Four New Species of Choanoflagellates from Arctic Canada

Four New Species of Choanoflagellates from Arctic CanadaAuthor(s): Irene Manton, Joan Sutherland and B. S. C. LeadbeaterSource: Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 189, No.1094 (Apr. 29, 1975), pp. 15-27Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/76957 .

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Proc. R. Soc. Lond. B. 189, 15-27 (1975)

Printed in Great Britain

Four new species of choanoflagellates from Arctic Canada

By IRENE MANTON, F.R.S.

University of Leeds, England

JOAN SUTHERLAND

Department of Biology, Carleton University, Ottawa, Canada

AND B. S. C. LEADBEATER

Department of Botany, University of Birmingham, England

(Received 24 July 1974)

[Plates 1-6]

By means of electron microscopy applied to wild material prepared as dry whole mounts, descriptions are given of external morphology, including lorica construction, of four new species of collared flagellates, namely: Pleurasiga caudata, Salpingoeca longicaudata, Parvicorbicula serrulata and Diaphanoeca aperta. Reasons are given for the choice of generic names although future changes in some generic boundaries are expected. Aspects of the ecology and geographical distributions are discussed in a preliminary way.

INTRODUCTION

This paper contains the first results to be published from three journeys carried out in the summers of 1972 and 1973 for the purpose of collecting Arctic nanoplankton in a form suitable for subsequent electron microscopical study. In each of the areas visited the nanoplankton contained an assemblage of coloured and colourless forms, the latter dominated by collared flagellates, which become extremely conspicuous when treated in this way. The relative opacity to electrons conferred by the high silica content of the costaet, forming the basket-like lorica, is a major factor in facilitating observation of these organisms; for further information on chemistry see Thomsen (I973) and Leadbeater & Manton (I974).

Though none of the four new species to be described was specially abundant, they were all encountered in more than one water sample and two were recorded in more than one locality. Since the nanoplankton as a whole varied from sparse (West Greenland) or very sparse (Hudson Bay) to relatively abundant (Resolute Bay) our present findings must be regarded as qualitatively significant though much fuller information will be needed regarding the overall geographical and

t The terminology to be used follows Leadbeater 197:za. A costa is a rib-like component of a lorica and is itself composed of linearly attached sub-units known as costal strips.

[ 15 ]



16 Irene Manton, Joan Sutherland and B. S. C. Leadbeater

seasonal incidence of the various taxa before any quantitative assessments will be possible.

A division of labour among the three authors should perhaps be noted at the outset. The senior author (I. M.) has been responsible for all the electron microscopy and for some of the collecting in all three areas. The junior author (J. S.) took a major share in collecting and in several ancillarv processes but has been too far away geographically during compilation of the paper itself to be held responsible for the interpretations given. Finally the third author (B. S. C. L.) has contributed the identifications of all the collared flagellates, including the four new ones, and his name should therefore be used in the subsequent citation of any of the new species as Leadbeater in Manton et al. (1975, the present communication).

It should further be noted that Latin has on this occasion been omitted on the ground that we now regard these organisms as animals (see, for example, Lead- beater I972a; Leadbeater & Manton 1974) to which the zoological rules of nomenclature apply.

MATERIALS AND METHODS

The material came from many freshly gathered water samples brought directly from the sea to a shore base and processed there for subsequent electron microscopy in Canada or England. The three geographical areas were: West Greenland at the Danish Arctic Station at Godhavn, Disko Island (lat. 69? 30' N; long. 530 30' W) visited in late June -early July 1972, Hudson Bay at Churchill (lat. 58? 44' N; long. 94? 00'W) visited in late July 1973, and Resolute Bay on Corn- wallis Island (lat. 740 40' N; long. 95? 00' W) visited in late August 1973.

Water samples were taken at various depths ranging from the surface to 5, 10 or 20 m. After being brought ashore and left to stand under cool conditions for a short time, or overnight, each sample was poured through a fine nylon mesh (usually 25 Vm pore size) to remove detritus and the larger phyto- and zooplankton. The remaining contents were then concentrated either centrifugally or with the aid of a filter. By working in units of 2-41 a residue sufficient for making dried whole mounts or for embedding was usually obtained and in either of these conditions the material is suitable for long distance transport.

