Amphisbetia ramifera, Watson, 2019

Watson, Jeanette E., 2019, Bathyal and abyssal hydroids (Hydrozoa, Leptothecata) from southeastern Australia, Memoirs of Museum Victoria 78, pp. 65-72 : 67-69

Amphisbetia ramifera sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:0BB245B8-E3F4-

421C-928A-CA2C1FB84A30

Figure 2 c, d

Record. QM G337425 . Holotype, one microslide. Coll: near Flinders Island, eastern Bass Strait , Victoria, 40.386 S, 148.928 E to 40.383 S, 148.951 E, 932–1151 m, beam trawl, 21/05/2017.

Description. A branched stem fragment 5 mm long with four alternate branches on each side; stem and branches monosiphonic. Two tubular subopposite hydrothecae on stem internode, adcauline walls separated, nodes strong, transverse, deeply indented. Apophysis long, narrowing distally to transverse node, an axillar hydrotheca pointing along hydrocladium.

First branch internode long, athecate, expanding slightly to a strong opposed V-shaped joint. Branch internodes same as stem, nodes may be absent but where present transverse to slightly oblique, strongly contracted. Hydrothecae opposite, tubular, base of one hydrotheca usually slightly downwardly displaced with respect to that opposite. Lower adcauline wall of each pair adnate, wall straight to weakly convex basally, the convexity increasing towards free wall; free wall weakly convex or concave to margin. Abcauline wall smoothly concave, some walls slightly bulging just above base. Floor transverse to internode, a small downward septum from adnate wall passing into internode. Margin deep saddle-shaped, flanked by a pair of long, sharp lateral cusps.

Perisarc thick, colour (preserved material) shining golden brown.

Remarks. The fragment is probably an apical branch of a larger colony. The hydrothecae closely resemble Amphisbetia minima ( Thompson, 1879) , a common shallow water species in Australia and New Zealand. A. minima invariably has short unbranched stems unlike the branching habit of A. ramifera . In colony size and branching habit, A. ramifera resembles Amphisbetia maplestonei ( Bale, 1884) but in contrast to A. maplestonei the hydrocladial hydrothecae of A. ramifera are in contact with each other, do not have an abcauline intrathecal septum and the marginal cusps are much more prominent. No other Australian species of Amphisbetia has the smoothly outward-curved hydrothecae and such prominent marginal cusps as A. ramifera .

Figures

Figure 2. a–f. a, b, Zygophylax concinna. a, branch internodes with hydrothecae. b, hydrotheca. c, d, Amphisbetia ramifera sp. nov. c, stem with subopposite hydrothecae and axillar hydrotheca. d, branch with opposite hydrothecae. e, f. Lytocarpia parvispiralis sp. nov. e, holotype colony. f, hydrothecae, lateral view.