Idiosepius paradoxus

Geographic Range

Idiosepius paradoxus , the Japanese pygmy squid, is native to the western Pacific Ocean, near the waters of Japan, northern Australia, and South Korea. It can be found in the whole Indonesian Pacific region ranging from South Africa to Japan to Southern Australia.

• Biogeographic Regions
• australian australian
  • native native
• indian ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Idiosepius paradoxus is a benthic species living in shallow, inshore waters.

• Habitat Regions
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

Idiosepius paradoxus can grow up to 16 mm in mantle length. In one study off Japan, female size ranged from 4.2 mm to 18.8 mm in mantle length and 15 mg to 796 mg in wet body weight. The males ranged from 4.2 mm to 13.8 mm in mantle length and wet body weight ranged from 10 mg and 280 mg.

The smallest of the cephalopods, I. paradoxus varies in colors and size. Size and maturation varies with season as they produce two generations a year. They are sexually dimorphic, with the females larger than the males.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Idiosepius paradoxus does not have a larval stage. Instead their development is direct. Having a toothed beak is a sign of pedomorphosis compared to other cephalopods that have toothed beaks in their para-larval forms.

• Development - Life Cycle
• neotenic/paedomorphic

Reproduction

Sexes are separate and fertilization is internal. One of the male’s arms is differentiated and contains a hectocotylus at the tip. This arm is then jammed into the female’s body cavity. Courting can occur and this is done in this species by means of changing color, body movements or the combinations of both. Male Idiosepius paradoxus mature faster than females in both the cool and warm seasons.

• Mating System
• polyandrous polyandrous

Males tend to copulate with females while they are laying eggs. Males choose copulation over courtship with females whenever the occasion arises. Since they are quick to act, a male sometimes mistakes other males as females and implants his spermatangia into a male. These pygmy squid become sexually mature after 1.5-2 months. For over a month the female lays 30-80 eggs every 2-7 days when kept in a lab setting. Spawning occurs late February to mid-May and from June to late September. In a natural setting, eggs are laid in a flat mass onto substrates.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

Idiosepius paradoxus has a life span of 150 days, likely the longest living Idiosepius species. The longer life span is possibly due to Idiosepius paradoxus having a slower growth rate in lower temperatures. They have two generations with differing sizes. In the warm season they become sexually mature faster but are smaller and in the cool season they grow larger over the winter, but take a longer time to become sexually mature.

Behavior

Idiosepius paradoxus stays near the coast and lives in the algae or beds of sea grass such as eelgrass. It adheres to the substrate using an adhesive organ that is located on the dorsal mantle.

• Key Behaviors
• motile motile
• sedentary sedentary

Communication and Perception

No specific studies have been conducted for Idiosepius paradoxus , but in general, Decapodiformes can change color, body patterns, and texture. These changes can possibly be used to communicate with each other and are used in mating, camouflage, and eluding predators. To see color changes they need to have a well-developed eye and rely on visual sense to locate food. A highly advanced olfactory sense aids them in their benthic lifestyles in the sea grass.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Idiosepius paradoxus prefers to feed on crustaceans, gammarids , grass shrimp , and mysids . Although an initial study concluded I. paradoxus does not attack fish, a later study showed the contrary. When attacking fish the pygmy squid usually only eats the muscle mass and leaves the bones intact, usually as complete skeletons. Idiosepius paradoxus cannot completely paralyze larger fish and ingests only part of the fish.

The feeding habits have been described in detail in the literature, with two phases: 1) attacking, which includes attention, positioning, and seizure, and 2) eating.

Once I. paradoxus sees its prey it approaches with arms facing the hard shell of the crustacean until it gets to an attacking distance of less than 1 cm. The Japanese pygmy squid attacks very fast, and captures the prey with tentacles grabbing at the junction between the crustacean's shell and its first abdominal segment pulling the crustacean into its arm crown.

Idiosepius paradoxus will attack prey up to twice its size. The pygmy squid paralyzes shrimp within one minute, using a cephalotoxin. The prey must be held in the right position otherwise it will not be paralyzed, and I. paradoxus must shift where it is grasping the prey. On occasion more than one pygmy squid will attack the same prey. Usually the first attacker will get the meal. After capturing the prey, I. paradoxus swims back to sea grass to attach while it eats.

