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[Pygmy Squid Phylum: Mollusca] [Class: Cephalopoda] [Order: Idiosepida] [Family: Idiosepiidae]
About nine (9) species of pygmy squids belong in the superorder Decapodiformes. They are a group of tiny marine animals with bilateral symmetry.
Check out these fascinating fun facts about the dwarf squid species, including where they live, what they eat, and how these diminutive cephalopods reproduce.
The distribution tends to be concentrated in the warm, shallow marine waters of the Indo-Pacific region.
For example, they are more widespread around the soft-bottom coastal vegetation zones and sheltered waters of:
Pygmy squids flourish best around sandy or muddy seabeds, nearshore reefs, coastal lagoons, mangrove shallows, and seagrass beds.
They are found most often in calm and sheltered coastal zones at depths ranging between one (1) and twenty (20) metres.
Living among grassy plants and leaf litter means they can use their adhesive 'glue glands' to stick to the underside of grass blades for food and hide among the leaves for protection.
Some of the typical squid characteristics are reiterated in these miniscule cephalopods. Yet, several unusual traits, such as being minute and rounded, help set them apart from their close relatives, cuttlefish (Sepiida) and octopus (Octopoda).
Many of the fun facts about squids support their extraordinary appearance and behavioural traits. For example, a sticky dorsal organ is one of the defining features of members in the family Idiosepiidae.
The "glue gland" (located on the dorsal mantle) allows them to attach themselves to seagrass and other surfaces, meaning they can rest, hide, and prepare for ambush hunting.
Here's the thing:
Even though they have large eyes, their body is short and they have quite a wide fin around the posterior section of the bulbous shaped mantle.
Like many of the bobtail squid species, they use chromatophores to change the mottled body colouration. In fact, they can make it almost transparent and become close to invisible when they're hiding among vegetation.
Their extremely small size ranks them among some of the smallest cephalopods in the world. The mantle length of most adults rarely grows longer than twenty (20) millimetres.
Idiosepius paradoxus (northern pygmy squid) is considered as being the smallest in the species with a mantle size of fifteen (15) millimetres (0.6 inches).
By comparison, the female Austrorossia australis is one the biggest of all bobtail squids, with a total mantle length of about 6.3 centimetres (2.5 inches).
The pygmy squid diet is simple but specialised. Due to their tiny sizes, they tend to eat equally small crustaceans, especially copepods, amphipods, and mysid shrimp.
In general, most of the squid phylum display similar eating habits and hunting behaviours. While clinging to algae or seagrass, these tiny cephalopods deploy a rapid extension of their tentacle to capture prey and consume it with their two-part beak (called a rostrum).
Interesting Fact: Small squids are mid-level predators that help to control excessive populations of fish larvae and microscopic crustaceans. They're also an important food source in coastal food webs for other animals, such as marine mammals and seabirds.
When scientists first collected specimens from the Gulf of Thailand in 1991, they described the Thai pygmy squid (ปลาหมึกแคระไทย in Thai language) as one of the smallest squid species in the world.
One of their distinctive traits is the dorsal adhesive organ on their back, used for sticking to surfaces. They also have a ventral light organ that can store bioluminescent bacteria. It's used for counterillumination and camouflage, to help reduce predation.
Thai pygmy squids have a short, somewhat bulbous-shaped mantle, an anatomical feature that is typical in bobtail squids (Sepiolida). They use chromatophores to exhibit various colours, including black, brown, and green, sometimes with an iridescent shimmer.
The dorsal body of the females, sometimes referred to as the maximum mantle length (ML), is around ten (10) millimetres (0.4 inches).
Whereas, the males are one of the tiniest living cephalopods and they rarely grow much bigger than seven (7) millimetres long (0.28 inches).
As the scientific name suggests, Idiosepius thailandicus squids are native to the shallow, coastal waters of the Indo-Pacific. They are particularly common near the shores of Rayong province and Chanthaburi on the eastern seaboard of Thailand.
You find them inhabiting the littoral zones, shallow waters near the shoreline, where seaweed, mangroves, and seagrass beds are present.
Like most species of pygmy squids, their main diet consists of organisms that are bigger than themselves, such as tiny crustaceans and ghost shrimps (Palaemonetes paludosus) in particular.
Mating in pygmy squids is complex, but most short-lived marine invertebrates can increase the chances of survival through a high reproductive output.
After the males transfer their spermatophores, the females lay eggs in gelatinous masses and attach them to substrates or cover them in sand until they hatch.
Pro Tip: Even though the IUCN Red List assessed the Thai pygmy squid as "Data Deficient" in 2009, they are one of the species we look for when we go scuba diving in Pattaya, Samae San, and the island of Koh Chang.
The lifespan of dwarf squids is short, typically less than six (6) months long. So, similar to most cephalopods, they tend to exhibit rapid maturation and repeated spawning events.
Being dioecious animals means males and females are separate individuals with their own reproductive organs. So, the timing for the mating behaviour usually occurs during the darkness, a time when squids are most active.
During the courtship ritual, males try to attract females by displaying major colour changes combined with specific body movements. It's also common for some species to signal their readiness by releasing pheromones.
Then...
The male uses a special arm (called a hectocotylus) to transfer packets of sperm (called spermatophores) into the mantle cavity or the buccal area of the female (close to the mouth).
Following a successful fertilisation, the female will lay a small cluster of oval shaped, translucent eggs, and attach them to seagrass blades, mangrove roots, or macroalgae.
It's a brief process that rarely lasts more than a few minutes. There is no parental care and the adults will die soon after mating and egg-laying - a phenomenon known as semelparity.
One of the surprising squid facts is their high level of intelligence and their ability to be well-camouflaged. Still, they face a number of natural predators in their coastal habitats - and some human-related threats as well.
In the wild, the main predators are reef fish (e.g., cardinal fish, damselfish, and wrasses), crabs, bobtail squids (Sepioloidea), and some wading birds (especially egrets and herons).
Some of the most significant threats to their long term survival are caused by human-related activities, such as:
Important: Even though the International Union for Conservation of Nature (IUCN) does not see any specific risk for the population status of pygmy squids (family Idiosepiidae), some notable threats from habitat loss do exist.
Note: The short video [2:51 minutes] presented by 'Deep Marine Scenes' contains even more pygmy squid facts with rare footage of the Japanese pygmy squid (scientific name Idiosepius paradoxus).