Monotheca australis ( Kirchenpauer, 1876 )

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 : 74-75

Monotheca australis ( Kirchenpauer, 1876)

Fig. 1H–N

Plumularia obliqua var. australis Kirchenpauer, 1876: 49 , pl. 6, fig. 10.— Von Lendenfeld, 1885a: 474.— Stranks, 1993: 8.

Plumularia australis Bale, 1884: 143 , pl. 12, figs 7, 8.— Von Lendenfeld, 1885a: 475.— Bartlett, 1907: 42.— Mulder and Trebilcock, 1916: 77, pl. 10, figs 1–1b.— Bedot, 1921: 26.— Stechow, 1921: 260.— Blackburn, 1938: 316.— Blackburn, 1942: 108.— Watson, 1973: 189.— Staples and Watson, 1987: 218.— Watson, 1992: 220.

Plumularia compressa Bale, 1882: 31 , pl. 15, fig. 5.— Bale, 1884: 142, pl. 12, figs 9, 10, pl. 19, figs 39, 40.— Von Lendenfeld, 1885a: 475.— Stranks, 1993: 9.

Plumularia aurita Bale, 1888: 784 , pl. 19, figs 16–19.

Monothecella australis — Stechow, 1923a: 13.— Stechow, 1923b: 221.— Leloup, 1932: 160.

Monotheca australis . — Watson, 2003: 252.

Material examined. The Kirchenpauer dry hydroid collection in Museum Victoria holds material ( NMV F58239) labelled (presumably in Kirchenpauer’s handwriting) ‘ Monopyxis australis Port Phillip ( Australien) on Zostera sp. c. 1865’.

Material in author’s collection: i) from the seagrasses Amphibolis antarctica and Amphibolis griffithi ; Torquay, Victoria, depth 3 m, 7 June 1970. Queenscliff, Victoria, depth 3 m, coll: J. Watson, 15 October 1986. Portland, Victoria, depth 3 m, 14 May 1969. Tipara Reef, Gulf St Vincent, South Australia, depth 5 m, coll: J. Watson, 24 November 1970. Starvation Bay, Western Australia, depth 2 m, coll: J. Watson, 11 January 1986. Point Peron, Western Australia, depth 3 m, coll: J. Watson, 26 January 1986. Whitfords Reef, Marmion, Western Australia, depth 4 m, coll: J. Watson, 6 February 1986. Cockburn Sound, Western Australia, depth 6 m, 12 October 1983. Starvation Bay, Western Australia, depth 6 m, coll: J. Watson, 13 January 1986. ii) from seagrasses Posidonia australis and Posidonia sinuosa ; Gulf St Vincent, South Australia, depth 10 m, coll: J. Watson, 14 December 1968. Gulf St Vincent, South Australia, depth 12 m, 10 November 1968. Whitfords Reef, Marmion, Western Australia, depth 3 m, coll: J. Watson, 22 November 1983. Whitfords Reef, Marmion, Western Australia, depth 24 m, coll: J. Watson, 30 January 1986.

Description (from mounted and preserved material). Stems to 7 mm high, arising from a hydrorhiza reptant on seagrass leaf, stolons broad and flat with flexion joints. Stems monosiphonic, unbranched, sometimes with a short athecate basal internode, following internodes all of same length, cylindrical, smooth, widening to distal apophysis; node above apophysis transverse, narrow.

Hydrocladia alternate, in one plane, one distal on internode, given off below node on an upwardly directed apophysis with slightly oblique distal node. Hydrocladium with a short proximal athecate internode with thick walls and a strong, almost transverse distal node, hydrothecate internode considerably longer than athecate internode, base slightly convex, distal end blunt, ending below hydrothecal margin, no intranodal septa.

Hydrotheca seated in a concavity of internode, occupying almost entire internode, slightly laterally compressed, posterior quarter of abcauline wall strongly convex, then becoming straight to margin, base of hydrotheca divided into two segments by a strong intrathecal septum passing obliquely backwards into hydrotheca from margin, a small circular foramen in floor of hydrotheca, location variable from midbase to posterior of hydrotheca; margin perpendicular to or slightly oblique to hydrocladial axis, rim weakly to noticeably sinuous, margin slightly everted with thickened perisarc.

Nematothecae of two different shapes and sizes: one cauline similar to laterals in axil of hydrocladial apophysis, a small cylindrical hydrostatic pore (mamelon of former authors) on apophysis beside base of nematotheca; one hydrocladial median inferior on hydrothecate internode between base of hydrotheca and node, base robust, cup incipiently bithalamic, scoop shaped, sometimes without a line of demarcation between cup and base, closely adpressed to wall of hydrotheca, a distinct flange connecting abcauline wall with internode; twin lateral nematothecae bithalamic, directed outwards or downwards in front of hydrotheca, base large, cup excavated adcaudally to base.

One to three gonothecae borne on lower stem, male and female often on same stem; gonothecae large, turgid, inserted on a short, smooth pedicel below apophysis, standing out perpendicularly from stem or recumbent to substrate, abcauline (upper) wall inflated, adcauline wall straight to weakly convex, body narrowing distally to an upwardly bent cylindrical neck with a wide circular thickened aperture with broadly everted rim. Immature female gonophore with several ova, reduced to one large planula at maturity.

Perisarc of stems thick, translucent white when young, becoming pale-straw coloured with age; gonotheca brown, female gonophore cream.

Figures

Figure 1. A–G, Monotheca amphibola sp. nov. (drawn from holotype and paratypes). A, fertile stem with male and female gonothecae; B, hydrocladium and hydrotheca; C, median inferior nematotheca; D, cauline nematotheca; E, one of twin lateral nematothecae; F, axillar nematotheca; G, hydrorhizal nematotheca. H–N, Monotheca australis. H, infertile stem; I, hydrocladium and hydrotheca; J, female gonotheca with developing larva; K, median inferior nematotheca. Note clear demarcation between cup and peduncle (I) and its absence (K); L, axillar nematotheca; M, one of twin lateral nematothecae; N, axillar hydrostatic pore (axillar nematotheca not shown). Scale bar: A, 1 mm; B, I, H, 0.2 mm; C–G, K–N, 0.1 mm; J, 0.5 mm.