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Records of the Australian Museum (2009) Vol. 61 
its bayonet-shaped collar chaetae similar. In S. tetraceros, on 
the other hand, the tube is white to light caramel coloured, 
obtusely triangular in cross-section, has a very low MLR and 
fine transverse growth markings extending laterally from it 
(Fig. 44A). Its operculum bears three main horns, of which 
the dorsolateral pair is branched thrice and the ventral horn 
is branched twice; the two branches of its dorsolateral horns 
are roughly equal to each other in size, as also are those of 
the ventral horn. The spines along the branches are somewhat 
longer, lighter in colour, not as chitinous and stiff as those in 
S. semperi. In its bayonet-shaped special collar chaetae (Fig. 
45C,D), the serrated distal part of the chaetal shaft is shorter 
than the blade, and the boss is smoothly sloping rather than 
squarish. Inter-radiolar membranes are fringed (Fig. 45B). 
Considering the sizes of the above two lots of specimens, 
there is every indication that S. semperi var. acroceros 
Willey is a juvenile form of S. semperi. There appear to be 
no significant differences between Serpula quadricornis 
Grube (1878: 275, pi. XV, fig. 6) and Spirobranchus semperi 
Morch, 1861. Hence they are synonymized. 
Spirobranchus sp. 5 
Figs 58A-D, 59A-H 
Material examined. Several specimens from Doom Island and Sop Island, 
Sorong, (0.50°S 131.17°E), West Irian (former Dutch West New Guinea), 
Indonesia; found growing on the tips of coral at 1-2 m depth, BMNH 
1992.357-366, coll, by T.G.Pillai, 24 May 1971. According to label in jar: 
identified by ten Hove in 1988 as S. tetraceros (Schmarda). 
Description 
Measurements. Maximum external tube diameter, 2.0 
mm; total lengths of worms, 9.7-8.6 mm; width of thorax 
1.3-1.5 mm. Lengths of operculum and peduncle, 2.5-3.0 
mm, opercular disc plus horns, 1.0-1.2 mm, and diameters 
of opercular plate, 1.5-1.6 mm. Abdominal lengths, 5.5-14.4 
mm. Numbers of branchial radioles range from 12 per side 
to 17 on the left and 18 on the right. 
Tube. Colour white; grows on coral (Fig. 58A), complete 
tube of a specimen, with much of coral newly laid over 
it removed, shown in latter figure; a row of transversely 
elongated chambers present ventrolaterally (Fig. 58B). 
Viewed from above (Figs 58C,D), has a low, more or less 
smooth MLR, and a flattened area on either side of it, the edge 
of the latter forming a lateral ridge. Obliquely transverse, 
smooth, shallow ridges and grooves on either side of the 
MLR may appear to be arranged in a row. 
Worm. Operculum on left side, no rudimentary operculum 
on right; opercular plate circular, bearing three main horns; 
up to two main dichotomies may be present on each (Fig. 
59B-D). Accessory spines at the end of and along the main 
branches: elongated, tapering, and mainly single. Fissures 
are present along the main branches, even extending into 
the dichotomies (Fig. 59C), apparently not having closed 
up as in other species. Peduncular wings unfringed (Fig. 
59A,F). As seen in transparency through opercular peduncle 
of a post-juvenile specimen (Fig. 59F), a hollow is present 
ventrally, towards the centre of the opercular plate. Maximum 
number of 18 branchial radioles counted per side, arranged 
in a circle; their pinnule free tips being somewhat longer and 
thicker than the pinnules that precede them (Fig. 59E). Inter- 
radiolar membranes unfringed or bear a single papilla (Fig. 
59A,D,E). Thorax consists of 7 chaetigers; apron present; 
abdominal uncinal tori lateral; two short pygidial papillae 
present (Fig. 59A). 
Chaetae. Special collar chaetae bayonet-shaped, with a 
square boss in those that have not undergone abrasion (Fig. 
59G), less squarish in partially abraded ones (Fig. 59H); 
their blades broad towards the boss, taper abruptly, and are 
only slightly longer than, or equal to length of serrated part 
of shaft plus boss. Uncini: saw-shaped; thoracic uncini with 
12 or 13 teeth plus anterior gouge; anterior abdominal uncini 
with 8-10 teeth plus anterior gouge. 
Remarks. Spirobranchus sp. 5 from from Sorong, Indonesia, 
is superficially similar to S. tetraceros from the Kimberleys, 
but there are important differences between them. Although 
the tubes in both are white, there are differences in their form. 
Tubes of adult S. tetraceros are obtusely triangular and bear 
only a single low, thin longitudinal ridge, the MFR. On the 
other hand, tubes of S. sp. 5 are less obtuse, more or less 
circular in cross-section, and bear not only a prominent and 
smooth MFR, but also a FFR at each dorsolateral angle of 
the trapezium. However, the opercular processes appear to 
be similar. The coral habit of S. sp. 5 (Fig. 58A), is similar 
to that described by Smith (unpublished thesis, 1985) for 
his S. tetraceros species B, from the GBR with the tubes 
following “sinuous paths between and along branches that 
are invested with coral skeleton.” 
Further work is necessary to determine whether the 
species that grows on coral tips in Sorong, Indonesia, belongs 
to S. tetraceros (Schmarda) or a new species. 
Spirobranchus sp. 6 
Fig. 60A-G 
Material examined. BMNH 1972.250: one specimen with its tube, Tizard 
Bank, South China Sea, located between Vietnam and the Philippines, 
Bassett-Smith China collection; separated by H. Zibrowius in 1972 from a 
collection of DendrophyIlia gravis, BMNH 1889.9.24.16, in Coelenterata 
Section, presented by Lords of the Admiralty. 
Description 
Measurements. Maximum diameter of tube 2.5 mm; total 
length of worm 27.5 mm; length of operculum and peduncle 
6.5 mm, length of operculum and its horn 2.5 mm, length of 
horn 0.6 mm, width of thorax 1.5 mm, length of abdomen 
16.0 mm, number of abdominal segments about 115. 
Tube. White, porous along sides, apparently caused by a 
boring sponge; a single simple, very low, median longitudinal 
ridge present. 
Worm. Operculum arises close to the base of left radiolar 
crown, rudimentary operculum absent. Opercular plate 
circular, bears a somewhat dorsally located column which, 
in turn, bears three bifid horns, two of them dorsolateral, and 
the third ventral (Fig. 60A-D). Each dorsolateral horn has a 
pair of short pointed spines, located dorsolaterally, close to its 
tip, and another shorter spine, dorsally, almost at its tip (Fig. 
60A-D). Fower branch of bifid dorsolateral horns, in turn, 
ends in a bifid spine with their tips pointing away from the 
