Pillai: Serpulid polychaetes from the Australian Kimberleys 
149 
Figure 37. A-H, Spirobranchus baileybrockae n.sp. from holotype, AM W21421: (A) dorsal view 
of whole worm; ( B ) right dorsolateral view of operculum; (C) operculum viewed from anterior 
end; ( D,E ) bayonet-shaped special collar chaetae; (F) thoracic uncini; (G) anterior abdominal 
uncini; ( H) posterior abdominal uncini. 
longitudinal ridge which projects conspicuously over the 
aperture, and its surface is pitted on the sides and flanges 
giving it a somewhat “foraminous appearance”. On the 
other hand, tube-colour in S. tetraceros (Schmarda, 1861) 
as observed in the Kimberleys collection is white in adults, 
may be white to bluish-grey in juveniles, but not pink or 
rose, and does not have a pitted surface and a “foraminous 
appearance”. 
Secondly, the number and form of the main opercular 
horns in the Kimberleys holotype agree fully with Bailey- 
Brock’s Fijian specimens. In both they consist of a circle 
of 8 long unbranched horns, which are not dichotomously 
branched, each bearing a regular single row of medial spines, 
as well as a short dichotomously-branched spine arising from 
the centre of the latter circle of long spines. In contrast, the 
number of main horns in S. tetraceros from the Kimberleys 
is 3, and they are dichotomously branched. Furthermore, 
inter-radiolar membranes are not fringed in S. baileybrockae 
but fringed in S. tetraceros. 
Another species that needs to be compared with S. 
