Abstract
Limnadia stanleyana hatches as a lecithotrophic nauplius with a well-developed
naupliar region and a globular post-naupliar region, the latter comprising the rudiments
of 10 post-mandibular segments, a growth zone, and a telson. Development
proceeds through five naupliar stages. Feeding begins late in stage III. Action of a
naupliar feeding apparatus sustains the larva through stages IV and V. During these
stages, the maxillulary and maxillary segments, the carapace, and the first six trunk
segments become well developed. At the fifth moult, metamorphosis occurs to a
juvenile conchostracan. The naupliar feeding apparatus is lost, the first six pairs of
trunk limbs become functional, and feeding in the adult manner begins. The seventh
and succeeding trunk segments are delayed in development. In the development of postmandibular
segments, mesodermal somite segregation precedes ectodermal segment
delineation. Post-mandibular segments behind the tenth are proliferated by a growth
zone comprising an external ring of ectoderm and paired lateral rows of mesoteloblasts.
Artemia salina hatches as a nauplius similar to that of L. stanleyana, and
develops in an identical manner through the first four naupliar stages.
The larval development of L. stanleyana is typical of Conchostraca. The larval
development of A. salina is typical of Anostraca and differs from that of L. stanleyana
only in passing through nine naupliar stages before metamorphosis. The larval development
of the Notostraca differs from that of Conchostraca and Anostraca only in ways
related to increased lecithotrophy, metamorphosis being attained more directly. A
primitive mode of development can be identified for the Branchiopoda and interpreted
as a derived form of the developmental pattern of the Cephalocarida. Sanders' hypothesis
of a cephalocaridan-like ancestry of the Branchiopoda is upheld by the evidence
of development. Post-mandibular segment formation in branchiopods remains
primitive, and lacks the specializations found in Cirripedia and Malacostraca. Segment
formation cannot be employed as a criterion of phylogenetic affinity in Crustacea.
Subject
Animal Science and Zoology,Ecology, Evolution, Behavior and Systematics
Cited by
107 articles.
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