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

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

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

Movement Peristalsis Facilitated by compartmentalization of coelomic fluid

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

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

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

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

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…

Various epitokous forms

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

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

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

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

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