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J.E. Watson 
which have a hydrocladial median inferior nematotheca on a 
stout immovable base. The term monothalamic is usually 
applied to this structure, assuming that the distal cup is openly 
contiguous with its supporting peduncle. Detailed examination 
of fresh, preserved and mounted material of this suite of 
species (synonymised in M. australis, see discussion later) 
clearly shows that the cup is seldom completely open, and 
there is usually a faint line of demarcation between the cup 
and its base. The term monothalamic is therefore abandoned 
in the present context and the nematothecae regarded as 
incipiently bithalamic. For this reason, the genus Monothecella 
is untenable and is here synonymised in Monotheca. 
Material. 
In the following account, a large amount of material collected 
over four decades by the author and others around Australia is 
examined. Material is held in the collections of Museum 
Victoria, Melbourne, Australia (NMV), the Australian 
Museum, Sydney (AM), the South Australian Museum (SAM), 
the Western Australian Museum (WAM), the National 
Museum of New Zealand (NMNZ) and in the author’s personal 
collection. 
Family Plumulariidae McCrady, 1859 
Monotheca Nutting, 1900 
Colony small, caulus erect, monosiphonic, simple or sparingly 
branched, divided into internodes without hydrothecae. 
Hydrocladia alternate, consisting of two internodes, the distal 
one bearing a hydrotheca with one median inferior nematotheca 
and two superior lateral nematothecae seated on a distal 
enlargement or a bifurcation of the internode. Gonangia fixed 
sporosacs, usually borne on proximal part of the stem, ovate or 
sac shaped, without protective appendages. 
Monotheca amphibola sp. nov. 
Fig. 1A-G 
Material examined. NMV F147479, holotype, microslide (malinol 
mounted), fertile colony from leaves of the seagrass Amphibolis 
antarctica, 200 m offshore from Queenscliff, Victoria, depth 2 m, 
coll: J. Watson 23 March 2008. NMV F147481, remainder of holotype 
colony, alcohol preserved. Paratype, NMV F147480, microslide 
(malinol mounted), fertile colony on leaves of the seagrass Amphibolis 
antarctica, 200 m offshore from Queenscliff, Victoria, depth 2 m, 
coll: J. Watson 23 March 2008. 
Description from holotype and paratype. Stems to 3.5 mm 
long, monosiphonic, arising at regular intervals from hydrorhiza 
running more or less straight up seagrass leaf; stolons wide, 
ribbon-like with a narrow perisarcal flange with numerous 
internal flexion joints. Proximal stem with four or five strong 
transverse joints, succeeding cauline internodes variable in 
length, longer on taller stems, perisarc smooth and thick with 
several strong, more or less equally spaced transverse internal 
septa, nodes broad V-shaped overlapping joints. 
Hydrocladia alternate, distal on cauline internode, on a 
short, strong apophysis, directed almost perpendicularly 
outward from stem, distal node of apophysis slightly oblique 
to transverse; proximal hydrocladial internode short, athecate, 
distal node strongly oblique. 
Hydrothecate internode moderately long and deep with 
two distinct internal opposing septa; hydrotheca distal on 
internode, facing upward at an angle of c. 45° to hydrocladium; 
cup shaped, slightly broader than deep, adcauline wall weakly 
concave to straight, abcauline wall distinctly concave, margin 
circular, entire, rim not everted, perisarc thin, a large sinuous 
abcauline perisarcal flange passing from margin downwards 
to beyond base of hydrotheca; a smaller triangular adcauline 
flange passing from hydrothecal margin to hydrocladium. 
Nematothecae small, bithalamic, one on cauline internode, 
about one-third distance up internode and on same side as 
hydrocladium, base moderately long, adpressed to internode, 
cup slightly adcaudally excavated, one axillar, on front of stem 
beside apophysis, cup slightly elliptical, one hydrocladial 
median inferior on hydrothecate internode, not moveable, base 
long, stout and bent, cup small, adcaudally excavated and 
adpressed to flange of internode, not quite reaching base of 
hydrotheca; twin laterals standing erect, distal on hydrocladium 
below hydrothecal flange but not reaching hydrothecal margin, 
cups slightly adcaudally shortened; stolonal nematothecae 
scattered along hydrorhiza, base long, slightly tapering, cup 
circular, shallow. 
Male and female gonothecae often borne on opposite sides 
of same caulus, large, similar in shape, irregularly ovoid, 
borne on a pedicel inserted below proximal stem apophysis; 
some gonothecae recumbent to substrate, others standing out 
perpendicular to stem; walls of gonotheca smooth, no distinct 
operculum, a thin diagonal apical fold usually marking site of 
future rupture; female gonophore packed with many 
moderately large ova. 
Monotheca amphibola, measurements (/tm) 
Hydrorhiza, width 
160-170 
Stem internode 
length 
272-360 
width at node 
36-40 
Apophysis, adcauline length 
32-56 
diameter at distal node 
40-52 
Hydrocladium 
length adcauline athecate segment 
32-36 
basal length of thecate internode 
176-200 
Hydrotheca 
length, base to margin along axis 
100-108 
diameter at margin 
116-128 
Nematotheca 
cauline, length of base 
40-50 
cauline, depth of cup 
28-20 
cauline, diameter of cup 
28-32 
axillar, length of base 
30-36 
axillar, depth of cup 
12-14 
axillar, diameter of cup 
28-34 
