Zygophylax concinnus ( Ritchie 1911 )

Watson, Jeanette E., 2018, Some Hydroids (Cnidaria, Hydrozoa) from the Great Australian Bight in the collection of the South Australian Museum, Zootaxa 4410 (1), pp. 1-34 : 5-7

Zygophylax concinnus ( Ritchie 1911)

Figure 2A–D

Lictorella concinna Ritchie, 1911: 823 , pl. 88, figs 3, 4.

Material examined. SAM H2331, preserved material; two microslides ( SAM H2572, H2573). PIRSA Stn IBMP 5c.

Description. Several broken infertile stems growing from a common hydrohizal mass of tubular stolons. Tallest stem (re-assembled) 80 mm high and 1.75 mm wide at base. Lower stems fascicled, polysiphonic tubes straight, youngest branches and hydrocladia monosiphonic. Branching irregularly alternate, more or less in one plane, highest branches lax, distance between primary branches variable, secondary and tertiary branching common, many monosiphonic hydrocladia dichotomously bifurcated at 0.35—0.5 mm above apophysis, monosiphonic branches sometimes with internodes at irregular intervals with tansverse nodes. No nematothecae.

Cauline apophysis directed upwards, distal node transverse, a pedicellate hydrotheca in axil. Hydrothecae alternate on monosiphonic branches, some given off singly from outer polysiphonic tubes of stem, on pedicel of one to three short distinct segments and very variable in length, nodes transverse. Hydrotheca tubular, adcauline wall convex, abcauline wall almost straight (lateral view), body widening to about one third distance up from base, diaphragm distinct, well above base, slightly tilted to transverse. Margin transverse to hydrothecal axis, rim circular, slightly everted, often with several replications.

Colour (preserved material) translucent white, polysiphonic part of stem pale honey brown.

Remarks. In their descriptions of Zygophylax antipathes ( Lamarck 1816) and Zygophylax rufa ( Bale 1884) and other authors [ Watson (1973), Schuchert (2015)] mentioned the distinctive reddish colour and planar morphology of the colonies. Rees & Vervoort (1987) however commented that colonies of Z. antipathes may not always be branched in one plane. The lightly fascicled distal branches and monosiphonic hydrocladia of the present specimen are flaccid rather than stiffly pinnate, not reddish in colour and have no nematothecae. The strongly segmented pedicel, forked hydrocladia and the gracile aspect of Z. concinnus do not agree with the accepted definition of either Z. antipathes or Z. rufa .

I have examined a digital image of the alcohol preserved lectotype colony and microscopically examined four unstained microslides (AM Y287) of the type series of Lictorella concinna Ritchie, 1911 (= Z. concinnus ) loaned by the Australian Museum. The material was dredged from 25–30 m at 9–10 km offshore from Sydney, New South Wales. The image shows 10 polysiphonic stem fragments stripped of hydocladia growing on an alcyonarian(?) stem. The slides display no bifurcated hydrocladia, the hydrothecal pedicels consist of one or two segments, the distal segment being consistently very long, and there are no nematothcae. The present specimen falls within the range of dimensions of the type series and despite the longer distal pedicel segment the similarities of the present specimen with Z. concinnus outweigh the differences. As these differences may be an artefact of maturity or environment, until more comparative fertile material is found I consider the present material to be Z. concinnus .

Distribution. Temaperate eastern Australia (New South Wales); a new record for the Great Australian Bight.

A. Stem from colony SAM H2331. B, Branch with dichotomously bifurcated hydrocladium. C, hydrocladium and hydrotheca. D, Hydrotheca showing segmented pedicel.