Marine biologyLesson 2 of 3 in the course Marine animals

Elasmobranch Anatomy, Jaw Suspension, and Evolutionary Classification

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Elasmobranchs include modern sharks, rays, skates, and sawfish. Their anatomy reveals how cartilaginous fishes feed, move, and maintain buoyancy without a swim bladder.

Elasmobranchs are cartilaginous fishes: their skeletons are made primarily of cartilage rather than bone. They typically have five to seven pairs of gill slits, with each pair opening separately to the exterior. Their bodies also have rigid dorsal fins and small, tooth-like placoid scales on the skin.

All flashcards

What are the typical gill and fin features of elasmobranchs?
They generally have five to seven pairs of gill slits that open separately to the exterior, as well as rigid dorsal fins.
What are placoid scales?
Small, tooth-like scales on the skin. Their structure is one of the characteristic features of elasmobranchs.
What does jaw suspension describe?
It describes how the jaws connect to or receive support from the cranium and nearby structures. Elasmobranchs show several patterns, including amphistyly, orbitostyly, hyostyly, and euhyostyly.
What are claspers, and what do they do?
Claspers are structures formed from the inner margins of male pelvic fins. They transfer sperm during reproduction.
How do elasmobranchs maintain buoyancy without a swim bladder?
They rely in part on large, oil-rich livers. The stored oil may also provide nutrients when food is scarce.

Quiz questions

  1. When did the oldest unambiguous total-group elasmobranch, Phoebodus, appear?Answer: In the Middle Devonian, around 383 million years ago.
  2. During which periods were hybodonts dominant elasmobranchs?Answer: The Triassic and Early Jurassic.
  3. In its narrow sense, what does Elasmobranchii refer to?Answer: The crown group of modern sharks, rays, and their descendants.
  4. Which two major lineages are commonly recognized among living elasmobranchs?Answer: Selachii, the sharks, and Batomorphi, the rays, skates, and sawfish.
  5. What does molecular evidence support about batoids?Answer: They form a monophyletic group with a common ancestor and all its descendants.

Based on the Wikipedia article Elasmobranchii, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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