Epithallial Cells Research Articles

The genus Leptophytum (Melobesioideae, Corallinales, Rhodophyta) in NW Spitsbergen

Three species of the genus Leptophytum, viz. the generitype L. laeve, L. foecundum and the new Arctic endemic L. jenneborgii nov. sp. are described from localities in NW Spitsbergen. A fourth species, related to L. laeve, may also be present and its status requires further comparative studies with Lithothamnion tenue described from western Greenland. Leptophytum jenneborgii is restricted to sublittoral sites around Vasahalvøya, between 8 and 30 m depth growing on hard substrates (usually on Lithothamnion glaciale) and forming encrusting to foliose thalli up to 10 cm in diameter. New lamellae develop in an unattached‐superimposed pattern, overgrowing the parent thallus, so that individuals can reach at least 1.5 cm in thickness. Thallus organization is dorsiventral, with a noncoaxial hypothallium (producing rare patches of coaxial cells) and an ascending perithallium with short subepithallial and flattened epithallial cells. Multiporate conceptacles have convex or flattened roof and develop specialized (thinner‐wider) pore cells lining the canals. This character combination supports a position in the genus Leptophytum, as recently emended by Athanasiadis & Adey (2006), and simultaneously distinguishes L. jenneborgii from its Arctic and North Atlantic congeners. Like Leptophytum arcticum nov. comb., that is only known from Uddebay on the east coast of Novaja Zemlya, L. jenneborgii shows a restricted distribution on the presumed north periphery of maximum ice cover during the latest glaciation. It is suggested that these two species represent the first evidence of algal glacial survivals in this part of the Arctic.

A comparative study between Lithothamnion minervae and the type material of Millepora fasciculata (Corallinales, Rhodophyta)

Lithothamnion minervae is a crustose coralline alga recognized as a common rhodolith-forming species in the western Mediterranean basin. The species was erected in order to give a correct name and an unequivocal definition to the coralline mjsidentified for a long time as Lithothamnion fruticulosum. Details of the plant, such as the epithallial cells and the tetrasporangial or bisporangial and uniporate conceptacles are described on recently collected samples. It is shown that the two plants in the original collection of Millepora fasciculata belong to different taxa, and therefore a - previous lectotypification (Woelkerling in Woelkerling & Lamy 1998) is superseded. The smaller of the two plants, which belongs to an undescribed species of Clalhromorphum, is selected here as the new lectotype of M. fasciculata. The larger plant in the collection belongs to a species of Lithothamnion; it differs from L. minervae in having a smaller range of chamber diameters of multiporate conceptacles, embedded multiporate conceptacles filled with palisade cells and smaller perithallial cells.

CONCEPTACLE STRUCTURE OF THE PARASITIC CORALLINE RED ALGA CHOREONEMA THURETII (CORALLINALES) AND ITS TAXONOMIC IMPLICATIONS1

The major diagnostic features for erecting the red algal subfamily Choreonematoideae (Corallinales) were a combination of 1) absence of both cell fusions and secondary pit connections, 2) conceptacle roof and wall comprised of a single cell layer, and 3) presence of tetrasporangial pore plugs within a uniporate conceptacle in the monotypic taxon Choreonema thuretii (Bornet) Schmitz. Because this alga is a parasite, the absence of secondary cell connections is most likely an adaptation to a reduced thallus. This study shows that all conceptacles are not composed of a file of cells but rather a single layer of epithallial cells that are underlain by a thick layer of calcified acellular material; both epithallial cells and the calcified layer are produced by peripheral sterile cells. Although the outermost tetrasporangial pore canal is uniporate, there is a calcified acellular multiporate plate recessed just below the rim. The plate is produced by interspersed sterile cells and is continuous with the calcified layer supporting the conceptacle. These unique structures are likely due to parasitism rather than to the ancestral state. Based on these results and a reexamination of published micrographs depicting lenticular cells in Austrolithon intumescens Harvey et Woelkerling, we propose that both subfamily Choreonematoideae and Austrolithoideae are closely allied with subfamily Melobesioideae. This distant relationship to its host (Corallinoideae) plus a combination of unique conceptacle and unusual type of parasitism indicates that C. thuretii is an alloparasite and that it is likely the most ancient red algal parasite studied to date.

