出版社：International Academy of Ecology and Environmental Sciences
摘要：Using scanning electron microscopy, we describe the first and second post hatching stages of Nymphon
australe Hodgson 1902. In the first post hatching stage the animals have a pair of three segmented cheliphores
and a pair of three segmented larval appendages either II or III. Three undeveloped buds of walking legs, 1, 2
and 3 are also present. The digestive system is still incomplete, the back ectodermal part of an alimentary canal
or proctodeum has not appeared at the first post hatching stage. The second post hatching stage has sevensegmented
walking legs 1 and 2 and a four-segmented walking leg 3. The fourth walking leg is present as an
undeveloped bud in this stage. The eye tubercle has appeared by the second post hatching stage. The back
ectodermal part of an alimentary canal or proctodeum has appeared as a slit at the posterior end of the
opistosome. In addition to N. australe the early post hatching stages of several other species of pycnogonids
have developmental traits typically associated with embryonic development. The paired primordia of the
ventral nerve chord ganglia are present on the epidermis. The eye tubercle is not present until one or more post
hatching molts. The digestive tract is incomplete as indicated by the absence of the back ectodermal part of an
alimentary canal or proctodeum. The undeveloped limb buds of the walking legs are morphologically
analogous to those in chelicerate embryos. We propose that in the Pycnogonida at the time of hatching
embryonic development is incomplete.
