Abstract. Advances in morphological and molecular studies of metazoan evolution have led to a better understanding of the relationships among Rotifera . Acanthocephalans and Rotifers Provide Clues for the Study of Determining the phylogenetic relations of the Acanthocephala to other animal. Acanthocephala is a phylum of parasitic worms known as acanthocephalans, thorny-headed This makes determining relationships with other higher taxa through The three rotifer classes and the Acanthocephala make up a clade called.
Except for the absence of the longitudinal fibres the skin of the proboscis resembles that of the body, but the fluid-containing tubules of the proboscis are shut off from those of the body.
The canals of the proboscis open into a circular vessel which runs round its base.
From the circular canal two sac-like projections called the lemnisci run into the cavity of the body, alongside the proboscis cavity. Each consists of a prolongation of the syncytial material of the proboscis skin, penetrated by canals and sheathed with a muscular coat. They seem to act as reservoirs into which the fluid which is used to keep the proboscis "erect" can withdraw when it is retracted, and from which the fluid can be driven out when it is wished to expand the proboscis.
Nervous system[ edit ] The central ganglion of the nervous system lies behind the proboscis sheath or septum. It innervates the proboscis and projects two stout trunks posteriorly which supply the body.
Each of these trunks is surrounded by muscles, and this nerve-muscle complex is called a retinaculum. In the male at least there is also a genital ganglion.
Some scattered papillae may possibly be sense-organs. Reproduction[ edit ] The Acanthocephala are dioecious an individual organism is either male or female. There is a structure called the genital ligament which runs from the posterior end of the proboscis sheath to the posterior end of the body. In the male, two testes lie on either side of this. Each opens in a vas deferens which bears three diverticula or vesiculae seminales.
The male also possesses three pairs of cement glands, found behind the testes, which pour their secretions through a duct into the vasa deferentia. These unite and end in a penis which opens posteriorly.
In the female, the ovaries are found, like the testes, as rounded bodies along the ligament. From the ovaries, masses of ova dehisce into the body cavity, floating in its fluids for fertilization by male's sperm. After fertilization, each egg contains a developing embryo. These embryos hatch into first stage larva.
The fertilized eggs are brought into the uterus by actions of the uterine bell, a funnel like opening continuous with the uterus. At the junction of the bell and the uterus there is a second, smaller opening situated dorsally. The bell "swallows" the matured eggs and passes them on into the uterus. Immature embryos are passed back into the body cavity through the dorsal opening. From the uterus, mature eggs leave the female's body via her oviductpass into the host's alimentary canal and are expelled from the host's body within feces.
Other features[ edit ] A curious feature shared by both larva and adult is the large size of many of the cells, e.
Polyploidy is common, with up to n having been recorded in some species. The acanthocephalans lack an excretory system, although some species have been shown to possess flame cells protonephridia. Gammarus lacustrisa small crustacean that feeds near ponds and rivers, is one invertebrate that the thorny-headed worm may occupy. This crustacean is preyed on by ducks and hides by avoiding light and staying away from the surface. However, when infected by a thorny-headed worm it becomes attracted toward light and swims to the surface.
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In Maximum Parsimony MP trees, the phylogeny, but no statistical support for the associ- alignment is used to choose the tree with the shortest ation was given, and a subsequent paper describing the path that accounts for the nucleotide changes.
Consid- analysis was not published. The first rigorous molecu- ering that there are over 34 million possible topologies lar study of aschelminth phylogeny Winnepenninckx for even a 10 taxon tree, MP trees can take a lot et al.
MP analysis generally does not sequences from the acanthocephalan M. In Maximum Likelihood ML ous nematodes, a gastrotrich, a nematomorph, and trees, a maximum likelihood value for character state a priapulid.
In the analyses, NJ, ML, and MP trees were found to be congruent in regard to the relationship between ro- tifers and acanthocephalans with remarkably strong statistical support.Rädertierchen / Rotifer - Leben im Schlamm - life in the mud - microorganism under microscope
CP values were similarly high, and decay analyses not shown indicated that even 20 steps were insufficient to decay the two clades. One problem with the study is that the rotifer P. Numbers above and below have 18S rRNA genes that evolve much more rapidly each fork represent the percentage of 1, bootstrap replicates than other metazoans, and it is possible that unequal that support the branch in the MP and NJ trees, respectively.
Values are shown only when greater than In dices greater than Opisthorchis viverrini, would be expected if unequal rate effects were a factor Ovi. See Garey et al. The tree in other details of the analysis. The MP tree revealed the and P. In additional analyses, the A more recent study Garey et al. To date, The mitochondrial genome contains a number of the monogonont B. One of the most conserved is that of quences have been published. Therefore, the presently the mitochondrial 16S rRNA gene which is inherited available molecular data cannot discriminate between independently from the nuclear rRNA genes.
We se- any of the trees in Figure 1 concerning the relation- quenced a bp fragment of the 16S rRNA gene ships among the three rotifer classes. Although the et al. For example, the 87 Figure 4. The tree from Figure 3 drawn with branch lengths proportional to evolutionary distance to illustrate the unequal evolutionary rates of rotifers and acanthocephalans.
