Monotheca flexuosa ( Bale, 1894 )

Watson, Jeanette 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, pp. 71-91 : 76-78

Monotheca flexuosa ( Bale, 1894)

Fig. 2 A–G

Plumularia flexuosa Bale, 1894: 115 , pl. 5, figs 6–10.— Bartlett, 1907: 42.— Shepherd and Watson, 1970: 140.— Watson, 1973: 187.— Watson, 1982: 106, fig. 4.11e.— Watson, 1992: 220.— Stranks, 1993: 10.

? Plumularia flexuosa . — Bedot, 1921: 27.— Blackburn, 1938: 315.

Monotheca flexuosa . — Stechow, 1921: 260.— Stechow, 1925: 246.— Hirohito 1974: 37, fig. 17.– Watson, 1996: 78.— Watson, 2000: 48, fig. 37A, B.— Vervoort and Watson, 2003: 369.— Watson, 2003: 252.— Watson, 2005: 540.— Bouillon et al., 2006: 368.

Monotheca pulchella . — Medel and Vervoort, 1995: 58, fig. 25.— Medel and López-González, 1996: 202.— Watson and McInnes, 1999: 111.— Vervoort and Watson, 2003: 369, 373, fig. 90J–L.— Bouillon et al., 2004: 172, fig. 92G–K.

Material examined. Microslides in the Bale collection, Museum Victoria, labelled in Bale’s handwriting are: NMV F58754, ‘Catalogue number 206, Plumularia flexuosa , mouth of Snowy River, Dr Macgillivray, 1889’ and three other slides, NMV F58755, all labelled ‘ Plumularia flexuosa, Snowy River, Dr Macgillivray, 1892 ’ (Bale’s catalogue number 205).

Material in author’s collection: Popes Eye reef, Port Phillip , fertile colonies on invertebrate and algal substrates, coll: J. Watson, depth 10 m, 20 September 2008 . St Leonards pier, Port Phillip , depth 3 m, infertile colonies on red alga, coll: J. Watson, 10 August 2008 . Clifton Springs, Port Phillip , jetty piles, depth 1.5 m, fertile colonies on algae, coll: J. Watson, 30 November 2005 . Clifton Springs, Port Phillip , jetty piles, depth 1 m, fertile colonies on green alga Caulerpa scalpelliformis , coll: J.Watson, 16 September 2006 . Clifton Springs, Port Phillip , jetty piles, depth 1.5 m, fertile colonies on green alga Caulerpa scalpelliformis , coll: J. Watson, 23 October 2008 . Pearson Island , South Australia, infertile stems on red alga Mychodea carnosa , depth 37–45 m, coll: J. Watson, January 1969 . Channel Island, Darwin , Northern Territory, depth 6 m, coll: J. Watson, July 2006 .

Description. Hydrorhiza of thin tubular stolons reptant on invertebrate substrate, sometimes intersecting in tangled knots, on algal substrate stolons often flattened with flexion joints. Caulus of same diameter as stolon, monosiphonic, flexuous, variable in length, up to 20 mm, base of stem smooth with a few irregular transverse joints; short stems unbranched, some longer stems with one or two orders of short side branches, stem internodes long.

Hydrocladia alternate, in one plane, borne on a strong apophysis below cauline node, apophysis curving smoothly away from internode, distal node transverse with rounded shoulder. Hydrocladial athecate internode long, cylindrical, straight to slightly curved, walls smooth, increasing slightly in diameter distally; distal node transverse, deep, a transverse septum behind node, typically several transverse internal septa in internode.

Hydrothecate internode about same length as athecate internode, almost entirely occupied by hydrotheca, proximal node narrow, deep, inserted into shoulder of athecate internode; internode slightly distally inflated, terminating behind margin of hydrotheca, a faint intranodal septum sometimes in internode below hydrotheca. Hydrotheca cup shaped, adcauline wall convex, set deeply into internode, abcauline wall weakly concave, margin circular, transverse to hydrothecal axis, rim delicate, a slight thickening below margin.

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 ×

6 µm, abundant in coenosarc and nematothecae;

discharges sideways.

ii) small?isorhizas, capsule elongate, 5–7 × 2 µm, 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.

Figures

Figure 2. A–G, Monotheca flexuosa. A, part of stem; B, hydrocladium, lateral view; C, hydrocladium, ventral view; D, male and female gonothecae on same stem; E, median inferior nematotheca; F, cauline nematotheca; G, one of twin lateral nematothecae. Scale bar: A, D, 0.5 mm; B,C, 0.2 mm; E–G, 0.1 mm.