Vertebrata simulans (Harvey) Kuntze and Polysiphonia ceramiiformis P.Crouan & H.Crouan

MOLECULAR IDENTIFICATION

Two rbc L sequences for Vertebrata simulans and three for Polysiphonia ceramiiformis from the British Isles (four of which were newly determined) were identical, and also identical to a newly determined sequence of P.ceramiiformis from Spain. These sequences were resolved in the phylogeny in a highly supported clade including eight other members of the genus Vertebrata (Fig. 2). Relationships among members of the clade including V. simulans were unresolved. The most closely related species in the phylogeny is V. byssoides (Goodenough & Woodward) Kuntze with 5.3% divergence in the rbc L gene. Two cox 1 sequences were generated for both V. simulans and P.ceramiiformis . The three sequences from the United Kingdom including specimens morphologically identified as V.simulans and P. ceramiiformis were identical, while the sequence of P.ceramiiformis from Spain differed by 1 bp from the British specimens. MORPHOLOGICAL OBSERVATIONS

Vertebrata simulans and Polysiphonia ceramiiformis are predominantly erect (Fig. 3A, D), attached to their substratum by short prostrate axes with unicellular rhizoids that are cut off from the pericentral cells. They have ecorticate axes with 10-13pericentral cells. Axes are 100-300 µm in diameter, with segments 0.3-0.8 L/D (length/diameter). Branches are formed mostly every 2-9 segments, replacing trichoblasts.

Polysiphonia ceramiiformis has a soft succulent texture and branches form corymbose, characteristically forcipate apices (Fig.3 A-C). Vertebrata simulans is more slender and, in addition to indeterminate branches, it has abundant branchlets that remain short and spine-like (Fig. 3 D-F).

Reproductive structures were not observed in specimens of P.ceramiiformis studied here, but tetrasporangia,spermatangia and cystocarps were described in Maggs & Hommersand (1993). Vertebrata simulans has tetrasporangia 40-70 µm in diameter, formed in short lateral branchlets, in short spiral series (Fig. 3G). Sexual reproductive structures are unknown except for the observation of spermatangia on a tetrasporophyte (Maggs & Hommersand 1993).