When the fastest evolving rotifer sequence P. When the fastest acanthocephalan sequence C. Taxon labels are defined in Figure 3. The tree shown is a NJ tree. See Kumar et al. The same topology was recovered with all NJ analyses and with ML analysis with multiple rate categories but not with MP or ML analysis without multiple rate categories see text.
Taxon abbreviations and Genbank accession numbers: PCR products were cloned into M13 and sequenced in both directions. Sites with gaps were not used in the analyses. Recent morphological analyses from a Rotifera and Acanthocephala as the 18S rRNA study number of laboratories seem to be converging on the in Figures 3 and 4.
While the Nemathelminthes are most prob- ation and multiple substitutions at the same site is ably the sister group of Spiralia Lophotrochozoa important for the fast evolving mitochondrial 16S within Protostomia Ehlers et al.
MP analysis does not carry out those correc- Gnathostomulida named Gnathifera have been hypo- tions, and produced a tree similar to tree B in Figure 2, thesized as the sister taxon of Platyhelminthes within with Acanthocephala as a sister taxon to Rotifera. Similarly, when ML analysis was carried out without correcting for site to site variation, Acanthocephala appeared as the sister taxon to Rotifera, but when Molecular evidence for the position of the analysis was repeated with multiple rate categor- Rotifera-Acanthocephala within the Bilateria ies four categories: It is well established that rRNA more distant taxa that have few uniting characters.
More recent studies based on the In most textbooks, rotifers are placed among the 18S rRNA gene have extended the entire clade to aschelminths e.
Acanthocephala - Wikipedia
Other views support and Halanych et al. Some cladistic studies of analysis is consistent with the 18S rRNA gene findings the entire Metazoa consider the pseudocoelom an im- Figure 5. Schram, ; Eernisse et al. It appeared basal to the bilateria, an artifact now recog- is clear that the aschelminths are polyphyletic, but nized as caused by unequal rate effects Aguinaldo the more rigorous treatments of aschelminth taxa of- et al.
Loren- apulida to include Tardigrada.
Recently, Aguinaldo zen, ; Wallace et al. With careful attention to unequal rate effects, they provided evidence that the protostomes consist of two clades: Since ecdysozoans generally lack spiral cleavage which is present in spiralians, we prefer to use the term Spir- alia instead of Lophotrochozoa see Malakhov, and Nielsen, for descriptions of cleavage in nematodes. For example, the develop- Figure 6. Proposed position of Rotifera within the Bilateria based mental pattern of growth by molting under the control on morphological and molecular data.
The annelid-mollusc lineage of the steroid hormone ecdysone has been confirmed refers to the bulk of the non-ecdysozoan protostomes, but not neces- among Arthropoda, Nematoda, and Tardigrada see sarily all of them. Only a few key characters are given.
Blastopore becomes the anus. Ventral lateral nerve chord Ahlrichs, Molting by ecdysis Aguinaldo et al. Filiform sperm without accessory centriole Ahlrichs, Biciliary terminal cell in the protonephridia Ax, Jaws composed of rods imbedded in a cuticular matrix Ahlrichs, Conclusions and future directions 8: The molecular and morphological evidence is over- whelmingly in favor of a close relationship between Rotifera and Acanthocephala.
Analyses of nuclear 18S rRNA and mitochondrial 16S rRNA genes strongly favor a sister relationship between Bdelloidea and Acanthocephala, one of three possible relationships sequencing the complete mitochondrial genome of B. It is important for new molecular analyses to be versial.
In this regard, the time is ripe for a series of carried out rigorously, with special attention paid to rigorous ultrastructural comparisons of the epidermis alignments, unequal rate effects, site to site variation, underlying the rotatory organ of bdelloid rotifers to the and multiple substitutions at the same site.
Similarly, ultrastruc- The position of Rotifera is becoming clearer as tural studies should be carried out to compare rotifer morphological and molecular evidence are considered adhesive glands and acanthocephalan cement glands.
We propose a scheme Figure 6 that places The molecular data supporting the sister group Rotifera among the Bilateria and appears to be con- relationship between Bdelloidea and Acanthocephala sistent with many of the more recent molecular and appears very strong, but it is based on only two genes morphological studies. Gnathostomulida because they all have jaws com- The sequences of more genes from more rotifer taxa posed of rods imbedded in a cuticular matrix Rieger should be analyzed, particularly from Seison.
We are currently which in turn is the sister group to Ecdysozoa. Molecu- Landefeld for technical assistance. Morphogenetic hormones and their glands in arthropods: Nickol for provid- Haffner, K. Organisation und systematische Stellung der ing frozen M. We also thank Acanthocephalen. Liz Wurdak and four anonymous reviewers for helpful M. Evidence of 18S ribosomal DNA comments. Ap- References plication and accuracy of molecular phylogenies.
The evolutionary relationships of rotifers and acanthocephalans | Thomas Near - triplexxx.info
Evidence for a clade evolution and phylogenetic inference. An empirical test of bootstrapping Ahlrichs, W. Zur Ultrastruktur und Phylogenie von Seison as a method for assessing confidence in phylogenetic analysis.