Whole mounts were made both on glass slides and on prepared carriers brought ready made with carbon-on-formvar support film. Drops from the concentrate were either put onto the appropriate surface and the contents killed by exposure for 30 s to the vapour from 2 % osmium tetroxide, or the whole concentrate was squirted into ice cold 2 % osmium tetroxide made up in cacodylate buffer at pH 7. Drops from the fixed material could then be used for drying down or the osmic fixative could be removed after centrifugation and replaced by the cacodylate buffer from which preparations could also be made. Once dried, all such preparations must be thoroughly but gently washed in distilled or de-ionized water, a process which must not be hurried and should take up to 15 min or more to carry out, after which a final drying leaves them clean enough for immediate



Four new specie8 of choanoflagellates 17

shadoweasting on return to England. The preparations can then be examined in an electron microscope; details of those used will be found in the legends and in the acknowledgements below.

For the field work in 1972 we are extremely grateful to the University of Copenhagen for their powerful backing, not only in permitting use of the Danish Arctic Station at Godhavn, Disko Island, West Greenland, but also in sending supplementary equipment from Denmark for our use. The staff of the Arctic Station, especially Peter Milan Petersen and Harry Christensen and family, together with the ship's crew of Porsild, also contributed essentially to the success of the visit. In 1973 we are similarly grateful to Carleton University, Ottawa, for lending equipment to accompany us to Churchill, Hudson Bay, and to the University of Toronto for permitting access to their I.B.P. base at Resolute Bay, Cornwallis Island, and especially to the camp manager, Dr Cornelius Anema who, though single handed, gave us invaluable help in the management of small boats and in many other ways.

The electron microscopy has involved a Siemens Elmiskop IA at Carleton University, Ottawa, an A.E.I. Corinth microscope at the University of Notting- ham, England, an A.E.I. 801 microscope at the University of Lancaster and two A.E.I. EM6B electron microscopes, respectively at the University of Nottingham and at Imperial College, London.

We are indebted for personal help in preparing coated grids and in shadowing finished preparations to K. Oates (formerly of Leeds and now of Lancaster) and to Roger Britton (formerly of Leeds and now of Ottawa).

Finally we are indebted financially to the Royal Society for a travel grant in 1973, to Carleton University for a contribution towards the cost of the visit to Churchill and to the Science Research Council for a continuing grant to the senior author which defrayed travelling expenses in Greenland in 1972 and the cost of working out the results.

To all these persons and institutions we offer our best thanks.

OBSERVATIONS

Pleurasiga caudata sp.nov.: figures 1-7 on plate 1

Lorica tulip-shaped with a slender 'tail', composed throughout of slender rod- shaped costal strips, each slightly curved and mutually joined by their overlapping ends except at the anterior edge of the lorica basket where the attachment of the longitudinal costae to the transverse costal strips is median (= T joins). Dimen- sions of the lorica basket: 17-20 vm long x 8-13 ,m wide with the tail up to 13 Pm long. Tail composed of several (sometimes 3) longitudinal strips. Lorica composed of 6 longitudinal costae, each with 4 component strips, and with a few additional costae, each of a single strip limited to the hind end. Transverse costae 3, located respectively at the levels of the distal ends of the first, second and fourth costal

2 Vol. I89. B.




strips (counting forwards from the posterior end of the basket). Components of the anterior transverse costa each with a central, flattened, dilation acting as a facet for attachment of the tip of the corresponding longitudinal costa. Similar facets on the middle transverse costa unoccupied. On the posterior transverse costa, facets imperfect or absent but one sometimes present, unoccupied. Protoplast ovoid, located near the hind end of the lorica basket; dimensions when dry: 4 zm long x 2 vm wide, with a single flagellum 12-14 ,tm long surrounded by a sparse ring of tentacles apparently not more than 10-15 in number and up to 7 ,um long.

Type specimen: figure 1. Type locality: Button Bay near Churchill, Hudson Bay (lat. 58? 44' N; long. 940 22' W), in July 1973.

This species is placed in the genus Pleurasiga Schiller mainly because of the very close resemblance to P. sphyrelata Thomsen (I973). There is also a general though less close resemblance to the type species of Pleurasiga (P. orculaeformis Schiller) recently examined electron microscopically by Leadbeater (I973), who also discusses various problems involved in the use of this generic name. Compared with P. sphyrelata, P. caudata possesses a conspicuous 'tail' (figure 1), has fewer longitudinal costae (figures 1-3), the facets on the transverse costae are rounded instead of square (figures 4-7), and the tips of the longitudinal costae do not project.

Several specimens were obtained in two gatherings made at about midday on 24 July 1973 in Button Bay (Hudson Bay), one (sample VII) near the shore at a depth of 2 m on the bottom among stones and Fucoids and at a local temperature of 12 'C and the other (sample IX) about 100 m further out to sea, at a depth of 5 m and at the prevailing open-water temperature of 2 'C.

