Tripoma arboreum Hirohito, 1995

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 155-156

Tripoma arboreum Hirohito

Figures 5A–C

Tripoma arboreum Hirohito, 1995: 98 , figs 28a–e, pl. 6, fig. A.— Watson and Vervoort, 2000: 249, figs 1A–D, 2A–J.— Watson and Vervoort, 2001: 156, fig. 3a–b.

Material examined. Stn 63, NMV F91311, several infertile colonies, the tallest 40 mm high on a primnoid gorgonian, specimen alcohol preserved. Stn 97, TM K2771, specimens alcohol-preserved. NMV F91332, Stn 97, malinol-mounted microslide.

Description. Colonies erect, branched, the tallest 75 mm high. Hydrorhiza reptant on stem of host, tubular, undulating, sometimes contorted. Erect stems arising from hydrorhiza, some hydrothecae arising directly from stolon. Most stems polysiphonic, several younger stems monosiphonic and unbranched, older stems with increasingly polysiphonic. Stem internodes variable in length, cylindrical, smooth, nodes usually distinct, transverse to slightly oblique, marked by a constriction in perisarc. Apophyses alternate, long, distal on internode, directed upwards at c. 45° to internodal axis, often shifted slightly around stem, distal node of apophysis transverse, sometimes extended into two or three segments, each with deep transverse node.

Hydrothecae inverted conical, long, slender, slightly asymmetrical in section, arising from stem apophysis, usually a well to poorly marked internode between apophysial segment and hydrotheca; adcauline wall weakly convex, abcauline wall straight to weakly concave, a ring of tiny punctae near base of hydrotheca, a band of remnant tissue extending diagonally upwards into hydrotheca from desmocyte ring. Margin with 2 long, sharp triangular cusps separated by deeply scalloped embayments, demarcation between margin and hydrothecal body faint, operculum splits into at least 4 thin flaps. Perisarc of hydrotheca delicate, thinning markedly to margin.

Colour. Colony pale honey-yellow, distal parts and hydrothecae almost colourless.

Measurements (µm)

Hydrorhiza diameter 80–160 Stem length of internode 960–1200

width at node 59–86

diameter at node 72–88

adcauline length of proximal apophysis 52–100

diameter at proximal apophysial node 64–80

length of apophysis including extensions 80–200 Hydrotheca length including pedicel 770–941

length, base to apex of cusps 784–848

width of margin across base of cusps 200–264

depth of opercular embayment 136–160 Distribution. Japan, Tasman Sea and Bass Strait, Australia ( Watson and Vervoort, 2001).

Remarks. The material conforms to the descriptions of colonies of Tripoma arboreum given by Watson and Vervoort (2000, 2001). A feature not noted in previous descriptions is a line of very small punctae in some hydrothecae a short distance above the distalmost apophysial node, passing transversely to obliquely across the hydrotheca and then continuing upward as a line of granules, gradually merging with the hydrothecal wall below the margin. Tissue remnants attached to the granules in some hydrothecae suggest they provide support for the hydranth.

Figures

Figures 5A–C. Tripoma arboreum, stn 97. A, part of stem. B, hydrotheca with closed operculum. C, hydrotheca with operculum open. Scale bar: A, 1 mm; B, C, 0.5 mm.