Complicated evolution of the caprellid (Crustacea: Malacostraca: Peracarida: Amphipoda) body plan, reacquisition or multiple losses of the thoracic limbs and pleons

Abstract

The Caprellidea (Crustacea) have undergone an interesting morphological evolution from their ancestral gammarid-like form. Although most caprellid families have markedly reduced third and fourth pereopods (the walking thoracic limbs) and pleons (the posterior body parts), one family, Caprogammaridae, has developed pleon with swimming appendages (pleopods), whereas another family, Phtisicidae, possesses well-developed functional third and fourth pereopods. The unique character status of these families implies that there has been reacquisition or multiple losses of both pereopods and the pleon within the Caprellidea lineages. Although the Caprellidea are fascinating animals for the study of morphological evolution, the phylogenetic relationships among the Caprellidea are poorly understood. One obstacle to studying the evolution of the Caprellidea is the difficulty collecting samples of caprogammarid species. In this study, we obtained live samples of a Caprogammaridae species, and confirmed that its pleon and pleopods could perform similar locomotive functions and swimming movements as observed in gammarids. From the phylogenetic analyses on 18S ribosomal RNA gene sequences, we identified three distinct clades of Caprellidea.Ancestral state reconstruction based on the obtained phylogeny suggested that once lost, the third and fourth pereopods were regained in the Phtisicidae, while the pleon was regained in the Caprogammaridae, while we could not exclude the possibility of independent losses. In either case, the caprellid lineage underwent a quite complicated morphological evolution, and possibly the Caprellidea may be an exception to Dollo's law.

A Phylogeny and Classification of the Amphipoda with the establishment of the new order Ingolfiellida (Crustacea: Peracarida)

“…Like their study, the present work also shows a primarily phronimid-phrosinid clade and a vibiliid-cyllopodid clade. Another example, the good conformity between the results of a morphological study ) and a molecular study (Ito et al 2011) in the case of the caprellid amphipods, was described earlier in this paper.…”

“…reduced the suborder Caprellidea to the status of a superfamily within the suborder Corophiidea based on a morphological cladistic study. Later, Ito et al (2011) came to the same conclusion based on molecular studies. When morphological and molecular results coincide, it increases the confidence in the hypothesis.…”

Hidden diversity and cryptic speciation refute cosmopolitan distribution inCaprella penantis(Crustacea: Amphipoda: Caprellidae)

“…The phylogenetic relationships between Caprellidea are poorly understood, making the selection of an appropriate outgroup difficult. Recent molecular analyses carried out by Ito et al (2011) based on the 18S gene have indicated that a close relationship between Cyamidae (another family belonging to suborder Caprellidea) and Caprellidae exists. Thus, the COI gene sequence from one Cyamidae species, Cyamus ovalis Roussel de Vauz eme, 1834, obtained from GenBank (accession no.…”

Long-distance dispersal, low connectivity and molecular evidence of a new cryptic species in the obligate rafter Caprella andreae Mayer, 1890 (Crustacea: Amphipoda: Caprellidae)

“…The phylogenetic relationships among Caprellidea are poorly understood, making the selection of an appropriate outgroup difficult. However, recent molecular analyses carried out by Ito et al (2011) Haplotype genealogy was also investigated by building a network of haplotypes using TCS version 1.21 (Clement et al 2000) with a 90 % statistical parsimony connection limit. All sequences were deposited in GenBank (accession numbers: JX988531-JX988603).…”