Review of the genus Monotheca (Hydrozoa: Leptolida) from Australia with description of a new species and a note on 
Monothecella Stechow, 1923 
81 
waters are distinguished by their slender, flexuous stems with 
longer internodes, while those from the cool-temperate 
waters have sturdier stems with shorter internodes and 
smaller hydrothecae. Dimensions of these two groups are 
compared in the above table. 
Despite the considerable structural and dimensional 
differences between the two morphological extremes, 
intergradation does occur, hence M. hyalina is recognised as 
a single but somewhat variable species. It is often difficult to 
obtain a good lateral view of the hydrotheca as they tend to 
twist forward in microslide preparations. M. hyalina is an 
algal epiphyte; some specimens from Tasmania have a large 
apical stolonal plate to securely anchor stems in a rigorous 
oceanic environment. 
Examination of New Zealand material and a review of 
descriptions of Ralph (1961b) and Vervoort and Watson 
(2003) suggests that the New Zealand material is not M. 
hyalina because: i) the hydrotheca is pitcher-shaped with a 
short, concave free adcauline wall, ii) there is a partial 
intranodal septum below the hydrotheca, iii) there is an 
axillar nematotheca in the apophysis of the stem, and iv) as 
the New Zealand specimens usually have more than one 
hydrotheca on the hydrocladium it is excluded from 
Monotheca as defined here. It is likely that the New Zealand 
material is an undescribed species of Plumularia. It is 
noteworthy that Leclere et al. (2007) in their molecular 
analysis demonstrate that M. hyalina from New Zealand is 
outside the group, thus supporting the conclusion that the 
New Zealand species is not M. hyalina. 
Type locality. Queenscliff, Victoria, Australia. 
Known distribution. Southern Australia. 
Monotheca obliqua (Johnston, 1847) 
Fig. 4 A-E 
Plumularia obliqua Johnston, 1847: 106, pi. 28, fig. 1.— Bale, 
1884: 138, pi. 12, figs 1-3.- Bartlett, 1907: 43.- Mulder and 
Trebilcock, 1910: 116. — Mulder and Trebilcock, 1916: 76, pi. 11, figs 
1-le. - Jaderholm, 1919: 22, pi. 5, fig. 6.- Stechow, 1919: 113.- 
Bedot, 1921: 28,-Billard, 1927: 342.- Broch, 1933: 31, fig. - 
Leloup, 1934: 15.— Billard, 1936: 9.— Blackburn, 1938: 315.— 
Blackburn, 1942: 108.- Hodgson, 1950: 39, fig. 68.- Rossi, 1950: 23, 
fig. 4b.— Pennycuik 1959: 180.— Watson, 1973: 189.— Millard and 
Bouillon, 1974: 9,34, fig. 8A-D.- Millard, 1975: 396, fig. 125A-B.- 
Garcia-Corrales, Aguirre Inchaurbe and Gonzalez Mora, 1978: 56, 
fig. 25.— Millard, 1978: 196 et seq.— Watson, 1979: 234.— Boero, 
1981a: 197.- Hirohito, 1983: 69. - Boero, 1984: 103, fig. 8.- Boero 
et al., 1985: 29 - Gili and Garcfa-Rubies, 1985: 48, fig. 5B.— Isasi and 
Saiz, 1986: 70.— Roca, 1987: 151.—Gili, Vervoort and Pages, 1989: 89, 
fig. 17A.— Boero and Bouillon, 1989: 39, fig. 1. Garcia Rubies, 1992: 
265.— Park, 1992: 294 Cornelius, 1995: 142, fig. 33.— Bouillon et al„ 
1995: 61.— Hirohito, 1995: 275, fig. 94d-f.— Watson and Mclnnes, 
1999: 111.- Bouillon et al., 2006: 368. 
Monotheca obliqua .— Stechow, 1923b: 17.— Leloup, 1932: 
160.— Yamada, 1959: 78.— Rho and Park, 1986: 99.— Ryland and 
Gibbons, 1991: 538, fig. 9.— El Beshbeeshy, 1995: 404.— Medel and 
Lopez-Gonzalez, 1996: 202.— Watson, 1973: 529.— Watson and 
Mclnnes, 1999: 111 — Vervoort and Watson, 2003: 369.— Watson, 
2005: 541, fig. 15.- Bouillon et al., 2006: 368. 
Plumularia (Monotheca) obliqua.— Stechow and Uchida, 1931: 
565. 
Plumularia obliqua australis.— Stranks, 1993: 8. 
Material examined. NMV F101686, infertile colony. New Island, 
Archipelago of the Recherche, Western Australia, depth 20 m on red 
alga, coll: J. Watson, February 2003. WAM Z29970, fertile colony. 
New Island, Archipelago of the Recherche, Western Australia, depth 
20 m, on brown alga, coll: J. Watson, February 2003. 
Material in author’s collection: fertile colony. Popes Eye reef. 
Port Phillip , Victoria, on stem of Macrorhynchia whiteleggei, depth 
6 m, coll: J. Watson, 7 November 2009. Infertile colony. Popes Eye 
reef. Port Phillip, Victoria, depth, 3 m, on thallus of Sargassum sp., 
coll: J. Watson 29 December 2009. 
Description. Hydrorhiza reptant on substrate, tubular, 
somewhat rugose. Stems to 7 mm long, monosiphonic, straight 
to sympodial, internodes moderately long, widening to distal 
node; node transverse to slightly oblique, often a distinct 
shoulder in perisarc and an internal septum above, sometimes 
one to three strong internal septa in proximal part of 
internode. Apophysis of stem short, upwardly directed, 
situated well below node, widening to a strong distal shoulder. 
Hydrocladia alternate, short, in one plane, distal on 
internode, athecate internode with one to three internal 
septa, distal node transverse. Hydrothecate internode almost 
completely occupied by hydrotheca, internode with one or 
two faint septa below hydrotheca, sometimes a short, faint 
septum passing into hydrotheca from distal septum; internode 
distally inflated, pushing base of hydrotheca upward, 
prehydrothecal chamber short, triangular with internal 
triangular septum. 
Hydrotheca scoop shaped, abcauline and adcauline walls 
smoothly convex, margin cut obliquely back to internode, 
rim slightly everted, a thickening behind rim. 
Cauline and hydrocladial median inferior nematothecae 
similar in shape and size, bithalamic, moveable, base 
moderately long, cup fairly wide, cauline nematotheca about 
one-third distance up internode on side opposite 
hydrocladium, standing out from internode, base connecting 
with a large foramen of internode, hydrocladial median 
inferior nematotheca adpressed to prehydrothecal chamber, 
just reaching floor of hydotheca; twin laterals directed 
outwards from an indentation in distal protuberance of 
internode, base short, stout, cup deeply adcaudally excavated; 
a nematotheca in axil beside apophysis; a dome-shaped 
axillar hydrostatic pore with small terminal aperture, 
sometimes also a small secondary pore on adcauline shoulder 
of apophysis. 
Male and female gonothecae borne on the same colony 
but not on same stems, of same shape and size, large, conical, 
circular in section, perisarc fairly thick with tendency to 
proximal rugosity, typically one borne on a short, thin 
pedicel beside an apophysis near base of stem; aperture 
transversely truncate, occupying entire width of gonotheca, 
closed by a sheet of tissue. Female gonophore containing 
many large ova. 
Perisarc of stems pale brown basally, becoming colourless 
distally, gonotheca pale brown, gonophores flesh-coloured. 