Salpingoeca longicaudata sp.nov.: figur-es 8-14 on plate 2

Lorica consisting of a single chamber, 15-17 pm long x 6-8 pm wide, composed of 5 (sometimes locally 4 or 6) longitudinal costae, each of 2 linearly attached slender cylindrical costal strips overlapping where they join; delimited anteriorly by 2 transverse costae, one terminal and the other parallel to it at about one sixth

DESCRIPTION OF PLATE 1

Pleurasiga caudata from Button Bay (Hudson Bay) FIGURE 1. A complete cell, micrograph Y 7080 (Siemens, Ottawa) (magn. x 3000).

FIGURE 2. Anterior end of a lorica showing the flagellum and the tips of a few tentacles Y 7753.7 (Corinth, Nottingham) (magn. x 4000).

FIGuRE 3. An empty lorica, otherwise complete; for details see figures 4-7. Micrograph Y 7060 (Siemens, Ottawa) (magn. x 6000).

FIGUREs 4 AND 5. Parts of the lorica of figure 3 (magn. x 15000). FIGURES 6 AND 7. Parts of the two transverse costae in figure 3 showing the expanded facets

more clearly (magn. x 20 000).



Jlanton et al. Proc. R. Soc. Lond. B, volume 189, plate 1

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Four new species of choanoftagellates 19

of the length of the chamber behind it; transverse costal strips of both rings joined by their ends to the subtending longitudinal costae; at the posterior end, the longitudinal costae converging to subtend a caudal appendage of exceptional length (up to 100 pm) composed of up to 13 linearly attached costal strips overlapping at their ends and becoming thinner distally. The protoplast enclosed by a conical membrane within the lorica chamber, attached to its base and equalling it in length, width when full 3-5 ,tm; the single flagellum exceeding 20 ,tm in length, surrounded by a ring of about 40 tentacles up to 6 pm in length, sometimes with terminal swellings.

Type specimen: figure 14. Type locality: Godhavn, Disko Island, West Green- land (lat. 69? 30' N; long. 530 30' W), surface water near the harbour, temperature 3.5 ?C on 26 June 1972. Also found at Kronprinzens Ejland (at 10 m depth), Fortuna Bay (surface), Skansen (surface 1 km off shore), Hvitfisk0je (10 m depth), 'Bird Cliffs' (20 m depth) and other places near Godhavn, all at the prevailing water temperature of ca. 4 ?C between 23 June and 4 July, 1972. Also found, on 17 and 18 August 1973, in 3 out of 10 samples taken at Resolute Bay, Cornwallis Island and representing depths of 5 m and 10 m at a prevailing water temperature of ca. -1 'C.

The generic name Salpingoeca Gr0ntved has been chosen because of the resemblance of the lorica chamber, in form and structure, to that of the type species, S. natans Gr0ntved, also present in arctic waters (Bursa i96i; Manton, unpublished) and described electron microscopically from Denmark byLeadbeater (I972 b) and Thomsen (I973). S. longicaudata differs from all other known species of the genus by its exceptionally long, jointed, 'tail' and by the absence of the pro- nouncedspinespresent at the anterior end inS. natans, S. spinifera Throndsen (1970) and S. cruciformis Leadbeater (I974a). Though apparently absent from Europe,


Salpingoeca longicaudata from Resolute Bay (except figure 14); all micrographs taken with the A.E.I. 801 electron microscope in the Department of Biology, University of Lancaster.

FIGuRE 8. Empty lorica showing almost the whole length of the tail; micrographs Y 7599.16 and 19 (magn. x 2000).

FIGURE 9. Part of the tail in figure 8 more highly magnified to show details of the two ends of costal strips in this region; micrograph Y 7599.18 (magn. x ca. 10000).

FIGURES 10 AND 1 1. Details of the lorica in figure 8 more highly magnified to show the shapes and manner of attachment of costal strips in the various regions; micrograph Y 7599.17 (magn. x 10000).

FIGuRE 12. An empty lorica still containing traces of the conical skin normally surrounding the protoplast; micrograph Y 7598.4 (magn. x 4000).

FIGURE 13. Lorica containing its protoplast with tentacles and flagellum anteriorly and with traces of the subtending membrane posteriorly; micrograph Y 7599.15 (magn. x 4000).

FIGURE 14. Lorica complete with protoplast and tentacles and with most of the flagellum exposed, from Godhavn, West Greenland; micrograph Y 4401.41 (magn. x 3000).




