Pillai: Serpulid polychaetes from the Australian Kimberleys 
159 
Figure 45. A-I, Spirobranchus tetraceros (Schmarda, 1861). A,B, a worm from AM W21441: (A) dorsal view of whole worm; (B) ventral 
view of anterior end of the latter worm; shows the branched horns, mottled ventral side of peduncle, fringed interbranchial membranes, 
pinnule-free radiolar tips, raised uncinal pads, the last two meeting mid-ventrally and the apron which is contracted into a triangular lobe, 
since the worm was fixed within its tube, and the long-shafted abdominal chaetae. C-F, chaetae from same specimen: ( C,D ) bayonet-shaped 
special collar chaetae; ( E,F ) thoracic uncini. G-I, a specimen from AM W21441: (G) dorsal view of anterior end, highly contracted, showing 
fringed opercular wings and fringed inter-radiolar membrane; (H) ventral view of anterior end showing inter-radiolar membranes, ventral 
lobe of collar, thoracic tori not meeting ventrally since the worm was evidently fixed outside its tube, the apron, and anterior abdominal 
chaetae with long shafts; (/) opercular spines viewed from the anterior end showing three main horns. 
specimens with a single low median longitudinal ridge, and 
fine transverse growth markings extending laterally from 
it (Fig. 44A). Tube of juvenile from AM W21397 is white, 
with a high, wavy median ridge and a low dorsolateral ridge 
on either side of it (Fig. 46A,B); fine, shallow, transverse 
ridges present at irregular intervals, between longitudinal 
ridges and along flanks. 
Worm. Colour (in alcohol): operculum and wings blue 
dorsally, and light blue with elongated blue specks ventrally; 
opercular plate white, its rim bright pink, as also are the tips 
of the horns. Although thorax and radioles in the juvenile 
specimen are colourless, they are bluish to purplish blue in 
the others. Basal two-thirds of branchial radioles, including 
inter-radiolar membrane, dark purplish blue; abdomen light 
purplish-blue anteriorly, gradually becomes colourless 
posteriorly. Operculum occurs on left side, no rudimentary 
operculum on right; opercular plate circular (Figs 44C, 
45A,B,G-I, 46D,E,M,L). Distal end of operculum in 
a juvenile specimen is bulbous; its somewhat concave, 
circular plate bears apparently four, but really three, main 
branched horns arising from a common base, two of which 