Epithallial and initial cell fine structure in species of Lithothamnion and Phymatolithon (Corallinales, Rhodophyta)

Transmission electron microscopy was used to study the ultrastructure of epithallial, subepithallial, and initial cells in three species of Lithothamnion: L. glaciale, L. corallioides, and L. sonderi, and four species of Phymatolithon: P. laevigatum, P. purpureum, P. lenormandii, and P. calcareum (Corallinaceae, subfamily Melobesioideae). One of the principal characters used to delimit Lithothamnion is the flared morphology of its epithallial cells. Ultrastructural examination showed that this flared appearance is produced by the trapezoidal outline of the outermost cell wall of the intact epithallial cell, incombination with the presence of the remnant proximal wall of shed epithallial cells. Unlike most coralline species studied ultrastructurally, none of the three species of Lithothamnion had chloroplasts in their epithallial cells. Absence of chloroplasts distinguished epithallial cells from chloroplast-rich initial cells, allowing easy discrimination of these cell types. Extensive wall ingrowths developed on the distal face of initial cells; upon division of an initial cell to produce an epithallial cell and a new initial cell, the ingrowths were inherited by the newly formed epithallial cell. Decalcification of cell walls occurs as part of the process of epithallial cell turnover; subsequent recalcification may then occur. Secondary calcification was present in the wall layer between the remnant proximal wall and the distal epithallial cell surface in L. glaciale and L. corallioides. Lithothamnion corallioides was unique in having an electron-dense hemispherical structure on the distal face of each epithallial cell; this feature may prove to be a useful taxonomic character. In Phymatolithon, the number of epithallial cells per filament varied from none to three. Terminal epithallial cells were domed and much larger than the subterminal epithallial and initial cells. The outer face of the surface epithallial cell was covered by a thick layer of organic material containing the outlines of extracted small crystals of CaCO3, but calcification was very light. Healthy-looking epithallial cells had chloroplasts with thylakoid spacings similar to that of the discoidal chloroplasts of subepithallial cells. Initial cells preparing to divide were surrounded by a thick organic wall. The derivatives of the division were equal in size and until they enlarged, the pair was collectively surrounded by the persistent wall of the old initial cell. The lower cell, the new initial cell, developed distal wall ingrowths, whereas the upper cell, the new epithallial cell, inherited the ingrowths of the parent initial cell. Distal wall ingrowths were still present even in senescent epithallial cells. Epithallial cell morphology has played an important role in the taxonomic separation of Phymatolithon from Lithothamnion. Epithallial fine structure demonstrates additional, systematically useful characters, such as the presence of chloroplasts in the epithallial cells of Phymatolithon and their absence from epithallial cells in Lithothamnion, that are consistent with the recognition of Phymatolilhon. Ultrastructural study also provides new criteria for the proper identification of epithallial and initial cells in Phymatolithon.

A developmental explanation for the Corallina- and Jania-types of surfaces in articulated coralline red algae (Corallinales, Rhodophyta)

Thallus surface features associated with epithallial cells and trichocytes provide systematic characters useful for distinguishing some members of the tribes Janieae and Corallineae (Corallinales, Rhodophyta). Electron microscopical study of representatives of the genera Corallina, Jania, Haliptilon, and Cheilosporum suggests an anatomical basis for these character states. The C-type surface, which is the prevalent type in the subfamily Corallinoideae, is formed by filaments presenting apical (transverse) faces to the thallus surface. In contrast, the longitudinally elongate epithallial profiles and asymmetrical trichocyte bases characteristic of J-type surfaces are both manifestations of the same underlying structure: the more delicate J-type species present the longitudinal face of the filaments to the thallus surface. If these interpretations are correct, it should be possible to infer the surface type from the anatomical information; conversely, some basic anatomical information could be inferred from the surface type. Based on the anatomy of J. pusilla, a C-type surface was predicted and, upon examination, was found. A striking feature of the two species of Jania with a J-type surface was the absence of a layer of intercalary initial cells, a layer that in most coralline algae produces epithallial cells distally and cortex cells proximally. The absence of an initial cell layer may be part of the developmental program that results in a J-type surface. Parallels can be drawn to the anatomy of some nonarticulated species.

