Sporolithon sinusmexicanum J.Richards & Fredericq, 2018

Sporolithon sinusmexicanum J.Richards & Fredericq sp. nov. ( Figs. 3–23 View FIGURES 3–8 View FIGURES 9–17 View FIGURES 18–23 )

Holotype: LAF 6956A ( Figs. 3–17 View FIGURES 3–8 View FIGURES 9–17 ), Sackett Bank , NWGMx (28° 38.0’ N; 89° 33.028’ W), 65–68 m deep, leg. J. L. Richards & S. Fredericq, 7.ix.2014 GoogleMaps .

Additional material examined: LAF 6970B ( Figs. 18–23 View FIGURES 18–23 ), Dry Tortugas Vicinity , SEGMx (24° 31.494’N; 83° 19.793’W), 69 m deep, leg. J. L. Richards & S. Fredericq, 10.ix.2014 (collected from site in field), 15.xii.2014 (collected from microcosm) GoogleMaps .

Etymology: The specific epithet refers to the Gulf of Mexico, the locality of the holotype and Florida specimen.

Description

DNA sequences: DNA sequences from the holotype: rbc L (GB accession = KY994126), psb A (GB accession = MF034549), LSU (GB accession = KY980437), and UPA (GB accession = KY980429); and from the Florida specimen: LSU (GB accession = KY980438), rbc L (GB accession = KY994127), and psb A (GB accession = MF034550).

Morphology and Habit: Thallus non-geniculate, forming biogenic rhodoliths that are smooth to warty ( Fig. 3 View FIGURES 3–8 ) or with numerous protuberances ( Fig. 18 View FIGURES 18–23 ). Found growing in benthic rhodolith beds at a depth of 65– 69 m.

Vegetative Anatomy: It was not determined with certainty if thallus construction is dimerous or monomerous, though some areas of the thallus appeared putatively monomerous. New vegetative layers ( Fig. 4 View FIGURES 3–8 ) formed by a secondary hypothallium with one to two layers of basal filaments ( Fig. 5 View FIGURES 3–8 ). Hypothallial cells rectangular in shape, 11.5–20 μm long x 3–7 μm wide. Perithallium with abundant cell fusions ( Figs. 6 View FIGURES 3–8 , 20 View FIGURES 18–23 ); secondary pit connections not observed. Perithallial cells 6.6–19 μm long x 7–10.6 μm wide. Meristematic cells 4.2–12 μm long x 7.8–15.3 μm wide ( Figs. 7, 8 View FIGURES 3–8 , 20, 21 View FIGURES 18–23 ). Epithallium ( Figs. 7, 8 View FIGURES 3–8 , 20, 21 View FIGURES 18–23 ) a single layer of armored epithallial cells that are 2–3 μm long x 4–7.8 μm wide, with thick, heavily calcified cell walls and a trapezoidal-shaped lumen.

Reproduction: Tetrasporangial sori are sloughed off after spore release. Sori were observed in the process of sloughing off the surface of the rhodoliths ( Figs. 9–13 View FIGURES 9–17 , 22 View FIGURES 18–23 ). Pores with rosette cells that remained intact (n=5) showed 10–12 rosette cells surrounding each tetrasporangial compartment pore ( Fig. 14 View FIGURES 9–17 ). Sections showed tetrasporangial compartments at the protuberance tip ( Figs. 15–17 View FIGURES 9–17 ) and no buried tetrasporangial structures embedded in the perithallium ( Figs. 15 View FIGURES 9–17 , 19 View FIGURES 18–23 ). Intact tetrasporangial compartment measured 83 μm long x 59 μm wide (n=1), subtended by a stalk cell 14 μm long x 28 μm wide (n=1) ( Fig. 16 View FIGURES 9–17 ). Tetrasporangial compartments surrounded by paraphyses with non-elongated cells at the base of tetrasporangial compartments ( Figs. 16, 17 View FIGURES 9–17 ). Female and male structures were not observed.

Distribution: Sackett Bank, NWGMx, and the vicinity of the Dry Tortugas, SEGMx.

Comments: Unidentified spherical inclusions were observed in the perithallium of specimen LAF 6970B, which may be unidentified life history stages of microalgal organisms ( Fig. 23 View FIGURES 18–23 ), as reported in Krayesky-Self et al. (2017).