Pillai: Serpulid polychaetes from the Australian Kimberleys 
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Figure 50. A-F, Spirobranchus elatensis n.sp. (A) tube viewed from above. It increases in width quickly towards its anterior end. There 
is an apparently flattened area on either side of the median longitudinal ridge, along the edge of which is a lateral longitudinal ridge; 
( B ) lateral view of the same tube. It shows that the apparently flattened area on either dies of the median longitudinal ridge is actually 
inclined towards the lateral longitudinal ridge. Fin-like extensions occur along the median longitudinal ridge, the highest one being at 
the aperture; (C) left lateral view of the operculum and peduncle; ( D ) the operculum and peduncle viewed from the ventral side, showing 
fringed peduncular wings; (E,F) bayonet-shaped collar chaetae; note the square boss, serrations all round the distal end of the shaft, and 
the blade that is longer than the serrated distal end of the shaft plus the boss. 
Remarks. Spirobranchus elatensis n.sp. is superficially 
similar to certain other taxa described in the past from the 
Indo-Pacific in possessing a dome-shaped to somewhat 
conical opercular plate with reduced horns borne at its apex. 
They are S. semperi var. acroceros Willey (Pillai, 1960: 18, 
fig. 7A-C); S. tricornigerus (Grube), Pillai (1960: 20, fig. 
7D-G), Spirobranchus tricornis (Morch), Straughan (1967: 
244, fig. 14b-d), and S. semperi var. acroceros Willey, 
Mohammad (1971: 300), which were synonymized with S. 
tetraceros by ten Hove (1970: 3-5). 
Ten Hove (1970: 6, figs 1, 2, 15 & 16) also describes 
a specimen from Bahrein with a conical operculum and 
