Croisettea pakualapa F.P. Cabrera & A.R. Sherwood, 2022

Cabrera, Feresa P., Huisman, John M., Spalding, Heather L., Kosaki, Randall K., Smith, Celia M. & Sherwood, Alison R., 2022, Cryptic diversity in the genus Croisettea (Kallymeniaceae, Rhodophyta) from Hawaiian mesophotic reefs, Phycologia 61 (6), pp. 572-583 : 578-581

Croisettea pakualapa F.P. Cabrera & A.R. Sherwood sp. nov.

Figs 22–26

DESCRIPTION: Thalli single, composed of non-perforate blades with smooth to minutely dentate margins, rose pink in colour. Thalli with a soft, slippery consistency, 1.0 cm long by 0.6 cm wide and 50–100 µm thick, and orbicular in shape. Cruciately divided tetrasporangia scattered in the cortex of both blade surfaces, typically spherical and regularly cruciate, 14–18 × 14–18 µm. Medulla with a loose arrangement of elongate stellate cells 30–50 µm in diameter, bearing 6–8 radiating arms 2–4 × 50–100 μm; cortex of 1–2 layers of small isodiametric cells, 2–5 μm in diameter.

HOLOTYPE: ARS 09948/ BISH 780907 , Manawai (Pearl and Hermes Atoll), Hawai‘i, USA (27°44.48ʹN, 175°57.50ʹW, 84 m depth, collected 15 September 2014 by B. Hauk). GenBank accessions: r bc L, OM621860 ; COI, OM509722 .

ETYMOLOGY: The species epithet pakualapa refers to “a sprawling, tapered limu found on the ridge” (see Table S3 for more details on how the species name was developed by the CWG).

DISTRIBUTION: A single specimen collected from Manawai (Pearl and Hermes Atoll), Hawai‘i, USA; at a depth of 85 m.

Morphology and ecology

Only a single blade was collected, non-stipitate, 1.0 cm in height, 0.6 cm wide, with smooth to minutely dentate margins ( Figs 22– 23 ). Blade cross section 50–100 µm thick ( Fig. 24 ). Tetrasporangia scattered in the cortex of both blade surfaces, typically spherical and regularly cruciate, 14 × 14 to 18 × 18 µm ( Fig. 25 ). The inner cortex is composed of 1–2 layers of small, isodiametric cells, 2– 5 μm in diameter, which subtends one or two layers of periclinally elongated outer cortical cells covering the subsurface cells ( Fig.25 ). Medullary stellate cells 30–50 µm in diameter, bearing 6–8 radiating arms 2–4 × 50–100 μm ( Fig. 26 ). Gametangial reproduction not observed.

The single blade was collected at Manawai (Pearl and Hermes Atoll, PMNM) at a depth of 85 m. Although mode of attachment was not identified, this small blade was collected on a flat sandy surface, adjacent to a ridge.

Figures

Figs 22–26. Morphology and anatomy of Croisettea pakualapa sp. nov. Fig. 22. Live holotype specimen, BISH 780907. Scale bar = 1 cm. Fig. 23. Pressed voucher (visible cut from obtaining tissue for DNA extraction, BISH 780907 (holotype, tetrasporophyte). Scale bar = 1 cm. Fig. 24. Cross section through blade showing medullary filaments, BISH 780907. Scale bar = 50 μm. Fig. 25. Cortical cells and tetrasporangia in surface view, BISH 780907. Scale bar = 100 μm. Fig. 26. Detail of a stellate cell. BISH 780907. Scale bar = 50 μm.