Toy T T I M L Text Presented to the U Niversity of Glasgow As a Th E Sis Fo R the Degree of Ph* D* Mtiy. 19U8
Total Page:16
File Type:pdf, Size:1020Kb
BOMB ASPECTS OP THE BIOLOGY, QV VSHEBUPIS ITOAgPH*. (MOHTAPP ). toy D. B. QaavXe. T t i m l T ext Presented to the University of Glasgow as a thesis for the degree of Ph* D* Mtiy. 19U8. ProQuest Number: 13849331 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13849331 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 T ffik . # Qw&aa&M- 1. Introduction. Pag* 1 . 2 . AdauMrledgraent a . " 2. 3 . larva# t The Ident IfloatIon of the Vellgar# a# The problem* Page 3# b# The veliger* * #* 2# Fluctuation* in Abundance and Vertical Distribution of the Veliger* a# The problem* Page 13* b* Seasonal fluctuations in abundance* * 16* o* Vertical distribution* " 19# d# Diurnal movements* n % fetamorphoals of the Larva* a* The prdblem Page 28* b* The anatomy of the vellger* Page 30* o* The apet* " 38* d* The anatomy of the spat* w 39* 9* The Spat# a* The spatting on plane surfaces* Page 56* b* Mortality of the spat* * 8 l* «• Spasming# a# Sate of eater propulsion* Page 72* b . Shell movements* " 99* c* Spanning* " t07* d* Seasonal gonad changes. " fid* Growth* a* The problem Page 127* b# Growth in th e young* M 131* o# Growth in the adult* n 435* a. Sunsnary* Page 1i|S* 9. Seferenoea* Page 153* 10. a* Appendix 1 t Water propulsion data* b* Appendix 2 $ Growth data* c* Appendix 3 * Digging movements. Introdoctlon. The original plan in this Investigation was to study the general biology of Venerupls pullastre (Montagu) • It was soon realised that the work would hare to be confined to certain phases of the life history and these were chosen in an effort to cover the sect ions in which the information on marine Lamellibranchla. such as *QB fol* f« be inadequate* As a result, the work viewed as a whole may lack continuity and coherence* In the main* the investigation centres on the larval and spat stages of the life history; a part which feu boon largely neglected in LoraelllbrRnchia other than oysters* The efforts of Thor son, culminating in his extensive report (Thorson 192*6} on the reproduction and larval development of Danish marine bottom invertebrates, have assisted greatly in correlating and furthering work in this field* In a d d itio n to th e la rv a l and spat work, some emphasis has been placed on breeding, and while the results from this work are in no way conducive, they may be of interest in a comparative way. According to Winckworth (personal eommunicat.ion 191*8), until recent years the genus Venerupls has been grouped with Panhia and Tapes into one genus, sometimes called Tapes and sometimes by the older name Papilla* Winckworth recommends Thiele* s (1935) arrangement in which, for the species being studied here, the name Venerupls pullastra (Montagu) ie recognised* In addition the species 2* /species w ill occasionally be referred to by tbs name "oloaf , end D’Arcy Thompson (I9h7» p*288) is cited as the authority, although the name is used extensively in fltorth America* The author is Indebted to Professor C*M* Yonge, Ph.D., D.Sc*, F*R*S», for providing faeilities to carry out this work and for hie constant help and encouragement* Grateful acknowledgment is also due to Dr* H*F* Steedfoan, and o th e r raenber© o f th e s ta f f o f th e Department of Zoology* Appreciation is expressed to Mr. R. Elmhirst, Director of the Karine Station, M illport, and to meabers of his staff for assistance in many ways* 3. fhg, V eU g tt* The literature on the ident ificat ion of the veliger larvae of lamellibrenchs le not extensive* Stafford (1942) was one of the first to do important work on th e subject* He in d ic a te d s u ita b le methods o f in v e s ti gation and figures, and describes eight Canadian Atlantic species* Ohdner (191U) has identified several species from Rovigno and his figures for Saxicava and Li pa are good* Readier ( 1926 ) in one of the better papers on the subject, described several North Sea speoies and his figures are clear and accurate* Lebour (1937* 1938a* 1*3») did extensive work on lamellibranch larvae and has d escrib ed 17 species from Plymouth* Unfortunately, both the figures and the descriptions are vogue and are conse quently of limited use. Miyazaki (1935* 1936a, 1936b) has given useful descriptions of 8 species of Japanese lamellibrench veliger s. Werner (1939) in an excellent paper, goes into the problem in detail and studies shell structure of the veliger and uses hinge teeth and ligaments as diagnostic features* He also found the erstwhile prodlesocoach could be divided into a first and a second prodissoconch on the basis of shell development