Pillai: Serpulid polychaetes from the Australian Kimberleys 
133 
Figure 25. A-C, Hydroides trihamulatus n.sp.—an older specimen from AM W202943: (A) anterior end 
of worm showing structure of adult operculum; ( B, C ) two more views of same operculum. D-F, Hydroides 
ancorispina Pillai, 1961: ( D ) tube, note the granular overlay and the pair of longitudinal ridges running 
along the crest of the tube, with a narrow groove between them; ( E) worm showing operculum and ar¬ 
rangement of anterior abdominal tori; (F) another view of operculum. 
Hydroides novaepommeraniae (including H. grubei and 
H. malleolaspina sensu Imajima [1982]); H. malleolaspina 
Straughan: (including H. ancorispina Pillai) and H. recta 
sensu Dew (1959). Ten Hove (1994: 108) and Fiege & Sun 
(1999: 114) include H. ancorispina in the “H. ancorispina/ 
malleolaspina complex”. The holotype of Hydroides 
ancorispina Pillai, 1971: BMNH 1968.148 was, therefore, 
re-examined during the present study. Its operculum as 
described by Pillai (1971: fig. 6A,B); and (Fig. 25D-F), in the 
present paper, is very different from that of H. malleolaspina 
Straughan (1967: 222, fig. 7a). The modified coronal spine 
of the former is a smooth, somewhat laterally compressed 
column, and totally lacks both medial and terminal processes. 
It does not possess a sub-terminal constriction before its 
hammer-shaped end as in H. malleolaspina (Straughan, 
1967: fig. 7a), and also does not end distally in a beak-like 
medial projection as in specimens from the South China Sea 
described- as Hydroides ancorispina/malleolaspina by Fiege 
& Sun (1999: 114, fig. 5A,B), although it is superficially 
similar. Sun & Yang (2000: 124, fig. 5A,B) give a good 
description of the operculum of H. malleolaspina from the 
waters off China. Hydroides ancorispina possesses a corona 
with seven processes including the modified columnar 
process (Pillai, 1971: 108, fig. 6B), while//, malleolaspina 
has a higher number, 10, recorded by Straughan (1967: 222), 
including the hammer-shaped modified coronal process. 
Hence H. ancorispina is considered to be distinct a species 
from H. malleolaspina in the present account. Incidentally, 
the modified columnar coronal process of H. ancorispina is 
iridescent, a character overlooked before, even after more 
than 30 years in alcohol. 
Etymology. The specific name trihamulatus refers to the 3 
chitinous hooks borne by the modified coronal process in 
adults, one medial and curved towards the centre of the crown, 
and the other two located terminally and directed laterally. 
