|
Vol. 51 No. 8, 2012
Morphogenesis of Adult Traits during the Early Development of Mespilia globulus Linnaeus, 1758 (Echinodermata: Echinoidea)
Chisato Kitazawa1,*, Chiaki Kobayashi1, Mami Kasahara1, Yuki Takuwa1, and Akira Yamanaka2
1Biological Institute, Faculty of Education, Yamaguchi Univ., Yoshida 1677-1, Yamaguchi 753-8513, Japan
2Laboratory of Environmental Biology, Graduate School of Medicine, Yamaguchi Univ., Yoshida 1677-1, Yamaguchi 753-8512, Japan
Chisato Kitazawa, Chiaki Kobayashi, Mami Kasahara, Yuki Takuwa, and Akira Yamanaka (2012) We observed the development of Mespilia globulus L. (Temnopleuridae) and Hemicentrotus pulcherrimus
A. Agassiz, 1863 (Strongylocentrotidae) and focused on the formation of
adult traits by light and scanning electron microscopy. In M. globulus,
a primary pore canal constructing a part of the adult water vascular
system appeared at the left and right coelomic sacs in the prism stage.
The left and right primary pore canals respectively elongated to the
left lateral and right dorsal ectoderm and opened to the outside, and
then the right one disappeared until the 2-armed larval stage. On the
other hand, the primary pore canal of prisms of H. pulcherrimus
formed on the left side only. We first confirmed the existence of
different types of asymmetrical primary pore canal formation at the
prism stage in sea urchins. In 2-armed larvae of M. globulus,
a cell mass was formed by invagination and pinching off of the left
oral ectoderm. At the 6-armed larval stage, the developing cell mass
attached to the hydrocoel, and together they formed an adult rudiment.
In contrast, the left larval ectoderm of 6-armed larvae of H. pulcherrimus
began to invaginate between the postoral and postdorsal arms and formed
an amniotic cavity. The amniotic cavity had attached to the hydrocoel
by the 8-armed larval stage for adult rudiment formation. This is the
1st report describing how adult rudiment formation depends on the cell
mass in the early larval stage of M. globulus
larvae. From these results, we propose that asymmetrical primary pore
canal formation is initiated in the embryonic stage with some
modifications in formational modes among species, and that the
heterochronical start of adult rudiment formation by the cell mass may
allow a sufficient period to develop and protect the rudiment.
Key words: Echinoid, Mespilia globulus, Primary pore canal, Cell mass, Adult rudiment.
*Correspondence: Tel: 81-83-9335347. Fax: 81-83-9335347. E-mail:chisak@yamaguchi-u.ac.jp
|
