Sporolithon indopacificum Maneveldt & P.W.Gabrielson, 2017

Maneveldt, G. W., Gabrielson, P. W. & Kangwe, J., 2017, Sporolithon indopacificum sp. nov. (Sporolithales, Rhodophyta) from tropical western Indian and western Pacific oceans: First report, confirmed by DNA sequence data, of a widely distributed species of Sporolithon, Phytotaxa 326 (2), pp. 115-128 : 118-123

Sporolithon indopacificum Maneveldt & P.W.Gabrielson sp. nov. ( Figs 3–15 )

Holotype:— L 3964509 !, 06.vi.2016, leg. J. S. Kangwe, J. Nene & K. Mohammed, collection number T16 /01 ( Fig. 3 ), free-living rhodolith occurring intertidally (and exposed at low water of spring tide) in a mixed rocky/muddy substrate, variably also dominated by seagrasses and algal turfs. Fragments of the holotype are in UWC and NCU.

Isotypes:— L 3964510!, L 3964511! and UWC T 16/01. Fragments of the isotypes housed in L are also in NCU.

Type Locality:— Tanzania. Zanzibar Island, Chwaka Bay , Mapopwe Creek (06°10 ’ 38.24 ” S; 39°25 ’ 41.27 ” E) .

Etymology:— ‘ indopacificum ’ in reference to the species’ distribution in both the tropical western Indian and Pacific oceans.

Description

DNA Sequences:—Three rbc L sequences were obtained, one from the holotype, L 3964509, 1384 bp long (GenBank MG051266) and one from each isotype L 3964510 (GenBank MG051267) and L 3964511 (GenBank MG051268), both 691 bp long, and from the holotype a psb A sequence (GenBank MG051270), 850 bp long ( Table 1). Over comparable lengths the rbc L sequences were identical to each other. Both the rbc L sequences and the psb A sequence are diagnostic for S. indopacificum .

Habit and morphology:—Plants non-geniculate, free-living as spherical rhodoliths measuring roughly 35–50 mm in diameter ( Fig. 3 ). Thalli lumpy with crowded, mostly contiguous, swollen protuberances ( Figs 3, 4 ). Surface texture matt with freshly collected, living plants brownish pink to maroon in colour. Individual rhodoliths comprise solely this species overgrowing itself in a superimposed manner of variably thin (60 μm) to thick (> 1200 μm) crusts ( Fig. 5 ).

Anatomy:—Thallus dorsiventrally organised, monomerous and haustoria absent ( Figs 6, 7 ). Medulla extremely thin and plumose (non-coaxial) ( Figs 6, 7 ), composed of 3–10 filaments aligned more or less parallel to substratum, measuring no more than 50 μm thick. Medullary filaments comprise square to elongate cells, measuring 10–37 μm in length and 5–8 μm in diameter. Cortex comprises the bulk of the thallus ( Fig. 6 ). Cortical filaments comprise square to elongate cells, measuring 5–30 μm in length and 4–12 μm in diameter. Contiguous medullary and cortical filaments joined primarily by secondary pit connections; cell fusions absent to rare. Subepithallial initials square to rectangular, measure 5–15 μm in length and 5–12 μm in diameter, and are similar in size to subtending cells. Epithallial cells single layered (2 layers when shedding), flattened with flared upper corners ( Fig. 8 ), and measure 3–5 μm in length and 4–12 μm in diameter. Trichocytes absent (thus far not observed in any species of Sporolithales).

