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Records of the Australian Museum (2009) Vol. 61 
Figure 52. (A), Spirobranchus sp. 4: bayonet-shaped special collar chaetae from within collar fascicle. B-I, from type material of Spiro- 
branchus maldivensis Pixell, 1913, BMNH 1924.6.14.114: ( B ) tube, showing median longitudinal ridge, which consists of fin-shaped 
parts, some of them low, others triangular, still others forwardly directed truncated rods; (C) thorax and operculum viewed from left side; 
(. D ) dorsolateral view of anterior end of worm and operculum; (£) anterodorsal view of opercular plate showing its concentric rings and 
lack of processes; (F) ventral view of thorax; (G) bayonet-shaped collar chaeta; note long serrated area of shaft preceding the boss, and 
that length of the blade is approximately equal to that of serrated area of shaft plus boss; ( H ) thoracic uncini; (/) anterior abdominal uncini. 
abdomen are present from the 2nd or 3rd anterior abdominal 
segment onwards (Fig. 5 IB). 
Remarks. Spirobranchus sp. 4 superficially similar to S. 
tetraceros with regard to the branched opercular spines 
borne on a circular opercular plate. However, although the 
peduncular wings in S. sp. 4 and S. tetraceros are fringed, 
those of the former possess a double row of numerous 
papillae (Fig. 50A,C,E), while those of the latter possess a 
single row of papillae (Fig. 46D,L). There also appears to be 
a difference in the maximum number of branchial radioles 
attainable, about 23 in S. sp. 3, but more, about 28-30 in the 
Kimberleys S. tetraceros, for instance. Further studies are 
needed S. sp. 3, including its tube. 
