Biology: Phylum Arthropoda, Class Ostracoda

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Questions and Answers

What is unique about the size and shape of male and female ostracod carapaces?

They are identical in size and shape

They are similar in shape but differ in size (correct)

They are completely different in both size and shape

They are similar in size but differ in shape

How many growth stages do ostracods undergo through molting?

Up to nine growth stages (correct)

Ten to twelve growth stages

Five to seven growth stages

No growth stages, they grow continuously

What is the basis for classifying ostracods into different groups?

Only the size of the valves

Shape and size of carapaces only

Five groups of features including shape, ornamentation, and hinge characteristics (correct)

Only the shape of the valves

What is unique about the valves of pelagic ostracods?

They have less CaCO3 and produce oil droplets Signup and view all the answers

Where can benthic ostracods be found?

In all aquatic environments from the abyss to the shoreline Signup and view all the answers

What is the characteristic of thermospheric ostracods?

They live in shallow, warm waters Signup and view all the answers

What is the temperature range of psychrospheric ostracods' habitat?

Around 4-6°C Signup and view all the answers

Why is great care necessary when classifying ostracods?

Because of their sexual dimorphism and ontogenetic variations Signup and view all the answers

What is the key feature that ostracods share with other arthropods?

Bilateral symmetry of their body form Signup and view all the answers

What is the primary component of the ostracod carapace that is commonly preserved in the fossil record?

Calcareous Signup and view all the answers

In which type of aquatic environment are ostracods not found?

Terrestrial Signup and view all the answers

When did the first freshwater forms of ostracods occur?

Carboniferous Signup and view all the answers

What is the average size of an ostracod carapace?

1 mm long Signup and view all the answers

What is the shape of the ostracod carapace?

Ovate, kidney, or bean-shaped Signup and view all the answers

How do the two valves of the ostracod carapace connect?

At the dorsal side Signup and view all the answers

What is the purpose of the ligament in ostracod articulation?

To facilitate valve movement Signup and view all the answers

Study Notes

Phylum Arthropoda: Subphylum Crustacea, Class Ostracoda

Body Form and Symmetry

Ostracods have bilateral symmetry in their body form, similar to other arthropods.

Carapace Composition and Features

Ostracod carapace consists of two valves (right and left) connected at the dorsum by a hinge and separate at the ventral.
Carapace composition: chitinous (rarely fossilized) and calcareous (fossilized).
Size: range from 0.3‒3.0 mm long, average size typically about 1 mm long.
Shapes: ovate, kidney, or bean-shaped.
Outer surfaces can be smooth or ornamented with pits, striations, reticulations, spines, sulci, tubercles, or wings-shaped (alae).

Muscle Scars and Articulation

Valves of a shell are not commonly the same size, so one overlaps the other.
Articulation can be done by ligament (chitinous material, unfossilized), hinge (teeth, sockets, ridges, and grooves), ridges on the duplicature, or adductor muscles.

Ontogeny and Sexual Dimorphism

Ostracods show sexual dimorphism, with males and females having carapaces of differing size and shape.
They grow by molting up to nine growth stages.
Dimorphic two shells are typically similar in everything but not in size. Male-shell is generally longer than the female-shell.

Taxonomy and Classification

Ostracods classification is generally based on 5 groups of features: general shape, size, convexity of valves, and the portion of greatest thickness; position of and amount of overlap of the valves; ornamentation; hinge characteristics; and structures due to sex differences.
The living ostracods are further classified in many cases by variations in their appendages and other soft parts.

Distribution and Ecology

Ostracods are found in almost all aquatic environments, including fresh and marine waters, within the water column, and on/in the substrate.
They can be pelagic (planktonic) or benthic (on/in the sea floor).
Thermospheric ostracods live in shallow, warm waters ( > 10° C), while psychrospheric ostracods inhabit cold, deep waters (≥ 500 m, temperature around 4 to 6° C).

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Description

This quiz covers the characteristics and features of Ostracoda, a class of crustaceans within the phylum Arthropoda. Learn about their body structure, symmetry, and habitats.