S. longicaudata may have been seen bv Bursa (I96I) at Igloolik, on the coastal shelf of Foxe Bay (southwest of Baffinland at lat. 690 20.5' N, long. 82? 43.5' W) since he includes at least two drawings (Bursa I96I, fig. 17E and F) among the range of forms attributed to S. natans with the light microscope, which might instead refer to our present species.

This species shows with unexpected clarity the extent to which the ultimate position of individual costal strips must be predetermined, since, in spite of superficial uniformity, subtle differences of shape are characteristic of the various regions. Thus while all costal strips are slender rods, those of the transverse costae are adjusted to their position on the circumference of a circle by being curved (figures 8-14). The longitudinal costae are locally differentiated in other ways. Thus the distal tips of the five longitudinal costae of the lorica chamber are delicately but sharply apiculate (figures 11, 12) where they project beyond the anterior transverse costa. The costal strips of the tail, on the other hand have two sharp points of dissimilar length separated by a slight depression at one end but are smoothly tapered at the other (figure 9), the latter being consistently directed towards the subtending lorica; in addition there are marked differences of width exhibited by the different segments of the tail, the uppermost one being substantially thicker than any other (figure 10) while the terminal segments at the distal end are much thinner (figure 8). In some regions of the lorica the number of component strips is more precisely controlled than in others. Thus while 5 longitudinal costae, each composed of two linearly attached segments, seems at first sight to be invariable, this fixity in fact depends on the accurate numerical control of the anterior terminal segments. Elsewhere, supernumerary costal strips, if formed, can be accommodated without difficulty by doubling others, such doubled segments being not uncommon in parts of the transverse costae (figure 11) and at the base of the lorica chamber (figures 11, 13, 14) in longitudinal ones. Com- parable adjustment to deficiencies can also sometimes lead to the five longitudinal


Parvicorbicula serrulata from Resolute Bay; all taken with the Siemens Elmiskop IA in the Department of Biology, Carleton University, Ottawa, unless otherwise stated.

FIGURE 15. A complete specimen; micrograph Y 7441 (magn. x 3000). FIGURE 16. A relatively undamaged empty lorica; mnicrograph Y 7450 (magn. x 5000). FIGURE 17. A protoplast in a slightly damaged lorica showing the flagellum and tentacles;

micrograph Y 7360 (magn. x 4000). FIGURE 18. Hind end of a broken lorica showing numerous costal strips converging to a

point, in contrast to the low number (7 or 8) of longitudinal costae at the anterior end of the lorica (figures 15-17); micrograph Y 7710.5 (A.E.I. 801 at Cambridge Culture Centre) (magn. x 5000).

FIGURE 19. A complete cell showing the flagellum clearly but not the tentacles; further details of the lorica in figures 21 and 22; micrograph Y 7749.2 (Corinth microscope, Nottingham) (magn. x 3000).



Manton et al. Proc. R. Soc. Lond. B, volumne 189, plate 3

17~~~~~~~~~t

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FIGURES 15-19. For descriptionis see opposite.

(Facing p. 20)



Mlantont et al. Proc. R. Soc. Lond. B, volume 189, plate 4

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Four new species of choanoftagellates 21

costae in the lorica wall being subtended by only four costal strips at the base; hence the local numerical variation mentioned in brackets in the formal description above.

Parvicorbicula serrulata sp.nov.: figures 15-24 on plates 3 and 4

Lorica basket-like with a 'tail' as long or longer than the basket, both composed of strongly flattened costal strips with fine serrations along their edges. Dimensions of the basket: 12-16 ,um long x 10-14 ,m wide, the tail up to 16 ,m long. Longi- tudinal costae in the basket 7 or 8, each of 3 linearly attached component strips, sometimes supplemented by additional strips (up to 10 in all) limited to the hind end and all converging to a point posteriorly; the tail composed of 3-S (often 4) linearly attached strips joined to the base of the basket by a tuft of 2 or 3 parallel strips. Transverse costae 2, respectively located at the levels of the second and third components of the longitudinal costae (counting up from the base), transverse costal strips mutually joined by their ends but attached laterally to the longitudinal costae and forming T joins with these at the anterior margin of the lorica. Protoplast located in the posterior end of the lorica basket within a delicate translucent conical membrane, ovoid ca. 6 ,m long x 3 ,um wide, with a single flagellum up to 16 tm long and a ring of 25-30 tentacles, each up to 5 Lm long.

