78 
J.E. Watson 
Nematothecae all of same size and shape, bithalamic, 
moveable, fairly robust, base long, cup circular, slightly 
adcaudally shortened, three nematothecae on cauline 
internode, one on apophysis, the other axillar and one, variable 
in position, about one-third to mid-distance up internode, 
hydrocladial median inferior reaching one-quarter distance 
along hydrotheca, twin laterals extending well beyond rim of 
hydrotheca. 
Gonothecae of both sexes borne thickly in a single row 
along lower stem or sparsely along branches. Male and female 
gonothecae the same shape, top-shaped when young, ovoid to 
barrel shaped at maturity, distally truncate, pedicel inserted 
beside apophysis of stem, upwardly bent, tapering into base of 
gonotheca; walls smooth to faintly undulated, aperture distal, 
transverse, circular, produced into a short thick neck of 
variable height closed by a low dome or shallow concavity. 
Male gonophore with rod-shaped spadix, mature female 
packed with large ova. 
Cnidome: 
i) large microbasic euryteles capsule bean shaped 15-16 x 
6 pm, abundant in coenosarc and nematothecae; 
discharges sideways. 
ii) small ?isorhizas, capsule elongate, 5-7 x 2 pm, tubule 
short; abundant in coenosarc and tentacles. 
Perisarc of hydrocaulus and gonothecae fairly thin, thicker 
at base of stems. Colonies transparent white, basal stem region 
brown in older colonies, male gonophores white, often with a 
shining bluish tinge, mature ova in female gonophore yellow. 
Monotheca flexuosa, measurements (p m) 
Hydrorhiza, width 
50-80 
Stem 
internode length 
344-400 
diameter at node 
36-44 
length of apophysis (adcauline wall) 
48-52 
Hydrocladium 
length of athecate internode 
116-128 
width at distal node (shoulder) 
50-58 
length of thecate internode (measured along 
base) 
164-200 
Hydrotheca 
length of abcauline wall 
132-148 
length of adcauline wall 
136-60 
diameter of margin 
140-152 
Gonotheca 
length (excluding pedicel) 
560-696 
maxiumum diameter 
280-320 
Nematotheca 
length of base 
45-55 
diameter of cup 
40-50 
Remarks. All microslides of Monotheca flexuosa in the Bale 
collection of Museum Victoria are designated syntypes by 
Stranks (1993). I designate NMV F58754 as lectotype of 
Monotheca flexuosa. 
The systematic importance of the presence, absence or 
position of the cauline nematotheca has been much discussed 
by authors (e.g. Medel and Vervoort, 1995). In many southern 
Australian specimens of M. flexuosa, cauline nematothecae 
are present in the proximal one-third to mid-cauline internode, 
suggesting precise position is of little or no diagnostic value 
for identification of the species. 
Stems of M. flexuosa from sheltered habitat are usually 
much longer, and more flexuous and silky in appearance than 
those from more rigorous habitats. The longer stems may bear 
a single row of up to 15 female gonothecae whereas shorter 
stems have fewer gonothecae, usually near the base of the 
stem. No correlation with environmental conditions or habitat 
could be found to explain the presence, absence or length of 
the terminal neck of the gonotheca. 
M. flexuosa is the most abundant and widespread species 
of Monotheca in Australia. In southern Australia, it is fertile 
from late spring to autumn (November to March) when 
colonies occur on many invertebrate substrates (mussels, 
ascidians, polychaete tubes), on some flabellate red algae and 
the green algae Caulerpa scalpelliformis and Caulerpa 
remotifolia. 
An unusual endoparastic association between M. flexuosa 
and the red alga Mychodea carnosa was reported by Watson 
(1973). The stolons of the hydroid penetrate the outer medulla 
of young Mychodea fronds, producing external hydrocauli at 
intervals. As the alga grows, its tissue is gradually broken 
down by the hydroid stolons so that eventually the alga is 
attached to the substrate only by the hydrorhiza of the hydroid. 
Hydrocauli emerging from the algal medulla differ somewhat 
from the normal epiphytic form, comprising one or two short 
cylindrical basal internodes bearing one or two large 
nematothecae, followed by normal hydrocauline internodes. 
Type locality. Mouth of Snowy River, Victoria, Australia. 
Known distribution. Temperate and tropical Australia, New 
Zealand, Strait of Gibraltar. The species may prove to be 
cosmopolitan. 
Monotheca hyalina (Bale, 1882) 
Fig. 3A-I 
Plumularia hyalina Bale, 1882: 41, pi. 15, fig. 9.— Bale, 1884: 141, 
pi. 12, figs 4, 5.— Bartlett, 1907: 422 — Bedot, 1921: 28.— Trebilcock, 
1928: 24, pi. 6, fig. 6.- Watson, 1975: 170, fig. 29.- Stranks, 1993: 11. 
Monotheca hyalina — Stechow, 1921: 260.— Watson, 1996: 78.— 
Watson, 1997: 529.- Bouillon et al„ 2006: 368. 
Not Plumularia hyalina — Ralph, 1961b: 41, fig. 5a, b.— Ralph, 
1961c: 109. 
Not Monotheca hyalina.— Vervoort and Watson, 2003: 371, fig. 
90F-I. 
Material examined. NMV F59052, microslide; NMV F59053, 
microslide. Bale collection. Museum Victoria, locality Queenscliff, 
Victoria. 
Material in author’s collection : Floutman Abrolhos Islands, 
Western Australia, infertile colony on Sargassum and red alga, depth 
6-10 m, coll: J. Watson, 12 October 1986; Hopetoun, Western 
Australia, female colony on brown alga, depth 2 m, under ledge, coll: 
J. Watson, 13 January 1986. Boatswains Rocks, South Australia, 
