Sporolithon sinusmexicanum J.Richards & Fredericq, 2018

Richards, Joseph L. & Fredericq, Suzanne, 2018, Sporolithon sinusmexicanum sp. nov. (Sporolithales, Rhodophyta): a new rhodolith-forming species from deepwater rhodolith beds in the Gulf of Mexico, Phytotaxa 350 (2), pp. 135-146 : 136-137

Sporolithon sinusmexicanum J.Richards & Fredericq sp. nov. ( Figs. 3–23 )

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

Additional material examined: LAF 6970B ( Figs. 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) .

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 ) or with numerous protuberances ( Fig. 18 ). 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 ) formed by a secondary hypothallium with one to two layers of basal filaments ( Fig. 5 ). Hypothallial cells rectangular in shape, 11.5–20 μm long x 3–7 μm wide. Perithallium with abundant cell fusions ( Figs. 6 , 20 ); 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 , 20, 21 ). Epithallium ( Figs. 7, 8 , 20, 21 ) 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 , 22 ). Pores with rosette cells that remained intact (n=5) showed 10–12 rosette cells surrounding each tetrasporangial compartment pore ( Fig. 14 ). Sections showed tetrasporangial compartments at the protuberance tip ( Figs. 15–17 ) and no buried tetrasporangial structures embedded in the perithallium ( Figs. 15 , 19 ). 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 ). Tetrasporangial compartments surrounded by paraphyses with non-elongated cells at the base of tetrasporangial compartments ( Figs. 16, 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 ), as reported in Krayesky-Self et al. (2017).

Figures

FIGURES 3–8. Specimen LAF 6956A, vegetative anatomy. FIG. 3. Thallus habit with numerous protuberances. Scale bar 9 mm. FIG. 4. Surface view (upper bracket) and vertical fracture showing new vegetative layer (middle bracket) over older layer (lower bracket). Scale bar 176 μm. FIG. 5. Secondary hypothallium (upper bracket) over older vegetative layer (lower bracket). Scale bar 52 μm. FIG. 6. Perithallium showing cell fusions (arrows). Scale bar 34 μm. FIG. 7. Perithallium (lower bracket), epithallium (upper bracket) and intercalary meristem (arrow). Scale bar 24 μm. FIG. 8. Meristematic cells (M) and armored epithallial cells (arrows) with intact cell roofs (circle pointers). Scale bar 11 μm.

FIGURES 9–17. Specimen LAF 6956A, reproductive anatomy. FIG. 9. Dissecting microscope view of tetrasporangial sori (arrows). Scale bar 2 mm. FIGS. 10–11. Magnified views of sori. Scale bars 0.7 mm, 0.8 mm. FIG. 12. Surface view of tetrasporangial sorus undergoing sloughing off. Scale bar 400 μm. FIG. 13. Magnified view of sorus edge showing disintegrating pores (arrows) and rosette cells. Scale bar 110 μm. FIG. 14. Intact tetrasporangial pore (P) and rosette cells (R). Scale bar 24 μm. FIG. 15. Longitudinal section of protuberance showing tetrasporangial compartments at protuberance tip (arrow) and perithallium with no overgrown tetrasporangial compartments. Scale bar 400 μm. FIG. 16. Tetrasporangial compartments (arrows). Scale bar 70 μm. FIG. 17. Tetrasporangial stalk cell (arrow) and paraphyses surrounding tetrasporangial compartments with non-elongated cells at the base of the compartments (circle arrows). Scale bar 28.5 μm.

FIGURES 18–23. Specimen LAF 6970B.FIG. 18. Thallus habit showing numerous protuberances.Scale bar 6 mm.FIG. 19. Longitudinal section through protuberance showing perithallium with no overgrown tetrasporangial compartments. Scale bar 1.05 mm. FIG. 20. Epithallium (upper arrowhead), intercalary meristem (lower arrowhead) and perithallium (right bracket) showing cell fusions in the xaxis (arrows) and z-axis (circle pointers). Scale bar 4 μm. FIG. 21. Armored epithallial cells (arrows), one showing intact cell roof (circle pointer), and meristematic cells (M). Scale bar 14 μm. FIG. 22. Dissecting microscope view of thallus surface showing tetrasporangial sorus (arrow). Scale bar 1 mm. FIG. 23. Perithallium showing unidentified spherical inclusions (arrows), which may be unidentified life history stages of microalgal organisms. Scale bar 43 μm.