Type specimen: figure 19. Type locality: Resolute Bay, Cornwallis Island (lat. 743 40' N; long. 950 00' W) found in 5 out of 11 samples taken at depths of 5 and 10 m and at a prevailing water temperature of ca. -1 0C on 17, 18 and 22 August 1973. Fragments also recorded on two occasions at Button Bay, near Churchill, Hudson Bay.

The generic name Parvicorbicula has been provisionally adopted for this very distinctive species because it is already in use for three other taxa with flattened costal strips and a basket shaped lorica, namely P. infundibuliformis Leadbeater


Parvicorbicula serrulata from Resolute Bay (except figure 20); microscopes as stated. FIGURE 20. Anterior rim of an empty lorica from Button Bay near Churchill (Hudson Bay,

sample VII); micrograph Y 7154 (Siemens Ottawa) (magn. x 10000). FIGURE 21. Tail of the specimen in figure 19 showing shapes and manner of attachment of

the four component costal strips; micrograph Y 7749. 7 (Corinth microscope, Nottingham) (magn. x 10000).

FIGURE 22. Part of the base of the lorica from the specimen in figure 19 showing the mode of attachment of the tail and some of the longitudinal strips of the lorica itself; micrograph Y 7749.6 (Corinth microscope, Nottingham) (magn. x 10000).

FIGURE 23. Part of the anterior edge of a broken lorica showing T joins and the shapes of individual costal strips, both longitudinal and transverse; micrograph Y 7305 (Siemens, Ottawa) (magn. x 10000).

FIGuRE 24. Longitudinal costal strips near the base of a broken lorica showing their mode of attachment; micrograph Y 7600.25 anterior edge of conical membrane formerly enveloping protoplast also visible (arrows) (A.E.I. 801 microscope, Lancaster) (magn. x 10000).




and P. campaniformis Leadbeater (I 973), the latter described from the Adriatic Sea and subsequently encountered in South Africa (Manton, unpublished), and P.

pulchella Leadbeater (I974a) so far only known from the Bay of Algiers. Apart from the flattened costae and cognate details, the general morphology of the lorica in all these taxa is not unlike that usual in the more ordinary species of Parvi- corbicula such as P. socialis which is also abundant in arctic waters, especially at Resolute. Continued use of the generic name Parvicorbicula for our present species must nevertheless not be interpreted as excluding an eventual reconsidera- tion of generic boundaries involving these taxa.

As in Saljpingoeca longicaudata, the finer details differentiating costal strips in various parts of the lorica and tail of P. serrulata indicate a high degree of pre- determination regarding their ultimate positions. Thus the component strips of transverse costae tend to be tapered to a blunt point at each end (figures 20, 23, etc.) whereas those of the longitudinal costae are truncate or rounded at one end and pulled out into a smooth conical point at the other (figures 18, 22, 24, etc.). The orientation with respect to this tapered point is moreover consistently such that it is directed towards the base of the lorica no matter whether the strip in question forms part of the tail (figure 21) or part of the basket (figure 22, etc.). The mechanism responsible for this precise arrangement and orientation is unknown.

Diaphanoeca aperta sp.nov.: figures 25-32 on plates 5 and 6

Lorica barrel-shaped, open at both ends, with a long fringe of slender projecting costae round each opening. Overall length 45-50 um, width at the anterior end 17-25 ,m, at the posterior end 25-35 ,m. Number of longitudinal costae 12, each composed of 9 or 10 costal strips with overlapping ends and with two, firmly constructed, transverse costae located respectively at a distance of 2 costal strips from the anterior end of the lorica and 3 or 4 costal strips from the posterior end. Transverse costal strips L-shaped, tapered at one end and sharply upturned at the other, those from the anterior ring thicker than those from the posterior ring but both thicker than the longitudinal costae; all upturned tips in both transverse costae directed towards the anterior end of the lorica and each individually attached to the corresponding longitudinal costa. Protoplast located centrally, ca. 8 ,um long x 5 ,um wide, with a flagellum ca. 40 tm long and a ring of about 50 tentacles, each up to 8 Vm long.

Type specimen: figure 27. Type locality: Resolute Bay, Cornwallis Island (lat. 740 40' N, long. 95? 00' W), encountered in 6 out of 11 water samples representing depths of 5, 10 and 20 m, at a prevailing temperature of ca. -1 0C on 18, 20, 22 and 28 August 1973.

The genus Diaphanoeca Ellis at present contains four species including this one, all with relatively large loricas built up from slender costal strips and with a

conspicuous fringe of projecting longitudinal costae at the anterior end. There are two other genera with anteriorly projecting costae, namely Acanthoeca Ellis and

Acanthoecopsis Norris. The first is clearly differentiated by the pronounced spiral



Manton et al. Prcc. R. Soc. Lond. B, volume 189, plate 5

...411 S | Z S I _ a . ..wS^.X:. |..

