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Aspects of priapulid development
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleontologigruppen.
2008 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The phylum Priapulida is a small group of marine worms that is allied with the nematodes, kinorhynchs, loriciferans and nematomorphs in a clade called the Cycloneuralia or Introverta. Together with the arthropods they are generally considered to comprise the Ecdysozoa, a clade of moulting animals. A number of recent priapulid species possess features that resemble the predicted Ecdysozoan ancestor. In addition, recent molecular studies have also shown that they are basal within the Ecdysozoa/Cycloneuralia (Garey 2001, Webster et al. 2006). Their putative basal position thus makes priapulids highly interesting research objects for understanding the evolution of Ecdysozoa.

Earlier investigations of the early embryology of the priapulid Priapulus caudatus are critically revised with the aid of modern techniques and equipment, confirming earlier studies that the early cleavages are highly symmetrical, total, subequal, radial and stereotypical. New results show that up to the sixth cleavage, the spindles are oriented along the animal/vegetal axis at both poles. This unique cleavage pattern has only limited similarities to other animals. During the sixth cleavage two cells move inwards and gastrulation commences. If the mesoderm is derived from both cells, its origin differs from that of many other protostomes.

Two previously undescribed larval stages of P. caudatus; the light bulb shaped hatchling and the first lorica larva are described. The second lorica larva superficially resembles the previously described type 2 lorica larva (Higgins et al 1993). Differences between the second lorica larva and the type 2 lorica larva, with respect to possible ecophenotypical variation and sub-specialization, are described.

Preliminary data are presented on musculature development of P. caudatus. Preliminary data have also been obtained on the early development of a second priapulid, Halicryptus spinulosus. Comparison of Halicryptus and Priapulus may help to resolve developmental ground pattern of the priapulids.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis , 2008. , s. 45
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 451
Nyckelord [en]
Earth sciences, Priapulus caudatus, Priapulida, Ecdysozoa, larval development, embryology
Nyckelord [sv]
Geovetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-9004ISBN: 978-91-554-7240-5 (tryckt)OAI: oai:DiVA.org:uu-9004DiVA, id: diva2:172290
Disputation
2008-06-13, Norrlands, Geocentum, Villavägen 16, 75236, Uppsala, 10:00
Opponent
Handledare
Tillgänglig från: 2008-05-22 Skapad: 2008-05-22Bibliografiskt granskad
Delarbeten
1. Early embryonic development of the priapulid worm Priapulus caudatus
Öppna denna publikation i ny flik eller fönster >>Early embryonic development of the priapulid worm Priapulus caudatus
2008 (Engelska)Ingår i: Evolution & Development, ISSN 1520-541X, E-ISSN 1525-142X, Vol. 10, nr 3, s. 326-338Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The early cleavage up to gastrulation is described here for the priapulid worm Priapulus caudatus, contradicting and clarifying earlier partial reports on this topic. The cleavage pattern up to gastrulation is highly symmetrical, total, subequal, radial, and stereotypical. Gastrulation is intermediate between epiboly and invagination, and the mesendoderm may be derived from both cells of the first cleavage, thus differing significantly in its origin from that of many other protostomes. Priapulids occupy an increasingly important position in studies of animal evolution as they appear to be relatively basal within the new clade Ecdysozoa (panarthropods plus cycloneuralians); and have been described as both morphological and genetic living fossils. The insights derived from priapulids combined with new data published recently on kinorhynchs and tardigrades imply a substantial developmental diversity among basal ecdysozoans, and weakens the hypothesis that irregular cleavage is plesiomorphic to the entire clade. Further study is required to reconstruct basal cleavage patterns in both this clade, and indeed, the Bilateria as a whole.

Nationell ämneskategori
Geovetenskap och miljövetenskap
Identifikatorer
urn:nbn:se:uu:diva-97375 (URN)10.1111/j.1525-142X.2008.00241.x (DOI)000255552300009 ()
Tillgänglig från: 2008-05-22 Skapad: 2008-05-22 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
2. Hatching and earliest larval stages of the priapulid worm Priapulus caudatus
Öppna denna publikation i ny flik eller fönster >>Hatching and earliest larval stages of the priapulid worm Priapulus caudatus
2009 (Engelska)Ingår i: Invertebrate biology., ISSN 1077-8306, E-ISSN 1744-7410, Vol. 128, nr 2, s. 157-171Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Here we describe the hatching and morphology of the earliest larval   stages of the priapulid worm Priapulus caudatus for the first time. The hatching larva differs considerably from previously described larvae  not only in its general body shape but also in its lack of a proper lorica including the typical lorica tubuli. Furthermore, no mouth opening or pharyngeal teeth have formed as yet, and the number and  arrangement of scalids differ from that of later larvae. The hatching larva molts and emerges as the first lorica larva. This larva partially   resembles earlier described lorica larvae, but there are a number of  important differences; the first lorica larva is smaller, and the mouth   opening as well as pharyngeal teeth are still yet to form. The second   lorica larva is equipped with four rings of pharyngeal teeth; it shows striking similarity to the previously described larva of P. caudatus,  i.e., the larva-type 2, only differing in the scalid pattern. We conclude that the first two larval stages of P. caudatus have not been described previously. We suggest that discrepancies between the earliest lorica larvae described here and in earlier publications might depend on sub-speciation or ecophenotypic modification of larvae collected from different localities. Our findings highlight the  importance of studying the development of non-model organisms such as priapulids under controlled laboratory conditions.

Nyckelord
Priapulida, Scalidophora, Cycloneuralia, Ecdysozoa, development
Nationell ämneskategori
Biologiska vetenskaper
Identifikatorer
urn:nbn:se:uu:diva-97376 (URN)10.1111/j.1744-7410.2008.00162.x (DOI)000266490400005 ()
Tillgänglig från: 2008-05-22 Skapad: 2008-05-22 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
3. Muscle development in the priapulid worm, Priapulus caudatus
Öppna denna publikation i ny flik eller fönster >>Muscle development in the priapulid worm, Priapulus caudatus
Manuskript (Övrigt vetenskapligt)
Identifikatorer
urn:nbn:se:uu:diva-97377 (URN)
Tillgänglig från: 2008-05-22 Skapad: 2008-05-22 Senast uppdaterad: 2010-01-13Bibliografiskt granskad

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