BIOL 3270 – Zoology Napier
Fall 2021
Lab Assignment 3
Answer the following questions by typing your answers directly into the document below each question. This
assignment is due Monday November 15 at 2:00PM in the dropbox. An assignment turned in at 2:01PM is considered
late and will incur a late penalty as outlined in the syllabus.
1. What features of the head are homologous between the lamprey, shark, and perch? (10 pts.)
Lamprey, shark and perch share a number of head features. One of the primary homologous features is the presence of
a cranium in which there are also complex sensory organs. These organs include:
1. Brain: tripartite brain, meaning it is genetically divided into distinct forebrain, midbrain and hindbrain regions.
The hindbrain is also segmented.
2. Pituitary gland: secretes hormones that are heavily involved in the growth, reproduction, metabolism, and
general homeostasis of the organism.
3. Telencephalon (cerebrum): present at the anterior end, and is involved in various things including sensory
processing
Other homologous features between lamprey, shark and perch heads include paired eyes and the presence of one or
more nostrils.
2. Explain why must sharks swim continuously (or remain in areas with moving water currents) whereas bony fish do
not. How are bony fish able to not swim and survive? (5 pts.)
Sharks must swim continuously in order to move water through their gills and pick up oxygen. As they have no
mechanism to close or cover their gills, they must constantly push water over their gills to receive adequate oxygen.
Sharks also need to swim in order to prevent themselves from sinking to the seafloor. Relying only on the oil in their liver
is not enough to keep the sharks afloat, so they must keep swimming in order to maintain a pressure gradient via their
heterocercal caudal fin that prevents them from sinking. Comparatively, fish gills are covered by an operculum, which
enables them to effectively open and close their gills oxygen. The operculum moves water back and forth over the gills,
and is able to open and close even if the fish isn’t swimming (allowing the fish to still take up oxygen whilst not actually
moving). Bony fish also possess a swim bladder, which enables them to remain buoyant without needing to swim. The
swim bladder shrinks and expands by adjusting its internal gas pressure, which enables the fish to maintain a neutral
buoyancy without needing to create a pressure gradient like sharks do..
3. What is the function of the spiracles? Why is it important that rays and skates retained the spiracle while some
sharks lost it? (5 pts.)
Spiracles are modified gill slits that take in water and ventilate the gills. They are important in ensuring the organisms
gills receive enough water to provide them with the necessary amount of dissolved oxygen they need to survive. It is
important that rays and skates retained the spiracles because it enables them to take in water for gill ventilation whilst
still allowing them to be partly buried in the sand. As skates and rays hunt for their prey buried in the seafloor, they
need their spiracles to move water to their gills without giving up their location to prey. Sharks that swim on the seafloor
retained their spiracles for the same reason as the skates and rays, however sharks that live higher up in the water
column (away from the seafloor) do not need spiracles to ventilate their gills as the water can move over their gills and
ventilate them directly.
Fall 2021
Lab Assignment 3
Answer the following questions by typing your answers directly into the document below each question. This
assignment is due Monday November 15 at 2:00PM in the dropbox. An assignment turned in at 2:01PM is considered
late and will incur a late penalty as outlined in the syllabus.
1. What features of the head are homologous between the lamprey, shark, and perch? (10 pts.)
Lamprey, shark and perch share a number of head features. One of the primary homologous features is the presence of
a cranium in which there are also complex sensory organs. These organs include:
1. Brain: tripartite brain, meaning it is genetically divided into distinct forebrain, midbrain and hindbrain regions.
The hindbrain is also segmented.
2. Pituitary gland: secretes hormones that are heavily involved in the growth, reproduction, metabolism, and
general homeostasis of the organism.
3. Telencephalon (cerebrum): present at the anterior end, and is involved in various things including sensory
processing
Other homologous features between lamprey, shark and perch heads include paired eyes and the presence of one or
more nostrils.
2. Explain why must sharks swim continuously (or remain in areas with moving water currents) whereas bony fish do
not. How are bony fish able to not swim and survive? (5 pts.)
Sharks must swim continuously in order to move water through their gills and pick up oxygen. As they have no
mechanism to close or cover their gills, they must constantly push water over their gills to receive adequate oxygen.
Sharks also need to swim in order to prevent themselves from sinking to the seafloor. Relying only on the oil in their liver
is not enough to keep the sharks afloat, so they must keep swimming in order to maintain a pressure gradient via their
heterocercal caudal fin that prevents them from sinking. Comparatively, fish gills are covered by an operculum, which
enables them to effectively open and close their gills oxygen. The operculum moves water back and forth over the gills,
and is able to open and close even if the fish isn’t swimming (allowing the fish to still take up oxygen whilst not actually
moving). Bony fish also possess a swim bladder, which enables them to remain buoyant without needing to swim. The
swim bladder shrinks and expands by adjusting its internal gas pressure, which enables the fish to maintain a neutral
buoyancy without needing to create a pressure gradient like sharks do..
3. What is the function of the spiracles? Why is it important that rays and skates retained the spiracle while some
sharks lost it? (5 pts.)
Spiracles are modified gill slits that take in water and ventilate the gills. They are important in ensuring the organisms
gills receive enough water to provide them with the necessary amount of dissolved oxygen they need to survive. It is
important that rays and skates retained the spiracles because it enables them to take in water for gill ventilation whilst
still allowing them to be partly buried in the sand. As skates and rays hunt for their prey buried in the seafloor, they
need their spiracles to move water to their gills without giving up their location to prey. Sharks that swim on the seafloor
retained their spiracles for the same reason as the skates and rays, however sharks that live higher up in the water
column (away from the seafloor) do not need spiracles to ventilate their gills as the water can move over their gills and
ventilate them directly.