The Corallinaceae (Rhodophyta) from the Ross Sea (Antarctica): a taxonomic revision rejects all records except Phymatolithon foecundum

A study was carried out to determine the status and disposition of Corallinaceae recorded from the Ross Sea (Antarctica), viz. Clathromorphum lemoineanum, Leptophytum coulmanicum, L. laeve and L. foecundum. A re-examination of the type of Lithothamnion coulmanicum (basionym of Leptophytum coulmanicum) showed that it is referable to the genus Phymatolithon because it possesses epithallial cells whose outermost walls are rounded to flattened and meristem cells that are as short as or shorter than their immediate inward derivatives. Such characters were also evident in specimens from McMurdo Sound. Moreover, because all the specimens studied had a conceptacle chamber roof c. 300 μm in diameter, a thallus thickness of up to 1 mm, and buried old conceptacles, they are conspecific with P. foecundum. Studies of specimens from Terra Nova Bay identified as C. lemoineanum and of specimens from Franklin Island identified as L. laeve showed that they should all be referred to P. foecundum. Furthermore, judging by the description and illustrations given by Zaneveld & Sanford [Blumea 26: 205–23 1 (1980)], records of P. foecundum (as L. foecundum) from Cape Hallett and Moubray Bay can be confirmed. Therefore, P. foecundum is the only member of Corallinaceae confirmed to occur in the Ross Sea (Antarctica).

Re-instatement of Leptophytum and its type Leptophytum laeve: taxonomy and biogeography of the genera Leptophytum and Phymatolithon (Corallinales, Rhodophyta)

In a recently published examination of the newly re-discovered holotype of Leptophytum (Lithophyllum) laeve, the characters of the holotype specimen were judged to be taxonomically inadequate. Consequently, an epitype was selected which was determined to belong to Phymatolithon lenormandii, rendering Leptophytum and its type L. laeve junior synonyms of Phymatolithon and P. lenormandii, respectively. We have re-studied the holotype specimen in Stockholm, and in this paper we demonstrate that it is consistent with the protologue and exhibits features that are fully consistent with the modern circumscription of Leptophytum laeve, based on population studies. Our results demonstrate that the holotype specimen is taxonomically adequate and that the selection of an epitype was not necessary. Accordingly, we propose the reinstatement of Leptophytum Adey 1966, based on its type L. laeve (Foslie) Adey (basionym: Lithophyllum lenormandii f. laeve Foslie 1891). The genera Leptophytum and Phymatolithon Foslie are similar in some anatomical respects (such as in having diminutive sub-epithallial initials, i.e. meristem cells, a polystromatic non-coaxial hypothallium, and roundish to flattened epithallial cells in transverse section). The genera differ somewhat in morphology and markedly in most reproductive features (such as spermatangial systems, origin of gonimoblasts, position of conceptacle primordia, and the presence or absence of distinct asexual conceptacle pore cells). The taxonomic, ecological and biogeographic characteristics of the two genera lead us to conclude that the similarities between Phymatolithon and Leptophytum have very likely resulted from parallel evolution.

Lectotypifícation of Lithophyllum arcticum (Corallinales, Rhodophyta) and a study of its relationships within the Melobesioideae

