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Records of the Australian Museum (2009) Vol. 61 
tetraceros identified by workers in the past appear to 
consist of a complex of species, and detailed studies of 
different populations are needed to sort out their identities. 
Nevertheless, the Kimberleys specimens agree with the 
description of Spirobranchus tetraceros (Schmarda, 1861), 
and are, therefore, assigned to it. 
Ten Hove (1970a) believes that differences in opercula 
observed in collections from a particular area could well 
be variations within the same species. Examples are the 
conical operculum of a specimen from Spaanse Water, 
Curasao, and a similar one from Bahrein, shown in Figs 6 
and 15, respectively (ten Hove, 1970a). Similar variations 
have been reported in populations from the Indo-West 
Pacific, e.g., Spirobranchus semperi var. acroceros Willey, 
Pillai (1960: 18, fig. 7A-C), Spirobranchus tricornigerus 
(Grube), Pillai (1960: 20, fig. 7D-G), and Spirobranchus 
tricornis (Morch), Straughan (1967: 244, fig. 14b-d). 
Trinomial nomenclature was used in some instances to 
designate specimens/populations that were different from 
a nominal species with regard to certain characters, as 
varieties of that species, e.g., S. tricornigerus Grube, 1878 
var. racemosus Pillai (1971) from Sri Lanka, and S. tricorn¬ 
igerus decoratus Imajima (1982) from Micronesia. Imajima 
and ten Hove (1984) recognized them as being identical and 
named them as a distinct species Spirobranchus decoratus 
Imajima, 1982. Both varieties have the following common 
characteristics: tube pink on a white background, triangular 
in cross-section, with a high median longitudinal ridge, 
and 5 longitudinal rows of pits; operculum bears three 
main branched processes, compact and directed parallel 
to the plane of the opercular disc rather than away from 
it. Peduncular wings fringed; branchial radioles arranged 
in a circle on each side; inter-radiolar membranes present. 
Special collar chaetae bayonet-shaped; thoracic uncini and 
anterior abdominal uncini have about 12 teeth. 
From descriptions of the species which follow, it will 
be seen that the opercular horns and opercular plate 
in certain Spirobranchus collections/populations from 
different Indo-West Pacific locations are so superficially 
similar to those of S. tetraceros that they can, upon 
cursory examination, be assigned to the “ Spirobranchus 
tetraceros- complex”. 
However, more detailed comparisons between samples 
or populations, and of character combinations, including 
tube form, and colour (differences in the latter, presumably 
having a biochemical basis), structure of opercular 
processes and chaetae, could reveal distinct species of 
Spirobranchus. For instance, Smith (unpublished thesis, 
1985) describes three unnamed species belonging to the 
S. tetraceros group, species A, B, and C, from NSW and 
Queensland. Moreover, ten Hove (1994: 113) states: “in 
1970, I united various nominal taxa from circumtropical 
origin in a single species: S. tetraceros. Nowadays I realize 
that this has been an oversimplification, the taxon tetraceros 
probably contains a number of species ... “ 
It would, therefore, appear more useful, in the long 
run, to acknowledge that certain collections had been 
unidentifiable for one reason or another, and retain them 
as un-named taxa, while awaiting the results of further 
research, rather than designate them as belonging to 
currently unrecognized taxonomic categories, such as “... 
complexes” or “... groups”. 
Spirobranchus sp. 2 (juveniles) 
Fig. 47A,C 
Material examined. Kimberleys, Western Australia; 3 specimens, growing 
on and thinly covered over by easily removable coral, AM W21432, east 
of Montalivet Island, 15°06'S 125°18'E, intertidal, 6 m, 16 Jul. 1988, st 
50; coll. P.A. Hutchings. 
Description 
Measurements. Maximum measurements follows: tube 
diameter 1.5 mm, total length of worm 8.7 mm, width of 
thorax 0.9 mm, length of operculum and peduncle 8.7 mm, 
operculum 1.0 mm, abdomen 0.9 mm. 
T\ibe. Colour faintly pink. Three longitudinal ridges present 
dorsally, and one along each flank, as well as narrow 
transverse ridges (Fig. 47A). Median longitudinal ridge 
high and wavy; those on either side of it and along the flanks 
are low. Outlines of the longitudinal ridges irregular due 
to the presence of short digitate processes extending from 
them, apparently freshly overlaid with coral. 
Worm. Operculum on the left side; consists of a conical, 
pitted, calcareous cap; distal end of latter slanted, blunt and 
lacks processes (Fig. 47B,C); peduncular wings fringed 
anteriorly. Maximum number of radioles counted 10 per 
side; a fringed inter-radiolar membrane present. Prostomial 
ocelli not discernible, thoracic chaetigers number 7, an 
apron present; highest number of abdominal segments 
among the three specimens, 55. Neurochaetae with long 
shafts present throughout the abdomen, the last 25-30 
segments with longer and more slender chaetae. 
Remarks. The tube form and colour in the above juveniles 
are different from those of juvenile S. tetraceros. While 
those of the above juveniles are pink, those of S. tetraceros 
are white, possess a high sinuous median longitudinal ridge 
and a low one along each flank (Fig. 46A,B), but lacks 
the fine digitate processes seen in the present juveniles, 
the latter perhaps formed by new coral encrustation. The 
smallest available juvenile operculum of S. tetraceros is 
shown in Fig. 46B-E. As seen from the scales against 
the figures, its opercular plate and horns are quite small, 
but the plate is not conical as in the present juveniles. In 
the present state of our knowledge of the ontogeny of the 
various species of Spirobranchus, it is difficult to assign 
the present juveniles with conical opercula (Fig. 47B,C) 
to any particular species. 
Similar specimens were described by Pillai (1960: 
21-22, fig. 8F-I), as a new species, Conopomatus 
sectoconus, under a new genus Conopomatus, which 
also included C. acuiconus. Ten Hove (1970) correctly 
synonymized Conopomatus with Spirobranchus, while 
considering the operculum of C. sectoconus to be similar 
to that he described as the juvenile condition of the S. 
tetraceros “complex”. Further studies would be needed to 
confirm whether the juvenile Spirobranchus sp. described 
above, those described b Pillai (1970) and ten Hove (1970) 
occur in Spirobranchus tetraceros (Schmarda, 1861). 
