Marine red algae (Rhodophyta) of economic use in the algal drifts from the Yucatan Peninsula, Mexico Author Resendiz, María Luisa Núñez Author Dreckmann, Kurt M. Author Sentíes, Abel Author Wynne, Michael J. Author Tejera, Hilda León text Phytotaxa 2019 2019-01-09 387 3 219 240 http://dx.doi.org/10.11646/phytotaxa.387.3.3 journal article 10.11646/phytotaxa.387.3.3 1179-3163 13724318 Eucheumatopsis isiformis (C.Agardh) Núñez Resendiz, Dreckmann & Sentíes Thallus cartilaginous, red pink or dark red, 15–50 cm in length, with cylindrical axes in cross section, 850–2200 μm in diameter. Main axes branching irregularly; branches and main axes with smooth margins or covered by numerous spine-like branches, arranged radially or alternately opposite, 1–2.5 mm in length ( Fig. 22 and 26 ). Multiaxial organization with a filamentous medulla and a pseudoparenchymatous cortex ( Fig. 23 ). Medulla composed of a dense mass of thick filaments, 1.8–6 μm in diameter, with numerous simple rhizoids. Inner cortex with six layers of stellate or rounded cells, 8.8–28.4 μm x 5.2–12 μm in diameter and 34–106 μm x 40–140 μm in diameter, respectively; outer cortex with two layers of ellipsoidal cells, 6–13 μm x 3.5–4.4 μm in diameter, markedly pigmented. Cystocarps developed on short laterals, with a single large central fusion cell from which diploid gonimoblast filaments radiate, 360–498 μm x 400–640 μm in diameter ( Fig. 24 ). Tetrasporangia zonately divided, 30–40 μm x 10–15 μm in diameter, embedded in the cortical cells, each sporangium arising laterally from a stellate basal cell ( Fig. 25 ). Taxonomic comment: Until recently, this species had been previously treated as Eucheuma isiforme (C.Agardh) J.Agardh. From molecular evidence this genus was found to be paraphyletic ( Núñez Resendiz et al. 2019 ), so the new genus Eucheumatopsis Núñez Resendiz, Dreckmann & Sentíes was described to accommodate the species E. isiformis , this name is reinstated.