Metamorphosis in Craniiformea revisited: Novocrania anomala shows delayed development of the ventral valve
- PDF / 943,916 Bytes
- 9 Pages / 595.276 x 790.866 pts Page_size
- 93 Downloads / 157 Views
ORIGINAL PAPER
Metamorphosis in Craniiformea revisited: Novocrania anomala shows delayed development of the ventral valve Andreas Altenburger • Andreas Wanninger Lars E. Holmer
•
Received: 18 January 2013 / Revised: 29 April 2013 / Accepted: 4 May 2013 Springer-Verlag Berlin Heidelberg 2013
Abstract We revisited the brachiopod fold hypothesis and investigated metamorphosis in the craniiform brachiopod Novocrania anomala. Larval development is lecithotrophic and the dorsal (brachial) valve is secreted by dorsal epithelia. We found that the juvenile ventral valve, which consists only of a thin layer that was previously described as periostracal, is not a valve and is not secreted by the same epithelia as the dorsal valve. It is secreted by the attachment area of the larva at the posterior-most tip of the posterior larval lobe. The same attachment area is used by larvae of rhynchonelliform brachiopods during metamorphosis to cement their pedicle to the substrate. N. anomala is therefore not initially attached by a valve but by material corresponding to pedicle cuticle. This is different to previous descriptions, which had led to speculations about a folding event in the evolution of Brachiopoda. We show that the ‘‘brachiopod fold hypothesis,’’ which argues that brachiopods are transversely ‘‘folded’’ across the ontogenetic anterior–posterior axis, should be rejected at least with respect to the craniiforms. The data now suggest that the Craniiformea may be a derived group within the
Communicated by A. Schmidt-Rhaesa. A. Altenburger (&) Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark e-mail: [email protected] A. Wanninger Department of Integrative Zoology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria L. E. Holmer Department of Earth Sciences, Palaeobiology, Uppsala University, Villava¨gen 16, 75236 Uppsala, Sweden
Rhynchonelliformea. This interpretation suggests that the last common ancestor of the Craniiformea has lost the pedicle and the ventral valve in early juvenile development. Characters that have previously been considered to be shared between the Craniiformea and the Linguliformea (clade Inarticulata), such as a through-gut and missing hinge articulation, may thus be secondarily derived characters of the Craniiformea within the Rhynchonelliformea. Keywords Ontogeny Development Craniiformea Phylogeny Morphology Body plan Evolution
Introduction Brachiopoda is a marine animal phylum with a rich fossil record and approximately 370 recent species divided into the three clades, Craniiformea, Rhynchonelliformea, and Linguliformea (Williams et al. 1996; Zezina 2008). The evolution of the brachiopod body plan with two valves that enclose the soft tissue and a pedicle that attaches the animal to the substrate has puzzled researchers since the naming of the phylum by Dume´ril (1806). Brachiopods have since been deemed related to various phyla such as molluscs, bryozoans, and annelids and recently, based on molecular data,
Data Loading...