Reproduction:—No gametangial material observed. Tetra/bisporangial chambers clustered in sori in a superficially raised layer( Figs4 , 9,11–13 ),3–5cells(incl.epithallial cell)above surrounding thallus surface.Individual tetra/bisporangial chambers uniporate ( Figs 10, 14 ), clustered in large groups ( Figs 9, 11 ), and have floors flush with ( Fig. 12 ) to sunken ( Fig. 13 ) 4 cell layers below surrounding vegetative surface. Chambers longitudinally elliptical, measuring 30–45 μm in diameter and 85–110 μm high, separated by 0–4 sterile paraphyses (mostly 0–1) comprised of 3–5 elongate cells each ( Figs 14, 15 ) that are no different to immediately surrounding vegetative filaments. Chambers possess a basal layer of elongate cells ( Fig. 15 ). Chamber pores measure 8–17 μm in diameter and surrounded by 8–13 rosette cells ( Fig. 10 ) that are no different from the surrounding sorus surface cells. Entire tetra/bisporangial sori appear to be sloughed off from the outer thallus ( Fig. 4 ); no buried chambers observed. Chambers bear only one tetra/bisporangium ( Figs 14, 15 ) measuring 65–90 μm in length and 25–40 μm in diameter. Most sporangia not cleaved ( Fig. 14 ). Other sporangia either zonately arranged bisporangia ( Fig. 15 ) or incompletely divided tetrasporangia with ‘T’-shaped pattern of division ( Fig. 14 ). Tetra/bisporangia bear apical pore plugs ( Figs 10, 14, 15 ) and borne on a single stalk cell ( Fig. 14 ).

Distribution:— Fiji and Tanzania based on DNA sequences.

Figures

FIGURES 3–8. Vegetative anatomy of the holotype of Sporolithon indopacificum (L 3964509). 3. Holotype specimen showing lumpy growth form with swollen, crowded protuberances (scale bar = 10 mm). 4. Magnified view of the protuberances showing their contiguously fused nature and numerous superficial sori (white arrowheads) scattered across the protuberances. Note that sori are often abraded or shed from the surface (black arrowheads) (scale bar = 2 mm). 5. Vertical section showing layers of S. indopacificum crusts (L) overgrowing itself in a superimposed manner (scale bar = 200 μm). 6. Vertical section through the monomerous thallus showing the epithallus (arrowhead) and a predominantly thick cortex (C) subtended by a thin medulla (M) (scale bar = 100 μm). 7. Vertical section of the ventral region of the thallus showing a plumose medulla (M) and cortical filaments (C) joined primarily by secondary pit connections (arrowheads) (scale bar = 50 μm). 8. Vertical section of the dorsal region of the thallus showing a single layer of flared epithallial cells (arrow) subtended by a layer of subepithallial initials (i). Note the layer of senescent epithallial cells (e) being shed, the primary pit connections between adjacent cortical filaments (black arrowheads) and a single, rare cell fusion (white arrowhead) (scale bar = 20 μm).

FIGURES 9–15. Tetrasporangial anatomy of the holotype of Sporolithon indopacificum (L 3964509). 9. Scanning electron micrograph (SEM) showing two tetra/bisporangial sori in surface view (arrowheads) (scale bar = 200 μm). 10. SEM showing a magnified view of several tetra/bisporangial chambers in surface view. Note the open, unoccluded pores (P), intact pore plugs (p) and the rosette cells surrounding the pores (scale bar = 15 μm). 11. Transverse section through two contiguously fused protuberances showing an extensive sorus (arrowheads) (scale bar = 300 μm). 12. Vertical section through the edge of a raised sorus (S) showing tetra/bisporangial chambers with floors (black arrowhead) that are flush with the surrounding vegetative surface (white arrowhead) (scale bar = 50 μm). 13. Vertical section through the edge of a raised sorus (S) showing tetra/bisporangial chambers with floors (black arrowhead) that are sunken below the surrounding vegetative surface (white arrowhead) (scale bar = 50 μm). 14. Vertical section through a sorus showing several tightly abutting, longitudinally elliptical tetra/bisporangial chambers bearing mostly uncleaved sporangia (t) borne on a single stalk cell (black arrowheads). Note the sporangial chamber pore plugs (white arrowheads), a ‘T’-shaped divided tetrasporangium (T) and the sterile paraphyses of elongate cells (arrow) between two adjacent tetra/bisporangial chambers (scale bar = 50 μm). 15. Magnified view through a sorus showing three tetra/bisporangial chambers, one of which bears a zonately arranged bisporangium (B). Note the sporangial chamber pore plugs (white arrowheads) and the layer of elongate cells at the base of the sporangial chambers (black arrowheads) (scale bar = 30 μm).