Neogoniolithon rugulosum W.H.Adey, R.A.Townsend & Boykins, 1982: 17

Maneveldt, G. W., Merwe, E. Van Der & Keats, D. W., 2015, Taxonomic review of Hydrolithon samoënse (Corallinaceae, Corallinales, Rhodophyta) and other taxa found to be conspecific, Phytotaxa 192 (4), pp. 230-253 : 248-250

Neogoniolithon rugulosum W.H.Adey, R.A.Townsend & Boykins, 1982: 17

( Figs 45–50 )

Basionym:— Neogoniolithon rugulosum W.H.Adey, R.A.Townsend & Boykins, 1982: 17 .

Synonyms:—None.

Holotype:— USNC, D. Child, 71-53-2.

Paratypes:— USNC! Hawaii: Hawaii, Hilo Bay , 71-59-1 ; Oahu, Hanauma Bay , 71-53-4, 71-53-22 .

Type Locality:—Palea Point, Hanauma Bay, Oahu, Hawaii.

Etymology:— ‘ rugulosum ’, rugulosus = somewhat wrinkled ( Stearn 1973). The epithet refers to the rugulose, somewhat wrinkled nature of the thallus surface.

Distribution:—The species has only been reported from Hawaii ( Adey et al. 1982) and Fiji ( Littler & Littler 2003, South & Skelton 2003).

Appearance and vegetative anatomy:—The following description is based solely on the prepared micro-slides of the paratype material sent on loan from USNC (71-53-4). No representative specimens for this taxon were available for verification.

Thalli thin and adherent, measuring up to 295 μm thick. Paratype material encrusting to only slightly lumpy and rugulose (see Adey et al. 1982).

Thallus monomerous and dorsiventrally organised ( Fig. 45 ). Medullary region consists of a central plumose (non-coaxial) core ( Fig. 47 ) with square to rectangular cells that measure 6–17 μm in length and 4–11 μm in diameter. Cortical filaments comprise squat to rectangular cells that measure 3–10 μm in length and 5–14 μm in diameter. Cell fusions abundant ( Figs 46, 47 ); secondary pit connections not seen. Subepithallial initials square to rectangular ( Fig. 46 ) and measure 7–15 μm in length and 6–10 μm in diameter. Epithallial cells squat to elliptical, measure 2–9 μm in length and 3–10 μm in diameter and occur singly (up to 2 when shedding) ( Fig. 46 ). Trichocytes common at that thallus surface, occur singly and paired ( Figs 45, 46 ), with pairs separated within clusters by normal vegetative filaments. Individual trichocyte chains comprise 2 cells; a megacell and a support cell. Trichocytes rectangular to elongate and measure 16–27 μm in length and 10–15 μm in diameter. Buried trichocytes not observed. Data on vegetative characters in the paratype are summarized in Table 1.

Reproduction:— Paratype slide lacked gametangial material.

Tetrasporangial conceptacles small ( Fig. 48 ) and more-or-less flush with the thallus surface to slightly raised above it, measuring 136–200 μm in external diameter. Conceptacle chambers elliptical to spherical, and measure 70–104 μm in diameter and 30–50 μm high, with the roof 25–31 μm thick. Conceptacle roof 2–4 (mostly 3) cells thick, comprising a single squat to elliptical to spherical epithallial cell, a single columnar meristematic cell that is 2.5–5 times the length of the epithallial cell, and with or without 1–2 small inner cells ( Figs. 49, 50 ). Conceptacle floor located 6–12 cells below the surrounding thallus surface. A ring of enlarged, domed cells lines the base of the pore canal and is oriented more-or-less vertically, and do not project into the pore canal ( Fig. 49 ). Remains of interspersed sterile filaments that gave rise to the pore canal cells often still visible ( Figs 48, 49 ). Central columella not observed. Mature zonately divided tetrasporangia often fill the chamber completely ( Fig. 48 ). Tetrasporangia measure 20–43 μm in length and 7–27 μm in diameter. Bisporangia not observed. Tetrasporangial conceptacles shed individually although senescent buried conceptacles, containing apparently viable tetrasporangia were observed; infilling of buried conceptacles not observed.

