Topic
Facetotecta
About: Facetotecta is a research topic. Over the lifetime, 29 publications have been published within this topic receiving 578 citations.
Papers
TL;DR: It is concluded that five pairs of lattice organs represent an autapomorphy for the Thecostraca, which supports the monophyly of this taxon.
Abstract: Hoeg, J.T. and Kolbasov G.A. 2002. Lattice organs in y-cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca. — Acta Zoologica (Stockholm) 83 : 67‐79 Scanning and transmission electron microscopy (SEM and TEM) were used to study lattice organs in facetotectan y-cyprids from the White Sea and from Norwegian and Bahamian waters. The larvae represent at least four and possibly five different species of Facetotecta. Y-cyprids have five pairs of lattice organs in the head shield (carapace) organized into two anterior pairs and three posterior pairs. Both groups of lattice organs are arranged around a large central pore. The facetotectan lattice organs are elongate areas with a longitudinal keel, just as in the Ascothoracida and some Cirripedia Acrothoracica. The terminal pore of the organs is situated posteriorly in all five pairs. TEM confirms that the organs have the same general morphology as in the Cirripedia and Ascothoracida, namely, a cuticular chamber into which project ciliary segments from the chemosensory cells. Unlike Cirripedia the cuticular roof of the chamber lacks any pores. We conclude that five pairs of lattice organs represent an autapomorphy for the Thecostraca, which supports the monophyly of this taxon. In the ground pattern the terminal pore is posterior in all five pairs. The anterior position of the pore in lattice organ pair 2 is apomorphic for the Cirripedia, while within this taxon an anterior position also in pair 1 is apomorphic for a monophylum comprising the Thoracica and the Rhizocephala. Minute pores in the roof of the organs is another apomorphy of the Cirripedia, but its elaboration into pores visible with SEM may have been subject to some homoplasy. Since lattice organs are omnipresent in the settling instar of the Thecostraca they probably serve a critical role for the function of these cypris or cypris-like larvae.
68 citations
TL;DR: Swimming is suggested to represent the underived mode of locomotion for the crustacean nauplius, and that nau pliar swimming directly results in nauPLiar feeding which also is underived.
Abstract: The plesiomorphic mode of crustacean development is widely accepted to be via a larva called the nauplius. Extant taxa like the Cephalocarida, Branchiopoda, Ostracoda, Mystacocarida, Copepoda, Cirripedia, Ascothoracida, Facetotecta, Euphausiacea and Penaeidea hatch from an egg as a free-living nauplius. Other crustaceans show an embryonic phase of development suggestive of a naupliar organization. Several features of the nauplius larva have been proposed as diagnostic characters for the Crustacea: a median (nauplius) eye; at least three pairs of head appendages (antennules, antennae, mandibles); a posteriorly directed fold (the labrum) extending over the mouth and a cephalic (nauplius) shield. The relationship between trilobite protaspis with at least four appendages and the crustacean nauplius remains unclear, but reports of a copepod orthonauplius with four appendages are rejected. Swimming is suggested to represent the underived mode of locomotion for the crustacean nauplius, and that naupliar swimming directly results in naupliar feeding which also is underived.
56 citations
TL;DR: It is inferred that lattice organs are among the most highly modified sensilla in all Crustacea and they have in most cases lost all external resemblance to a seta.
Abstract: Lattice organs are peculiar chemoreceptors found only in the Crustacea Thecostraca (Facetotecta, Ascothoracida, Cirripedia). In these taxa, five pairs occur in the head shield (carapace) of the terminal larval instar (y-cyprid, ascothoracid larva, cyprid), which is the settlement stage. Lattice organs represent an autapomorphy for the Thecostraca but their evolutionary origin and possible homologues in other Crustacea remain obscure. We have used scanning electron microscopy to describe the setation pattern of the head shield in late nauplii of one species of Ascothoracida, one species of Facetotecta and several species of the Cirripedia Thoracica, Acrothoracica, and Rhizocephala. The naupliar head shield always carries two pairs setae situated anteriorly near the midline. Each of these setae carry a single pore, and positional, structural and ontogenetic evidence show that these setae are homologous in all the examined species and that they represent precursors of the two anterior pairs of lattice organs of the succeeding larval stage, viz., the ascothoracid larva (Ascothoracida), y-cyprid (Facetotecta), and cyprid (Cirripedia). This leads us to infer that lattice organs are among the most highly modified sensilla in all Crustacea and they have in most cases lost all external resemblance to a seta. The nauplii of the Rhizocephala carry an additional three pairs of setae situated more posteriorly on the head shield and they could be precursors of the three posterior pairs of lattice organs. All other species examined lack these posterior setae, except the Facetotecta which have one posteriorly situated pair.
41 citations
TL;DR: The nauplius is the earliest free-living stage in the development of most crustaceans, except in the majority of the Malacostraca, and several character states of the nauPLius larva are used as constitutive for the Crustacea as a whole.
39 citations
TL;DR: The morphological hypothesis that the cirripedes form a monophyletic group, with the Acrothoracica as sister group to the Thoracica + Rhizocephala, strongly supports the model of evolution that fits the data best, and maximum parsimony approaches.
Abstract: Until now morphological and molecular datasets have failed to agree on phylogenetic relationships within the Crustacea Thecostraca (=Facetotecta, Ascothoracida, and Cirripedia). Three recent phylogenetic studies using 18S ribosomal DNA sequences from selected Cirripedia (Thoracica, Rhizocephala, and Acrothoracica) and Ascothoracida revealed Acrothoracica and Ascothoracida as a monophyletic group. This result disagrees with several larval and spermal morphological features supporting Cirripedia as a monophyletic group. We reanalyzed the same molecular data set including a new Facetotecta sequence using neighbor-joining and maximum likelihood, but incorporating the model of evolution that fits the data best, and maximum parsimony approaches. Our results strongly support the morphological hypothesis that the cirripedes form a monophyletic group, with the Acrothoracica as sister group to the Thoracica + Rhizocephala. Moreover, all the phylogenies showed the Facetotecta as the sister group to the rema...
38 citations
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| Year | Papers |
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| 2021 | 1 |
| 2019 | 3 |
| 2014 | 1 |
| 2012 | 1 |
| 2009 | 1 |
| 2008 | 2 |