Three separate collections of the type material of Kjellman's Lithophyllum arcticum are re‐examined and a lectotype is selected. It is confirmed that the thallus is unattached, at least 4.5 cm in diameter, composed of up to eight superimposed more or less discoidal lamellae, provided with concentric striations on the surface. Individual lamellae are usually 100 to 200 μm thick (reaching 1 mm), developing dorsally from the main thallus and expanding centrifugally. The internal organization is dorsiventral with a polystromatic hypothallium, giving rise to an ascending perithallium with small subepithallial initials and rectangular (in TS) epithallial cells. It is found that patches of coaxial‐like growth occur sporadically in the hypothallium and the perithallium, and that ventral lamellae may grow back‐to‐back. Somatic cells exhibit both large and narrow cell fusions. Pore plates of the raised multiporate conceptacles are slightly sunken to flattened and perforated by 16 to 31 pores. Pore canals are conical (narrowing towards the top) and are bordered by filaments composed of both undifferentiated and slender‐elongate cells. Old conceptacles are overgrown by vegetative filaments and empty chambers are embedded in the perithallium. Collectively these features indicate that L. arcticum belongs to the subfamily Melobesioideae. The development of an unattached‐superimposed thallus, patches of coaxial growth, short subepithallial initials and specialized pore cells suggest a position either in Mesophyllum, or in an amended Leptophytum to include even species with coaxial patches and unattached‐superimposed habit (characters presently segregating Leptophytum from Synarthrophytorn). The holotype of Lithophyllum zonatum from East‐Finnmark, previously considered to be related to L. arcticum, is re‐examined and shown to belong to a different species. A previous Arctic record of Mesophyllum lichenoides from Spitsbergen is abolished, and thus the disjunct distribution of I. arcticum in relation to Mesophyllum suggests a position in the Synarthrophyton‐Leptophytum complex which shows a bipolar to temperate distribution.

Mesophyllum capense (Rosanoff) comb. nov. (Rhodophyta, Corallinaceae) from South Africa

Lithophyllum capense Rosanoff (Rhodophyta, Corallinaceae) was described on the basis of herbarium specimens in Lamouroux's and Lenormand's herbaria in Caen, France. The specimens were epiphytic on Gelidium sp. from The Cape of Good Hope, South Africa. The structure and systematics of the lectotype and paratype specimens are compared with material collected recently in South Africa. The plants have markedly prominent, multiporate tetrasporangial conceptacles and belong to the subfamily Melobesioideae. The presence of monomerous growth, a single layer of non-flared epithallial cells, subepithallial initials that are as long as or longer than subtending cells and simple spermatangial systems on the floor and walls of male conceptacles place this species in the genus Mesophyllum: comparison with other known species of this genus shows that Mesophyllum capense (Rosanoff) comb. nov. is a distinct species with a distribution restricted, as far as is known, to South Africa.

Mesophyllum macedonis, nov. sp. (Rhodophyta, Corallinales), a putative Tethyan relic in the North Aegean Sea

A new species of the widespread genus Mesophyllum Lemoine is described. Mesophyllum macedonis nov. sp. grows in shallow (c. 0·5 m depth) waters, tolerating wide temperature fluctuations (12–26 °C) at a salinity of 32–35‰, protected from direct wave and light exposure. The species forms weakly attached rose-coloured clumps with whitish margins on rocky substrata. Its thallus is composed of superimposed foliose lamellae (to 170 μm thick) with dorsiventral organization, non-coaxial hypothallium, limited perithallial growth (to 60 μm thick), rectangular epithallial cells and solitary terminal trichocytes. Tetrasporangial conceptacles are raised and have convex roofs perforated by up to 108 pores that are bordered by filaments composed of slender and occasionally elongated cells. Tetrasporophytes were first observed in 1984 and their occurrence monitored without finding gametophytes or other populations at the type locality or elsewhere on the coast of the Sithonia Peninsula. A comparative study of literature data and material of selected congeners shows that M. macedonis shares most of its characters with M. ornatum (Foslie et Howe) nov. comb. from the Bahamas and Mariana Islands, and M. incisum (Foslie) Adey from southern Australia and New Zealand. Biogeographic scenarios that may explain the restricted distribution of the new Mediterranean endemic are discussed.

