T A N E ( 1 9 6 6 ) 12 : 1 3 - 3 6

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FRESH WATER PHYTOPLANKTON AND PHYTONEKTON FROM LAKE ROTOITI

by Julie L. Carr

Lake Rotoiti is one of the largest Roto ma lakes. It i s about twelve miles from Rotorua, extends to a depth of 350 feet, and covers some 129 square miles (8250 acres). During a period of three months from November 1965 to January 1966, during the summer, plankton hauls were performed at two weekly intervals from six stations, using a plankton net of fine nylon gauze, (F ig . 1) .

In doing these studies it was necessary to recognise the plankton, therefore this essay is in part a treatise on the types of plant plankton likely to be found in Lake Rotoiti, and as such it i s intended to be a simple guide, to the generic level, for identificatory purposes.

An introduction to plankton, methods of collecting, mounting and staining, and the value of the kind of data to be obtained will also be given.

Plankton are organisms which are very easily obtained. They float or swim about in the water at all depths in the euphobic zone (that region to which light penetrates), and may even sink below it. As the largest types are only just visible to the naked eye, and the majority of them are micro­scopic, the various types can only be recognised by using a microscope. As a whole they have the effect of clouding the water, making it smell, or effecting a tinge of colour. Of course other things in the water (detritus) can also do this, but amongst the detritus (which consists of decaying vegetable and animal matter including plankton, colloidal minerals, and particles of soi l or the products of the weathering of the earths crust,) there are bound to be living creatures.

Plankton are not evenly dispersed throughout the euphobic zone either horizontally or vertically, but occur in patches. When out in a boat around our coasts you may have noticed the boat running through places where the water seems to be a different colour, or smells . These are particularly noticable patches of plankton. Vertically the plankton are found in patches such as on the surface of the water. They may be grouped around the thermocline where the temperature of the water drops sharply with depth. These patches of plankton can occur in the sea, in lakes, and even in small bodies of water. Apart from these patches plankton may vary in kind, i . e . from bay to bay, or from one side of a lake to the other. This sort of thing also occurs with numbers, i .e. at Otamarai there might be a predominance of Melosira, whereas at Okawa bay there could be mainly Spirogyra with Melosira in the minority.

A series of plankton hauls will reveal the presence of dominant plankton, i .e. those plankton which are domineering either with respect to s ize , or weight of numbers. Among these there will also be plankton that are not so obvious but never the l e s s persistant from week to week, and then again there may be plankton that make a transitory appearance, arising from no­thing for a few weeks and then vanishing a month or a fortnight later.

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COLLECTING PLANKTON

There are two methods:— 1. Plankton net. 2. Sampling bottle.

Plankton Net These are nets made of fine nylon gauze, held open at the top by a

wire frame, and emptying into a glass or plastic bottle at the bottom. (See Fig. 1.) The top of the net i s attached to a strong string which i s paid out from a wooden reel.

With a net, two types of sample may be taken, namely a vertical sample or a horizontal sample.

Horizontal Sample

The amount of line to be paid out i s first measured out. It is a good idea to have the line graduated in feet or metres by means of indelible marking ink, or coloured cotton or string wound round the line at intervals. The line i s then secured firmly to the boat. As the boat cruises at a slow speed (the speed depending on the breaking strain of the line, construction of the net, and the fragility of the plankton) the plankton net is thrown overboard to one side of the stern, and the line paid out. You will find that the boat will slow down once all the line is fully paid out. As a rule, the shorter the line the easier the net is able to stay on the surface, but care should be taken to s e e that the line is not too short as to get caught in the propeller of an outboard motor for example. The net is then towed over the required distance and drawn out of the water when the boat passes the final point in the run. The net i s first thrown out as the boat passes the point where the run starts. The boat should be stopped immediately the run is finished, and when the forward motion ceases the net i s dunked about five times in the water over the side of the boat. The plankton caught on the side of the net should thus be freed and collected in the small volume of water in the collecting bottle, the main volume of water draining away. The sample from the collecting bottle i s then poured into another bottle, and saved for examination. The net is washed immediately the sample has been removed, by reversing the bottle and turning the net inside out, and again dunking it in the water, rubbing it with the hands if necessary.

