Pillai: Serpulid polychaetes from the Australian Kimberleys 
163 
Section 2 
Descriptions and comparisons with some collections of Spirobranchus 
from other locations in Australia and the Indo-West Pacific Oceans 
Spirobranchus acuiconus (Pillai, 1960) 
Fig. 47D-F 
Conopomatus acuiconus Pillai, 1960: 21-23, fig. 8A-E. 
Spirobranchus acuiconus (Pillai, 1960).—ten Hove (1970: 5). 
Type material. HOLOTYPE, Conopomatus acuiconus Pillai, 1960, BMNH 
1959.4.14.4, Pearl Banks, Sri Lanka, coll. T.G. Pillai; re-examined during 
present study. 
Description 
Measurements. Tube in 4 fragments, white and bears a low, 
smooth medial longitudinal ridge and a lateral longitudinal 
ridge along the edge of a flattened part of tube on either side 
of the median longitudinal ridge (Fig. 37A). Total length 
of worm is 11. 4 mm; width of thorax 1.0 mm; length of 
operculum and peduncle 3.2 mm; length of operculum alone, 
1.6 mm. Number of radioles: 12 plus operculum on left and 
14 radioles on the right. Operculum has about 13 transverse 
annuli, superficially certain species of Vermiliopsis (Fig. 
37B,C). However, it is calcareous, its peduncle winged, and 
wings fringed, unlike in Vermiliopsis in which the operculum 
is chitinous, and its peduncle wingless. 
Remarks. Ten Hove (1970: 5) correctly synonymized 
Conopomatus sectoconus Pillai, 1960, with Spirobranchus 
tetraceros. However, there is no evidence as yet for 
Spirobranchus acuiconus (Pillai, 1960), to be synonymized 
with S tetraceros. A transversely annulated calcareous 
operculum lacking opercular horns or vestiges, as in S. 
acuiconus, has not been recorded in individuals belonging 
to populations of S. tetraceros in the Indo-Pacific area. It 
would, therefore, be useful to keep S. acuiconus distinct 
until evidence to the contrary emerges through future studies. 
Spirobranchus arabicus (Monro, 1937) 
Fig. 48A-H 
Spirobranchus giganteus var. arabica Monro, 1937: 317. 
Spirobranchus arabica .—Hartman (1959: 599). 
Material examined. Syntypes: 6 specimens with their tubes, BMNH 
1937.9.2.545-548, Arabian south coast, depth 38 m, 18°03'30"N 
57°02'30"E, Murray Expedition, Station 45, 29 March 1933; labelled 
syntypes of Spirobranchus giganteus var. arabica Monro. 
Description 
Measurements. Based on three larger tubes, maximum 
external diameter, including the median longitudinal ridge, 
5.6 mm; total length of longest worm, 39.0 mm; lengths of 
operculum and peduncle 9.0 mm, thorax 7.0 mm, abdomen 
23.0 mm; number of abdominal segments 86; number of 
radioles, 34 on each side. Longest operculum and widest 
thorax in another specimen: 2.2 mm and 3.6 mm, respectively. 
Tube. Overall colour, light to bright pink or pinkish red; one 
tube brownish mauve. Isolated or small clusters of granules 
of tube material occur irregularly on the surface (Fig. 48A). 
Anterior end of the tube may be peristome-like with short 
ridge-like extensions strengthening it. A high, wavy, median 
longitudinal ridge present, more or less continuous along 
its entire length in some tubes (Fig. 48A), or naturally 
interrupted or broken off in places in others. Very faint 
transverse ridges are present throughout, with alternating 
thin bands of light and dark pink coinciding with them and 
the grooves in between. Transverse ridges may be raised 
along the flank (Fig. 48A) to form a faint single or double 
longitudinal ridge, with a narrow, shallow longitudinal 
groove between them in the latter. 
Worm. Operculum on left side, no rudimentary operculum; 
adult opercular plate dome-shaped (Fig. 48C) to somewhat 
convex (Fig. 48B), with up to about 4 processes of variable 
length which may bear short lateral processes (Fig. 48B). 
All older specimens have a colonial coelenterate (Hydroida: 
Hydractiniidae ) growing on the operculum (Fig. 48B). The 
horny anastomozing perisarc of the latter is very closely 
bonded with the opercular disk and horns, and is very difficult 
to remove without damaging the latter. Opercular wings 
fringed anteriorly. A juvenile operculum (Fig. 48D) has a 
short conical cap with a dorsally directed peak and lacks 
processes as well as the epizoic coelenterate. Colour of the 
radioles in alcohol light to dark blue; up to 34 radioles per 
side counted, arranged in a circle, their pinnule-free tips are 
moderately long and much thicker than the pinnules. Inter- 
radiolar membranes wide and pleated between radioles, but 
are not fringed (Fig. 48B); apron present. 
Chaetae. Bayonet collar chaetae (Fig. 48E,F) similar to 
those usually encountered in the larger species of the genus 
in having a squarish boss; moderately long serrations present 
along blade; unserrated notch absent. Compared to most 
other species with similar bayonet chaetae, a long part of 
chaetal shaft itself is serrated distally, the latter almost equal 
to the length of the blade. Thorax uncini (Fig. 48G) bear 13 
teeth in a single row and an anterior gouged process; anterior 
and posterior abdominal uncini similar (Figs 48H), bearing 
about 9 and 11 teeth, respectively, in addition to the anterior 
gouged process; long-shafted abdominal chaetae present 
throughout the abdomen. 
Remarks. The new species, Spirobranchus arabicus, is 
similar to S. tetraceros from the Kimberleys with regard 
to the circular opercular plate bearing branched horns, the 
arrangement of radioles in a circle, bayonet collar chaetae 
having a prominent squarish boss and thoracic uncini bearing 
about a dozen teeth. Ten Hove (1970: 3) synonymized 
the present species with S. tetraceros. However, there are 
important differences between them. The tube in S. arabicus 
is bright pink to pinkish-red. It is circular in cross-section 
in older specimens, and bears a high, wavy, fin-like median 
longitudinal ridge (Fig. 48A). Inter-radiolar membranes are 
