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Records of the Australian Museum (2009) Vol. 61 
Figure 46. A-M, Spirobranchus tetraceros (Schmarda, 1861); A-K, specimen from AM W21397: (A,B) tube, showing high, wavy median 
longitudinal ridge and a low lateral ridge on either side of it; ( B ) tube with worm in situ; (C) worm viewed ventrolaterally; (D,E) operculum 
viewed dorsally and anterodorsally, respectively; (F,G) bayonet collar chaetae; ( H ) thoracic uncini; (/) distal part of an anterior abdominal 
neurochaetae; ( J) anterior abdominal uncini; (K) posterior abdominal uncini. L,M, a specimen from AM W21449: (L) dorsal view of 
anterior end; (M) anterodorsal view of operculum, showing three main dichotomous branches, and a low peak at the centre, inter-radiolar 
membranes and fringed peduncular wings. 
are dorsolateral, and the third ventral (Figs 44B, 45G,I, 
46E,L,M). Opercula of 7 specimens from AM W21449, as 
well as those of others examined are similar and bear three 
main processes. In an older specimen, dorsolateral process 
is branched thrice, the ventral one twice. Peduncular wings 
fringed with digitate processes anteriorly (Figs 44A, 45G, 
46B-D,L,M). In a specimen from AM W21449 there is a 
small peaked process, centrally, at the base of the three 
horns (Fig. 46L,M). Radioles arranged in a circle on each 
side (Fig. 45B,H), their numbers ranging from 11 pairs in 
the juvenile specimen described above to 28/29 radioles 
in a specimen from AM W202956 with a total length of 
41.0 mm; their pinnule-free tips longer than the pinnules 
that precede them. Inter-radiolar membranes fringed, 
extending distally to about Vs to Vi length of radioles (Figs 
44B, 45B,H, 46C,L). Prostomial ocelli not discernible, 
but a pair of light-caramel patches sometimes seen in the 
corresponding positions. Thoracic chaetigers number 7, 
apron present (Figs 45B,H, 46C). Uncinal tori in thorax of 
adults occur on conspicuously raised pads with the distances 
between corresponding pairs decreasing posteriorly, leaving 
a triangular area between them; 5th and 6th pairs may meet 
mid-ventrally, as in specimens fixed within their tubes (Fig. 
45B), or may be separated when worms are fixed outside 
the tube (Fig. 45H). In juveniles uncinal tori do not occur 
on conspicuous pads (Fig. 46C). 
