Lobataria newtoni, Watson, 2008

Watson, Jeanette E., 2008, Lobataria newtoni gen. et sp. nov., (Hydrozoa, Anthoathecata, Tubulariidae) from southern Australia, Memoirs of Museum Victoria 65, pp. 179-184 : 180-181

Lobataria newtoni sp. nov.

Material examined. Holotype: NMVF 157465 , 1 fertile stem, alcohol preserved, Blairgowrie jetty, Port Phillip , Victoria, Australia, coll: J. E. Watson, 4 Nov 2007, depth 2 m; attached to old bivalve shell buried in sand . Paratype: NMVF 157466 , 12 fertile stems, alcohol preserved, Blairgowrie jetty, Port Phillip , Victoria, Australia, coll: J. E. Watson, 4 Nov 2007, depth 2 m. Paratype, NMVF 157467 , two fertile stems, alcohol preserved, Rye, Port Phillip , Victoria, Australia, coll: D. A. Staples, 23 Apr 2008, depth 2 m.

Description from holotype and paratype (live material). Hydroid solitary, hydrorhiza a simple undulating tubular stolon with thick perisarc, extending for a short distance from base of hydrocaulus over bivalve shell.

Hydrocaulus long and slender, narrow proximally, circular in section, increasing in diameter from base to hydranth, perisarc firm, closely and deeply corrugated proximally, corrugations continuing at irregular intervals for some distance above base, perisarc extending upwards into a filmy inflated collar below hydranth; hydrocaulus filled with parenchyme, no endodermal canals, ridges or partitions.

Hydranth moderately large, vasiform, aboral tentacles long, filiform, hollow, arranged in a single whorl of 28–34, base of tentacles oval; nematocysts abundant on proximal part of tentacles, becoming scattered distally along tentacle; about 24 short filiform oral tentacles arranged in a tight tuft of two rows.

Blastostyles arising just above aboral tentacles, moderately long, trailing between the tentacles, bearing 30–50 gonophores in clusters in various stages of development. Immature gonophore globular, tending to pyriform at maturity: just prior to maturity a long finger-like process protrudes from a central apical orifice; at maturity apex surrounded by four radially arranged tall transparent lobate flanges which extend halfway down gonophores, edge of flange armed with a conspicuous row of large stenoteles (stenotele [i]).

Mature gonophore containing a single actinula pushing spadix to one side. Actinula at release with ten capitate aboral tentacles, directed alternately up and down and six filiform oral tentacles, aboral pole large, dome-shaped.

Measurements (mm) from holotype and paratypes Hydrorhiza, width 0.2 – 0.4 Hydrocaulus

Length 10 – 40 width at base 0.3 - 0.4 Hydranth diameter of basal collar 0.7 – 0.8 maximum length of aboral tentacles 9 maximum length of oral tentacles 2

width of aboral tentacle at base 0.4 – 0.5 Blastostyle, length 3 – 8 gonophore, length mature 0.5 –1 peduncle of blastostyle, proximal width 0.3 - 0.5 Actinula overall length at release 0.9

Six kinds of nematocysts in three morphological categories present: stenoteles of four sizes and shapes, a desmoneme and a microbasic mastigophore each of one size.

Description, measurements (μ m) and distribution of nematocysts

Key to abundance: A = abundant, C = common, N = not common, R = rare.

Colour. Hydrocaulus pale brown, hydranth flesh-pink, tentacles transparent white; developing female gonophores orange, changing to strawberry red at maturity; male gonophores paler, actinula white, spadix brown.

Etymology. The species is named for Andrew Newton, diving colleague and underwater photographer.

Remarks. Lobataria newtoni occurs on old bivalve shells buried at one to two centimetres in the sandy seabed on open sandy to silty seabed in shallow water with mild current flow. It is anchored to shells by a hydrorhiza comprising a short, sticky stolon coated with sand grains. The stolon often passes underneath the shell fragment to more securely anchor the hydrocaulus to the substrate. Most hydrocauli are solitary and widely scattered across the seabed although small patches of up to 10 hydranths rarely occur ( fig. 1 ). This habit is similar to Tubularia acadiae ( Petersen, 1990) , which also attaches to old shell but the hydrocaulus of that species is canaliculate. Observations indicate L. newtoni occurs and is reproductive from summer to winter when water temperatures in Port Phillip range from 10°C (July) to 20°C (February).

Formation of the blastostyle commences early in the life of the hydranth. The developing gonophore contains many small eggs, but at maturity only one becomes an actinula. The large apical flanges surmounting the gonophore while rather variable in shape are typically lobate to ear-shaped. The peripheral band of large stenoteles bordering the flange is visible in living material even at low magnification. At release, most actinulae immediately settle on adjacent shell fragments and within a few hours develop a short hydrocaulus; exceptionally, juveniles sometimes attach to an adult stem, giving an appearance of a falsely branched hydrocaulus.

The lifespan of individual hydrocauli could not be ascertained as, despite searching one month after the first summer collection, all hydranths had disappeared from the originallocality,onlyafewbarestemsremaining.Recolonisation soon occurs, with new hydrocauli re-establishing in the same general microhabitat. Hydrocauli may have a very short life span or are rapidly lost due to fish or invertebrate grazing. An undescribed nudibranch of the genus Cumanotus ( R. Burn, pers. comm.) was found feeding on unprotected tissue above the perisarcal collar at the base of some hydranths.

Figures

Figure 1. Group of Lobataria newtoni, Blairgowrie, Port Phillip, Victoria, depth 2 m, July 2008.