In this article we will discuss about the classification of siphon ales.
Family Caulerpaceae:
Plants are coenocytic, branched, slenderly filamentous, or quite large and then differentiated into rhizoidal, stoloniferous and erect portions, the latter assuming a great variety of forms. The coenocyte has firm wall braced internally by a system of trabeculae.
Reproduction is by segregation of portions of the contents of a branch to form dimorphic swarmer’s, probably gametes, which are discharged through elevated papillae.
Genus Brtopsis:
This alga is found to be restricted particularly in warm seas with a few exceptional species which grow in cold waters.
The coenocytic plant body exhibits a very remarkably conspicuous development being differentiated into a comparatively inconspicuous prostrate rhizome-like portion creeping along the substrtaum (Fig. 83A) having anchored to it by the rhizoids and elaborately developed aerial erect axis with a dense and regular pinnate branching in acropetal succession.
The erect branches are feather-like with the axis bearing numerous branchlets (Fig. 83B).
The lower region of the axis is naked and the upper part bears pinnae of variable length. Each pinna is constricted at the point of origin. The rhizome also functions as an organ of perennation. The wall of the vegetative body is composed of cellulose and pectic substances. Internal to the wall is the cytoplasmic layer lining a continuous vacuole.
The cytoplasm contains numerous nuclei and small discoid to spindle-shaped chloroplasts having one pyrenoid each (Fig. 83C).
Vegetative reproduction is by the growth and decay of new and old parts. Sexual reproduction is anisogamous. The plants are dioecious. Markedly differentiated pear-shaped biflagellate anisogametes are formed in gametangia in two different plants (Fig. 83D & E). During reproduction the pinnae develop into gametangia being separated from the parent plant by means of septa.
Macro- and micro-gametes are formed in different gametangia from the protoplasmic contents of the pinnae which behave as gametangia.
The gametangia are distinguishable at maturity from the colour. The ones producing microgametes are yellow coloured, whereas, the others that produce macrogaraetes being green. The nuclei of the gametangia divide meiotically before taking part in the formation of gametes.
The macrogametes are about three times the microgametes and have one to two chloroplasts, a pyrenoid and an eye-spot (Fig. 83F). Whereas, the microgametes have a small yellow plastid without pyrenoid.
The gametes are liberated by the gelatinization of the wall of the gametangia at the apex (Fig. 83E). They swim around for some time and fuse together resulting in the formation of a zygote (Fig. 83G). The zygote remains quadriflagellate for a very short time, soon assumes round shape and germinates directly into new plant (Fig. 84).
The alga has an elaborate diploid phase. Meiosis being gametic the haploid phase is represented by the gametes only.
Some Indian species of Genus Brtopsis:
Bryopsis corymbosa J. Ag.; B. hypuoide’s Lamour.; B. pachynema Martens.; B. pennata Lamour.; B. plumosa (Huds.) Ag.; B. tenuissima Notaris.
Special features:
1. Very conspicuously developed coenocytic plant body being differentiated into a comparatively inconspicuous prostrate portion and an elaborately developed aerial erect axis with a dense and regular pinnate branching in acropetal succession.
2. Discoid to spindle-shaped chloroplast.
3. Vegetative reproduction by the growth and decay of the thallus.
4. Sexual reproduction anisogamous.
5. Elaborate diploid phase.
6. Gametic meiosis.
Genus Caulerpa :
All species of Caulerpa are marine being frequent in the quiet shallow waters of the tropics although there are some Mediterranean species. They cover extensive tracts of the sea-floor and favour relatively shallow water. Several of them are often rooted in sand or mud with their prostrate rhizome bearing colourless rhizoids with which they attach themselves with the substratum.
The production of deadly poisonous substance Caulerpicin has been recognized in Hawaii and in the Philippines, since freshly collected plants of Caulerpa eaten in salads causes health hazard.
The plant body is elaborate in form being differentiated into prostrate portion represented by creeping rhizome with rhizoids (Fig. 85A) and an aerial portion performing the function of assimilatory shoot, or assimilator which may be very variable in structure being either simple flat blade-like, or lobed or a highly complicated branched structure (Fig. 85B & G).
Internally, plant body is characterized by the complete absence of septation and is composed of closely apposed and intertwined coenocytic threads traversed by longitudinal and transverse skeletal strands (Fig. 85D to F) perhaps to increase the rigidity of the plant body. These are very remarkably developed in the rhizome portion and are completely absent or poorly developed in the rhizoids.
As such the entire plant body is a single multinucleate cell with a central vacuole and lining cytoplasm with numerous discoid chloroplasts. The longitudinal walls, as well as the wall of the skeletal strands are composed of callose, pectin, and similar other materials. But cellulose is completely absent.
Vegetative reproduction takes place by the growth and decay of new and old parts, resulting in the formation of innumerable plants.
Sexual reproduction, depending on species, may be iso- or anisogamous by the production of biflagellate swarmer’s which are more or less .pear-shaped. They are developed in the entire body except the rhizoids. Prior to their liberation, papillate outgrowths are developed (Fig. 85G).
Simultaneously with the development of papillae there starts the formation of gametes in the plant body. Before the formation of papillae the assunilators acquire a variegated appearance.
The swarmer’s are liberated in a mass of mucilage through the apices of the extrusion, papillae (Fig. 85 H & I). Is; some species, soon after the liberation of swarmer’s the whole plant dies. In certain species the whole plant can produce swarmer’s, whilst in others the reproductive area is limited.
The swarmer’s in Caulerpa clavifera are of two kinds—the macro- and micro-gametes (Fig. 85J and K). Gametic fusion in Caulerpa is commonly anisogamous (Fig. 85L).
Some Indian species of Genus Caulerpa:
Caulerpa crassifolia (Ag.) J. Ag.; C .fastigiata Mont. ; C. peltata Lamour.; C. racenosa (Fursk.) Web. van. Bosse.; C. sertulariodes Gmel.; C. taxifolia (Vahl.) Ag.
Special Features of Genus Caulerpa:
1. Coenocytic plant body with remarkable differentiation of aerial and prostrate portions.
2. Development of internal skeletal strands for mechanical support of different parts of the plant body.
3. Sexual reproduction both iso- and anisogamous.
4. Fusing gametes are pyriform bearing two flagella.
5. Gametes escape from the plant body through the ends of extrusion papillae in a mass of mucilage.