A comparative study of post-larval feeding mechanisms in the bivalvia

Mortimer, Joan E (1963) A comparative study of post-larval feeding mechanisms in the bivalvia. PhD thesis, University of Glasgow.

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Post-larval development in the two sub-classes of the Bivalvia, the Protobranchia and the Lamellibranchia, differs so markedly that it was necessary to deal with each separately. A description is given of post-larvae of three species of Nucula, belonging to the protobranch Fcmily Nuculidae, ranging in length from 160 mu, with test newly shed, to 650 mu, with both ctenidia and palps well developed. This post-larval phase persists at least a year and contrasts with the short larval phase of 60 hours recorded by Drew (1899 b and 1901) for Nucula proxima. The post-larval feeding mechanisms are of particular interest since they differ radically from that of the adult. Feeding activities begin in post-larvae approximately 170 mu long and are executed by the foot which, extended beyond the shell, waves to and fro, the cilia encircling its sole wafting particles into the mantle cavity and onto the pedal walls. A curious feature, located on the inner mantle surface, is an arc of cilia whose beat may help to draw in particles and certainly throws them onto the proximal wall of the foot where adoral ciliary tracts carry them to the mouth. In post-larvae exceeding 200 mu the activity of the pallial ciliated arc wanes as the ctenidia and palps develop. With two filaments in each inner demibranch the ciliary feeding mechanism begins to resemble that of lamellibranchs. Particles enter the mantle cavity in the respiratory water current produced by the ctenidia, collect on its surface, and proceed to the filament tips and along the underlying adoral pedal tract. Below this adoral tract the foot develops an antagonistic ciliary tract carrying rejected particles out of the mantle cavity. The palp lamellae of post-larvae 500 mu long establish a functional contact with the first filament of the inner demibranch and particles travel directly from one to the other. This type of feeding continues until the post-larva is 650 mu long when the pulp proboscides probably become functional. The posible phylogentic significance of the post-larval feeding mechanisms is discussed. Amongst the Lamellibranchia post-larvae belonging to five familes of the Anisomyaria and twelve families of the Eulamellibranchia were examined. In each of the anisomyarian families (Anomiidae, Pectinidae, Limidae, Ostreidae and Mytilidae) the post-larval feeding mechanism is distinctive and in the first four families tends to show a certain complexity. In these four families the monomyarian condition has considerable effect on ctenidial development and hence on the post-larval feeding mechanism. While in the Anomiidae and Pectinidae these effects appear somewhat disadvantageous, in the Limidae and Ostreidae they are modified by progressive changes in the pattern of ctenidial development. Consideration of the differences in rate and sequence of development reveals a common pattern of development in the four families. One characteristic of this developmental pattern is the disposition and period of activity of certain localized growth zones, the 'embryonic zones', which provide for the elongation and reflection of the filaments. In the Mytilidae the post-larval feeding mechanism exhibits a simplicity not found in other Anisomyaria. The basic pattern of ctenidial development is also distinctive particularily in regard to the locations and times of activity of the embryonic zones. In contrast to the Anisomyaria little variety was encountered amongst the twelve eulamellibranch families. The post-larval feeding mechanism closely resembled that of the Mytilidae but the basic pattern of ctenidial development was distinct from that of the latter. Siphon development was examined in the Eulamellibranchia and found to embody two principles: growth from a localized proximal zone and progressive fusion of the mantle folds. The method of siphon extension and withdrawal is described.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: C N Yonge
Keywords: Developmental biology
Date of Award: 1963
Depositing User: Enlighten Team
Unique ID: glathesis:1963-73616
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: https://theses.gla.ac.uk/id/eprint/73616

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