Capa & Murray: Australian Megalomma sabellid polychaetes 
205 
margins along some length of their radioles (Fig. 1G). 
However, it is not easy to distinguish between the two 
states (see also Fitzhugh, 1989, p. 21), and this may not be 
a significant character anyway. The species studied have 
longitudinal bands of cilia on the outer lateral edges (Fig. 
1H) as stated by Perkins (1984) but this features is not unique 
to Megalomma and they have been described in other genera 
[e.g., Laonome (Capa, 2007)]. 
The radioles are supported by rows of vacuolated cells 
(referred to as the radiolar skeleton). The number of rows is 
variable within the genus and also within some of the species. 
It has been stated by Tovar-Hernandez & Salazar-Vallejo 
(2008) that the maximum number of rows is 16, but some 
of the specimens described in this study (e.g., M. phyllisae 
n.sp., Fig. 4A) exhibit up to 30 cells in transverse section (see 
variability of rows in radiolar skeleton in Fig. 5). 
In Megalomma , the ventral lips terminate ventrally in 
parallel lamellae, as defined by Nicol (1931) and Fitzhugh 
(1989), seen between the ventral lappets of the peristomial 
collar, and some species also possess vesicles “formed by 
the outpocketing of the parallel lamellae” called ventral sacs 
(as in Fitzhugh, 1989) (Fig. II,J). 
Tovar-Hernandez & Salazar-Vallejo (2008) described 
for the first time the existence of a caruncle in some 
Megalomma species, as an erect, triangular ciliated lobe, 
between the dorsal lips. The examination of Australian 
specimens has determined the presence of a smooth “keel” 
in some species but its detailed morphology, ultrastructure 
or function has not been studied. It does not appear to be 
homologous to the caruncle, rather it is a smooth projection 
of the peristomium arising between the dorsal lips, forming 
a ventrally-directed ridge. 
Characters and states relating to chaetae and uncini should 
also be reconsidered, as there is probably more variation in 
the genus than has been recorded so far. Previous studies 
agree that notochaetae of the first chaetiger are elongate 
and narrowly hooded, as are the rest of the superior thoracic 
chaetae (Perkins, 1984; Fitzhugh, 1989, 2003; Tovar- 
Hernandez & Salazar-Vallejo, 2008), and that the inferior 
thoracic notochaetae are broadly hooded (Perkins, 1984; 
Fitzhugh, 1989, 2003; Tovar-Hernandez & Salazar-Vallejo, 
2008) but with hoods variable in length (Tovar-Hernandez & 
Salazar-Vallejo, 2008). Abdominal neurochaetae have been 
described as elongated, narrowly hooded chaetae (Perkins, 
1984; Fitzhugh, 1989, 2003; Tovar-Hernandez & Salazar- 
Vallejo, 2008) (Fig. IK) but they could be interpreted as 
broadly hooded (but with long tips) in some species (Fig. 
1L). The length of the thoracic uncini handle could also be 
considered as useful for discriminating between species as 
this varies from medium length (same length as the distance 
from main fang to breast) to long (twice the length of the 
distance from main fang to breast). 
The thoracic companion chaetae possess a proximal shaft 
or handle, generally similar in length to the thoracic uncini 
handle, and a distal membrane that has been described as 
teardrop-shaped by most authors (Perkins, 1984; Fitzhugh, 
1989, 2002, 2003), or as roughly symmetrical (Fitzhugh, 
1989; Tovar-Hernandez & Salazar-Vallejo, 2006; Giangrande 
et al., 2007), or as asymmetrical (Knight-Jones, 1997). 
After studying the position of the small rows of teeth and 
the orientation of the tip of the distal membrane, we have 
concluded that the membrane is asymmetrical (Fig. 1M). 
There is some variation in the form of the companion chaetae 
among different species, so this character may be useful from 
a systematic point of view. 
Note: generic diagnostic characters have been omitted 
from species descriptions, In Table 2, we have incorporated 
the new species into Knight-Jones’ operational “Groups”, and 
we have re-interpreted collar fusion, lappets and presence of 
pockets for some taxa. 
Megalomma phyllisae n.sp. 
Figs 2A-E, 3, 4A,B, 5A 
Material examined. Victoria. Holotype AM W13643, off Townsend 
Point, Comer Inlet, 38°48'S 146°33'E, 16 Dec. 1976, 1.5 m. Paratypes 
AM W35476 (2 spec., fragment from incomplete spec, on SEM stubs AM 
M082 and M083), same locality. 
Additional material. Megalomma suspiciens (Ehlers, 1904) ZMUH PE 
1304, syntypes (4 spec.), French Pass, New Zealand, 1 m, 1897. Megalomma 
trioculatum Reish, 1968 USNM 38409, paratypes (2), lagoon side of Engebi 
Island, Eniwetok Atoll, Marshal Islands, 7 Sep. 1956. 
Diagnosis. Species characterized by a combination of the 
following features: subdistal compound eyes in all except 
ventralmost radioles, radiolar skeleton with more than 25 
cells in transverse section, dorsal margins of collar fused to 
faecal groove forming flanking pockets on each side, caruncle 
absent, and inferior thoracic chaetae with progressively 
tapering distal tip (type B). 
Description. Holotype 135 mm long, 5 mm wide; with 
eight thoracic and 107 abdominal chaetigers. Crown slightly 
longer than thorax, 15 mm long, with 30 radioles on left side 
and 28 on right side arranged in two semicircles. External 
margin of radioles quadrangular (Fig. 2A,B). Tip of radioles 
shorter than pinnules (Fig. 2B). Radiolar skeleton composed 
of more than 25 cells in transverse section (Fig. 5A). All 
radioles except for last two pairs of ventral radioles with a 
subdistal compound eye, eyes diminishing in size to ventral 
radioles, spiral in shape on most radioles (although difficult 
to determine shape in small eyes). Dorsal lips with radiolar 
appendages as long as two thoracic chaetigers; with three 
dorsal pinnular appendages each. Caruncle absent. Low 
smooth keel (thickened and non-lamellate) projecting 
ventrally between dorsal lips, arising from raised triangular 
mound situated mid dorsal to dorsal lips. Ventral lips rounded 
and well developed; parallel lamellae and ventral sacs present 
(Fig. 2D). Posterior peristomial collar fused mediodorsally to 
the faecal groove, with short dorsal lappets equal in length to 
lateral collar margins, and with shallow dorsolateral U-shaped 
incisions on both sides forming deep pockets, reaching to 
second chaetiger (Fig. 2C); lateral collar margins smooth, and 
ventrally forming overlapping lappets with rounded anterior 
margins (Fig. 2D). Ventral shields quadrangular, separated 
from the neuropodial tori, all similar in width. First ventral 
shield longer than the rest, with m-shaped anterior margin 
(Fig. 2D). First chaetiger with superior and inferior elongate 
narrowly hooded notochaetae; superior longer than inferior. 
Rest of thoracic chaetigers with about 20 elongate narrowly 
hooded superior chaetae and several irregular rows of broadly 
hooded inferior notochaetae progressively tapering distally 
(type B) (Fig. 3A), in fascicles separated by large lamellate 
interramal lobe. Neuropodial tori slightly diminishing in 
width posteriorly. Uncini with around 13 rows of small 
and similarly sized teeth above main fang (Fig. 3D), well 
