Seiria mesophotica A.R. Sherwood, 2021

Sherwood, Alison R., Cabrera, Feresa P., Spalding, Heather L., Alvarado, Erika A., Smith, Celia M., Hauk, Brian B., Matadobra, Stephen J., Kosaki, Randall K. & Paiano, Monica O., 2021, Biodiversity of Hawaiian Peyssonneliales (Peyssonneliaceae, Rhodophyta): new species in the genera Incendia and Seiria, Phytotaxa 524 (1), pp. 14-26 : 20-24

Seiria mesophotica A.R. Sherwood sp. nov. ( Fig. 4A–J )

Type: — USA, Hawai‘i, off West Moloka‘i , 21.0455°N, 157.3524°W, 80 m depth, 28 November 2006, H. Spalding (holotype BISH 780873 ; ARS 09666; field code P4-189 -cont.8-#328) .

Description: Thallus crustose, prostrate, on coral rubble, brick red to dark, brownish maroon in color ( Fig. 4A,B ). Thallus moderately to heavily calcified, somewhat lobed or entire, mostly to completely adherent to substratum. Crusts thin, typically approximately 100 µm, ranging from 80–180 µm ( Fig. 4C–E ). Hypothallus filaments consisting of parallel files of cells ( Fig. 4G ), mostly unbranched, cells 4.6–8.8 µm in width and 18.2–27.7 µm in height, giving rise to perithallial assurgent filaments above and rhizoids below. Perithallial assurgent filaments arising at 60–90º angle from hypothallus ( Fig. 4C–E ). Perithallus thin, composed of short filaments that are mostly 4–8 cells long ( Fig. 4C–E ). Lower perithallial cells taller than broad, 14.5–24.8 µm in height × 5.9–8.0 µm in width ( Fig. 4D ). Perithallial cells becoming shorter towards upper portion of perithallus. Mid-perithallial fusion cells absent. Uppermost perithallial cells quasi-isodiametric, 7.8–15.8 µm width × 5.0–9.3 µm height ( Fig. 4E ). Cuticle on surface of perithallus 4–8 µm thick ( Fig. 4C–E ). Rhizoids 5.4–8.8 µm diameter, mostly short to medium length, unbranched, and unicellular ( Fig. 4F ). Hair cells absent ( Fig. 4H ). Gametangial reproduction not observed. Mature tetrasporangia 43–99 × 22–44 µm, cruciate decussate to irregularly cruciate ( Fig. 4I ), borne in raised, subcircular, scattered gelatinous nemathecia, nemathecial paraphyses up to 9 cells in length, 130 µm long ( Fig. 4J ).

Other examined material:— USA, Hawai‘i: Papahānaumokuākea Marine National Monument, Manawai (Pearl and Hermes Atoll), 27.9625°N, 175.8361°W, 67 m depth, 31 July 2019, S. Matadobra ( BISH 780874 ; ARS 09967; field code NWHI-833) .

Distribution and Habitat:— Known from the off West Moloka‘i in the Main Hawaiian Islands and Manawai of the Papahānaumokuākea Marine National Monument at mesophotic depths of 67- 80 m.

Etymology:— Named for the mesophotic depths at which the specimens were collected.

Identification using DNA sequence data:— A DNA barcoding analysis of COI sequences for the two specimens of Hawaiian Seiria ( MZ043099 and MZ043100 ) and available COI data for related taxa demonstrated less than 4% sequence divergence between the two Hawaiian specimens (3.3% difference between ARS 09666 and ARS 09967), and much greater distance to the type species, S. magnifusa K.R.Dixon (12.0-12.2%; Fig. 2 ). The rbcL phylogeny supported S. magnifusa as the closest relative to S. mesophotica , with 12.1-13.0% difference in the sequences of the two taxa ( Fig. 3 ).

Figures

FIGURE 2. Neighbor-joining framework based on Kimura-2-parameter distances of COI sequences of specimens of the Peyssonneliales, including Incendia and Seiria. Scale bar = substitutions per site.

FIGURE 3. Maximumlikelihood phylogenetic treeof rbcL sequences forIncendia,Seiria, andclosely related generainthe Peyssonneliales. Numbers along branches indicate nodal support (first value = bootstrap support, second value = Bayesian posterior probabilities). Nodes with full support are indicated with an asterisk. Scale bar = substitutions per site.

FIGURE 4. Habit and morphology of Seiria mesophotica sp. nov. (A). Image of specimen fragments (BISH 780873) immediately after collection. (B). Image of specimen (BISH 780874) immediately after collection. (C). Radial vertical section (RVS) through thallus illustrating the basal hypothallus (arrow), and perithallial assurgent filaments (arrowheads) (BISH 780873). (D). RVS showing large lower perithallial cells (arrows) (BISH 780873). (E). RVS illustrating small, quasi-isodiametric uppermost perithallial cells (arrows) and thick cuticle (arrowhead) (BISH 780874). (F). RVS showing unicellular rhizoids extending from the basal hypothallus (BISH 780873). (G). View of the underside of the crust, illustrating the parallel files of cells comprising the hypothallus (BISH 780873). (H). View of the top surface of the crust, showing regularly sized cells, and a lack of hair cells (BISH 780873). (I). RVS through a tetrasporangial nemathecium, with immature (arrow) and mature (arrowhead) tetrasporangia (BISH 780873). (J). Close up of a tetrasporangial nemathecium, illustrating a tetrasporangium (arrow) and paraphyses consisting of up to nine cells (arrowheads) (BISH 780873). Scale bars: A-B = 1 cm; C-H = 50 µm; I = 100 µm.