Memoirs of Museum Victoria 68:71-91 (2011) 
ISSN 1447-2546 (Print) 1447-2554 (On-line) 
http:// museum.com.au/About/Books-and-Journals/Journals/Memoirs-of-Museum-'Victoria 
Review of the genus Monotheca (Hydrozoa: Leptolida) from Australia with 
description of a new species and a note on Monothecella Stechow, 1923 
Jeanette E. Watson 
Honorary Research Associate, Marine Biology Section, Museum Victoria GPO Box 666, Melbourne 3001, Victoria, 
Australia (hydroid@bigpond.com) 
Abstract Watson, J.E. 2011. Review of the genus Monotheca (Hydrozoa: Leptolida) from Australia with description of a new species 
and a note on Monothecella Stechow, 1923. Memoirs of Museum Victoria 68: 71-91. 
Monotheca Nutting, 1900 is a genus with few known species worldwide. It is an artificial genus, as some species of 
the Plumulariidae sometimes have one or two hydrocladial hydrothecae and are thus borderline between Monotheca and 
Plumularia. This review considers only Australian species with consistently monothecate hydrocladia; species with more 
than one hydrotheca on the hydrocladium are considered to belong to Plumularia. Ten species referrable to Monotheca are 
reported from southeast Australia; three are synonymised here in other species, four are presently known to be endemic to 
Australia and one species. Monotheca amphibola, is described as new. The gonosome of Monotheca togata is described 
for the first time. Monothecella is synonymised in Monotheca. A key to the Australian species of Monotheca is given. 
Keywords Monotheca, artificial genus, eight Australian species, key to species; Monothecella synonymised. 
Introduction 
Monotheca Nutting, 1900 (type species Monotheca margaretta 
Nutting, 1900) is an artificial genus; Vervoort and Watson 
(2003) list 10 species and Bouillon et al. (2006) list eight 
species worldwide. Other authors, such as Millard (1975) and 
Hirohito (1995), synonymised Monotheca in Plumularia. In 
their phylogeny, Leclere et al. (2007) demonstrated that 
Monotheca with monohydrothecate hydrocladia ( M.pulchella, 
M. margaretta, M. obliqua) form a distinct clade within the 
Plumulariidae. 
Species of Monotheca reported from Australia are 
Monotheca obliqua (Johnston, 1847), Monotheca australis 
(Kirchenpauer, 1876), Monotheca compressa (Bale, 1882), 
Monotheca hyalina (Bale, 1882), Monotheca pulchella (Bale, 
1882), Monotheca spinulosa (Bale, 1882), Monotheca aurita 
(Bale, 1888), Monotheca flexuosa (Bale, 1894), Monotheca 
obesa (Blackburn, 1938) and Monotheca togata (Watson, 
1973). Four of these species — M. hyalina, M. pulchella, M. 
spinulosa and M. togata — are also reported from New 
Zealand (Vervoort and Watson 2003). A new species, 
Monotheca amphibola sp. nov., from seagrass habitat in 
southeast Australia, is described here. Some species assigned 
to Monotheca — for example, Plumularia excavata (Mulder 
and Trebilcock, 1910), Plumularia crateriformis (Mulder and 
Trebilcock, 1910), Plumularia epibracteolosa Watson, 1973 
and Plumularia meretricia Watson, 1973 sometimes have two 
hydrothecae on the hydrocladium and are thus borderline 
between Monotheca and Plumularia as defined here. In this 
review, only strictly monohydrothecate species are considered, 
and species that sometimes have more than one hydrotheca on 
the hydrocladium are referred to Plumularia. 
Although several species of Monotheca from Australia 
discussed in this paper as presently known are endemic to 
Australia there are some exceptions. These include M. obliqua 
known from the Posidonia oceanica seagrass meadows of the 
Mediterranean Sea (Boero 1981a, Boero et al. 1985; Fresi et al. 
1982, Bouillon et al. 2004), the eastern Atlantic (Calder 1997) 
and Japan (Hirohito 1983); M. spinulosa is known from South 
Africa, the South Atlantic (Millard 1975) and Japan (Yamada 
1959, Hirohito 1995); and M. flexuosa (as M. pulchella, see 
later discussion) is reported from the Mediterranean Sea and 
South Africa (Millard 1975). A key to species of Monotheca is 
given. 
With the exception of Monotheca flexuosa, which is an 
opportunistic species occurring on many substrates, all 
Australian species of Monotheca are epiphytic — M. obliqua, 
M. spinulosa and M. hyalina are associated with algae, while 
M. australis, M. compressa, M. obesa and M. amphibola sp. 
nov. occur on seagrasses. New Zealand species recorded as 
M. hyalina and M. flexuosa (see later discussion concerning 
their identity) are from algae. 
Monothecella Stechow, 1923. 
Stechow (1923a) erected the genus Monothecella for three 
species {Monotheca australis Kirchenpauer, 1876; Monotheca, 
aurita Bale, 1888; Monotheca compressa Bale, 1882), all of 