Vertical Sample

For a vertical sample you will need a lead weight under the bottle, or attached in a similar fashion to a sinker on a fishing l ine. The net will then sink straight down through the water when it i s thrown over the s ide . When the net has sunk to the required depth it is hauled straight up. When taking a vertical sample the boat should be devoid of any motion. If the boat is drifting the net should be thrown well over to the side it i s drifting towards, and the net hauled up as the boat passes over the top of it. In a current the net should be thrown up current, and hauled up as it passes past the boat going down current, or e lse the boat can be run over the top of the net, travelling in the direction of the current.

Vertical samples can be taken off wharves, and horizontal samples

SAMPLING BOTTLE FIG.2.

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taken from the end of the wharf to the shore. A net can be placed so that it remains fixed at a certain point where

there i s a current, and the water in the current will automatically flow straight through the net.

SAMPLING B O T T L E

A bottle can be lowered to a certain depth, unstoppered to let the water containing plankton to flow in, stoppered again, and hauled up.

There are bottles especially made for taking water samples at various depths. One type is called a van Doren bottle. These bottles are open at both ends. They are lowered to the required depth with both ends open so that the water flows through with no restriction. When they are required to be closed, a "messenger" is sent down the securing line, which released a mechanism on the bottle and c loses it simultaneously from both ends. These bottles are much too expensive to buy, unless the business of collecting plankton is to be taken seriously. See F i g . 2.

The whole water sample can be measured, the plankton in it killed and preserved so that they will fall to the bottom i .e. (settle). The surface water can then be siphoned, drawn (with a pipette), or decanted off, and the concentrated suspension of plankton looked at under the microscope.

PRESERVING, MOUNTING, AND STAINING

A good and easily obtainable preservative i s formalin. 3% formalin to 97% of water sample will kill and preserve the plankton satisfactorily. A weak solution of iodine can also be used, but this i s more expensive.

Unless the sample can not be examined right away it i s not a good idea to preserve the plankton. Preserving has the effect of removing the colour, disfiguring externally, and affecting the cell contents internally. Bes ides this, the locomotion of the plankton cannot be observed.

If any specimen is moving too quickly to be captured under the field in view under the microscope, a drop of Glycerine on the slide makes the sus­pending medium more dense, and thus s lows down the active ones. Glycerine can also be used to prevent a cover sl ip on a slide from squashing and breaking plankton such as Volvox.

Iodine can be used to stain starch in members of the Chlorophyceae (which have starch as a food reserve). Phytoplankton belonging to other Divisions can thus be eliminated in the identification if there is no black staining with Iodine.

Methylene blue can be used quite easily to stain the middle lamella, particularly in the Volvocales. Use just a drop of cone M.B. to a drop of the culture on the s l ide .

THE VALUE OF THE DATA OBTAINED

A plankton net must be very fine to catch plant plankton. The types of plankton caught vary with the degree of fineness of the net used. A coarse net will catch only large and complicated plankton, and very fine nets will have a good chance of collecting things like Chlamydomonas, as well as automatically catching the larger plankton. With the sampling bottle there are no such difficulties because the total water sample plus plankton i s

17

preserved, then all the plankton large or small are captured. However if the sampling bottle sample is poured through the net, then the coarseness of the net will again apply.

The amount of water that passes through the net can be calculated by multiplying the area of the open end of the net by the distance travelled, and this figure may be used, providing the speed of the boat is slow enough to allow all the water to pass through the net, and not to be deflected away. If the sampling bottle i s used then the total sample is measured (before the preservative i s added).

A sampling bottle can take a sample from a single required depth, but a vertical net sample will trap all the plankton from the required depth up to the surface. Therefore with a net, to find the plankton at a certain depth a sample will have to be taken above the required depth, and at the depth required, and the difference in plankton between the two is the sum of the plankton at the required depth.

