Lophotrochozoa

From Palaeos

Choanomonada
`--Metazoa
   `==Porifera (paraphyletic?)
      `==Radiata (paraphyletic?)
         `--Bilateria
            `==Acoelomorpha (paraphyletic?)
               |--Protostomia
               |  |--Ecdysozoa
               |  `--Lophotrochozoa
               `--Deuterostomia

Caribbean Reef Squid, Sepioteuthis sepioidea (Trchozoa, Mollusca, Cephalopoda, Teuthida, Loliginidae)

The Lophotrochozoa ("crest-bearing animals") are a diverse group that were only recently discovered through molecular phylogeny (if indeed they are a genuine clade, as is being considered increasingly the dominant view, rather than an artifact of the analysis). They include two of the most successful animal phyla, the Mollusca and Annelida. The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods, because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla.

The name "Lophotrochozoa" combines the two taxon names Lophophorata (which feed via a fringe of hollow tentacles, a lophophore) and Trochozoa (which have a unique larval stage, the trochophore lava). Lophophorata traditionally includes the Bryozoa, Brachiopoda and Phoronida, but recent authors have not regarded the Bryozoa as closely related to the other two, and hence Lophophorata as polyphyletic. Trochozoa includes the Annelida, Mollusca and Sipuncula. Also within the Lophotrochozoa are the Nemertea (ribbon worms) and Entoprocta.

Despite Lophotrochozoa only being established in 1995, a considerable degree of confusion already exists about the name's application. The issue has arisen because the original paper recognising Lophotrochozoa (Halanych et al., 1995) only included members of the Eutrochozoa and Brachiozoa in its analysis, separating them from Ecdysozoa and Deuterostomia. Since then, other taxa (primarily the Platyzoa and Bryozoa) have been suggested as being closer to Halanych et al.'s "Lophotrochozoa" than Ecdysozoa or Deuterostomia, but lying outside the clade formed by Eutrochozoa + Brachiozoa. Authors have differed on whether or not the name "Lophotrochozoa" should be extended to include those taxa. Some authors have subsumed all under Lophotrochozoa, while others have restricted Lophotrochozoa to the phyla originally covered, and used the name Spiralia (indicating the protostome phyla with spiralian embryo development) for the larger clade of Lophotrochozoa + Platyzoa. The position of Bryozoa remains extremely contentious - Cavalier-Smith (1998) suggested on morphological grounds that it was the sister to Lophotrochozoa sensu stricto (suggesting the name Trochozoa for Lophotrochozoa sensu stricto and Lophozoa for Trochozoa + Bryozoa), but Giribet, Distel et al. (2000) in a combined morphological/molecular analysis found that Bryozoa fell outside the clade Lophotrochozoa + Ecdysozoa.

Protostomia
`--o Lophotrochozoa [or Spiralia]
   `--+--Bryozoa [Ectoprocta]
      |--Platyzoa
      `--o Trochozoa 
         |==Coeloscleritophora† ("Procoelomata†")
         |--Nemertea [Nemertinea]
         |--o Eutrochozoa
         |  |?-Tullimonsterida †
         |  |--Mollusca
         |  |--Hyolitha †
         |  |--Sipuncula 
         |  `--Annelida
         `--o Brachiozoa
            |--Phoronida 
            `--Brachiopoda

[edit] Credits

Palaeos com MAK020412; Wikipedia Animal; this page MAK061012, edited CKT061015