Croisettea kalaukapuae 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 : 574-577

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

Figs 2 – 13

DESCRIPTION: Blades flat, thin, delicate, with smooth, pleated or undulate margins, blush to rose pink in colour, and with a soft, slippery consistency. Blades ranging from 1.5–35 cm long by 1.5–48 cm wide and 150–230 µm thick. Young blades vary in shape but typically slightly wider than high. Mature blades orbicular in shape and forming deep lobes. Blades single, erupting abruptly from a short, stiff stipe arising from a small discoidal holdfast that is usually attached to rhodoliths. Carposporophytes 600–900 µm in diameter, scattered over the blade. Tetrasporophytes and gametophytes isomorphic. Tetrasporangia scattered throughout the cortex, terminal, cruciately divided, 10– 14 × 10–24 µm.

HOLOTYPE: ARS 09739/ BISH 780911 , Kapou (Lisianski), Hawai‘i, USA (25°52.94ʹN, 173°57.73ʹW, 84 m depth, collected 15 September 2014 by R. Pyle and D. Wagner). GenBank accessions: rbc L, OM621858 ; COI, OM509720 .

ISOTYPES: BISH 780912 and BISH 780913 , collection details as for the holotype.

ETYMOLOGY: The species epithet kalaukapuae honours Laura Kalaukapu Low Lucas Thompson (1925–2020) for her advocacy for Hawai‘i’s cultural and natural resources, especially her significant contributions to the creation of the Papahānaumokuākea Marine National Monument, including her role as a founding member of the NWHI Coral Reef Ecosystem Reserve (see Table S3 for more information on how specific nomenclature was developed using traditional Hawaiian naming practices in collaboration with the Papahānaumokuākea Native Hawaiian Cultural Working Group, CWG).

DISTRIBUTION: Throughout the Papahānaumokuākea Marine National Monument including Manawai (Pearl and Hermes Atoll), Kapou (Lisianski Island) and Lalo (French Frigate Shoals), and exclusively collected from mesophotic depths, at 83– 85 m.

Morphology and ecology

Thalli are foliose, consisting of a single blade, 1.5–35 cm long and 1.5–48 cm wide, arising from a short, stiff, cartilaginous stipe, abruptly expanding into a broad, gelatinous blade ( Figs 2–6 ). Thalli ranging from blush to rose pink, sometimes tending to a pinkish brown colour. Blade margins are mostly pleated to undulate. Blades 150–230 µm thick in section ( Fig. 7 ) with peripheral cells ultimately bearing cortex of one or two layers of periclinally compressed inner cortical cells, 3–6 × 6–11 µm, and a cartilaginous stipe <0.6 cm in length and 1.0– 1.5 mm in diameter ( Fig. 8 ). Medulla lax with an interconnected network of darkly staining stellate cells, typically with central bodies 7–9 µm in diameter and long, thin arms 2–4 µm wide by 30–100 µm long ( Fig. 9 ), extending parallel to the blade surface. Stellate cells connected to the cortex of one or two layers of small isodiametric outer cortical cells 1–3 µm wide by 5–10 µm long ( Fig. 10 ).

Tetrasporangia scattered in the cortex and cruciately divided ( Fig. 11 ), 5–7 × 5–12 µm, on both surfaces and terminal in blade. Thalli are dioecious. Spermatangia are formed in nemathecia, scattered across median parts of the thallus; nemathecia develop on both sides of the blade, are darkly staining, and are elongate, with irregular margins ( Fig. 12 ). Spermatangia (3–6 µm in diameter) borne singly on spermatangial mother cells (10–30 µm long) in the outer cortex. Cystocarps are approximately 600–900 µm in diameter, slightly protruding from the thallus surface, and are distributed across the blade surfaces except in the basal region. Carpospores 10–15 µm in diameter, forming a singular dense mass ( Fig. 13 ).

These blades are relatively abundant on the mesophotic reefs in the PMNM (Manawai, Kapou and Lalo). They have been so far only documented from mesophotic depths (83–85 m). Blades are typically attached at a single point to coral rubble on a sandy bottom and are often observed to have a sprawling habit.

Figures

Figs 2–13. Habit, general morphology and anatomy of Croisettea kalaukapuae sp. nov. Fig. 2. Holotype specimen, male gametophyte (BISH 780911) in situ, collected at Papa’āpoho (Lisianski) at 84 m. Scale bar = 5 cm. Fig. 3. Paratype specimen (BISH 780917) in situ, collected at Lalo (French Frigate Shoals) at 83 m. Scale bar = 5 cm. Fig. 4. Live holotype specimen (BISH 780911), cleaned of epiphytes. Scale bar = 5 cm. Fig. 5. Live holotype specimen (BISH 780917), cleaned of epiphytes. Scale bar = 5 cm. Fig. 6. Voucher for BISH 780911 (holotype, tetrasporophyte). Scale bar = 5 cm. Fig. 7. Cross section through blade showing filamentous medulla and cortex, BISH 780911. Scale bar = 100 μm. Fig. 8. Cross section through stipe showing dense aggregation of narrow internal filaments, BISH 780910. Scale bar = 400 μm. Fig. 9. Squash preparation showing stellate cell. BISH 780912. Scale bar = 50 μm. Fig. 10. Cortical cells in surface view, BISH 780909. Scale bar = 50 μm. Fig. 11. Detail of cruciate tetrasporangia, BISH 780910. Scale bar = 50 μm. Fig. 12. Cross section through blade with arrows showing male nemathecium, BISH 780918. Scale bar = 100 μm. Fig. 13. Cross section through mature female cystocarp, BISH 780909. Scale bar = 200 μm.