80 
J.E. Watson 
colony detached from substrate, coll: J. Watson, 27 January 1969. 
Fluted Cape, Bruny Island, Tasmania, female colony, depth 16 m, on 
red alga, coll: J. Watson, 10 February 1972. Lawrence Rocks, Portland, 
Victoria, infertile colony on red alga, depth 16 m, coll: J. Watson, 14 
May 1969. Walkerville, Victoria, infertile colony detached from 
substrate, depth 3 m, coll: J. Watson, 1 March 1968. Nambucca Heads, 
New South Wales, infertile colony on coralline alga and ascidian, 
depth 13 m, coll: J. Watson, 11 January 1972. 
Description. Hydrorhiza of tubular rugose stolons reptant on 
substrate; stolons usually with internal flexion joints. Stems 
3-10 mm high, monosiphonic, straight to weakly sympodial, 
up to four short basal internodes with transverse joints above 
hydrorhiza. Succeeding stem internodes variable in length, 
longer ones typically on taller stems, smooth, expanding a little 
distally with a strong oblique V-shaped proximal node and a 
transverse distal node, usually an internal transverse septum 
below distal node at level of apophysis. 
Shorter stems with one, rarely two, short proximal athecate 
internodes, stem thereafter hydrocladiate; cauline internodes 
deeply and more or less irregularly septate with strong 
V-shaped proximal nodes and transverse distal nodes, and 
three or four strong transverse internal septa. Hydrocladia 
alternate, fairly long, given off in one plane from a short, 
strong apophysis distal on internode, apophysis curving 
smoothly out from internode, adcauline wall a shoulder with 
slightly oblique deep node, a cylindrical axillar hydrostatic 
pore on adcauline shoulder. 
Athecate hydrocladial internode long, deeply inserted in 
shoulder of apophysis, with deep transverse distal node and 
several complete internal septa. Hydrothecate internode longer 
than athecate internode, terminating in a protuberance 
separating the twin lateral nematothecae, hydrotheca set 
deeply in internode, a large prehydrothecal chamber expanding 
from proximal node to floor of hydrotheca; hydrotheca deep 
bowl shaped, base convex with a large foramen connecting 
with prehydrothecal chamber; in lateral view abcauline wall 
convex, adcauline wall completely adnate to internode, in 
ventral view walls expanding in a smooth curve from base, 
narrowing just below margin, rim slightly thickened but not 
everted; margin hemispherical, wide in ventral view, abcauline 
side straight, adcauline side deeply concave, in lateral view, 
wall a broad sinous curve down to internode. 
Three nematothecae on hydrothecate internode, 
hydrocladial median inferior about halfway along 
prehydrothecal chamber, small, bithalamic, moveable, 
adpressed to internode, base tapering, cup slightly adcaudally 
shortened, twin laterals of same shape as median, standing 
erect on each side of strong terminal protuberance of internode, 
tucked within hydrothecal margin, cup circular to slightly 
laterally compressed but not excavated; no cauline 
nematothecae. 
Gonotheca large, one to several in a row on lower stem, 
conical, widening from a short indefinite pedicel inserted beside 
apophysis, walls of gonotheca smooth to obscurely undulated, 
truncated distally by a transverse, weakly concave aperture 
without operculum; female gonophore with 15-20 large ova. 
Perisarc of slender stems thin, much thicker in shorter, 
robust stems. 
Colour of live colonies where known, buff to yellow, 
gonophores yellow. 
Monotheca hyalina, measurements (/tm) 
Slender group 
(warm 
temperate) 
Robust group 
(cool 
temperate) 
Hydrorhiza, width 
112-120 
88 
Stem 
length of internode 
456-640 
304-400 
width at node 
80-120 
80-112 
distal width of apophysis 
80-100 
92-112 
Hydrocladium 
length of athecate 
internode 
80-220 
80-120 
length of hydrothecate 
internode 
200-296 
184—212 
Hydrotheca 
length of abcauline wall 
193-220 
152-160 
length of adcauline wall 
160-186 
80-116 
width of margin front view 
160-192 
128-168 
Nematotheca 
basal length of median 
inferior 
35^12 
16-26 
diameter of cup 
42-52 
40-60 
basal length of lateral 
40-50 
30^10 
diameter of cup 
40^16 
44—50 
Gonotheca 
length, including pedicel 
960-1400 
920 
maximum width (margin) 
720-900 
680 
Remarks. There is no known type material of Monotheca 
hyalina ; a microslide NMV F59052 in the Museum Victoria 
Bale collection labelled in Bale’s handwriting ‘ Plumularia 
hyalina Queenscliff, February 1881’ was nominated as 
probable syntype by Stranks (1993). I select this microslide as 
lectotype of Monotheca hyalina. 
Monotheca hyalina is very variable in height of the stem, 
and slenderness and robustness of the hydrocaulus, in the 
presence or absence of intranodal septa and size of the 
hydrotheca. In some specimens, the prehydrothecal chamber 
is so reduced that the hydrocladial median inferior 
nematotheca extends one-third the length of the hydrotheca. 
Specimens from warm-temperate southern Australian 
