Worm Anatomy Slides
STEAM Biology & Engineering Lab
Specimen: Lumbricus terrestris
Comparative Anatomy & Biomechanics
Earthworm Anatomy & Systems
Investigate organ specialization, closed circulatory transport, and hydrostatic propulsion in subterranean ecosystem engineers.
Lab Safety
Scalpels & Pin Protocol
Dissection
Internal Morphology
STEAM Focus
Peristaltic Soft Robotics
01
Biological Classification
Meet Lumbricus terrestris
Phylum: Annelida (Segmented Worms)
Metamerism
Body divided into repetitive segments called metameres (~100–150), separated internally by membranes called septa.
Enables localized movement & structural resilience.
True Coelom
Coelomate organisms possess a fluid-filled body cavity lined with mesoderm that functions as a hydrostatic skeleton.
Provides structural support without rigid bone.
Soil Engineers
Digest leaf litter and mineral grains, aerating subterranean soil horizons and cycling organic nitrogen and phosphorus for plant roots.
Crucial foundation of terrestrial soil health.
Key Fact: Earthworms lack lungs. Gas exchange occurs directly through their thin, moist cuticle into capillaries.
02
Safety First
Dissection Rules & Tool Protocol
Mandatory Lab Standards
Personal Protective Equipment
- Splash Goggles: Kept on throughout the entire lab until trays are rinsed.
- Nitrile Gloves: Protect skin from chemical preservative fluids.
- Specimen Rinsing: Pat worm dry with a paper towel before cutting.
Sharp Tool Technique
- Cut Away: Always direct scalpel or scissor blades away from yourself and partners.
- Shallow Incision Only: Cut only the skin! Do not slice deeply into internal organs.
- The 45-Degree Pin Rule: Insert pins outward at a 45° angle to keep working area clear.
Ethics & Respect: Treat biological specimens with dignity and academic purpose at all times.
Rule: No scalpel walking
03
Phase 1 Investigation
External Anatomy & Orientation
Before Making Any Cuts!
Orientation
Anterior vs Posterior
The anterior end is closer to the clitellum and thicker. The posterior end extends further away to the anus.
Head end = darker & pointed
Surface
Dorsal vs Ventral
The dorsal (top) side is dark, rounded, and has a visible dorsal vessel line. The ventral (belly) side is lighter and flatter.
Ventral = felt with setae
Landmark
The Clitellum
A swollen, saddle-like glandular band spanning segments 32–37. Secretes a mucus cocoon to house eggs during reproduction.
Primary anatomical landmark
Locomotion
Bristles (Setae)
Four pairs of microscopic chitinous bristles per segment. Gently rub your finger along the belly to feel their friction grip.
Provides traction in soil
Student Action Check: Place worm Dorsal side UP in dissecting pan before proceeding!
04
Phase 2 Dissection
The Dissection Technique
Precision Over Force
1
Anchor Worm
Place your specimen dorsal-side UP. Insert one dissecting pin through the prostomium (tip of head) and another near the posterior tip at 45° angles.
Holds specimen taut without ripping delicate tissue.
2
Shallow Incision
Make a shallow pinch cut just posterior to the clitellum. Insert scissor tip and cut forward along the mid-dorsal line toward segment 1.
Warning: Lift scissors upward to avoid puncturing organs!
3
Pin Skin Flaps
Gently spread the body wall. Use a probe to sever thin internal septa membranes. Pin skin flaps outward to the wax tray like an open book.
Add a few drops of water to keep organs glistening.
Pro Tip: Angle all pins outward so your magnifying lens and fingers can move freely above the dissection bed.
05
Anatomy Mapping
Key Internal Organ Systems
Anterior Segments 1–35
Aortic Arches (5 Pairs)
Circulatory
Dark vascular bands looping over the esophagus (segments 7–11). They act as muscular pumping accessory hearts in a closed circulatory system.
Crop & Gizzard
Digestive
Crop: Soft, thin-walled food storage pouch.
Gizzard: Rigid, highly muscular organ that grinds food with ingested sand grains.
Seminal Vesicles
Reproductive
Prominent creamy-white, lobed organs located around segments 9–12. Store maturing sperm (earthworms are simultaneous hermaphrodites).
Ventral Nerve Cord
Nervous
Thin, whitish cable running along the ventral floor underneath the digestive tract, punctuated with segmental ganglia.
Alimentary order: Mouth → Pharynx → Esophagus → Crop → Gizzard → Intestine → Anus
06
STEAM Connection
Hydrostatic Skeletons & Soft Robotics
Bio-Inspired Engineering
Peristaltic Biomechanics
Annelids generate movement via antagonistic muscle layers exerting pressure against non-compressible coelomic fluid:
Circular Muscle Contraction:
Worm elongates and thins, pushing forward into soil pores.
Longitudinal Muscle Contraction:
Worm shortens and thickens, anchoring setae to pull body forward.
Biomimetic Soft Robots
Engineers build pneumatic soft robots modeled directly after worm peristalsis:
- Pipeline Inspection: Crawl through confined, irregular subterranean utility pipes.
- Disaster Search & Rescue: Navigate unstable rubble and collapsed masonry.
- Medical Endoscopy: Flexible atraumatic locomotion through internal human tissues.
STEAM Engineering Challenge: How would you program pneumatic chambers to replicate peristalsis?
