J Mol Evol (1996) 42552-559
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O Springer-Verlag New York Inc. 1996
18s rRNA Suggests That Entoprocta Are Protostomes, Unrelated
to Ectoprocta
L.Y. ~ a c k e ~B.
, ' ~inne~enninckx:R. De wachter? T. ~ackeljau?P. ~mschermann?J.R.
are^'
' Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA
Departement Biochemie, Universiteit Antwerpen (UIA), Universiteitsplein 1, B-2610 Antwerpen, Belgium
Koninklijk Belgisch lnstituut voor Natuurwetenschappen, Vautierstraat 29, B-1040 Bmssel, Belgium
Institut fiir Biologie 111, Albert-Ludwig-Universitat-Freiburg,
Schanzlestrasse 1, D-79104 Freiburg, Germany
Received: 27 May 1995 / Accepted: 8 January 1996
Abstract. The Ento- and Ectoprocta are sometimes
placed together in the Bryozoa, which have variously
been regarded as proto- or deuterostomes. However, Entoprocta have also been allied to the pseudocoelomates,
while Ectoprocta are often united with the Brachiopoda
and Phoronida in the (super)phylum Lophophorata.
Hence, the phylogenetic relationships of these taxa are
still much debated. We determined complete 18s rRNA
sequences of two entoprocts, an ectoproct, an inarticulate
brachiopod, a phoronid, two annelids, and a platyhelminth. Phylogenetic analyses of these data show that (1)
entoprocts and lophophorates have spiralian, protostomous affinities, (2) Ento- and Ectoprocta are not sister
taxa, (3) phoronids and brachiopods form a monophyletic clade, and (4) neither Ectoprocta or Annelida appear
to be monophyletic. Both deuterostomous and pseudocoelomate features may have arisen at least two times in
evolutionary history. These results advocate a SpiraliaRadialia-based classification rather than one based on
the Protostomia-Deuterostomia concept.
Key words:
Ectoprocta - Entoprocta - Phoronida
- Brachiopoda - Lophophorata - 18s rRNA - Molecular phylogeny - Oligochaeta
Polychaeta
-
Hirudinida -
Abbreviations: N J : neighbor-joining; MP: maximum parsimony
Correspondence to: J.R. Garey
Introduction
The phylum Entoprocta (Kamptozoa) comprises about
150 species of small, sessile, solitary or colonial species
(Emschermann 1985). In their life cycle and larval form
they show some similarities to the Ectoprocta, which
prompted Nielsen (1977) to place both taxa together in
the Bryozoa (moss animals). According to Jagersten
(1972) the Entoprocta can be derived from mollusc-like
ancestors, i.e., coelomate protostomes. Nielsen (1994),
on the other hand, sees a definite affinity between the
Entoprocta/Ectoprocta and the Platyhelminthes (flat
worms) and Nemertini (ribbon worms). Other authors
(Clark 1921; Cori 1936) have denied any close relationship between Ecto- and Entoprocta and consider the latter as neotenic annelid trochophorae (Emschermann
1982, 1985). All these postulated relationships have been
questioned because the Entoprocta possess only a small
mesenchymous body cavity, which points to a pseudocoelomate or even acoelomate origin (e.g., Hyman 1951;
Brusca and Brusca 1990). Moreover, the phylum Ectoprocta (moss animals sensu stricto) is also often united
with Brachiopoda (lamp shells) and Phoronida (horseshoe worms) in the (super)phylum Lophophorata or Tentaculata (e.g., Valentine 1973; Zimmer 1973; Gutmann
1978; Emig 1984). These three groups are mainly joined
on the basis of their overall tripartite body plan and the
presence of a lophophore, which is a horseshoe-shaped,
ciliated, tentacular feeding organ containing coelomic
extensions. Yet, the phylogenetic relationships of the lo-