Remarks:—The context within which N. rugulosum was described (see Adey 1970; Adey et al. 1982) was at a time when the genus Neogoniolithon was considered to represent all Mastophoroid taxa bearing monomerous thalli that bore a predominantly coaxial core of medullary filaments. In contrast, Hydrolithon was considered to encompass all Mastophoroid taxa bearing dimerous thalli ( Adey 1970). As described above, N. rugulosum has a predominantly plumose core of medullary filaments. It is now widely accepted that the thallus construction alone cannot be used to separate genera within the Corallinaceae ( Penrose & Woelkerling 1992, Kato et al. 2011). Of particular importance within the family Corallinaceae is the development of the tetrasporangial conceptacle roof (including the shape and orientation of the pore canal cells) and the trichocyte arrangement ( Kato et al. 2011). In N. rugulosum the pore canals of tetrasporangial conceptacles are lined by a ring of conspicuous, enlarged (elongated) cells that are orientated more or less perpendicular to the roof and not by narrow filaments that tilt into the pore canal creating the appearance of

FIGURE 45 . Vertical section of the monomerous thallus showing cortical filaments (C) bearing a number of solitary and paired trichocytes at the surface (arrows), and plumose medullary filaments (M) (scale bar = 60 μm). FIGURE 46 . Magnified view of the outer thallus showing a single epithallial cell layer (arrowhead), a subepithallial initials (i), the first cortical cell (c), cell fusions (f) between adjacent cortical filaments, and a solitary and paired trichocytes (t) (scale bar = 15 μm). FIGURE 47 . Vertical section of the lower portion of the thallus showing plumose medullary filaments with a cell fusion (f) between two adjacent filaments (scale bar = 15 μm). FIGURE 48 . Section through a tetrasporangial conceptacle showing mature tetrasporangia (t) and the remains of an interspersed sterile filament (arrowhead) that gave rise to the conceptacle roof (scale bar = 30 μm). FIGURE 49 . Oblique magnified view of a tetrasporangial conceptacle roof showing the ring of enlarged cells (arrowheads) lining the base and length of the pore canal, the remains of both a peripheral (left arrow) and an interspersed (right arrow) sterile filament that had given rise to the roof filaments, and a tetrasporangium (t) (scale bar = 15 μm).

FIGURE 50 . Magnified view of the roof of a tetrasporangial conceptacle showing the roof comprised of mostly 3 cells (e, i, c) (scale bar = 15 μm).

papillae. Also, the persistence of sterile filaments interspersed amongst the tetrasporangia provides evidence that N. rugulosum has a tetrasporangial conceptacle roof development that is more similar to that of the genus Hydrolithon than of the genus Neogoniolithon . Combined, these features circumscribe N. rugulosum to the genus Hydrolithon . Furthermore, the structure of the tetrasporangial conceptacle roof (a single squat to elliptical to spherical epithallial cell, a single columnar meristematic cell that is 2.5–5 times the length of the epithallial cell, and with or without 1–2 small inner cells) suggests that the species is synonymous with H. samoënse .

Keats and Chamberlain (1994) suggested that N. rugulosum was probably conspecific with H. samoënse , but stated that because the tetrasporangial conceptacles were larger (160–200 μm) in the former species, and because the conceptacle roof structure they considered characteristic, was not visible in the published description of N. rugulosum , this could not be verified. Examination of a paratype slide of N. rugulosum has shown that N. rugulosum more than likely has the tetrasporangial conceptacle roof development characteristic of the genus Hydrolithon , that the tetrasporangial conceptacle dimensions do not differ between the two taxa ( Table 2) and more importantly, that the former species has the tetrasporangial conceptacle roof structure characteristic of H. samoënse . Incidentally, Adey et al. (1982: 15) made mention of N. caribaeum as a “pair species” to N. rugulosum , a species this research has also shown to be conspecific with H. samoënse . Consequently N. rugulosum is also considered a heterotypic synonym for H. samoënse , the latter species having nomenclatural priority.

Figures

FIGURES 45–50. Vegetative and tetrasporangial anatomy of Neogoniolithon rugulosum (USNC 71-53-4).