07
Synthesis & Clean-Up
Debrief & Station Protocol
Disposal & Lab Review
Station Sanitation Steps
- Wrap specimen in paper towel & discard in designated biohazard bin.
- Remove dissecting pins, count all 8 pins, dry, and return to magnetic pad.
- Wash dissecting tray and tools with disinfectant soap and air-dry.
- Wipe lab bench with sanitizing wipes; dispose gloves in regular trash.
Post-Lab Inquiry Prompts
- Why does a worm need a gizzard while humans rely on teeth for mechanical digestion?
- How does segmentation allow survival if an accidental partial injury occurs?
- Complete analysis questions in your Student Dissection Guide.
Lab Notebook Due: Labeled internal anatomy diagram + 4 analysis prompts
Worm Dissection Student Guide
Earthworm Dissection Guide
STEAM Life Science • Phylum Annelida • Lumbricus terrestris
Student Lab Notebook
Page 1 of 3
Student Name
Lab Partner
Period / Class
Date
Pre-Lab Safety Readiness Sign-Off
Goggles & gloves equipped Scalpel cutting away from body 45° pin insertion technique verified
1
External Morphology Observations
Examine your preserved specimen under good light. Gently roll the worm between your fingertips to locate the dorsal and ventral surfaces. Test the ventral surface for tiny bristle-like setae.
| Anatomical Landmark | Diagnostic Characteristic | Your Specimen Observation |
|---|
| Total Body Length | Measure along ruler in pan | |
| Dorsal vs. Ventral Color | Dark rounded top vs. light belly | |
| Clitellum Position | Swollen saddle (approx seg 32–37) | |
| Setae Texture Test | Sandpaper grip felt on belly | |
2
External Sketch & Labeling
Required labels: Anterior, Posterior, Prostomium, Clitellum, Setae
Draw external dorsal view of specimen with orientation indicators:
Turn page for Internal Dissection Protocol • Check with instructor before cutting EARTHWORM-DISSECT-01
Internal Anatomy Dissection
Step-by-step incision and organ system identification
Page 2 of 3
Step 1: Anchor
Pin anterior prostomium and posterior tip into wax bed at 45° angle.
Step 2: Snip
Pinch skin posterior to clitellum; make shallow dorsal cut forward to head.
Step 3: Separate
Use blunt probe to tease septa membranes away from digestive tract.
Step 4: Pin Open
Pin skin flaps outward at 45° on both sides. Add drops of water to moisten.
Internal Organ Identification & Diagramming
Label 1–8 using Word Bank below
1. Mouth & Pharynx
Muscular suction pump (seg 1–6)
2. Aortic Arches (5 Pairs)
Pumping vessels over esophagus
3. Seminal Vesicles
Creamy lobed sperm sacs (seg 9–12)
4. Crop
Soft thin-walled food pouch
Anterior
Pharynx
Worm Dissection Teacher Key
Dissection Teacher Guide & Key
Teacher-Facing
STEAM Life Science • Lab Logistics, Timing & Pacing Reference
Page 1 of 2
Per-Station Materials Setup (Pairs of 2)
• Biological Equipment
1 Preserved earthworm (7–9")
1 Dissecting pan with wax bed
8 T-pins / dissecting pins
• Dissection Tools
1 Fine-point dissecting scissors
1 Blunt dissecting probe
1 Hand lens / magnifier (5x–10x)
• Safety & Clean-Up
2 Pairs chemical splash goggles
2 Pairs nitrile gloves
Paper towels & dropper with water
Instructional Pacing Breakdown (55-Minute Block)
0:00 – 0:10 (10 min)
Slide Deck Direct Instruction
Review safety, pinning angle, taxonomy, and peristalsis engineering link.
0:10 – 0:22 (12 min)
Phase 1: External Anatomy
Tactile setae test, segment counting, clitellum identification, and sketch.
0:22 – 0:42 (20 min)
Phase 2: Internal Dissection
Incision posterior to clitellum, teasing septa, pinning body wall, organ mapping.
0:42 – 0:55 (13 min)
Clean-Up & Synthesis
Biohazard disposal, tool sanitation, pin count, and STEAM analysis completion.
Dissection Pitfalls & Troubleshooting
Pitfall 1: Cutting Too Deep
Students often push scalpel blades straight down, shredding the crop, gizzard, and aortic arches. Intervention: Mandate using fine-point scissors with the blade tip tilted upward against the underside of the dorsal body wall.
Pitfall 2: Forcing Flaps Open
Skin flaps will tear if pulled without severing internal septa. Intervention: Demonstrate using a blunt probe to stroke parallel between the gut tube and body wall to release septa before pinning.
Pitfall 3: Dried Specimen Tissues
Preserved organs dry quickly under room air, becoming unrecognizable brown smudges. Intervention: Have students add 3–4 drops of tap water directly onto the opened cavity every 5 minutes.
Differentiation & Accommodations
For Reluctant / Squeamish Students: Assign the role of "Lead Data Documenter & Anatomical Navigator." They read steps, manage pins, take macro photos, and record findings while their partner executes cuts.
Advanced / STEAM Extension: Have students calculate the mechanical advantage of the gizzard or draft a CAD schematic of a 3-chamber peristaltic soft actuator with valve timings.
