Discantenna tumba Gordon & Taylor 2010, n. sp.

Discantenna tumba n. sp.

(Figs 3A–D, 4 A–C)

Material examined. Holotype: NIWA 61242, from cruise TAN0104, Stn 3, 42°45.48– 42°45.18’S, 179°59.47– 179°59.54’ W, “Graveyard” Seamount, Chatham Rise, 943–1097 m depth, collected 15 April 2001. Paratypes: NIWA 61243, same locality as holotype.

Distribution. “Graveyard Seamount Complex”, north-central Chatham Rise, New Zealand, 943–1097 m.

Etymology. From Latin tumba, grave, alluding to the provenance of the species.

Description. Colony with a narrow encrusting base, initially uniserial, becoming biserial, up to 2 mm long, its distal end developing an erect column that flares outwards at its summit as a shallow, circular discoidal structure, 2.57 mm diameter, in which zooids are centripetally arranged; colony height 2.46 mm.

Ancestrula with a subcircular protoecium, large, 0.19 mm wide, the peristome angled upwards relative to the substratum, its distal end upturned frontally, the aperture transversely oval, the sides of the peristome produced as an expanded lamina on either side.

The first budded autozooid is orientated at 45° to the axis of the ancestrula; it initiates biseriality by budding two daughter zooids in quick succession, their respective peristomes directed alternately to the left and right; succeeding peristomes likewise alternate, forming about 10 in all before budding the conical capitulum. As each peristome forms it is produced at a higher elevation from the substratum than the preceding one so that, from the side, the colony appears stepped, the peristomes being supported upon a solid crest of calcium carbonate that spreads somewhat laterally upon the substratum; all external skeletal surfaces pseudoporous. Free peristome length up to 0.67 mm, aperture diameter 0.08 mm.

Apical disk bereniciform; long zooidal peristomes (free peristome length up to 0.60 mm) angled obliquely outwards from the depressed centre of the disk; peripheral common bud thin, with a narrow marginal lamina pierced by pseudopores and a skeletal microstructure of distally imbricated foliated crystallites.

Brood chamber simple, oval (0.72 mm wide in transverse direction), densely pseudoporous, not pierced by zooidal peristomes but at least one peristome may cross its surface; ooeciostome 0.08 mm wide, terminal and medial, its cowl-like distal rim concealing the ooeciopore.

Remarks. This species is so far known only from the type locality, which yielded one fertile and three infertile colonies. As noted above, the colony form of this new species most closely resembles Penciletta penicillata but the brood chamber has a simpler morphology and each colony gives rise to a single erect column whereas many columns may be produced in colonies of P. pencillata.