Hydrodendron arboreum
Creators: name: Watson, Jeanette E.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Hydrozoa
Leptothecata
Haleciidae
Hydrodendron
Hydrodendron arboreum

description: Hydrodendron arboreum (Allman, 1888)
Figure 11A–C
Halecium robustum Allman, 1888: 10, pl. 4, figs 1-3.- Stranks, 1993: 7.
Halecium arboreum Allman, 1888: 89 (= Halecium robustum).
Hydrodendron arboreum - Rees and Vervoort, 1987: 20. - Vervoort, 1987: 88, fig. 10.2.- Peña Cantero, 1991: 50, pl. 2, figs a-f, pl. 63, fig. a.- Branch and Williams, 1993: 11, fig. - Peña Cantero and García Carrascosa, 1996: 13, figs 2A-F, 63E.- Peña Cantero and García Carrasocosa, 1999: 212 et seq.
Hydrodendron arborea - Rees and Thursfield, 1965: 110.- Millard, 1977: 11, fig. 2E-G.
Ophiodissa arborea - Stechow, 1923a: 5.- Stechow, 1923b: 92.- Totton, 1930: 142, fig. 2a.- Briggs, 1939: 11.- Yamada, 1959: 35.- Vervoort, 1972: 25.- Blanco, 1994a: 156. - Blanco, 1994b: 188.
Ophiodes arboreus - Ritchie, 1913: 10, 15, figs 2-3.- Stechow, 1913a: 144. - Stechow, 1913b: 9, 87.- Billard, 1914: 8.- Jäderholm, 1919: 6, pl. 1, fig. 6. - Stepanjants, 1979: 110, pl. 21. fig. 1A-V. - Naumov, 1956: 464, 647.
Material examined. NMVF 147474, Station 105, five microslides displaying branch fragments; some preserved infertile fragments. NMV F147475, Station 107, one microslide of two branch fragments; some preserved fragmental material.
Description. Hydrorhiza a tangle of thin, tubular, rugose stolons Stem (or branch) fragments 10 - 20 mm long, thick and woody, irregularly fascicled; ultimatebranches monosiphonic; each new branch arising from side of a hydrophore; basal internode of some branches very long with several proximal constrictions, succeeding branch Internodes moderately long but variable, walls smooth, increasing slightly in diameter distally to hydrophore, nodes oblique to transverse, sloping away from hydrotheca, varying from a deep septum to a mere narrowing in perisarc, a tumescence above and often below node; longer internodes often with several weak proximal twists.
Hydrophores alternate, one on internode about two thirds distance up internode, length variable, hydrophore typically curving outwards at variable angles from internode, diameter about same internode; adnate to internode by a thick web of perisarc for three quarters of length then becoming free below hydrotheca; free part of hydrophore cylindrical, adcauline wallweaklyconvex, abcaulinewallstraighttoweaklyconcave; hydrophores typically in linear series, each arising from diaphragm of preceding hydrotheca.
Hydrotheca shallow saucer-shaped, expanding from diaphragm to margin; margin circular, rim everted in a flange; diaphragm transverse, strong, a row of desmocytes above; occasional replications of margin.
Nematophores sparse, randomly scattered on internodes, small, goblet-shaped with outrolled rim.
Perisarc of branches thick, thinner and fragile on younger hydrophores and hydrotheca.
Colour (preserved material) of older stems honey brown, younger branches pale yellowish to colourless.
Measurements (μm) Remarks. Many hydrothecae are damaged and reduced to a short collar just above the diaphragm. The few undamaged nematophores confirm the identity of the material as Hydrodendron arboreum Allman (1888). Allman (1888) and Totton (1930) describe large colonies to 25 cm high; the present fragmentary material may be branches of a similarly large colony.
Distribution. Exclusively Antarctic – Kerguelens, 192 m, McMurdo Sound 18 – 550 m, Gauss Station, Palmer Archipelago 92 m and Commonwealth Bay 100 – 545 m.
description: Published as part of Watson, Jeanette E., 2008, Hydroids of the BANZARE expeditions, 1929 – 1931: the family Haleciidae (Hydrozoa, Leptothecata) from the Australian Antarctic Territory, pp. 165-178 in Memoirs of Museum Victoria 65 on pages 175-176, DOI: 10.24199/j.mmv.2008.65.9, http://zenodo.org/record/4630462