Monotheca amphibola, Watson, 2011

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 : 72

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.

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.