People working on plankton have long been trying to design a net that lessens "avoidance", because it is a well known fact that the plankton that can move independently can "see the net coming" and move out of the way. This really applies to zooplankton but some of the larger motile plant plankton (phytoplankton) may avoid the net a l so . The sampling bottle technique avoids this avoidance to a great extent as it can be placed open at the required depth, and the plankton allowed to equilibriate around it before the bottle i s c losed. However the bottle surfaces may possible attract certain plankton more than others, i .e . algae that like to settle on a surface, or zooplankton such as Periphyton.

A combination of the two methods of collecting can be used. A number of samples from one required depth may be collected and poured through the plankton net. The coarseness of the net will still apply, but the single sample at a required depth i s still an advantage.

The types of plankton found in Potoiti did not vary much between stations and fortnightly intervals, although there were minor differences quantitatively. The types most in abundance were:— Melosira, Dinobryon, Staurastrum, Eudorina, Cosmocladium, and Spirogyra. Melosira and Dinobryon were found in abundance in every sample, and Cosmocladium in abundance towards the end of January.

CLASSIFICATION OF TYPES

According to L.H. Millener, V.J. Chapman and Barbara Segedin — 1965.

CYANOPHYTA ENDOSPORACEAE

Chroococcales Chroococcaceae

Coelosphaerium Microcystis

HORMOGONEAE Nostocales

Nostocaceae Nostoc, Anabaena.

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CHLOROPHYTA VOLVOCALES

Chlamydomonadaceae Chlamydomonas

Volvocaceae Pandorina, Eudorina, Pleodorina Volvox

CHLOROCOCCALES Selenastraceae

Selenastrum, Ankistrodesmus Hydrodictyaceae

Pediastrum Coelastraceae

Scenedesmus, Actinastrum ULOTRICHALES

Ulotrichaceae Ulothrix

Microsporaceae Microspora

OEDOGONIALES Oedogoniaceae

Oedogonium CONJUGALES

Eu-conjugate Zygnemaceae

Spirogyra Mougeotiaceae

Mougeotia Desmidioideae

Desmidiaceae Cosmocladium Cosmarium Closterium Sphaerozosma Onchynema Hyalotheca Staurastrum

CHRYSOPHYTA XANTHOPHYCEAE

Heterotrichales Tribonemaceae

Tribonema BACILLARIOPHYCEAE

Pennales Navicula, Asterionella, Tabellaria

Centrales Melosira, Dinobryon

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ap apical process

ch chloroplast chr chromatophore

ct cytoplasmic thread

cv contractile vacuole dc daughter colony or cell e eyespot ec egg cell fl flagella g girdle gc gelatinous cushion

gs gelatinous strand

h heterocyst I lorica

m mucilaginous envelope

mc median constriction n nucleus ric central nodule nP polar nodule

py pyrenoid r raphe s striae or septa sc semicell si sinus

tep tumbler end piece

v vacuole

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DESCRIPTION OF TYPES

CHLAMYDOMONAS Unicellular, motile, cell spherical — pyriform, elipsoidal,

or subcylindrical. Cellulose cell wall in one piece. 2-4 flagella, equal in length. Parietal cup shaped chloroplast. One (commonly) or more pyrenoids, posterior, or scattered in the chloroplast. 2-4 contractile vacuoles at base of flagella. Red eyespot laterally placed and usually anterior.

PANDORINA Colonial, free swimming, obvoid colony containing (4>8-16-

(32) globose or pyriform cel ls embedded in a common gelatinous mucilage. Cells arranged in a hollow sphere within the envelope. The ce l l s may be pressing close together giving the colony a hexagonal facetted appearance. Two flagella directed outwards from the colony and widely divergent after emerging from the colonial mucilage. (Flagella of pyriform ce l l s emerge from the broad anterior end). Cells have a parietal cup shaped chloroplast, one-several pyrenoids, a red eyespot placed anteriorly and laterally (they may be the same for all s ides of the colony, or different between the two poles). The colony swims in a rolling or tumbling fashion.

