Mesophyllum Sphaericum Sp. Nov. (Corallinales, Rhodophyta): A New Maërl-Forming Species From the Northeast Atlantic1

Abstract

Mesophyllum sphaericum sp. nov. is described based on spherical maërl individuals (up to 10 cm) collected in a shallow subtidal maërl bed in Galicia (NW Spain). The thalli of these specimens are radially organized, composed of arching tiers of compact medullary filaments. Epithallial cells have flattened to rounded outermost walls, and they occur in a single layer. Subepithallial initials are as long as, or longer than the daughter cells that subtend them. Cell fusions are abundant. Multiporate asexual conceptacles are protruding, mound-like with a flattened pore plate, lacking a peripheral raised rim. Filaments lining the pore canal and the conceptacle roof are composed of five to six cells with straight elongate and narrow cells at their base. Carposporangial conceptacles are uniporate, protruding, and conical. Spermatangial conceptacles were not observed. Molecular results placed M. sphaericum near to M. erubescens, but M. sphaericum is anatomically close to M. canariense. The examination of the holotype and herbarium specimens of M. canariense indicated that both species have pore canal filaments with elongate basal cells, but they differ in number of cells (five to six in M. sphaericum vs. four in M. canariense). Based on the character of pore canal filaments, M. canariense shows similarities with M. erubescens (three to five celled). The outermost walls of epithallial cells of M. canariense are flared compared to the round to flattened ones of M. erubescens, the latter being widely accepted for the genus Mesophyllum. The addition of M. sphaericum as new maërl-forming species suggests that European maërl beds are more biodiverse than previously understood.

Mesophyllum erubescens (Corallinales, Rhodophyta)—so many species in one epithet

“…Phylogenetic analyzes based on multiple markers SSU, rbcL, and psbA (Bittner et al 2011, Peña et al 2011 indicate that Mesophyllum is very likely a polyphyletic genus. Mesophyllum erubecens, based on specimens from Brazil that match the type specimen, is not in the same clade as M. lichenoides (Ellis 1768: 407) Me.…”

“…Mesophyllum erubecens, based on specimens from Brazil that match the type specimen, is not in the same clade as M. lichenoides (Ellis 1768: 407) Me. Lemoine (1928: 252), the generitype species from the NE Atlantic (Bittner et al 2011, Peña et al 2011.…”

Macroalgal-dominated coastal detritic communities from the Western Mediterranean and the Northeastern Atlantic

“…This is also the case for different Mesophyllum species, whose identification has to be revisited. In fact, Peña et al (2015) did not find M. lichenoides nor M. alternans in the Mediterranean but M. sphaericum and M. macroblastum (Kaleb et al, 2011;Peña et al, 2011), which creates certain doubts about the correct identification of most specimens corresponding to the genus Mesophyllum. The different algal communities considered in the selected literature (maërl beds, kelp forests and Peyssonnelia beds) have usually been described from a quantitative point of view, i.e.…”

Systematic survey of Lithothamnion, Melobesia and Mesophyllum species (Hapalidiaceae, Corallinales, Rhodophyta) recorded along the Atlantic coast of Mexico

“…The classification system of Harvey et al (2003) and Peña et al (2011) are used throughout this paper. The diameters and lengths of epithallial cells (epithallus), dorsal region (cortex) and basal layers (medulla) were measured.…”