By Irmeli Palmberg (auth.), Seth Tyler (eds.)
Turbellarian platyhelminths (or, as they're recognized now between cladistic systematists, free-living Platyhelminthes) contain a extensively dispensed assemblage of decrease worms present in marine, freshwater, or even sometimes in terrestrial habitats. The phylum Platyhelminthes might be extra well known for its parasitic participants because the significant parasitic teams of the tapeworms, flukes, and their family are extra speciose and feature larger effect on daily human lifestyles; however the turbellarians are extra diversified and, as population of almost any aquatic habitat, are extra frequent to boot. the various decrease turbellarians are quite uncomplicated in morphology and feature served as versions for ancestors of the Bilateria, i.e., the majority of the animal phyla. Others are really advanced organisms, particularly within the morphology in their reproductive structures that are hugely really expert. the bulk are free-living in aquatic habitats yet a few attention-grabbing parasitic and commensal species are stumbled on scattered one of the larger turbellarian taxa.
yet turbellarians are greater than simply taxonomic curiosities. they've got served as illustrative versions in examine on a number of uncomplicated lifestyles tactics. for instance, their excessive means for regeneration has made them the topic of a giant literature in developmental biology, the prevalence of mixoploidy and different karyological oddities between turbellarians has been vital in realizing evolution of the genome, and the wonderful constitution and biochemistry of the fearful process in turbellarians is revealing vital rules of the association of so-called primitive neural platforms.
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An alternative theory of patterning in planarians has been proposed by Chandebois (1984, 1985a, 1985b) and Sal6 & Baguna (1985). These authors suggest that planarian regeneration is an intercalary process whereby wound-healing itself initiates regeneration. , the restoration of all morphogenetic levels between margins along an anteroposterior or mediolateral system - follows automatically, so that cells adjacent but derived from different levels form new levels but of decreased size. The component of this theory that is important to data presented here is that of wound-healing.
On the second day, it was more rounded (Fig. 5 mm, and still evenly dark green, a color evidently caused by aggregation of algae in greater numbers here than in the rest of the animal (Figs 11, 12; compare with Fig. 8 in Hendelberg & Akesson, 1988). Green strands in the mother individual just in front of the buds were strands of dense parenchymal cells containing algae (arrowheads in Fig. 11). By the third day the bud was longer than broad (Fig. 4, arrowhead), and its ventral side was often more or less concave (Fig.
The differences in swimming direction of the mother individual and the bud, or the tendency of one to attach to the substratum 14 Figs 6-9. Scanning electron micrographs of C. relrogemma . 6) Posterior part of mother individual with 4-day-old bud. 7) Epidermal cilia at border between bud and mother individual; note line of demarcation where ciliary orientation changes. 8) Higher magnification of the area within the frame in Fig. 7. 9) Posterior end of a just-released bud. 10) Part of the torn surface of the bud in Fig.