Mesophyllum macedonis, nov. sp. (Rhodophyta, Corallinales), a putative Tethyan relic in the North Aegean Sea

A new species of the widespread genus Mesophyllum Lemoine is described. Mesophyllum macedonis nov. sp. grows in shallow (c. 0.5 m depth) waters, tolerating wide temperature fluctuations (12.26 °C) at a salinity of 32–35‰, protected from direct wave and light exposure. The species forms weakly attached rose-coloured clumps with whitish margins on rocky substrata. Its thallus is composed of superimposed foliose lamellae (to 170 μm thick) with dorsiventral organization, non-coaxial hypothallium, limited perithallial growth (to 60 μm thick), rectangular epithallial cells and solitary terminal trichocytes. Tetrasporangial conceptacles are raised and have convex roofs perforated by up to 108 pores that are bordered by filaments composed of slender and occasionally elongated cells. Tetrasporophytes were first observed in 1984 and their occurrence monitored without finding gametophytes or other populations at the type locality or elsewhere on the coast of the Sithonia Peninsula. A comparative study of literature data and material of selected congeners shows that M. macedonis shares most of its characters with M. ornatum (Foslie et Howe) nov. comb. from the Bahamas and Mariana Islands, and M. incisum (Foslie) Adey from southern Australia and New Zealand. Biogeographic scenarios that may explain the restricted distribution of the new Mediterranean endemic are discussed.

Application of neontological taxonomic concepts to Late Eocene coralline algae (Rhodophyta) of the Austrian Molasse Zone

Abstract. Traditionally, different diagnostic characters have been used in the identification of fossil and Recent coralline algal genera. The taxonomy of fossil coralline algae has focused on well calcified features such as basal filaments and conceptacle perforation. In contrast, the taxonomy of Recent material uses a combination of several features with a low fossilization potential, such as epithallial cells and structures of sexual reproductive organs. In the studied material of the Late Eocene Austrian Molasse Zone Lithoporella, Neogoniolithon, Spongites, Phymatolithon and Sporolithon are identified and described applying features of neontological taxonomic concepts. These features are: (1) the arrangement of basal filaments; (2) the occurrence of cell fusions; (3) the relative length of subepithellial initials; (4) the conceptacle perforation; (5) the orientation of filaments around the conceptacle pore; and (6) the type of conceptacle roof formation. Some of these features were thought to be unpresentable in fossil material until recently. The fossilization potential of diagnostic features and the identification of the documented genera and species are discussed in detail. Moreover, a checklist for the description of fossil taxa is provided.

Two new melobesioid algae (Corallinales, Rhodophyta), Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., in South Africa and Namibia

Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., the fourth and fifth species in this apparently southern hemisphere genus, are described from southern Africa. Synarthrophyton robbenense occurs on rock and shells in the subtidal zone. Its thalli are minutely warty, with the surface covered by short, narrow protuberances that are fused into elongate, scrolled structures. The surface [scanning electron microscopy (SEM)] is of the Leptophytum type. Mature tetra/bisporangial conceptacles have raised rims and sunken pore plates. The pore plates are composed of filaments made up of two or three cells plus an enlarged epithallial cell. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are narrower and more elongate than cells of the pore plate and surrounding vegetative filaments. Tetra/bisporangial pores are surrounded by five to eight rosette cells that tilt somewhat toward the pore in surface SEM view. Tetra/bisporangial conceptacles do not become buried in the thallus, but are shed on senescence, often leaving shallow craters on the surface. Synarthrophyton munimentum occurs on rocks and shells in low-shore tide pools, and on rock, shells, and kelp holdfasts in the subtidal zone. Thalli are usually smooth, occasionally warty, but never show protuberances that are fused into scroll-like structures. The thallus surface (SEM) is made up of Leptophytum-type epithallial cells. Tetra/bisporangial conceptacle roofs are volcano-shaped with a raised peripheral rim and sunken pore plate. The pore plates are composed of filaments made up of five to seven cells plus an epithallial cell. The rosette cells that surround the tetra/bisporangial pore are distinct from surrounding roof cells (SEM, surface view) in being narrower and sunken below the level of the surrounding pore plate. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are more or less similar in size and shape to cells of the pore plate and surrounding vegetative filaments.

