Sporolithon mesophoticum sp. nov. (Sporolithales, Rhodophyta) from Plantagenet Bank off Bermuda at a depth of 178 m Author Richards, Joseph L. University of Louisiana at Lafayette, Biology Department, Lafayette, LA 70504 - 3602, U. S. A. Author Gabrielson, Paul W. Biology Department and Herbarium, University of North Carolina at Chapel Hill, Coker Hall CB 3280, Chapel Hill, North Carolina 27599 - 3280, U. S. A. Author Schneider, Craig W. Department of Biology, Trinity College, Hartford, Connecticut, 06106, U. S. A. text Phytotaxa 2018 2018-12-28 385 2 67 76 http://dx.doi.org/10.11646/phytotaxa.385.2.2 journal article 10.11646/phytotaxa.385.2.2 1179-3163 13725901 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 .