Lecture 16: Phylum Annelida, Part 3

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1 Lecture 16: Phylum Annelida, Part 3
Invertebrate Zoology Lecture 16: Phylum Annelida, Part 3

2 Lecture outline Phylum Annelida, Part 3
Nervous system/Sensory structures Class Polychaeta (previous lecture) Class Clitellata (briefly) Movement Reproduction

3 Nervous System: Class Clitellata (briefly)
Overall, similar to Polychaeta Minimal anterior sensory structures Class Oligochaeta Some with ocelli Body sensitive to a variety of stimuli “Epithelial sense organs” Class Hirudinoidea Negatively phototactic; some become positively phototactic prior to feeding. Mammalian blood-suckers respond to high temperatures

4 Movement Peristalsis Facilitated by compartmentalization of coelomic fluid

5 Movement Peristalsis (cont.) Hirudinoidea No compartments
Entire body acts as a single segment for “inchworm”-like movement

6 Movement Crawling Common in Class Polychaeta
Antagonistic action of left vs. right side longitudinal muscles (similar to…?) Role of parapodia?

7 Reproduction: Polychaeta
Regenerative ability/asexual reproduction Example: Chaetopterus and the amazing Segment 14

8 Reproduction: Polychaeta
Sexual Reproduction: Overview Most Polychaeta are gonochoristic Gametes develop from peritoneal cells Primarily external reproduction Spawning via coelomoducts, nephridiopores, or body wall rupture

9 Reproduction: Polychaeta
Epitoky Transformation of part or all of a non-reproductive benthic polychaete (atoke) into a swimming reproductive form (epitoke) Key physical changes Gut dissolves Gametes packed into coelom Large eyes develop Parapodia become paddle-like Behavior Orgy on a moonlit night…

10 Various epitokous forms

11 Reproduction: Polychaeta
Early development Classic protostome pattern… Trocophore larvae Apical tuft sensory Prototroch ciliary band for movement

12 More advanced larvae Segments added from the posterior end (but anterior of pygidium)

13 Reproduction: Oligochaeta
Sexual Reproduction: Overview Simultaneous hermaphrodites Gonads located in a few anterior segments Note male and female structures

14 Reproduction: Oligochaeta
Sexual Reproduction: Mating & Fertilization Alignment Role of clitellum in mating Transfer of sperm into spermatheca Direct (via penis) Muscular sperm grooves

15 Reproduction: Oligochaeta
Sexual Reproduction Formation of cocoon & secretion of albumin (clitellum) Cocoon movement Acquires eggs, then sperm Fertilization within albumin matrix of cocoon Development Cocoons deposited Direct development Clitellum epithelium