First report of the melobesioid alga (Corallinales, Rhodophyta) Mesophyllum incisum (Foslie) Adey in South Africa

Mesophyllum incisum is reported and studied for the first time in South Africa. It has a thallus surface (SEM) with Leptophytum-type epithallial cells. Tetra/bisparangial conceptacles are mound-like and lack a peripheral rim but have a flattened pore plate. The rosette cells surrounding the tetrasporangial pores are distinct from surrounding roof cells (SEM, surface view) in being narrower, and sunken below the level of the surrounding pore plate. The cells of filaments bordering the tetrasporangial conceptacle pore canal differ from the other roof cells within the pore plate in being more elongate, narrower, and often more densely staining. Pore canal filaments also generally contain fewer cells than the surrounding filaments of the pore plate and the pore canal is more-or-less parallel sided. Our material agrees closely with the species as reported in Australia.

Antifouling effects of epithallial shedding in three crustose coralline algae (Rhodophyta, Coralinales) on a coral reef

Crustose coralline algae cover a substantial fraction of surfaces on the shallow parts of coral reefs. The shedding of surface layers of cells by three common species was studied using light and electron microscopy. All three species examined shed epithallial cells in one of two ways: synchronous epithallial shedding involving the simultaneous shedding of a sheet of cells across a large area of the thallus surface ( Sporolithon ptychoides and Neogoniolithon fosliei), or non-synchronous epithallial shedding which occurs when epithiallial cells degenerate individually ( Hydrolithon onkodes). Experiments were done to determine whether these types of epithallial shedding could produce an anti-fouling effect. Recruitment onto the surfaces of live and bleach-killed coralline fragments was compared for two synchronous and one non-synchronous shedding species. In all cases, the killed corallines became overgrown within a few weeks. Live corallines remained largely free of other organisms for the duration of the experiment. The results thus demonstrate that both types of epithallial shedding can influence recruitment in the reef ecosystem.

Fine structure of deep‐layer sloughing and epithallial regeneration in Lithophyllum neoatalayense (Corallinales, Rhodophyta)

SUMMARYTransmission electron microscopic study of Lithophyllum neoatalayense Masaki demonstrated that this alga used two mechanisms by which it sloughed cells from its surface. Epithallial filaments, produced by a layer of underlying initial cells, were two to four cells long. Terminal epithallial cells, those closest to the thallus surface, underwent senescence and shedding as previously described for other coralline algae. In addition, deep‐layer sloughing occurred. During this process, which is known for only one other coralline alga, cell death occurred uniformly within a surface layer 40‐50 μm thick. No pathogens or evidence of mechanical damage was detected. The zone of dead cells included the epithallial layer, the layer of initial cells, and some cortex cells beneath the initials. Pit plugs connecting living and dead cells at the edge of the necrotic zone were sealed by wall material deposited by the surviving cells, but cells within the necrotic zone showed no evidence of sealed pit plugs. The outermost surviving cells became new initial cells, which then divided to form new epithallial cells. Regeneration of the epithallial layer occurred before the thick layer of dead cells peeled away. The extensive deep shedding of both epithallial and initial cells in L. neoatalayense and the effectiveness of regeneration from cortex cells challenge the assumption that protection of initial cells is an important function of epithallial cells.

Reassessment of Palaeothamnium Conti, 1946 (Corallinales, Rhodophyta)

Palaeothamnium has been identified in many algal associations from the Late Cretaceous to the Miocene since its definition by Conti (1946b). Revision of Conti's original collection and of new material from the type localities in the Vienna Basin indicate that the developmental stages of the conceptacles of the type species P. archaeotypum are common in many other present-day and fossil coralline algae belonging to different genera of the subfamily Melobesioideae and therefore cannot be considered a diagnostic generic character. The presence of flat epithallial cells and long subepithallial initials together with a well-developed peripheral region in the type species leads us to consider Palaeothamnium as a younger heterotypic synonym of Lithothamnion Heydrich, 1897. However, according to modern melobesioid taxonomy, its attribution to Synarthrophyton Townsend, 1979 cannot be completely excluded. In addition, the type species of Palaeothamnium must be treated as a younger heterotypic synonym of Lithothamnion ramosissimum (Reuss, 1847) Piller, 1994.

