Ecdysozoan Phyla Notes

The Smaller Ecdysozoan Phyla

Aschelminthes (Part II)

• Pseudocoelom:
  • Body cavity without mesodermal lining.
  • Filled with fluid or gelatinous material.
  • Functions in circulation and as a hydrostatic skeleton.
• Muscular pharynx
• Cuticle
• Adhesive glands
• NOT monophyletic

Phylogeny

• Ecdysozoa are part of the broader Animalia clade.
• Other major clades include Protists, Basal Phyla, Spiralia, and Deuterostomia.

Ecdysozoa Diversity

• Loricifera: ~10 species, 50 mm
• Priapula: ~16 species
• Onychophora: ~110 species
• Nematoda: ~25,000 species
• Tardigrada: ~800 species
• Arthropoda: ~1,000,000 species

Ecdysozoan Pseudocoelomates

• Characterized by a cuticle that is molted.
• Belong to the Cycloneuralia group.
• Possess an eversible introvert with a stylet-bearing mouth.
• Includes:
  • Nematoda
  • Nematomorpha
  • Kinorhyncha
  • Loricifera
  • Priapulida

Ecdysozoan Phylogeny Interpretation

• Based on Dunn et al. 2008 research.
• Phylogenomic sampling improves resolution of the animal tree of life, as published in Nature 452(7188): 745–749.

Nematoda (Roundworms)

• Among the most abundant animals, with approximately 5 billion per acre in fertile soil.
• Lack cilia and possess amoeboid sperm.
• Have longitudinal muscles only.
• Exhibit high turgor pressure.
• Most species are dioecious (separate sexes).
• Several species are relevant to humans.

Nematoda Anatomy (Figure 13.2)

• General Features:
  • Pharynx, intestine, anus.
• Female Reproductive System:
  • Uterus, egg, ovary, lateral excretory canal, gonopore, renette, seminal receptacle, oviduct.
• Male Reproductive System:
  • Testis, vas deferens, ejaculatory duct, cloacal aperture, seminal vesicle, rectal gland, spicule.
• Cuticle Structure:
  • Annuli, epicuticle, cortex, medial zone, basal zone, hypodermal syncytium.
• Cross-section:
  • Dorsal nerve, muscle process, cuticle, hypodermis, pseudocoelom, pharyngeal muscles, excretory canal, lateral epidermal cord, muscle cell, ventral epidermal cord, ventral nerve.

Nematomorpha (Horsehair or Gordian Worms)

• Juveniles are parasites of arthropods.
• Lack a digestive system as adults.
• Free-living adult phase lays eggs in water.

Priapulida (Penis Worms)

• Cylindrical body with a spiny introvert used for burrowing.
• External fertilization; eggs sink to the sea floor where larvae develop into adults.

Kinorhyncha

• Marine burrowers. Burrow with snouts
• No cilia, but have many spiny scalids.
• Dioecious; larvae molt into adult form.

Loricifera

• Discovered in 1983.
• Introvert and thorax can be retracted into the lorica (tough, platelike cuticle).