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EUDORINA Colonial, free swimming ovate, obvoid or globose colony con­

taining 16-32-64 cel ls enclosed in a common gelatinous mucilage. Cells arranged in a hollow sphere at some distance from one another. Some­times protoplasmic connections between ce l l s may be seen. Frequently the ce l l s are in distinct transverse series. Two very long flagella (2x to 4x the diameter of the cell) diverging widely after emerging from the colonial mucilage. The ce l l s have a parietal cup shaped chloroplast with one-several pyrenoids, one red eyespot anterior and lateral, two contractile vacuoles at the bases of the flagella.

Asexual reproduction by means of auto colonies, each develop­ing into a plakea. All ce l ls in the colony usually produce daughter colonies.

The colony swims in a rolling or tumbling fashion.

VEGETATIVE EUDORINA

^° ° o © j ;

PLEODORINA Colonial, free swimming globose colony containing 32-128

spherical or ovoid ce l l s arranged in a hollow sphere at the periphery of a common gelatinous mucilage . The ce l l s are of two sorts; vegetative and reproductive. The vegetative cel ls are large and are at the posterior pole. The reproductive ce l ls are half the s ize of the vegetative ones, and are at the anterior pole. This cell differentiation is only seen in mature colonies. The ce l l s have a parietal cup shaped chloroplast with one-several basal pyrenoids, an eyespot anteriorly and laterally, two flagella, and two contractile vacuoles at the base of the flagella. Reproductive ce l l s often loose their flagella and eyespot and have a massive chloroplast with several pyrenoids. The colony swims in a rolling or tumbling fashion.

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VOLVOX Colonial, free swimming spherical or ovate colony of 500-50,000

cells arranged in a hollow sphere at the periphery of a common gelatinous mucilage. Protoplasmic connections between ce l l s in the colony are frequently seen. The ce l l s are ovoid having a parietal incomplete shaped chloroplast, cup shaped and laminate, towards the posterior of the cell , containing, one pyrenoid, one anteriorly located eyespot, and two flagella with two contractile vacuoles at their bases, and 2-5 contractile vacuoles irregularly distributed at the anterior end.

Asexual reproduction gives daughter colonies inside the parent sphere, formed by special gonidial ce l l s which withdraw to the inside of the sphere from the peripheral layer of ce l l s in the posterior half of the colony. These gonidial ce l ls are ten times the s ize of the vegetative ce l l s , and lack eyespots and flagella. They start as a single cell in a wart of mucilage later dividing in plankeal sequence to give a daughter colony.

J» \ • • • • • • • . V ,

VOLVOX ! > • • • • • • • • a „

SELENASTRUM

SELENASTRUM Colonial. Arcuate — lunate or sickle shaped cel ls with

acute pointed apices. They lie in groups of 4, 8, or 16 cel ls with their convex faces opposed. There is no gelatinous mucilage envelope. Several groups may appear to form a colony of 100 or more ce l l s . The ce l l s have one parietal chloroplast lying along the convex wall in young ce l l s , but completely filling the old ce l l s . There is one pyrenoid.

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ANKISTRODESMUS Cells acicular-crescent shaped-fusiform (spindle)

shaped, tapering to a point at both ends. They can be solitary, twisted about one another, or in loose aggregates. No gelatinous envelope. The chloroplast i s a thin parietal plate with or without one pyrenoid, which covers most of the cel l wall.

PEDIASTRUM Colonial (coenobium). Free floating, circular monostromatic

disc of 2-128 polygonal c e l l s . The plate may be entire or perforate. If the colony has 16 or more cel ls there i s a tendancy for them to be in concentric rings. The peripheral ce l l s of the disc may have one or two lobes or processes, or may be just emarginate with no processes. The interior ce l l s of the disc may be the same shape as the peripheral ones, or different. The chloroplast i s a parietal disc in young ce l l s , but in old cel ls it i s a diffuse reticulum. One pyrenoid. Unci-multinucleate.

ANKISTRODESMUS

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SCENEDESMUS Colonial (coenobium). The colony i s a flat plate of

2-4-(8-l6-32) ovoid, fusiform, crescent shaped, or oblong ce l l s arranged in a single, alternating or double series, with their long axes parallel to one another. The cel l wall can be smooth, or have spines, teeth, or ridges (spicate, granulate, corrugated). The chloroplast is a parietal longitudinal plate in young ce l l s and fills the entire cel l cavity in old c e l l s . Uninucleate.

