Are Snakes Vertebrates Or Invertebrates? A Detailed Look At Snake Anatomy

Snakes are some of the most iconic yet often misunderstood creatures on our planet. Their elongated bodies and lack of legs intrigue both young and old alike. But one question that often pops up in relation to snakes is – are they vertebrates or invertebrates?

If you’re short on time, here’s a quick answer: Snakes are vertebrates. They have an internal skeleton made up of vertebrae and spinal columns, classifying them squarely among other vertebrates like mammals, birds, and amphibians.

In this approximately 3000 word article, we will take an in-depth look at snake anatomy including their skeletal system, muscular system, circulatory system and nervous system. We will compare snakes to both vertebrates and invertebrates to clearly demonstrate why they fall into the vertebrate category.

The Vertebrate Skeletal System

Key Features of a Vertebrate Skeleton

Vertebrates are defined by several key anatomical features, with the vertebral column being the most prominent. The vertebral column is composed of small, interlocking bones called vertebrae that surround and protect the spinal cord. Other distinguishing features of vertebrates include:

• A skull that encloses and protects the brain
• A backbone with vertebrae
• A ventrally located heart with two, three, or four chambers
• A closed circulatory system
• Paired appendages like fins, limbs, or wings
• A digestive system with liver and pancreas glands

In addition to protecting internal organs, the vertebrate skeleton provides structural support, assists with movement via attachment sites for muscles, and facilitates gas exchange in land animals with the ribs aiding lung inflation.

The Snake Skeletal System

Like other squamates such as lizards, snakes exhibit features characteristic of vertebrates including:

• An articulated skull with fused but movable components
• A vertebral column comprising 200-500 vertebrae which form the snake skeleton
• Ribs attached to the elongated vertebral column

However, snakes differ from many other vertebrates in lacking paired appendages, and possessing uniquely adapted vertebrae and skulls for expansive jaw opening and swallowing large prey.

A 2017 study published in the Journal of Anatomy found snakes possess between 200-500 vertebrae compared to around 30-40 in most mammals. While snakes evolved from four-legged ancestors, evolution of their elongated body shape optimized for burrowing and climbing led to gradual limb loss.

Snakes maneuver with rippling body movements enabled by versatile vertebrae possessing ball-and-sockets joints giving flexibility in multiple planes.

Musculature in Vertebrates vs. Invertebrates

Muscles in Vertebrates

Vertebrates have a complex muscular system that allows for precise control of movement. There are over 600 different muscles in the human body alone! Vertebrates have skeletal muscles that attach to bones via tendons. Contraction of these muscles allows for locomotion and other movements.

Skeletal muscles are voluntarily controlled by the somatic nervous system. Vertebrates also have smooth muscles in organs like the stomach and intestines. These muscles contracted involuntarily to move food and other contents. Cardiac muscle makes up the heart, contracting rhythmically to pump blood.

The layered arrangement and versatility of vertebrate muscular systems allows for intricate movements.

Muscles in Invertebrates

Invertebrates generally have simpler muscular systems compared to vertebrates. Most invertebrate muscles are smooth muscles rather than the skeletal muscles found in vertebrates. Invertebrates like worms and mollusks use bands of smooth muscle to move by contraction and relaxation.

Arthropods like insects and crustaceans have striated muscles that allow for faster contractions. However, the overall muscular arrangement in invertebrates is less complex than vertebrates. While some invertebrates like octopuses have sophisticated nerve control over their muscles, allowing for complex movements, most invertebrates have more basic muscle systems designed for simpler actions.

The Muscular System of Snakes

The muscular system of snakes shares some features with both vertebrates and invertebrates. Like other vertebrates, snakes have a complex system of skeletal muscles that attach to vertebrae along the snake’s body. Contraction of these muscles allows snakes to locomote by slithering and sidewinding.

However, unlike most vertebrates, snakes lack limb musculature, giving them a more elongated invertebrate-like shape. Snakes also have very flexible skulls due to their intricately arranged head muscles, allowing them to swallow large prey items.

The combination of vertebrate and invertebrate muscular features in snakes provides them with an efficient, limbless body perfect for burrowing and climbing through their environments.

Circulatory Systems Across Species

Vertebrate Circulatory Systems

Vertebrates have closed circulatory systems with a heart that pumps blood through vessels. Oxygenated blood from the lungs flows to the heart, where it is then pumped through arteries to deliver oxygen and nutrients to tissues.

Deoxygenated blood returns to the heart through veins before being pumped back to the lungs to become re-oxygenated. This efficient system allows vertebrates to be active and maintain complex metabolisms.

Some key features of vertebrate circulatory systems include:

• A closed system of blood vessels including arteries, veins and capillaries
• A muscular heart with 2-4 chambers to pump blood
• Red blood cells containing hemoglobin to transport oxygen
• Valves in veins to prevent backflow of blood
• Higher blood pressure in arteries compared to veins

There are some variations in vertebrate circulatory systems based on activity levels and environment. For example, amphibians have a 3-chambered heart while birds and mammals have more efficient 4-chambered hearts.