Development of epithallial cells in Corallina officinalis and Lithophyllum impressum (Corallinales, Rhodophyta)

Abstract Transmission electron microscopy was used to examine the structure and development of epithallial cells in Corallina officinalis Linnaeus (Corallinoideae), a geniculate alga with an epithallus one functional cell layer thick, and Lithophyllum impressum Foslie (Lithophylloideae), a nongeniculate alga with multicellular epithallial filaments. Lithophyllum provided a particularly good system for unravelling the sequence of epithallial cell differentiation, because different developmental processes were spatially and temporally separated along the length of individual filaments four or five cells long. In C. officinalis, a common wall layer enclosed recently divided initial cells and their epithallial derivatives. Epithallial cells of both species developed prominent ingrowths of the cell wall exclusively on the distal cell surface; those of C. officinalis were branched and penetrated deep into the cell. In L. impressum, even the youngest generation of cells, those borne directly on initial cells, ha...

RECONSIDERING PREY SPECIALIZATIONS IN AN ALGAL‐LIMPET GRAZING MUTUALISM: EPITHALLIAL CELL DEVELOPMENT IN CLATHROMORPHUM CIRCUMSCRIPTUM (RHODOPHYTA, CORALLINALES)1

ABSTRACTThe association of the limpet Tectura testudinalis (Müller 1776) and the crustose coralline red alga Clathromorphum circumscriptum (Strömfelt) Foslie (Melobesioideae) is considered a species‐specific mutualism between grazer and prey. Anatomical features of C. circumscriptum, especially those associated with epithallial cells, have been viewed as being unusual and directly related to the mutualism. Transmission and scanning electron microscopic methods were used to investigate the structure and development of epithallial cells in C. circumscriptum. Contrary to prior reports, terminal cells of the epithallial filaments of C. circumscriptum undergo senescence and shedding much like epithallial cells in other members of the Corallinales; hence, multicellular epithallial filaments did not evolve in this alga simply because epithallial cells were unable to slough. Although epithallial cells in many coralline algae are lightly calcified, those in C. circumscriptum are heavily mineralized, more so than the underlying initial cells and cells comprising the cortex. As in other coralline algae, starch is absent from the epithallial cells of C. circumscriptum. The feature of having abundant chloroplasts in the epithallial cells of C. circumscriptum is shared by other species with multi‐cellular epithallial filaments and transiently by species with single epithallial cells. Except for having a thick epithallus, a feature found in other genera and in other species of Clathromorphum, the anatomy of C. circumscriptum is unexceptional.

Morphology, anatomy and reproduction of the eastern Mediterranean coralline Tenarea tortuosa and its relationship to members of the Lithophylloideae and Mastophoroideae (Rhodophyta, Corallinales)

One of the most characteristic organisms of the Mediterranean flora, the endemic coralline Tenarea tortuosa, has been collected along the Cretan coast and its vegetative and reproductive structures are reassessed. Gametophytes are described for the first time and are rare, observed only in one locality on the south coast. Reproductive structures suggest that the sexual life history is triphasic, but the present collections indicate unequal representation of males, carposporophytes and tetrasporophytes, and a dominance of bisporophytes suggesting that the alga is reproducing mainly asexually. The frond of Tenarea is formed by the coordinated growth of two elements (branches), growing back‐to‐back, each showing a simple Titanodema‐type of organization; i.e. a monostromatic hypothallium of sinuous cells and a single layer of obliquely borne epithallial cells. Contiguous cells of the two opposite branches are not connected by secondary pit‐plugs, and easily glide apart if decalcified. Natural splitting of the lamellae into its two branches may also occur, and single branches may fold regenerating the back‐to‐back organization. Analogous back‐to‐back growths occur in species of the distantly related genera Goniolithon (Lithophylloideae) and Leptophytum (Melobe‐sioideae) and apparently represent cases of convergence. The affinities of Tenarea to related genera are discussed.