ACTINASTRUM Colonial (coenobium). The colony consists of (4)-8-(16)

elongate ce l ls radiating from a common centre (not contained in a mucilaginous envelope). The cel ls are cylindrical, fusiform, or etaniform (truncate), with blunt or pointed ends, 4-8 times as long as they are wide. The chloroplast i s a parietal longitudinal strip, encircling approximately one third of the cel l . One pyrenoid.

SCENEDESMUS

ACTINASTRUM

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ULOTHRIX Unbranched filaments of indefinite length, often with basal

differentiation of a special holdfast cell . Some spec ies become free floating. The ce l l s are cylindrical, and contain a single parietal chloro­plast which i s scroll shaped and covers about two thirds of the way round the cel l . It extends to either the full length, or part of the full length of the cell . All ce l l s of the filament are capable of division and of forming zoospores or gametes.

ULOTHRIX

MICROSPORA

MICROSPORA Unbranched, unattached filaments. May be s e s s i l e when

young but usually free floating. The ce l l s are cylindrical and the walls are of two pieces each half being tumbler shaped (H shaped in cross section), which overlap in the mid region of the cel l . This junction breaks very easily, and empty halves of the cell and H fragments can be seen. The chloroplast i s either a dense irregularly padded parietal plate or net, or an open network (rosenkranz) form of reticulum. Uninucleate. No pyrenoids.

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OEDOGONTIUM Unbranched filaments of cylindrical ce l l s , attached by a

holdfast cell to the substratum, or free floating. The ce l l s have trans­versely striate distal ends (1-6 scar usually) resulting from cel l division Cells are sometimes slightly enlarged at their distal ends. Chloroplast reticulate, parietal, with many pyrenoids. Uninucleate.

OEDOGONIUM

SPIROGYRA SPECIES

SPIROGYRA Long unbranched filaments. Unattached and free floating.

Cells are cylindrical and may be as broad as they are long. Sometimes rhizoidal branches can develop laterally where the filament comes into contact with the substrate. The middle lamella in some species may be expanded into an H piece like Tribonema and Microspores. The chloroplast i s a parietal ribbon or ribbons (1-16) which are usually twisted spirally Vz - 3 turns in the cel l (rarely eight). The pyrenoids are numerous and are arranged in a linear series at equal distances along the ribbon, giving a periodically bulbous appearance to the chloroplast. Uninucleate.

2 7

MOUGEOTIA Unbranched filaments, floating and ephyphytic (with haptera).

(Outgrowths from the filament are much rarer than in Spirogyra). Cells are cylindrical and usually at least four times as long as they are wide. Most species have ce l l s with at least a single axial chloroplast (but a few species may have two) connected by a cytoplasmic bridge). The chloro­plast may be twisted in the mid region, but cells like this are only found between two groups of ce l l s having chloroplasts of differing orientation. Pyrenoids may be arranged in a single axial row, or scattered over the surface. Uninucleate.

r

MOUGEOTIA

mc

COSMOCLADIUM COSMOCLADIUM

Cells are connected to one another by bands of gelatinous material to give a rounded colony enclosed in a gelatinous envelope. The cel ls are Cosmarium like, showing an indented mid region in one plane, but none 90 degrees further around. The origins of the gelatinous strands are confined to minute pores situated on either side on the midconstriction, and are restricted to one face of the cell . There i s only one chloroplast, and it is axial with four parietal lobes. There is a single central pyrenoid.

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COSMARIUM Unicellular. Small compressed ce l l s with length only slightly

greater than breadth, and a deep median constriction to give two semicel ls . The cell wall may be ornamented with minute granules of verrucae. Each semicell contains a single axile chloroplast with four radiating plates. The pyrenoids are localised in the axial portion.

