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Under the Dock: What Barnacle and Sea Squirt Larvae Reveal

Grade 8 practice comparing barnacle, brine shrimp, limpet, sea squirt, sponge and fish embryos and larvae to infer relationships adults hide.

Grade 8ScienceInteractive · Printable

Aligned toMS-LS4-3

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Circle the answer, Sorting, Short answer

About this worksheet

What students practice

Students compare early body features of several animals to infer which ones are most closely related.
Students explain why early stages can show relationships that adult anatomy hides.

How to use

Read the lab story and look at Table 1 together, naming each early feature. Students then answer on their own; discuss the barnacle and limpet cone shells before the display-card task.

Curriculum

NGSS standard covered

MS-LS4-3

Compare patterns in embryo development across species to find relationships not seen in adult anatomy.

Preview

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Under the Dock: What Barnacle and Sea Squirt Larvae Reveal

Compare the earliest stages of dock animals to find relationships their adult bodies hide.

Part 1: Adults and early stages

Read the lab story and Table 1, then answer questions 1–5.

Settlement Panels at the Marine Lab

1Each summer, the Gray Rock Marine Lab on a northern Atlantic harbor runs a four-week program for teens. In June, fourteen-year-old Ronan Kaszuba and five other students hung clean plastic panels under the lab's floating dock. When they pulled the panels up in August, the panels were crusted with life: white barnacles, soft sea squirts, orange crusts of sponge and the tubes of small worms.

2Adult barnacles look like tiny volcanoes made of hard plates, glued head-down to the panel. Through the opening at the top, each one sweeps the water with feathery legs to catch food. The limpets on the rocks of the lab's seawall look similar from above: a cone-shaped shell clamped to the rock. For a long time, many naturalists grouped barnacles with the mollusks, such as snails, clams and limpets, because of their hard shells. Adult sea squirts look nothing like fish. Each one is a soft, rubbery sac with two openings. Water flows in one opening and out the other, and the animal filters food from it, much as a sponge does. Adult sea squirts have no backbone, no tail and no fins.

3Dr. Amara Quintero, the lab's biologist, showed the students the earliest stages of these animals under a microscope. Many animals that live attached to one spot as adults begin life as tiny swimmers. Their main body features form while the embryo is still inside the egg, and they show plainly in the larva that hatches. Dr. Quintero's chart, Table 1, adds two more animals for comparison: brine shrimp, which the lab hatches as food for its fish, and the Atlantic silverside, a small fish that schools near the dock.

4The sea squirt larva is shaped like a tiny tadpole. It swims for a few hours to about a day, then glues its head end to a surface. Soon after, it absorbs its tail, including the stiff rod and the nerve cord inside it, and grows into the sac-shaped adult. Barnacle larvae swim and molt for one to a few weeks before they settle head-down and begin to build their plates.

5Ronan's job is to write cards for the lab's dock display that explain which animals on the panels are related to each other.

Table 1. Adults and early stages of six animals
Animal	Adult body	Early body shape	Jointed limbs (early)	Tail with stiff rod	Nerve cord along back
Acorn barnacle	Cone of plates, glued down	Shield shape, one eye	3 pairs	No	No
Brine shrimp	Many jointed legs, swims	Shield shape, one eye	3 pairs	No	No
Limpet	Cone shell, clamps to rock	Tiny top, ring of beating hairs	None	No	No
Sea squirt	Soft sac with two openings	Tadpole shape	None	Yes	Yes
Bread crumb sponge	Soft crust full of pores	Oval, covered in beating hairs	None	No	No
Atlantic silverside	Fish with backbone and fins	Fish shape with a tail	None	Yes	Yes