25 ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~2

(.m agn. g R W x 2000). . .......

(mgn -: 2000) 2

FIGULRE 26. Part of an intact lorica with the contained protoplast showing tentacles and two bundles of supernumerary costal strips; mnicrograph Y 7718. 14 (801 mnicroscope, Cambridge) (mnagni. x 3000).

FiGURE 27i. The greater part, of an initact lorica with contained protoplast, shiowinig thle

flagellum and tentacles; micrographs Y 7736. 18 and 20, jolined (EMT6B, Nottingham) (nagn. x 3000).

V~~~~~~~~~~~~~~~~~~~~~~~~Fcn p. 22);



Manton et al. Proc. R. Soc. Lond. B, volurne 189, plate 6

28 _> 29t tr . .~~~~~~~~~~~~~~~~~77..

F:XS~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:

-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~n Y4 3

FiGUREs 28-32. For descriptions see opposite.



Four new species of choanoflagellates 23

deflexion of the costae with respect to the long axis of the lorica (for electron microscopy of A. spectabilis Ellis and A. brevipoda Ellis see Leadbeater (1972 a, b), Thomsen (I973), Leadbeater & Morton (I974)). Acanthoecop3is is less clearly differentiated from Diaphanoeca, though in at least some of the species attributed to it the lorica is more massively constructed (see, for example, A. unguiculata Thomsen 1973). Fortunately the attributes of our present species rule out either Acanthoeca or Acanthoecopsis as appropriate genera but in placing D. aperta in Diaphanoeca we recognize that the open posterior end in which this species differs from all others may at some future time justify erection of a new genus for it. Pending further information we are treating this character at present as no more than a specific differential, since in other ways there is a close general resemblance to D. grandis Ellis, also present in these waters but differing in costal details as well as in the persistently closed posterior end, retained even in emptyand damaged specimens.

The more important details differentiating costal strips in various parts of the lorica of D. aperta are illustrated in figures 28-32. The component strips of the posterior transverse costa (figure 31) are thinner and slightly simpler than those from the anterior transverse costa (figure 29) though all share the essential L shape in relation to the subtending longitudinal costae. The latter show a progres- sive reduction in width from the anterior end of the lorica backwards, excluding the terminal costal strips at both ends, which are exceptionally slender. The latter are illustrated in figures 30 and 32 at a magnification sufficient to permit recogni- tion of the characteristic differences between the two ends of one and the same costal strip in each case; in both, the anteriorly directed end is tapered and the


Diaphanoeca aperta from Resolute Bay continued. All micrographs taken with the A.E.I. Corinth microscope at Nottingham University.

FIGURE 28. Part of a broken lorica which yielded the more highly magnified details seen in figures 29-32; micrograph Y 7749.18 (magn. x 1500).

FIGURE 29. Part of the anterior end of the broken lorica illustrated in figure 28, showing the shapes and modes of attachment of the costal strips more clearly; micrograph Y 7749. 20 (magn. x 5000).

FIGURE 30. Anterior terminal costal strip from one of the longitudinal costae included in figure 29 to show the shapes of the ends and the general orientation with respect to the long axis of the lorica (for posterior equivalent see figure 32); micrography 7749.20 (magn. x 10000).

FIGURE 31. Part of the posterior end of the broken lorica illustrated in figure 28 showing the shapes and modes of attachment of longitudinal and transverse costae for comparison with the equivalent at the anterior end of the same specimen shown in figure 29; micrograph Y 7749.19 (magn. x 5000).

FIGURE 32. Posterior terminal strip from one of the longitudinal costae included in the field of figure 31 for comparison with the anterior equivalent in figure 30; micrograph Y 7749. 19 (magn. x 10000).




posteriorly directed end truncate or slightly bulbous. There is therefore no trace here of the inverted orientation characteristic of the costal strips in the caudal appendages of Salpingoeca longicaudata and Parvicorbicula serrulata.

DISusCsION

Two aspects of the four species introduced above are of special biological interest. One is the high incidence of caudal appendages of the various kinds and the other is the precision of assembly clearly detectable in the lorica substructure in all four species.

