BIOL 112 Lab 7
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Invertibrate Diversity II
Objectives:
- Describe how acoelomate, pseudocoelomate, and coelomate animals differ and give examples.
- Identify the characters that identify flatworms, lophophorates, molluscs, and annelids
- Distinguish among the flatworm classes.
- Distinguish among the brachiopod classes and explain how they are adapted to their habitats
- Distinguish among annelid classes
- Distinguish among the classes of molluscs
majority of animals in 3 groups:
- ecdysozoans
- lophotrochozoans
- deuterostomes
Lophotrochozoans
Triploblastic development (3 germ layers: ecto–, meso–, and endoderm; but not all coelomates)
Two characteristic structures:
- lophophore: ciliated feeding structure near the mouth
- trochophore: larval stage in annelids and molluscs.
Platyhelminthes
Flatworms — the most adorable-looking worms ever!
Acoelomate body plan
rely on diffusion for transport of nutrients from intestine to cells; no anus.
Majority are parasitic
hermaphroditic
Turbellaria
Free-living (non-parasitic)
Two eyespots called ocelli
muscular protrusive, retractable pharynx
(like a cetacean penis)
Trematodes
Parasitic Flukes
multiple hosts
Cestoda
Parasitic Tapeworms
Anchored to intestinal tract with scolex; forms the region of cell division.
Proglottids grow from scolex to ...; nothing more than reproductive sacks for eggs; break off when mature
No digestive system
Lophophorates / Brachiopods
Sessile organisms wth true coelom
characteristic lophophore for feeding and respiration
| Character | Inarticulata | Articulata |
|---|---|---|
| Pedicle | Temporarily attached | Permanently attached |
| Lophophore | Not supported | supported |
| Gut | complete | blind |
| Hinge | simple, smooth | complex, toothed |
| Shell | flexble, protein | inflexible, calcareous |
| Pedicale aperture | absent | present |
| Outer Chitin Layer | present | absent |
| Habitat | Vertical burrows in sediment | rocks |
Inarticulata
Simple shells (valves) with hole in anterior for pedicle "foot"
Soft, flexible valves made of protein
Articulata
Slightly more complex shells with wavy pattern and a hinge for the valves
Hard, calcium valves
Mollusca
snails, clams, cephalopods
bilateral symmetry, non-segmented body, and a true coelom
[supposedly] trochophore larval stage
- muscular foot
- visceral mass containing organs
- mantle which protects visceral mass and may secrete shell
- mantle cavity housing gills (ctenidium), anus, and excretory pores.
Polyplacophora
Chitons
Dorsal plates (not segments)
Gastropoda
Slugs and snails
Their body is twisted (tortion) so that their anus and mantle cavity are above their head.
Bivalvia
clams, scallops, oysters, and mussels
most closely resemble brachiopods
3-layered valves (inner forms pearls)
Siphons carry water in and out of the mantle cavity across the gills
Cephalopoda
chambered nautilus, squid, and octopuses
smart, with well-developed nervous systems.
closed circulatory systems.
Chambered nautilus is only remaining shelled cephalopod.
Annelida
segmented worms
well-developed digestive, circulatory, and nervous systems
"ring" segments divided by septa
trochophore larval stage
Polychaeta
bristle worms
fleshy appendages (parapodia) with setae (bristles) on each segment
sessile polychaetes construct tube houses (and will likely be filter feeders; feeding structure resembles lophophore)
eyes, antennae, and chemoreceptors
Hirudinea
Leeches
predatory or parasitic
Oligochaeta
earthworms
segmented body plan, reduced chitinous setae at each segment (except for first and last)
glandular clitellum secretes mucus layer for use in reproduction