16 Questions
What is unique about the size and shape of male and female ostracod carapaces?
They are similar in shape but differ in size
How many growth stages do ostracods undergo through molting?
Up to nine growth stages
What is the basis for classifying ostracods into different groups?
Five groups of features including shape, ornamentation, and hinge characteristics
What is unique about the valves of pelagic ostracods?
They have less CaCO3 and produce oil droplets
Where can benthic ostracods be found?
In all aquatic environments from the abyss to the shoreline
What is the characteristic of thermospheric ostracods?
They live in shallow, warm waters
What is the temperature range of psychrospheric ostracods' habitat?
Around 4-6°C
Why is great care necessary when classifying ostracods?
Because of their sexual dimorphism and ontogenetic variations
What is the key feature that ostracods share with other arthropods?
Bilateral symmetry of their body form
What is the primary component of the ostracod carapace that is commonly preserved in the fossil record?
Calcareous
In which type of aquatic environment are ostracods not found?
Terrestrial
When did the first freshwater forms of ostracods occur?
Carboniferous
What is the average size of an ostracod carapace?
1 mm long
What is the shape of the ostracod carapace?
Ovate, kidney, or bean-shaped
How do the two valves of the ostracod carapace connect?
At the dorsal side
What is the purpose of the ligament in ostracod articulation?
To facilitate valve movement
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).
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.
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