76 
J.E. Watson 
specimens are probably from the shallow water seagrass 
Posidonia australis common at Robe. As Bale did not designate 
a holotype I designate a microslide NMV F59056 of a fertile 
colony as lectotype of Monotheca compressa. 
Bale (1884, 1888, 1894) recognised the close relationship 
between M. compressa and M. australis, but nevertheless kept 
the two species separate — the main points of difference were 
length of stem, height and shape of the hydrotheca, position of 
the intrathecal septum and minor differences in shape of the 
neck of the gonotheca. Length of stem is an unreliable 
character as it may vary considerably between the same or 
different colonies according to environmental conditions and 
rate of growth. Height of the hydrotheca is quite variable over 
the range of material examined in the present study and is 
actually related to the degree of torsion around the intrathecal 
septum; shape of the base of the hydrotheca is also quite 
variable, some australis morphotypes being almost 
hemispherical in shape. The position of the foramen in the 
floor of the hydrotheca is also variable and depends on the 
degree of torsion of the hydrotheca around the intrathecal 
septum. It is more or less central in 75% of the australis 
morphotypes examined but is displaced towards the rear in the 
compressa form. Hydrothecae with a long, backwardly curved 
septum typical of Kirchenpauer’s australis occur in colonies 
from the cool temperate Amphibolis antarctica habitat, the 
septum in these hydrothecae penetrating at least halfway into 
the hydrotheca, providing a pivotal point for torsion of the 
hydrotheca. In the warm temperate Posidonia habitat, the 
hydrothecae are taller and the septum is often directed forward 
as a rudimentary intrathecal ridge rather than a deep inflexion. 
Gonothecae vary in size and shape from almost cylindrical to 
turgid, and no relationship between sexual dimorphism, 
habitat or geographical distribution could be found to account 
for these variations. 
Bale (1888) described Plumularia aurita from Botany, 
New South Wales. A microslide (NMV F58776) in the 
collection of Museum Victoria is the only known material of 
the species and was nominated syntype by Stranks (1993). As 
this is the only known specimen, by monotypy it is the holotype 
of the species. Bale’s description and figure of the hydrotheca 
of M. aurita shows no intrathecal ridge, yet examination of the 
microslide clearly shows a backwardly oblique ridge passing 
almost halfway into hydrotheca. The incipiently monothalamic 
hydrocladial median inferior nematotheca is the same as that of 
M. australis, and the single small gonotheca on the slide 
although somewhat damaged confirms the species as a 
morphotype of M. australis. Although Bale provided no 
ecological notes, the species was almost certainly collected 
from Posidonia seagrass in Botany Bay. 
The holotype microslide of Plumularia obesa Blackburn, 
1938, in the collection of Museum Victoria, consists of three 
small, infertile stems labelled ‘holotype NMV F70661, 
Plumularia obesa Blackburn, 1938, Reevesby Island, South 
Australia, December, 1936’. No other mounted or preserved 
material is known to exist. Since the microslide specimen was 
not cleared of tissue before mounting many critical structures 
are obscured, making it difficult to accurately measure 
important features. 
In his description of Plumularia obesa, Blackburn 
surprisingly compared the species with Plumularia spinulosa 
rather than comparing it with Plumularia australis, which he also 
recorded from the same locality. The hydrotheca of Monotheca 
obesa closely resembles the compressa form of M. australis from 
Posidonia seagrass, the major difference being the shorter and 
more robust hydrocaulus resembling Bale’s M. aurita. Blackburn 
described and figured the nematothecae of P. obesa as bithalamic 
with slender bases; however, examination of the type shows that 
the hydrocladial median inferior nematothecae have sturdy bases 
similar to those of P. australis. The bases of the twin lateral 
nematothecae are not slender as figured by Blackburn, nor are the 
cauline nematothecae of the holotype similar to the laterals and 
the bases are not so slender as to be considered truly moveable. 
Apart from the much smaller and more robust hydrocaulus, and 
taller hydrothecae, P. obesa is indistinguishable from the extreme 
compressa form of M. australis. Although the gonosome of P. 
obesa is unknown, I am confident that the species is a 
morphological variant of M. australis and, accordingly, I include 
it in the synonymy of M. australis. 
Monotheca australis is a highly variable species, the size 
of the colony and structural dimensions over the geographic 
range are closely related to substrate type and environmental 
conditions. 
Monotheca flexuosa (Bale, 1894) 
Fig. 2 A-G 
Plumularia flexuosa Bale, 1894: 115, pi. 5, figs 6-10.— Bartlett, 
1907: 42.- Shepherd and Watson, 1970: 140.- Watson, 1973: 187.- 
Watson, 1982: 106, fig.4.11e.- Watson, 1992: 220.- Stranks, 1993: 
10 . 
?Plumulariaflexuosa — Bedot, 1921: 27.— Blackburn, 1938: 315. 
Monotheca flexuosa — Stechow, 1921: 260.— Stechow, 1925: 
246.- Hirohito 1974: 37, fig. 17.-Watson, 1996: 78.- Watson, 2000: 
48, fig. 37A, B.— Vervoort and Watson, 2003: 369.— Watson, 2003: 
252.- Watson, 2005: 540.- Bouillon et al„ 2006: 368. 
Monotheca pulchella — Medel and Vervoort, 1995: 58, fig. 25.— 
Medel and Lopez-Gonzalez, 1996: 202.— Watson and Mclnnes, 1999: 
111.— Vervoort and Watson, 2003: 369, 373, fig. 90J-L.— Bouillon et 
al„ 2004: 172, fig. 92G-K. 
Material examined. Microslides in the Bale collection. Museum Victoria, 
labelled in Bale’s handwriting are: NMV F58754, ‘Catalogue number 
206, Plumularia flexuosa, mouth of Snowy River, Dr Macgillivray, 
1889’ and three other slides, NMV F58755, all labelled ‘ Plumularia 
flexuosa. Snowy River, Dr Macgillivray, 1892’ (Bale’s catalogue number 
205). 
Material in author’s collection'. Popes Eye reef. Port Phillip, fertile 
colonies on invertebrate and algal substrates, coll: J. Watson, depth 10 m, 
20 September 2008. St Leonards pier. Port Phillip , depth 3 m, i nf ertile 
colonies on red alga, coll: J. Watson, 10 August 2008. Clifton Springs, 
Port Phillip, jetty piles, depth 1.5 m, fertile colonies on algae, coll: J. 
Watson, 30 November 2005. Clifton Springs, Port Phillip, jetty piles, 
depth 1 m, fertile colonies on green alga Caulerpa scalpelliformis, coll: 
J.Watson, 16 September 2006. Clifton Springs, Port Phillip Jetty piles, 
depth 1.5 m, fertile colonies on green alga Caulerpa scalpelliformis, coll: 
J. Watson, 23 October 2008. Pearson Island, South Australia, infertile 
stems on red alga Mychodea carnosa, depth 37—45 m, coll: J. Watson, 
January 1969. Channel Island, Darwin, Northern Territory, depth 6 m, 
coll: J. Watson, July 2006. 
