Octopuses are a fascinating group of creatures that belong to the phylum Mollusca, class Cephalopoda. There are over 300 recognized octopus species that can be divided into 7 different classifications based on their physical characteristics, habitat, and behaviors. Understanding the different classifications of octopuses provides insight into the diversity and evolution of these intelligent invertebrates.
The 7 Classifications of Octopuses
The 7 major classifications of octopuses are:
1. Incirrata
The incirrate octopuses lack cirri and an internal shell. Most species in this group live in deep water. Examples are the Dumbo octopus, glass octopus, and vampire squid.
2. Cirrata
Cirrate octopuses have cirri, which are fleshy feeding appendages, and an internal shell. They are mostly deep-sea dwellers. Examples include the umbrella octopus, Grimpoteuthis, and Opisthoteuthis.
3. Arginautidae
This family includes the argonauts or paper nautiluses. The females secrete a thin, coiled shell while the males lack an external shell. They are pelagic octopuses living near the ocean surface.
4. Bathypolypodinae
Octopuses in this subfamily inhabit deep waters. They lack an ink sac and have reduced or no suckers on their arms. Examples are Bathypolypus and Vulcanoctopus.
5. Eledoninae
These are deep-sea octopuses with a sac-like body and web that connects their arms. This group includes only one genus, Eledone.
6. Octopodinae
This is the largest subfamily with over 100 species, including the common octopus, day octopus, and night octopus. Most occupy shallow, coastal waters and have an ink sac.
7. Megaleledoninae
This is a small group of 3 deep-sea genera, including the seven-arm octopus and spoon-arm octopus, with spoon-shaped suckers.
Unique Traits of Major Classifications
Each octopus classification has evolved distinct physical and behavioral adaptations for their habitat and lifestyle:
Incirrata:
– Lack of cirri
– Internal shell reduced or absent
– Deep sea dwellers
– Gelatinous/sac-like bodies
Cirrata:
– Presence of cirri for feeding
– Vestigial internal shell
– Deep sea habitats
Argonautidae:
– Females secrete a thin, coiled shell
– Males lack external shell
– Pelagic, live near ocean surface
Bathypolypodinae:
– No ink sac
– Reduced arm suckers
– Deep sea environments
Eledoninae:
– Sac-like body with arm web
– Single genus Eledone
– Abyssal plains habitats
Octopodinae:
– Ink sac present
– Coastal, shallow water habitats
– Most diverse and widespread
Megaleledoninae:
– 7 arms in some species
– Spoon-shaped arm suckers
– Deep sea adapted
Habitats and Behaviors of Octopus Classifications
The different octopus classifications inhabit specific marine environments and have behaviors adapted to their lifestyles:
| Classification | Habitat | Behavioral Adaptations |
|---|---|---|
| Incirrata | Deep ocean and seafloor | Slow movements, transparent body, bioluminescent in dark depths |
| Cirrata | Deep ocean bottoms | Crawl along seafloor, use cirri to capture food |
| Argonautidae | Warm, open ocean near surface | Females secrete shell for egg case and float near surface, males swim actively for females |
| Bathypolypodinae | Seafloor at abyssal depths | Little known, reduced arm suckers may aid crawling along seafloor |
| Eledoninae | Abyssal plains | Web connects arms for swimming and capturing prey |
| Octopodinae | Rocky coasts, coral reefs, seabeds | Ink defenses, camouflage, nimble movements, some live in shells |
| Megaleledoninae | Deep benthic environments | Spoon-shaped suckers adapted for habitat, otherwise little known |
Evolutionary Relationships Between the Classifications
Scientists are still working to uncover the evolutionary relationships and development of the different octopus groups. However, some insights into their connections include:
- The incirrate octopuses are believed to be basal or primitive, with the cirrates evolving later.
- Argonautidae octopuses are nested within Incirrata but have clear adaptations like the shell.
- Cirrata and Incirrata octopuses share common descent indicated by DNA studies.
- Octopodinae represent the largest and most diverse modern radiation of octopuses.
- Bathypolypodinae may be an early branching lineage from deep sea ancestors.
- Megaleledoninae and Eledoninae share common ancestry from a deep sea progenitor.
Additionally, some believe the octopuses evolved from a common ancestor with vampyromorpha (vampire squid). Others argue ancestors of octopuses split earlier from squid and cuttlefish lineages. More fossil evidence and molecular analysis is needed to clarify these relationships.
Threats Facing Different Octopus Species
Many octopus species face increasing threats, including:
Incirrata:
– Deep sea trawling disturbing seafloor habitats
– Entanglement in fishing gear
Cirrata:
– Impacts of deep sea mining
– Disturbance of seabed from trawling
Argonautidae:
– Bycatch from tuna and swordfishing
– Ingestion of plastic pollution near surface
Bathypolypodinae:
– Deep sea mining impacts unknown
– Disturbance of abyssal environments
Eledoninae:
– Seismic surveys on abyssal plains
– Expanding deep sea trawling
Octopodinae:
– Habitat loss from pollution and coastal development
– Overfishing for food markets
– Entanglement in discarded fishing gear
Megaleledoninae:
– Expanding deep sea mining
– Impacts on benthic habitats unknown
Conclusion
Octopuses display a fascinating diversity of forms and behaviors across 7 major classifications and numerous species. These marine invertebrates have adapted to habitats from shallow, tropical waters to the lightless ocean depths. However, expanding human activities across these environments increasingly threaten many octopus populations. Understanding the evolutionary relationships, ecology, and conservation status of the different octopus groups remains an important area of continuing research. Protecting the health of oceans and deep sea ecosystems will be key to preserving octopus biodiversity into the future.