The problems posed by the intricacies of lorica architecture will be solved, if at all, only with the aid of experimentation and study of living material by every available means. This ideally includes study of appropriate species in culture in the manner already begun by Leadbeater (1974b). It is known from electron microscopy of sections (Leadbeater & Manton I974) that costal strips are manufactured within the cell in membrane bounded cavities from which they emerge, fully formed, to the exterior. Assembly then follows, though the mechanism is uncertain. The most that can be said from our present evidence is that, at least in Salpingoeca longicaudata and Parvicorbicula serrulata the orientation of the longitudinal components in both lorica and tail is not only invariable but is also, consistently, with reference to the posterior tip of the lorica basket. Some organizational influence starting at this point and moving thence up the lorica and down the tail must mediate the orientation of individual strips though the nature of this force is as yet unknown.

These findings are concordant with descriptions of lorica replication provided with the light microscope in Stephanoeca ampulla (Ellis I929) and confirmed with the electron microscope on S. diplocostata Ellis and Savillea micropora (Norris) (Leadbeater I974b) in culture that assembly, in some tail-less species, begins at the hind end of the cell. The superficially anomalous condition of D. aperta, which lacks a tail but in which the hind end of the lorica is open, is not necessarily discordant with this interpretation though it raises the question, which only further observation can solve, as to whether, in such a case, a developmental stage exists in which the posterior end of the lorica is less open.

While it is obvious that the fringe of posterior costae in D. aperta is homologous with the hind end of the lorica basket in the other three species described here, rather than with their caudal appendages, it seems unlikely to be a meaningless coincidence that a group of four species, selected together from a somewhat extreme habitat for no better reason than the absence of previous descriptions, should all be found to possess posterior appendages of one sort or another. This could not have occurred in any of the temperate habitats previously examined e.g. Norway (Throndsen I969; Lea1dbeater I972a), Denmark (Leadbeater I972b; Thomsen I973), the Mediterranean and Adriatic Seas (Leadbeater I974a), the cold water off Cape Town, South Africa (Manton, unpublished), even though a minority of




tailed species occur in these, some of which, e.g. Diaphanoeca pedicellata, are also arctic, while several tail-less species (e.g. Parvicorbicula quadricostata, Acanthoecop- sis unguiculata Thomsen, etc.) are similarly shared. Nevertheless, like drip-tips on leaves in the tropics, it seems likely that some powerful ecological factor exists in arctic waters favouring parallel evolution of posterior appendages of differenit kinds in these organisms. Moreover such an effect is not limited to collared flagellates since the commonest arctic species of Dinobryon (a pigmented member of Chrysophyceae), D. petiolatum Willen, has a posterior extremity to its funnel- shaped sheath which, both in West Greenland and at Resolute Bay, can be almost as long as the tail in Salpingoeca longicaudata. The environmental component most likely to have such an effect is clearly ice.

Some of the ecological factors involved in the interaction between sea ice and the relevant biota have been investigated and placed on record, in general outline, by several observers. Thus the well-known brown colour of the lower layers of ice floes that develops in the course of a few weeks before and during the spring break-up of the continuous ice cover has been shown to represent intraglacial phytoplankton. Quantitative estimates of extracted chlorophyll A made by Spen- cer Apollonio (I96I) showed this to be substantially greater in the ice itself than in an equivalent volume of open water at Devon Island in June. Bursa (I963), summarizing communities in the water immediately under ice, recognizable with the light microscope in coastal waters of the arctic ocean near Point Barrow, Alaska, found both freshwater forms and marine diatoms, the latter increasing with depth, while pools of melt water on the ice surface were fresh. In a careful study of many ecologically relevant factors by three Japanese workers (Hiroshi, Kuniyuki & Hiroshi I967), the microenvironment within the lower layers of ice was shown to be reasonably stable and not unfavourable to life with respect to temperature and available nutrients but a maj or and potentially hazardous variable was osmotic. Desalination of the ice itself during freezing leads to the enclosure of tiny unfrozen pockets of highly concentrated salt solution within it. Any organism overwintering successfully in these would need to be able to withstand osmotic shocks of exceptional severity following changes of temperature either upwards or downwards.

