Is Mollusca Spiralia?

In Spiralia, the phyla Annelida and Mollusca, which are grouped as Lophotrochozoa due to their feeding structure of lophophore and trochophore larvae, contain the most diverse animal species.

What is the Synapomorphy for Spiralia?

Though quite diverse, the unifying synapomorphy for the Spiralia according to Giribet (2002 and 2008) and Edgecombe et al. (2011) is spiral cleavage (see Figure 2). This cleavage pattern is highly stylized and unlikely to have evolved more than once.

Do Spiralia have spiral cleavage?

In Spiralia, which include annelids, mollusks, and flatworms, “spiral cleavage” produces a highly stereotypic, spiral-like arrangement of blastomeres and swimming trochophore-type larvae with rotational (spiral) symmetry.

Which phylum have spiral cleavage?

Distribution of spiralian development across phylogeny Members of the molluscs, annelids, platyhelminths and nemerteans have all been shown to exhibit spiral cleavage in its classical form.

What are the major mollusk clades?

The predominant members of Trochozoa, however, are Annelida (the segmented worms) and Mollusca (the mollusks). These two form the clade “Eutrochozoa” in some analyses, but in others Mollusca and Brachiozoa are sister taxa.

What is spiral cleavage in biology?

Spiral cleavage – the process by which cells of the early embryo divide and spiral around the pole-to-pole axis of the embryo – is the most common mode of animal development.

What is a Synapomorphy of Bilateria?

In simple terms, bilaterians are animals with a distinct front, back, top, and bottom. Fundamental synapomorphies: An antero-posterior axis (rather than an oral-aboral axis) Bilateral symmetry (although this may be suppressed or overprinted in some) Presence of a flow-through gut with distinct mouth and anus.

Do rotifers have radial cleavage?

Rotifers and gastrotrichs have radial and “modified radial” cleavage, respectively. To place these two phyla in the position that results in the most parsimonious cleavage arrangement, they should be basal within the Eutrochozoa.

What is spiral cleavage?

What is Schizocoelous coelom?

Schizocoelous or schizocoely is the formation of coelom by splitting the mesodermal embryonic tissue. Generally, coelom is the body cavity that lays between the musculature of the body wall and the digestive tract.

Which phyla are considered Acoelomates?

The three phyla considered in this chapter are the Platyhelminthes or flatworms; the Nemertea or ribbon worms; and the Gnathostomulida or jaw worms.

What is Meroblastic cleavage?

Meroblastic cleavage is a type of cleavage that occurs in very yolky eggs like birds in which the egg cytoplasm and not the yolk divides (incomplete division). There are two types of meroblastic cleavage discoidal and superficial. Discoidal usually occurs in birds, reptiles, fishes etc.

What are the two major clades of Bilateria?

The lophotrochozoan clade is still relatively poorly represented in terms of genomic resources compared to the other two major clades of bilaterians; the Ecdysozoa (containing arthropods, nematodes and other related phyla) and the Deuterostomia (chordates, echinoderms and hemichordates) [4].

Do rotifers have a coelom?

Roundworms (Nematoda) and rotifers (Rotifera) have a body cavity (coelom) where organs are found and that can serve as a hydrostatic skeleton. Their coelom is called a pseudocoelom because it is not completely lined by mesoderm.

Is spiral cleavage unique to the Spiralia?

Previously, spiral cleavage was thought to be unique to the Spiralia in the strictest sense—animals such as molluscs and annelids which exhibit classical spiral cleavage.

Which molluscs exhibit spiral cleavage?

Members of the molluscs, annelids, platyhelminths and nemerteans have all been shown to exhibit spiral cleavage in its classical form.

Is there a Lophotrochozoa with spiral cleavage?

More recent research has established the Lophotrochozoa as a superphylum within the Metazoa. With this understanding, the presence of spiral cleavage in polyclad platyhelminths, as well as the more traditional Spiralia, has led to the hypothesis that spiral cleavage was present ancestrally across the Lophotrochozoa as a whole.