Macrorhynchia mulderi ( Bartlett, 1907 )

Watson, Jeanette E., 2011, New species, new records and redescriptions of Thecate hydroids (Cnidaria: Hydrozoa: Leptothecata) from Southern Australia, Zootaxa 3122, pp. 1-36 : 11-13

Macrorhynchia mulderi ( Bartlett, 1907)

Fig. 5 A–D

Aglaophenia mulderi Bartlett, 1907: 66 .– Mulder & Trebilcock, 1916: 73, pl. 10, figs 3a, 3b.– Bedot, 1921: 341. – Stranks, 1993: 12.

Lytocarpus mulderi – Watson, 1973: 195, fig. 73.

Material examined. NMV F171359, microslide, Port Phillip Heads, colony on Symplectoscyphus sp., depth 12 m, coll: J. Watson, 21/01/2006.

Hydrorhiza, diameter 112–128 Stem

lower stem length 1400–3300 lower stem width 112–152 internode length 240–256 width at node 76–84 Apophysis

abcauline length 64–84 width distal node 36–44 Hydrocladium

internode length 252–272 width at node 48–64 Hydrotheca

axial length 240–272 width at margin 128–164 Nematotheca

median, length 168–180 diameter of orifice 20–32 lateral, length 64–88 diameter of orifice 20–24 Description. The following description supplements that of Mulder & Trebilcock (1916) and Watson (1973). Colony infertile, consisting of three stems to 10 mm high; hydrorhiza a smooth tubular stolon running up stem of a species of Symplectoscyphus . Proximal stem long, ahydrocladiate, segmented by several obscure transverse septa, distal end of ahydrocladiate caulus with a single, or double large V-shaped joint; stem thereafter hydrocladiate. Cauline perisarc thick and smooth, internodes short, nodes transverse with an indistinct shoulder, hydrocladia alternate, one slightly frontal on each internode. Cauline apophysis moderately long with a strongly contracted distal node.

Hydrocladia with 6–8 hydrothecae; hydrotheca occupying entire hydrocladial internode, node transverse, distinct; two internal hydrocladiate intermodal septa, one complete, directed obliquely backwards from posterior third of base of hydrotheca, the other partial to complete, directed distally forwards from base of lateral nematotheca to node.

Hydrotheca almost tubular, at an angle c. 20° to hydrocladial axis, body divided into an ovoid posterior third by a forwardly curved complete septum connecting with hydrocladial septum, a quadrangular thinning of tissue at junction of septa. Margin of hydrotheca complexly and deeply cuspate, in lateral view ( Fig. 5 B,C) anterior cusp scimitar-shaped, followed by a deep cusp, separated from the next cusp by a shallow embayment, the second cusp appearing more rounded than the first, followed by a long, inwardly curved posterior cusp identical with the anterior; a long boat-shaped foramen extending from junction of median nematotheca with hydrotheca to base of anterior cusp. In anterior view ( Fig. 5 D) anterior cusp large, wide, blunt or sometimes shallowly lobate, the next cusp more sharply pointed than seen in lateral view, the next and outer ones bilobate (the latter responsible for the scimitar shape in lateral view).

Median nematotheca short, tubular, distal end directed away from hydrotheca, terminating well below hydrothecal margin, abcauline wall weakly sinuous, terminal orifice circular to lobate; lateral nematothecae tubular, pointing forward, narrowing distally to a small circular orifice behind hydrothecal margin, a small secondary basal orifice at junction with hydrotheca. One cauline nematotheca same as laterals on stem internode below apophysis.

Remarks. Macrorhynchia mulderi is a small, rare species, the first record being a poor description by Bartlett (1907) followed by better descriptions of Mulder & Trebilcock (1916) and Watson (1973). The dentition of the hydrothecal margin is extraordinarily complex for such a small species, the shape and overlap of the cusps making accurate description and illustration very difficult.

Distribution. Macrorhynchia mulderi is presently known only from Bass Strait and the eastern Great Australian Bight.

Figures

FIGURE 5. Macrorhynchia mulderi. A, hydrocladial internodes. B, C, hydrothecae, lateral views. D, hydrotheca, anterior frontal view, median nematotheca not drawn. Scale bar: A, 0.3 mm, B – D, 0.2 mm.