Lattice organs in y‐cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca

Abstract

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.

Cypris morphology in the barnacles Ibla and Paralepas (Crustacea: Cirripedia Thoracica) implications for cirripede evolution

“…Both these characters are synapomorphic for a clade comprising the Rhizocephala and the Thoracica. The Acrothoracica and all noncirripede Thecostraca (Ascothoracida, Facetotecta) have a posterior position of the pore in LO1 and a more plesiomorphic ''crest-in-trough'' type of lattice organs, indicating their ontogenetic origin from simple setae in the late nauplii (Jensen et al, 1994a,b;Høeg and Kolbasov, 2002;Kolbasov et al, 2008). The two distinct pairs of setae on the naupliar shield of Ibla are homologous to those found in many other thecostracan late nauplii and are precursors of the LO1 and LO2 pairs of lattice organs in the cyprid (Rybakov et al, 2003).…”

“…The central pore or porefield associated with both the anterior and posterior lattice organs (Figs. 2F and 7A) is the exit of a special gland and, since present also in the Facetotecta, apparently a ground pattern feature for the Thecostraca Høeg and Kolbasov, 2002). The anterior line of pores or pits in Paralepas have not previously been seen with SEM and might provide an interesting character at low taxonomic levels.…”

“…Paralepas has secondarily lost the terminal pores except in LO1. Further details in Høeg and Kolbasov (2002).…”

“…The gross anatomy of the cyprid is very similar in all cirripedes, but it sports a host of characters at the ultrastructural level that can provide important phylogenetic information. The lattice organs in the shield (carapace) were the first larval features used for a phylogenetic analysis of all Cirripedia, including the parasitic Rhizocephala (Jensen et al, 1994a,b;Høeg and Kolbasov, 2002;Buckeridge and Newman, 2006), but the diversity of antennular sensory organs and the morphology of the thorax and abdomen-telson also provide important character sets (Elfimov, 1995;Moyse et al, 1995;Kolbasov et al, 1999;Høeg and Kolbasov, 2002;Blomsterberg et al, 2004;Høeg et al, 2004a).…”

Antennulary sensory organs in cyprids of Octolasmis and Lepas (Crustacea: Thecostraca: Cirripedia: Thoracica): A scanning electron microscopic study

“…We have used SEM to study cyprids of Octolasmis angulata and to compare them with cyprids from three species of the Lepadidae. We put special emphasis on the sensory organs of the antennules as these structures are used in substrate choice of the settling larvae and present a large number of characters for phylogenetic analysis (Nott and Foster, 1969;Glenner et al, 1989;Clare and Nott, 1994;Høeg and Rybakov, 1996;Kolbasov et al, 1999;Høeg and Kolbasov, 2002). Our aim is not to use single characters in phylogenetic analysis, but rather to increase the morphological database on larval (cyprid) cirripedes, both for use in future cladistic analyses and to understand how cypris sensory organs correlate with very specific settlement substrata as seen for species of Octolasmis.…”