall are present 
from the third segment onwards. Indeed, they are quite long 
in the anterior segments, the length of the shaft alone being 
about 15 times as long as that of the distal trumpet-shaped 
part and its attenuated process (Fig. 55F). 
Juvenile specimen. With a width of only 1.5 mm at its 
anterior end, the juvenile tube is similar to the posterior 
part of adult tube. It is obtusely triangular in cross- 
section, has only a smooth median longitudinal ridge, and 
anteriorly directed transverse furrows, those at the anterior 
end foreshadowing the tooth-like processes that have yet 
to be developed (Fig. 55G). A wide flange present along 
each side. Irregular foramina formed by a boring sponge 
present even at this young stage. Total length of worm 7.0 
mm; operculum on left side, its two dorsolateral horns have 
the typical shape, but the ventral horn, which has yet to be 
developed, is represented only by a small knob (Fig. 55H-J). 
Opercular peduncle unfringed (Fig. 55H); radioles number 
5 on each side, arranged in a circle, which is evidently the 
plesiomorphous condition. Fength of thorax 3.5 mm; apron 
present; length of abdomen 3.5 mm, about half achaetous 
anteriorly, the remaining half with about 23 chaetigers; anal 
segment bears a pair of small rounded knobs (Fig. 55K), 
which are lacking in adults. 