COSMARIUM

CLOSTERIUM

CLOSTERIUM Unicellular. Lunate or arcuate elongate ce l l s , markedly

attenuated at the poles. Many species have cel l walls with longitudinal striae. (Not medianly constricted). The limits of a median girdle (from division) can sometimes be seen as transverse striae. There is a chloro­plast in each semicell . The chloroplast i s either entire, or with longitud­inal ridges radiating from a slender central axis . The pyrenoids are arranged in longitudinal axial series. At each pole there is a hyaline cytoplasmic region containing a conspicuous vacuole. The ce l l s are sometimes brownish in colour due to Fe compounds.

2 9

SPHAEROZOSMA Cells are permanently united in unbranched filaments.

Each semicell has a short apical process which i s interlocked with a similar process from another semicell] thus joining the cel ls into a filament. The ce l l s are small and compressed and moderately medianly constricted to give a sinus between two semicells . The cel l walls may be ornamented in a pattern of granules. Each semicell contains a single axial laminate chloroplast with one pyrenoid.

apsi sc ch SPHAEROZOSMA

ONCHYNEMA Cells are permanently united into unbranched filaments.

Each semicell has two long apical processes which overlap the cell next to it thus joining the ce l l s into a filament. The ce l l s are small, strongly compressed, and deeply medianly constricted. The semicel ls may be drawn into a spine, seen in front view. Each semicell contains a single axial laminate chloroplast with one pyrenoid.

3 0

HYALOTHECA Cells are permanently united into unbranched filaments.

There are no apical processes but the poles are flattened, one cell abutting on another. The median constriction is extremely slight. The ce l l s are cylindrical and discoidal. There is no ornamentation except for delicate transverse ridges just below the cell apices. The chloroplasts are axial, and have several longitudinal lobes extending to the cell walls . One pyrenoid situated in the centre of the chloroplast. Mature ce l l s have the chloroplast divided, each half for each semicell. But young cel ls have only one chloroplast for some time.

STAURASTRUM SPECIES

STAURASTRUM Unicellular. Radially symmetrical and usually triangular

in end view but some species may be strongly compressed and bilaterally symmetrical. The range of forms i s enormous. They all have a deep acute median constriction. The cell wall may be ornamented with granules, gesticulations, simple to emarginate verrucae, or spines . .The semicells contain a single axial chloroplast with a well defined lobe to each angle of the semicell . Pyrenoids may be in all lobes, or one in the axis. The genus i s the commonest of all desmids in fresh water plankton.

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TRD3ONEMA Filaments of cylindrical or barrel shaped cells, 2-5 times as

long as they are broad. Characteristically the cell walls are composed of two tumbler shaped (H shaped in cross section) pieces the nature of which can be seen at the ends of broken filaments. The two pieces overlap, and separate when the filament is broken, to leave an empty tumbler (or half H piece).

The chloroplast is composed of a few - many disc shaped chromatophores. No pyrenoids (oil or leucosin granules instead of starch), uninucleate.

Forms a yellow grey cloud of entangled threads usually in quiet waters.

TRIBONEMA

NAVICULA

NAVICULA The frustule (two overlapping halves of the cell wall) is

symmetrical in all three planes. The valves are elongate and are drawn out at either end to two round apices. The raphe, (vertical cleft in the valve) lies in a narrow axial field expanded laterally in the polar or central nodule regions, or not at all. A girdle view of the frustules shows a rectangular shape with no intercalary bands.

There are 2-(4,-8) laminate chromatophores lying on opposite sides of the girdle (sometimes overlapping).

Navicula is usually solitary or free floating.

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ASTERIONELLA The frustules are linear in valve view and both ends are

expanded. Usually six frustules are joined together to form a stellate shaped colony in one plane by means of mucilage at an inflated end. The valves are faintly transversely striated with an indistinct pseudoraphe (longitudinal clear space) through the sagittal axis.

There are two chromatophores lying on opposite sides of the girdle, (axially).

ASTERIONELLA

TABELLARIA

TABELLARIA The linear frustules (in valve view) are united into free

floating zig-zag chains at their corners by mucilage. Between the girdles there are numerous intercalary bands, and inside the cell wall there are longitudinal septa parallel to the intercalary bands, which reach almost to the centre of the cell. The cell may be inflated slightly in the median and polar regions. The cells have a faint, narrow, pseudoraphe slightly broader in the middle and at the ends. The cell has many very small discoid chromatophores.

