Sporolithon mesophoticum J.Richards, P.W.Gabrielson & C.W.Schneider, 2018

Richards, Joseph L., Gabrielson, Paul W. & Schneider, Craig W., 2018, Sporolithon mesophoticum sp. nov. (Sporolithales, Rhodophyta) from Plantagenet Bank off Bermuda at a depth of 178 m, Phytotaxa 385 (2), pp. 67-76 : 73

Sporolithon mesophoticum J.Richards, P.W.Gabrielson & C.W.Schneider , sp. nov. ( Figures 2–12 )

Holotype (designated here): NCU 658543 (BDA silica gel no. 2048): Plantagenet (Argus) Bank, ca. 30 mi. southsouthwest of Bermuda (31˚56’31.86” N, 65˚09’25.22” W), western Atlantic Ocean, 26.ix.2016, depth 178 m by submersible, leg. C. W. Schneider coll. no. 16–23–13.

Isotype: MICH 1210812. Fragment removed from holotype (see ICN Art. 8.3 Ex. 8).

Etymology: The specific epithet refers to the depth zone where the holotype specimen was collected.

Description: Thallus non-geniculate, forming a nucleated rhodolith with a thin crust (120–150 μm) growing over a core of consolidated sedimentary material and fragments of invertebrate organisms, putatively identified as bryozoans ( Figs 2–4 ), found growing in a mesophotic benthic habitat. Thallus construction monomerous, with a weakly developed hypothallium ( Figs 4–5 ). Hypothallial cells rectangular in shape, 14–19 μm long x 5–8 μm wide (n=4). In some locations two superimposed layers of thalli were observed, though extensive layering was not observed. Adjacent hypothallial and perithallial cells linked by cell fusions ( Fig. 6 ); secondary pit connections not observed. The upper perithallium was comprised of layers of wide, flattened cells, 3.1–5.1 μm long x 10.6–16.4 μm wide ( Figs 7–8 ). Meristematic cells also appeared wide and flattened, 2.5–6.1 μm long x 10.5–17.8 μm wide ( Figs 7–8 ). Epithallium ( Figs 7–8 ) a single layer of armored epithallial cells that are and very flattened, with thick, heavily calcified cell walls and a small round or slightly trapezoidal shaped lumen, 1.2–2.0 μm long x 4.8–7.0 μm wide (n=7) ( Fig.8 ). Tetrasporangial sori observed from surface view were flush to slightly raised above the thallus surface and showed tetrasporangial pores surrounded by 10–14 rosette cells ( Figs 9–12 ). No evidence of sloughing of tetrasporangial sori was shown, though no buried tetrasporangial compartments were observed in section views. Surface views of a sorus where upper cell layers were removed show compactly arranged tetrasporangial compartments ( Fig. 11 ).

DNA sequences: Holotype – rbc L ( GB accession = MK159181 ); psb A ( GB accession = MK159180 ).

Distribution: Presently known only from the type locality on Plantagenet Bank, Bermuda.

Figures

FIGURES 2–8. Sporolithon mesophoticum Holotype, NCU 658543. 2. Habit of holotype. Scale bar = 3 cm. 3. Fracture of rhodolith showing sedimentary composition of nodule below S. mesophoticum crust. Scale bar = 0.8 mm. 4. Partial surface and section view of thallus (brackets) over substratum consisting of sedimentary material including remains of invertebrate organisms (arrows). Scale bar = 138 μm. 5. Vertical fracture of thallus showing monomerous construction. Scale bar = 60 μm. 6. Cell fusion (arrow). Scale bar = 13.8 μm. 7. Section and partial surface view showing epithallial cell (arrow), meristematic cell (*), and layers of short, flattened perithallial cells (P). Scale bar = 9.2 μm. 8. Surface and section view of epithallial cell (bracket, arrow), and section views of putative meristematic cell (*) and perithallial cell (P). Scale bar = 6.3 μm.

FIGURES 9–12. Sporolithon mesophoticum Holotype, NCU 658543. 9. Surface view of tetrasporangial sori (arrows). Scale bar = 0.1 cm. 10. Surface view of tetrasprangial sorus with pores (arrows). Scale bar = 258 μm. 11. Surface view of tetrasprangial sorus with pores (arrows) including portion where upper cell layers were removed (bracket) showing top-down view of tetrasporangial compartments (stars). Scale bar = 164 μm. 12. Surface view of a tetrasporangial pore (*) with rosette cells (circle pointers). Scale bar = 27 μm.