Halecium brevithecum Watson 2008, sp. nov.

Halecium brevithecum sp. nov.

Figure 4A-C

Holotype NMV F147457, Station 41, one microslide displaying three branch fragments. Paratypes, NMV F147458, Station 40, one microslide displaying two branch fragments. NMV F147478, Station 98, one microslide displaying one branch fragment; some preserved material.

Diagnosis. Infertile stem or branch fragments of a presumably larger colony. Stem (branch) fascicled, polysiphonic tubes varying from knotted to parallel. Branching irregular, ultimate branches monosiphonic, given off from side of a hydrophore; branches beginning with three to five deeply indented transverse nodes, internodes thereafter moderately long, walls smooth, abaxial wall expanding smoothly into hydrophore; nodes transverse to weakly oblique, deeply incised into perisarc, a faint tumescence in internode above and below node.

Hydrophores indistinct, adcaudal wall adnate to internode, becoming free (although this scarcely visible) just below hydrotheca. Hydrotheca distal on internode, adcaudal wall adnate to internode; margin tilted at an obtuse angle away from internode; hydrotheca very shallow, expanding imperceptibly to rim; rim not quite reaching node, walls of hydrotheca thin; diaphragm transverse, strong. No marginal replications or linear series of hydrophores.

Gonotheca absent.

Measurements (μm)

Monosiphonic branch internode

length 520 - 800 width at node 200 – 240 Hydrophore, length 220 – 240 Hydrotheca

diameter at margin 220 - 240 depth, diaphragm to margin 20 – 32

Remarks. Unfortunately the material is meagre and infertile and the permanently mounted specimens poorly displayed. The species is remarkable for the shallowness of the hydrotheca which provides minimal support for the hydranth. There is indication of desmocytes above the diaphragm but the interior of most hydrothecae is obscured by tissue and adventitious material. There is an indication of incipient anastomosing of the ultimate branches.

Species with very shallow adnate hydrothecae considered were: Halecium beanii (Johnston, 1838), Halecium sessile Norman, 1866, Halecium ralphae Watson and Vervoort, 2001 and Halecium sp. 1 Vervoort and Watson, 2003. The diameter of the hydrotheca of Halecium brevithecum is, however, greater than in these species.

Etymology. The species is named for the remarkably short hydrotheca.