Synthecium elegans Allman, 1872

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 : 15-16

Synthecium elegans Allman, 1872

Figure 7A–B

Synthecium elegans Allman, 1872: 229 , fig.— Coughtrey, 1875: 285.— Allman, 1876: 266.— Hilgendorf, 1911: 541.— Jäderholm, 1917: 14, pl. 2, fig. 3.— Bale, 1924: 241.— Billard, 1925: 129, fig. 5.— Totton, 1930: 168, fig 22 a, b.— Blackburn, 1942: 111.— Millard, 1975: 236, fig. 77 A, B.— Hirohito, 1983: 6, 36, fig. 14.— Staples & Watson, 1987: 218.— Hirohito, 1995: 153, fig. 48 c–g, pl. 10, fig. C.— Vervoort & Watson, 2003: 249, fig. 59 A–D.— Bouillon et al., 2006: 399, fig. 185 P–S.

Material examined. SAM H2534, preserved material; one microslide ( SAM H2587). West of South Australia – Western Australia border, depth 180 m, trawl, coll: R. Southcott 1/07/1988 .

Description. Two damaged infertile stems to 15 mm long with hydrorhizal remnants. Hydrocladia opposite with up to seven pairs of hydrothecae, cauline and hydrocladial internodes long and slender, expanding from a proximal transverse node.

Hydrothecae paired, distal on internode, basal hydrocladial pair slightly offset. Hydrotheca tubular, long, most of same diameter throughout, some slightly flaring to margin, floor transverse, narrow, a small adcauline intrusion into internode, free adcauline wall half or slightly less than half length of adnate wall, margin circular, very slightly outrolled, no replication of rim. Perisarc thin around margin.

Stem, diameter at node 176–240 Hydrocladium

internode length 1000–1100 width at node 112–160 Hydrotheca

width at floor 120–144 length of adnate adcauline wall 568–640 length of free adcauline wall 240–360 diameter of margin 200–280 Remarks. It is difficult to distinguish between infertile species of Synthecium without information on colour of the living specimen. Synthecium elegans is similar to Synthecium subventricosum but may be distinguished by the slight distal expansion of the hydrotheca.

Distribution. Tropical and subtropical Indo-Pacific, New Zealand; a new record for the Great Australian Bight.