Ceramium
Ceramium:-
1. Classification:-
Division:- Rhodophyta
Class:- Rhodophyceae
Sub-class:- Floridae
Order:- Ceramiales
Family:- Ceramiaceae
Genus:- Ceramium
2. Habit and Habitat:-
> Ceramium occurs very commonly between tide levels and in deeper water being especially abundant along the Mediterranean coast.
> Some species may also thrive well in river water.
> The richly branched uniaxial plant body is recognizable from the banded appearance and the tong-like forking of the apical region of the branches, these are considered very valuable diagnostic characters
3. Thallus structure:-
> The plants grow in tufts varying from 2 to 30 cm. in length and remain attached to rocky substrata by means of multicellular rhizoids, which form the holdfast.
> The thallus is irregularly, dichotomously branched with the apices of filaments incurved.
> In-deep waters, Ceramium appears red in colour, while in shallow tidal waters it exhibits a yellowish green or reddish brown colour.
> Each filament consists of a central siphon and can be differentiated into nodes and internodes.
> In some species, in mature condition, the nodes cannot be clearly marked out owing to the presence of continuous cortical cells around them, while in others the nodal band of cortical cells becomes separated from one another by the axial cells.
> In some cases, spines may be developed from the primary cortical cells at the nodes.
4. Reproduction:- Ceramium reproduces both by and sexual method.
> The plants are heterothallic.
> Antheridia:-
- The antheridia or spermatangia are scattered over the entire surface of the thallus forming patches. They arise by the division of the cortical cells.
- Each antheridium is a single-celled structure, which remains enclosed in a thick gelatinous wall and contains a single nucleus and a dense cytoplasm.
- By a rupture at the apex of the antheridium a solitary male gamete or spermatium is liberated.
- The spermatium is highly vacuolated and contains a solitary nucleus.
> Archegonia:-
- The female sex organs (carpogonia or procarps) are produced terminally on short lateral branches.
- Each procarp branch is normally 4-celled and produced from the basal cell.
- The terminal cell of the carpogonium elongates at its tip forming a tubular trichogyne.
> Fertilization:- It occurs by the union of the spermatial nucleus with the carpogonial nucleus.
> After fertilization, the basal cell gives rise to a large auxiliary cell, on the side opposite to the procarp branch, into which passes the zygote nucleus.
> The auxiliary cell then by divisions gives rise to a number of gonimoblast filaments. From the tips of these filaments carpospores are produced, each of which on germination gives rise to the diploid tetrasporic plant.
> No well-developed cystocarp is produced, but the carpospores are partially protected by a number of short, laterals, upwardly projecting branches.
> The tetrasporophyte plant bears tetrasporangia, which arise in the cortical cells at the nodal regions.
> The nucleus of each tetraspore mother cell divides meiotically giving rise to four haploid tetraspores, which may be arranged cruciately or tetrahedrally.
> Each tetraspore, on liberation, reaches a suitable substratum and forms anew gametophytic plant by division.
> Life cycle:-
- The life history cycle in Ceramium, thus, exhibits a triphasic alternation of generations.
- In some species, some specialized spores, called paraspores, are formed on the tetrasporic (diploid) plants, but their germination has not been studied.
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