Whether, and if so which, collared flagellates overwinter in such positions is as yet unknown. It is therefore premature to consider precise ways in which inanimate projections, such as those composed of silicified costae, could contribute to survival although a positive selective value is strongly suggested. That each of our four species can tolerate winter darkness as well as cold and can survive the minimal osmotic shocks inseparable from the spring thaw in any part of the total environ- ment is obvious. Somewhat less expected was the apparent indifference of Pleura- siga caudata to temperature shocks the other way. At the time of our visit to the grain port of Churchill in July 1973 the shipping season had not yet begun since the northern inlets to Hudson Bay were still ice bound. P. caudata in Button Bay could not therefore have been a recent imigrant of the current year. At that time




the prevailing temperature in open water was 2 'C with floating ice always visible, at least on the horizon. The land temperature on the other hand could be very different since, with a southerly wind and uninterrupted sunshine for days on end, the shade temperature could reach 80 'F. Not surprisingly therefore the temperature of the sea, near the edge in shallow water, rose also. A transition from 2 to 12 'C or more could occur within a few feet, if not inches, and the fact that apparently healthy specimens of P. caudata were gathered in both these situations (see page 18) must mean that abrupt temperature changes of this order of magni- tude are tolerated.

This suggests that though an immediate introduction to the area from outside seems impossible an ultimate origin of P. caudata from the Atlantic Ocean is likely. This is somewhat supported by the known presence of a related species P. sphyrelata in Denmark (Thomsen I973 and also in South Africa (Manton, unpublished)). Conversely, a different origin seems likely for some or perhaps all, of the other three species. The prevailing direction of water flow in the North West Passage past Cornwallis Island is from west to east and though drift ice blown by the wind can move in any other direction none reaches as far as West Greenland in summer unmelted. Nevertheless Salpingoeca lonricaudata recorded from both places and probably also from Igloolik (see p. 20) seems likelyto be truly indigenous, overwintering locally even if introduced from the west.

All this indicates the need for further information on the local ecology and overall geographical distributions of the various taxa. Both types of enquiry are potentially important since the one has a direct bearing on a relatively poorly known part of the food chain relevant to the world's fisheries and the other might eventually permit use of some of these taxa as indicator species for bodies of water of diverse origin. For all these reasons it is greatly to be hoped that this work will continue.

REFERENCES

Apollonio, S. I96I The chlorophyll content of arctic sea-ice. Arctic 14, 197-199. Bursa, A. S. I96I The annual oceanographic cycle at Igloolik in the Canadian Arctic.

II. Phytoplankton. J. Fish. lRes. Bd, Can. 18, 563-615. Bursa, A. S. I963 Phytoplankton in coastal waters of the arctic ocean at Point Barrow,

Alaska. Arctic 16, 239-262. Ellis, W. N. 1929 Recent Researches on Choanoflagellata (Craspedomonadines) (freshwater

and marine) with description of new genera and species. Ann. Soc. r. zool. Beig. 60, 49-88. Hiroshi, M., Kuniyuki, I. & Hiroshi, F. I967 Ice flora (bottom type): a mechanism of

primary production in polar seas and the growth of diatoms in sea ice. Arctic 20, 114-132.

Leadbeater, B. S. C. 1972a Fine-structural observations on some marine choanoflagellates from the coast of Norway. J. mar. biol. Ass. U.K. 52, 67-79.

Leadbeater, B. S. C. 1972b Ultrastructural observations on some marine choanoflagellates from the Coast of Denmark. Br. phycol. J. 7, 195-21 1.

Leadbeater, B. S. C. 1973 External morphology of some marine choanoflagellates from the coast of Jugoslavia. Arch. Protistenk 115, 234-252.

Leadbeater, B. S. C. I974a Ultrastructural observations on nanoplankton collected from the coast of Jugoslavia and the Bay of Algiers. J. mar. biot. Ass. U.K. 54, 179-196.




Leadbeater, B. S. C. I974b A microscopical study of the marine choanoflagellate Savillea micropora (Norris) comb.nov. and preliminary observations on lorica development in S. micropora and Stephanoeca diplocostata. Protoplasma. (In the Press.)

Leadbeater, B. S. C. & Manton, I. 1974 Preliminary observations on the chemistry and biology of the lorica in a collared flagellate (Stephanoeca diplocostata Ellis). J. mar. biol. Ass. U.K. 54, 269-276.

Leadbeater, B. S. C. & Morton, C. I974 A light and electron microscope study of the choanoflagellates Acanthoeca spectabilis Ellis and A. brevipoda Ellis. Arch. Microbiol. (In the Press.)

Thomsen, H. A. I973 Studies on choanoflagellates. I. Silicified choanoflagellates of the Isefjord (Denmark). Ophelia 12, 1-26.

Throndsen, J. I969 Flagellates of Norwegian coastal waters. Nytt Mag. Bot. 16, 161-216. Throndsen, J. 1970 Salpingoeca spinifera sp.nov., a new plankton species of the Craspedo-

phyceae recorded in the Arctic. Br. phycol. J. 5, 589-602.



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Four New Species of Choanoflagellates from Arctic Canada