Spiralia I: Animals with Lophophores


As discussed previously, the monophyly of Spiralia is well supported by molecular and morphological evidence. We now consider "Lophophorata" animals with ciliated feeding appendages called lophophores. Note: there are other animals with lophophore-like appendages that we aren't considering, including:


Bryozoan lophophore from Iowa State University -
Department of Ecology, Evolution, and Organismal Biology
"Lophophorates" are morphologically similar in sharing: Currently there is no strong argument that animals with lophophores are one another's closest relatives, however...

they do display clear similarities:


Two major groups (and two minor):

The relationships of these groups are discussed below. Mostly, we are concerned with Bryozoa and Brachiopoda, which have substantial fossil. records.


Phoronid anatomy from Kennesaw University

Phoronida:

(No record) Represent what we might imagine to be the ideal ancestral lophophorate. Characteristics: Why do we,as paleontologists, care about critters with no fossil record? Because they illuminate the relationships of critters with good records. Consider Conway-Morris and Peel, 1995's notion of a sister-taxon relationship between brachiopods and the early Cambrian (Sirius Passet) taxon Halkieria. Sounded reasonable only as long as:

Brachiozoa?: Cohen et al., 1998 and Cohen and Weydmann, 2005 indicated that phoronids are a valveless form of brachiopod. More recently, however, Hausdorf et al. 2010 find Phoronida to be the sister taxon of a monophyletic Brachiopoda. They name the Brachiopoda + Phoronida clade "Brachiozoa."

Recently, Sutton et al., 2010 described Drakozoon kalumon, a soft-bodied lophophore-bearing creature of Silurian age that might represent an intermediate grade between phoronids and brachiopods. Unlike phoronids, it attaches to the substrate by a broad attachment, but unlike brachiopods, has no mineralized valves - only a broad soft-tissue "hood."


Brachiopod in anatomical position from Invertebrate Paleontology Knowledgebase

Brachiopoda:

(Cambrian - Rec.) General characteristics:


Antarctic terebratulid brachiopods from BBC Nature

Brachiopod ecology: Although brachiopods encompass much diversity, certain generalizations are valid throughout.


Major clades: Biostratigraphers and other nuts-and-bolts employers of practical paleontology have long employed a traditional Linnean taxonomy of brachiopods, that has been unsettled by the rise of Phylogenetic Systematics. The application of the latter has resulted in the elevation of previously obscure lower-order groups to prominence and the dismissal of time-honored groups as paraphyletic. Here, we attempt a compromise: a survey of the phylogenetic taxonomy of the major traditional Linnean groups based primarily on Carlson, 2007. For a more detailed phylogeny see 3D Brachiopod Images at UC Davis.

In traditional taxonomy brachiopods were divided between "articulates" - those possessing tooth-in-socket hinged articulations between valves, and "inarticulates" - those lacking such articulations that rely on soft tissue to control valves. The application of phylogenetic methods, in contrast, reveals three major clades:



Lingula dissection from Udo Savilli,
Arizona State University - BIO385
Rhynchonelliformea: (C. - Rec.) Corresponds to the traditional concept of "articulates."

Rhynchonelliform systematics: A complex topic. Your text provides a detailed list of currently acknowledged monophyletic rhynchonelliform taxa. Here, we present six groups that are heavily cited in traditional century literature. In some cases, their monophyly is not certain:


Evolutionary trends: The relative abundance of different groups of these common fossils imparts a distinct character to shallow marine deposits of different systems. Thus even a geologist wit no interest in brachiopods, per se, should learn to identify them:


Xianshanella haikouensis
The ancestral brachiopod: Because creatures like Lingula show up early it is tempting to regard them as the ancestral brachipod morphotype, especially given their mobility. Key Cambrian fossils seem to refute this: We are left with a picture of an attached ancestral brachiopod with an articulate but phosphatic shell. We await the key fossils.

But what does any of this tell us about everyone's favorite group?


Phylactolaemate bryozoan zooid from Biodidac

Bryozoa:

The taxonomic history of this group is complex. Nineteenth century workers first applied "Bryozoa" to the same critters that bear it today. By the turn of the 20th century, however, the discovery of entoprocts had complicated matters such that workers recognized two classes of "bryozoans:" During the 20th century, these were recognized as being only distantly related. With Entoprocta removed, "Ectoprocta" became a junior synonym of Bryozoa. Today some workers continue to use Ectoprocta, however.

You've probably seen them without knowing it. General characteristics:


Bryozoan systematics:



From NC State University BIO 402

Diversity trends:

Lophophorate Phylogeny:

The Linnean "subkingdom" Lophophorata has been recognized as problematic since the early days of phylogenetic systematics, and remains controversial.

Relatively certain:

This says little about bryozoans. They seem to be closer to Trochozoa than to Ecdysozoa or Deuterostomia in most molecular analyses. Alas, the bryozoan genome is as derived as its morphology, making it a difficult subject for molecular methods:

We await:

Stay tuned.
Additional reading:

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