Phyla Placozoa & Ctenophora PDF

Phyla Placozoa & Ctenophora BZ 212 Animal Biology - Invertebrates Fall 2024 Zach Grochau-Wright, PhD  Trichoplax adhaerens Polyplactoma mediterranea Characteristics of Phylum Placozoa Minute, flattened metazoans composed of ciliated upper and lower cell layers; ameboid and fibrous cells...

Phyla Placozoa & Ctenophora BZ 212 Animal Biology - Invertebrates Fall 2024 Zach Grochau-Wright, PhD  Trichoplax adhaerens Polyplactoma mediterranea Characteristics of Phylum Placozoa Minute, flattened metazoans composed of ciliated upper and lower cell layers; ameboid and fibrous cells in a “gel” layer in between; adults discoidal and asymmetrical or with polytomous branching. With six somatic cell types. Cells with desmosome cell-cell connections With unique shiny spheres, possibly defensive structures, in upper cell layer. Without a structural nervous system, muscles, or digestive system. Placozoa Feeding By User:Teuteul - This file was derived from: Exodigestion chez Trichoplax adhaerens.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=50449534 Placozoa Reproduction Asexual – Fission – Swarmer formation: budding process that yields numerous multicellular flagellated “swarmers” each of which forms a new individual. Sexual – Known to occur but not well studied.  https://youtu.be/ImKFUHJdcLE?si=eEyJOyiCAamN8ZSY Coordinated movement without a brain Phylum Ctenophora Ctenophora summary table Ctenophora Facts ~130 Species Common names: Comb jellies, sea gooseberries, sea walnuts. Most are small but some can up to a meter Exclusively marine, mostly pelagic Most are predators Movement through beating of cilia in Ctenes (comb-like rows) https://youtu.be/JfiFKievLVs?si=S3VIiYInjUP7DEE2 Rotational Symmetry Ctenophore musculature Feeding, Digestion & Transport Most are predatory, trapping prey with Colloblast cells on tentacles. Highly branched system of Gastrovascular canals throughout body. Lack dedicated respiratory and circulatory systems but gastrovascular system distributes nutrients to and probably collects waste from rest of body. Colloblasts Multicellular structures used for prey capture. Produce sticky “glue” to capture prey Apical sense organ Used for sensing orientation and pull of gravity. Simple net-like nervous system.  Reproduction & Development High regenerative ability. Possible asexual reproduction through damage/fragmentation. Most species hermaphroditic, some gonochoristic. Typically, gametes released through mouth, and fertilization is external but internal fertilization occurs in some species. Diploblastic (maybe triploblastic?) development  Open Questions Is Porifera or Ctenophora sister to all other animals? Is Placozoa sister to Cnidaria or Bilateria? Laumer et al. 2018 eLife