Marine mammals like seals have higher blood volume and red blood cell counts to store more oxygen.

Invertebrate Circulatory Systems

Invertebrates have a diverse range of circulatory systems. Some simple invertebrates like sponges and jellyfish rely on diffusion for gas exchange and nutrient transport. More complex invertebrates have developed circulatory systems but they are open rather than closed since blood flows freely within body cavities or sinuses.

Here are some of the circulatory system variants seen in invertebrates:

• Open circulatory system – Blood flows freely in cavities and surrounds organs. Seen in arthropods and molluscs.
• Closed circulatory system – Blood is confined in vessels but has openings to body cavities. Present in annelids and cephalopods.
• Accessory pulsatile organs – Contractile vessels to aid circulation like the hearts in insects.
• No heart or pumps – Circulation relies on body movements like in worms.
• Haemolymph as blood fluid – Contains plasma but often no red blood cells.

Without efficient transport, oxygen delivery is limited in many invertebrates. As a result, they are often smaller in size and have lower metabolic rates compared to vertebrates. Only the most active invertebrates like squid and octopus have developed closed circulatory systems.

The Snake Cardiovascular System

As reptiles, snakes have circulatory systems that fall somewhere between the vertebrate and invertebrate models. Snakes possess a three-chambered heart – two atria and one ventricle, similar to amphibians.

The ventricle pumps blood first to the lungs and body tissues simultaneously via a partially divided circulatory system.

Some unique traits of the snake cardiovascular system include:

• Single ventricle heart pumps blood at different pressures for pulmonary and systemic circuits.
• Incomplete ventricular septum allows oxygenated and deoxygenated blood mixing.
• Low blood pressure compared to mammals.
• Lower heart rates and reduced activity capabilities.
• Development of renal portal system to supply kidneys.

The snake circulatory system allows sufficient gas exchange and provides nutrients to tissues thanks to the large surface area of the snake’s elongated body. But it is not as efficient in oxygen delivery compared to the four-chambered hearts of mammals and birds.

This places some limitation on snake metabolism and activity levels.

Nervous System Complexity in Vertebrates and Invertebrates

The Vertebrate Nervous System

Vertebrates have highly complex nervous systems with a brain and a spinal cord protected by the vertebral column. The brain integrates sensory information and controls motor functions. It is divided into several interconnected regions like the cerebrum, cerebellum and brainstem which handle higher cognitive functions, movement coordination and vital involuntary activities respectively.

The spinal cord relays signals between the brain and the body. It has grey matter containing neuron cell bodies and white matter containing their wire-like axons.

This advanced nervous system allows vertebrates to have greater environmental awareness, faster information processing, more coordinated body movements and higher intelligence than invertebrates. For example, some primates and cetaceans have self-awareness, complex emotions, problem solving skills and cultural transmission of knowledge.

The Invertebrate Nervous System

Invertebrates generally have simple decentralized nervous systems. Lower invertebrates like jellyfish and flatworms have loose nerve nets to detect stimuli and trigger reflex reactions. Higher invertebrates like insects have ganglia clusters interconnected by nerve cords to handle sensory input and motor output.

But they lack a distinct brain to analyze information and coordinate sophisticated responses.

So most invertebrates exhibit stereotyped pre-programmed behaviors guided by innate instincts rather than advanced learned intelligence. Their nervous system design limits cognitive feats achievable by vertebrates.

According to zoologists, invertebrates like octopus and ants show some basic problem-solving abilities but their neuronal complexity is still orders of magnitude below many vertebrates.

The Snake Nervous System

As reptiles, snakes have the vertebrate features like a true brain enclosed inside a skull, a centralized spinal cord and advanced sensory organs. But studies show their brain structure is comparatively simpler than other reptiles.

Regions handling integration of visual, thermal and chemical signals are enlarged to suit their unique sensory ecology as sit-and-wait predators.

Various parts of a snake’s nervous system show alternating phases of rest and activity associated with periods of still ambush hunting and sudden striking at prey. So while snakes are certainly neurologically more sophisticated than invertebrates, their information processing capability is considered lower than many other vertebrate groups.

Nonetheless, some advanced behaviors like nest building, migration, hibernation etc indicate advanced neurological flexibilities.

Conclusion

In this detailed overview, we have analyzed the key anatomical systems of snakes and compared them both vertebrates and invertebrates. As evidenced by their vertebral columns, complex muscular networks, closed circulatory systems and advanced nervous systems, snakes clearly belong to the vertebrate family.

The next time someone asks if snakes are vertebrates or invertebrates, you now have the knowledge to confidently respond that they fall into the former category. Their unique physiology sets them apart from other vertebrates in some ways, but deep down, snakes are very much vertebrate creatures.