Pillai: Serpulid polychaetes from the Australian Kimberleys 
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opercular plate. Opercular peduncle elongated. Ventral horn 
ends in two spines, with their tips pointing away from the 
opercular plate. Peduncular wings unfringed (Fig. 60A-C). 
Number of radioles about 40 on each side, spirally arranged, 
with two whorls in each spiral; inter-radiolar membranes 
unfringed. Thorax has 7 chaetigers; apron present. Abdomen 
consists of about 115 segments. 
Chaetae. Bayonet-shaped collar chaetae with distal part 
of the shaft, boss and blade serrated; the blade itself is IV2 
as long as the combined length of the serrated distal part 
of the shaft and the boss in fully formed bayonet chaetae 
(Fig. 60E,F). Thoracic uncini saw-shaped, with 15 teeth 
arranged in a single row at one end of the (first) torus, 
and 11 at its other end, in addition to the anterior gouged 
process. Abdominal neurochaetae with 
flattened trumpet-shaped ends and long 
shafts projecting conspicuously beyond 
abdominal wall occur from first segment. 
Mid-abdominal neuropodia bear 2 or 3 
chaetae with trumpet-shaped distal ends 
and one side drawn out into a tapering 
spine (Fig. 60G). Abdominal uncinal 
tori lateral; anterior abdominal uncini 
bear about 9 or 10 teeth, and posterior 
abdominal uncini about 10 or 11 teeth 
in addition to anterior gouge. 
Remarks. Spirobranchus sp. 6 super¬ 
ficially resembles S. richardsmithi , 
but closer examination revealed the 
following important differences. The 
tube in S. richardsmithi possesses 
patches of mauve colour on a white to 
creamish background, being darker in 
some specimens that in others. As shown 
in Fig. 41 A,J, it has 3 to 5 low longitudinal 
ridges. On the other hand, the tube in S. sp. 
6 is white and bears a single, low, median 
longitudinal ridge only. Of the three horns 
arising from the central opercular column 
in S. richardsmithi, the dorsolateral pair 
is not dichotomously branched (Figs 
41 B-E,K,M,N; 42B,C,E,G); at the angle 
between the ventral and each dorsolateral 
horn, there is a short spine with its tip 
directed towards the opercular plate. The 
tips of the bifid ventral horn are also curved 
Figure 60. A-G, Spirobranchus sp. 6, BMNH 
1972.250, Bassett-Smith South China Sea collec¬ 
tion, Tizard Bank, located in the South China Sea, 
between Vietnam and the Philippines. A-D, different 
views of operculum: (A) left dorsolateral view; ( B ) 
anterodorsal view; (C) right lateral view; ( D ) anterior 
view; ( E,F ) bayonet-shaped collar chaetae showing 
the squarish boss and the chaetal blades longer than 
the serrated distal end of the chaetal shaft plus 
the boss; (G) abdominal chaeta showing flattened 
trumpet-shaped distal end and one side drawn out 
into a tapered process. 
towards the opercular plate. On the other hand, the opercular 
horns in S. sp. 6 are very different. Firstly, all its three horns 
are bifid (Fig. 60A-D). Secondly, the lowermost spine on 
each dorsolateral horn is curved away from the opercular 
plate. Thirdly, tips of the bifid ventral horn are curved away 
from opercular plate. There appears to be a difference. In 
S. richardsmithi a maximum of AV 2 whorls occurs in the 
branchial lobe of a specimen of total length 42.4 mm ; 3 V 2 
spirals in a specimen of total length 24.0 mm. In comparison, 
the condition in S. sp. 6, of total length 27.5 mm, is 
intermediate between the latter two, its 40 or so radioles on 
each side are arranged in only two spirals. The maximum 
number of teeth in thoracic uncini also appears to be different, 
being about 17 or 18 in S. richardsmithi and only about 15 
in S. sp. 3, in addition to the anterior gouged process. 