and structure* The size of the first prodiseoconch, designated as Prod* 1 * is relatively constant for any given species and is apparent ly a more reliable diagnostic feature than Prod* 1 1 , th e v setting size of the larva, which several authors have found to vary between wide limits; although Labour (1938b) has / set up a key for the identification of the various specie 9/ In /epee lee of Car&iura found at Plymouth* on the basis of moh measurements* Jorgensen, (19M>) describes and figures about 25 species of veligers from Banish waters sad on the whole this is a most useful work* The larvae of all commercial speoies of oysters haws been figured many times and these are prcfeably the best known of all marine lame 111- branoh veligers. A fact to be taken into consideration when des cribing lamellibranoh veliger 8 is that those who ere apt to make most use of the Identifications are the oceanographic plankton workers* whose material is usually preserved* The colour goes quickly and all that is left is the outline* its shape and else* and the hinge teeth and ligament* All this is present only if the material has not been t_oo well preserved for even neutral formalin^ in time becomes acid and dissolves f away the fragile shells* Colour, then, often a valuable aid in identification* is lost to the plankton research worker* as are other anatomical details such as the position of the digestive gland* and the presence or absence of eye- spot s or flagella* Therefore in the description to be given fear the larva of V. pullestra, attention will be directed to those diagnostic features remaining after fixation* The essential part of a description of a veliger Is the illustration* Ho amount of written description can take its place* Brewings of the complete animal will be given as well as the external j view of a single valve* Being the whole veliger* the tilt/ j i .j / t u t doe to the lift of the uafeonal region may vary a good deal# eo affect log the outline* The only cone i stent chape le Obtained from an external Tier of e single valve* Most authors on veliger Identification have relied entirely on camera lucida drawings} In addition to these it le believed that photomicrograph of the veliger will In the future be used to a greater extent* No phot omi orographic apparatus was available for the present investigation, eo the author*s own 35 am* camera was adapted for the purpose, end ell the photomicrographs in the thesis have been taken with the adaptation* The results are not as good as they might be, because of the difficulty in obtaining the correct focus* However, the photographs give much better represen tations of the larvae than the camera lucida drawings; and Hr* C*B* Rees of the Leith Laboratory of the Hull Oceano graphic Department, who has been studying lamelllbranch larvae from plankton recorder records, has found them to be of more value than drawings* Method* There are two main approaches to the study of lamelllbranch veligers from the point of view of identifica tion* The first is to study the succession of sizes of various forms as they appear and develop in the plankton and then associate the largest of these larvae with the newly settled spat* Xn turn, the spat are followed through individuals or groups of gradually increasing size until specific identification is possible* Peculiarly enough,/ /enough, it is the identification of the spat that is often mare difficult than the linking up of larva and spat* To Obtain the spat, cardboard egg separators dipped in a maxture of tar and pitch, separated by sheila of Octree * and strung on wire, were used* The cardboard soon became coated with algee^ detritus, and the normal sequence of fouling organisms, the whole of which provides an ideal settling surface for many species of l&mslllbranehs* In addition, sand and mud from the habitats of likely species may be sieved and ellutriated* The second approach to the identification problem is to culture the larvae, either from the fertilised eggs or by picking out numbers of any one species, and attempting to culture these throu^i to the spat stage* Both these methods were used, but the letter one was more successful end easier* Culture from the fertilized egg after natural spawning by the female may be carried out, but this was not always possible* The veligers picked out of the plankton tops kept in 2 litre l&rs stirred by the plunger system* They were fed with cultures of naked flagellates, but it was found that unfed veligers grew and astamorph osd as well as those which were fed* Groups with ©and or mud in the plunger Jar were no more successful than those without* There was no consistency about any of the culture results.