In plankton the cells of Tabellaria may be united in a manner similar to Asterionella.

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MELOSIRA Filaments of Melosira are cylindrical, with cells longer than

they are wide. Gelatinous cushions on each end of the valve pairs join the cells together . The two valves are circular in vertical view, and the ornamentation is concentric in the two parts. Species without a suculus (shallow annular structure) have the girdle ornamented, but if a suculus is present then the portion below it is smooth.

There are numerous discoid chromatophores. This is one of the most common of the Centrales, and may not

be thought of as a diatom because the valve view does not appear often under the microscope.

MELOSIRA

gc sc

DINOBRYON Free swimming or attached. The cells are contained in vase

like loricas, which are usually colonial, but may be solitary. The cellulose-silica lorica has a pointed base and an apex that opens out. The cell contained in the lorica is spindle-shaped and attached to the bottom of the lorica by a short cytoplasmic stalk, and has two flagella of unequal length which project out of the open end. The chromatophores are one or two in number, parietal and laminate (plate like), and yellow-brown in colour. There are two anterior contractile vacuoles, one pigment spot, and a basal granule of leucosin (food reserve).

The species pictured is D. sertularia, (flaring wide mouth).

3 4

MICROCYSTIS (POLYCYSTIC) Free floating colony of many spherical ce l l s . The ce l l s

are irregularly arranged in a mucilage to give a spherical, ovoid, or irregularly shaped colony. The ce l l s have pale - bright blue green con­tents which may appear to be purple-black due to numerous large pseudovacuoles.

MICROCYSTIS

COELOSPHAERIUM

COELOSPHAERIUM Free floating colony. The ce l l s are spherical or

sub — pyriform, and are arranged at the periphery of a colonial mucilage which is homogenous or with radiating fibrils. The colony may be spherical, ovate, or irregularly shaped. The cell contents are pale-bright-blue-green, either homogenous, or with numerous refractive pseudovacuoles.

3 5

NOSTOC The irregularly shaped colony i s composed of contorted trichomes

which are uniserriate unbranched threads of globose, bead-like, barrel-shaped, or cylindrical shaped ce l l s . The trichomes are enclosed in a firm mucilaginous sheath which may be obvious, or confluent with the colonial mucilage. The heterocysts (reproductive bodies) are intercalary, generally solitary in the trichome and of approximately the same s i ze and shape as the vegetative ce l l s .

The colonial mass retains its shape when removed from the water.

ANABAENA The colony i s an amorphous mass of tangled spiral or straight

trichomes composed of globose, barrel-shaped threads of cylindrical shaped cel ls . The trichomes may or may not have a watery sheath. The trichomes are enclosed in a delicate hyaline mucilaginous colonial mucilage.

The heterocysts are intercalary, generally solitary, and may be the same shape as the vegetative cell , or slightly larger. Akinetes (gonidia) are round, ovate, or cylindrical, either adjacent to or remote from the heterocysts. The colonial mass has no definite shape, and does not retain its shape when removed from the water.

3 6

Differences between Nostoc and Anabaena. — The colony of Nostoc is of definite shape although irregular, but Anabaena has no definite shape. Even when lifted out of the water Nostoc retains its shape when Anabaena does not. The trichomes of Nostoc are spiral or straight, but never con­torted. The trichomes of Anavaena are always much contorted (bent back upon themselves). Nostoc has a hyaline colonial and sheath mucilage which is very difficult to distinguish except with special methods, whereas Anabaena has very distinctive trichome sheaths and colonial mucilage.

Millener, L.H.,et al 1965 A Classification of Plants. Auckland University, N.Z.

REFERENCES

Hustedt, F. 1962 Die Kieselalgen. Weinheim Verlag. Von J. Cramer, New York. Johnson Reprint Corporation.

Prescott, G.W. 1961 Algae of the Western Great Lakes Area. Cranbrook Institute of Science. Bull. 30.

Smith, G . 1950 Fresh-water Algae of the United States. 2nd Ed. McGraw Hill.