Gnathiferans and Smaller Lophotrochozoans

1. Gnathiferans and Smaller Lophotrochozoans • Chapter 9

2. Protostomes Characteristics • Protostome groups consisting of two large clades the Lophotrochozoans and the Ecdysozoans. • Lophotrochozoans include 10 smaller protostome phyla. • Acoelomate, Pseudocoelomate or Eucoelomate bodies.

3. Protostome Characteristics Protostome • Development is characterized by: • blastopore becomes the mouth • Spiral / determinate cleavage • Schizocoely

4. Mouth Formation Blastopore becomes the mouth and the anus forms secondarily Future anus blastopore archenteron (primitive gut) mouth

5. Cleavage • Cleavage is the initial process of development after fertilization of the egg.

6. Radial Cleavage planes are symmetrical to the polar axisProduces regulative development

7. Spiral Cleavage: cleavage planes are oblique to the polar axisProduces mosaic development

8. Schizocoely blastocoel Mesodermal cells Split in mesoderm Developing coelom ectoderm endoderm mesoderm

9. Body Cavities in Triploblastic Animals

10. Acoelomate Characteristics No body cavity ectoderm mesoderm Gut endoderm

11. Pseudocoelomate Characteristics “false” body cavity ectoderm pseudocoelom mesoderm Gut endoderm the pseudocoelom is lined by mesoderm onONE side only

12. Gut Eucoelomate (Coelomate) Characteristics Have a “true” body cavity that is completely surrounded by mesoderm ectoderm coelom mesoderm endoderm

13. Coelomate or Eucoelomate Characteristics the coelom • is a closed, fluid filled cavity that surrounds the gut • mesodermal membranes (mesenteries) suspend organs in the coelom

14. The Lophotrochozoa

15. Lophotrochozoans Characteristics Organ level of organization Tissues are organized to form organs which are used to accomplish physiological functions. Triploblastic 3 Germ Layers endoderm mesoderm ectoderm 3 Tissue Layers gastrodermis mesoderm epidermis

16. Lophotrochozoans Characteristics Bilateral Symmetry • with anterior and posterior ends Cephalization • concentration of sensory organs in the head of the animal

17. Lophotrochozoans Characteristics Digestive System • complete (they have an anus!) • some regional specialization Circulation System • no system (or organs) • performed by the pseudocoelom fluid

18. Gnathifera There are 4 different phyla that are classified as Gnathifera. Rotifera Acanthocephala Gnathostomulid Micrognathozoa

19. Gnathifera Characteristics • Other than the Acanthocephalans all phyla posses small, cuticular jaws with a homologous microstructure.

20. Gnathifera Characteristics Eutely • each individual of a species has the same number of cells • growth occurs by cells getting bigger rather than dividing

21. P: Gnathostomulida : gnatho, “jaw”; stoma, “mouth” jaws and basal plate • Benthic, interstitial • Monociliated epidermal cells • Jaws and muscular pharynx • Often vermiform • Hermaphroditic • About 80 species have been described Gnathostomulid

23. P: MicrognathozoaLimnognathia maerski

24. Phylum Rotifera the rotifers

25. Phylum Rotifera: rota, “wheel”; fera, “to bear” • Includes about 1,800 described species. • Tiny metazoans (up to 3 mm), that are predominantly freshwater although some are marine and terrestrial (live in mosses).

26. The “wheel” animals { Head { Trunk { Foot

27. Corona • have a “crown” of cilia called a corona • the corona creates a current to bring food into the mouth

28. Corona of Foscularia species

30. Body Wall and Support • Most rotifers possess a gelatinous cuticle outside the syncytial epidermis. • They possess a skeletal lamina which produces the lorica and other surface structures.

31. Rotifers of the genus Keratella don't possess a foot. They are fast swimmers. Their lorica (shell) looks like a jigsaw puzzle and is covered with small spikes. There are long spines on each corner. The photograph shows how the cilia are grouped in tufts.

32. Kellicottia is a rotifer that lives in open waters like lakes. The long spines might prevent them from being eaten by predators.

33. Well developed and complex muscle bands

34. Body appears to be composed of segments, they are superficial segments.

35. Feeding • have a specialized feeding structure called the: mastax-trophi complex modified jaws within the mastax a modified muscular pharynx

36. Looking down into the corona….

37. Mastax-trophi complex

38. Some of the trophi (jaws): Malleate mastax Ramate mastax These are crushing/grinding forms.

39. Some of the trophi (jaws): Forcipate mastax Incudate mastax These are grasping, predatory forms.

40. Nervous and sensory system • cephalization, cerebral ganglia • dorsal and ventral nerve cords • eyes • Circulatory system • no system (no organs) • performed by fluid in pseudocoelom • Excretion • protonephridia and flame cells • cloacal bladder (collects wastes)

41. Reproduction Sexual • complex life cycle with different types of eggs • usually dioecious but in some groups, males are absent (parthenogenesis) • Parthenogenesis: unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)

42. Reproduction • 2 types of eggs: amictic & mictic Amictic eggs – Asexual Reproduction • diploid (mitotically produced) • can’t be fertilized • develop into diploid, amictic females

43. Reproduction Mictic eggs- Sexual and Asexual Reproduction • haploid (meiotically produced) • produced after some sort of environmental stimulus (eg. high density, change in temperature) • if unfertilized, develop into haploid males • if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females

46. Resting eggs of monogonot rotifers

47. Reproduction • Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!). • Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!