After capturing a crustacean, I. paradoxus inserts its buccal mass into the exoskeleton. The squid elongates the buccal mass to about the same length of its arm, and wiggles the mass around in all directions inside the crustacean's exoskeleton. While doing this, I. paradoxus ingests the flesh of the crustacean, and then discards it, leaving the exoskeleton completely empty yet intact. The crustacean’s perfectly intact exoskeleton looks like the organism has simply molted. The exoskeleton is usually emptied in 15 minutes for mysids, while the larger prey are sometimes not finished, leaving flesh attached to the exoskeleton.

Idiosepius paradox may externally digest its food first. External digestion makes it easier for the toothed beak to assist in shredding the flesh of a crustacean, which is removed using the buccal mass and enzymatic action. This enzyme is injected into the flesh allowing I. paradoxus to suck up semi-digested flesh. The specialized outer lip seems to be the organ assisting in external digestion. The lip contains goblet glandular cells in the lip gland that produces a mucous secretion. While eating the beak is moving in the buccal mass but it never passes the lips so it does not bite into the flesh.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore

• Animal Foods
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

Idiosepius paradoxus can be eaten by fish, birds, marine mammals, and other cephalopods.

Ecosystem Roles

Idiosepius paradoxus plays a role in being part of the food chain by being eaten and eating crustaceans and fish.

Economic Importance for Humans: Positive

Idiosepius paradoxus are easily harvested. The Idiosepiidae are good experimental animals because they have short life spans, are easily maintained, and readily reproduce in the lab. These animals are currently used to study reproduction and nervous systems but also have the potential for studies on age-related and/or hereditary problems.

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Idiosepius paradoxus on humans.

Conservation Status

They are present in large quantities, and will breed in captivity.

Additional Links

Encyclopedia of Life

Contributors

Sirisha Bupathi (author), Rutgers University, Kaycee Coleman (author), Rutgers University, David V. Howe (editor), Rutgers University, Renee Mulcrone (editor), Special Projects.

References

Kasugai, T., S. Shigeno, Y. Ikeda. 2003. Feeding and external digestion in the Japanese pygmy squid Idiosepius paradoxus . Journal of Molluscan Studies , 70: 231-236. Accessed December 22, 2010 at http://mollus.oxfordjournals.org/content/70/3/231.abstract .

Kasugai, T., S. Segawa. 2005. Life cycle of the Japanese pygmy squid Idiosepius paradoxus (Cephalopoda: Idiosepiidae) in the Zostera beds of the temperate coast of central Honshu, Japan. Phuket mar. biol. Cent. Res. Bull. , 66: 249-258. Accessed December 22, 2010 at http://www.pmbc.go.th/webpmbc/ResearchBulletin/Bull%2066%20%20pdf/25.%20Katsugai.pdf .

Kasugai, T. 2001. Feeding behavior of the Japanese pygmy cuttlefish Idiosepius paradoxus (Cephalopoda: Idiosepiidae) in captivity: evidence for external digestion?. Mar. Biol. Ass. UK , 81: 979-981. Accessed December 22, 2010 at http://www.cephbase.utmb.edu/refdb/pdf/7405.pdf .

Mangold, K., R. Young. 2003. "Idiosepiidae" (On-line). Accessed December 22, 2010 at http://www.tolweb.org/Idiosepiidae .

Myers, P. 2007. "Cephalopod development and evolution" (On-line). Accessed December 22, 2010 at http://scienceblogs.com/pharyngula/2007/07/cephalopod_development_and_evo.php .

Reid, A. 2005. Family Idiosepiidae. In P. Jereb & C.F.E. Roper, eds., Cephalopods of the World. FAO Species Catalogue for Fishery Purposes , 1 (4): 208-210. Accessed February 28, 2011 at ftp://ftp.fao.org/docrep/fao/009/a0150e/a0150e25.pdf .

Sato, N., T. Kasugai, H. Munehara. 2008. Estimated life span of the Japanese pygmy squid, Idiosepius paradoxus from statolith growth increments. Journal of the Marine Biological Association of the United Kingdom , 88: 391-394. Accessed February 28, 2011 at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1812896 .

Shigeno, S., Y. Masamichi. 2002. Organization of the nervous system in the pygmy cuttlefish, Idiosepius paradoxus Ortmann (Idiosepiidae, Cephalopoda). Journal of Morphology , 254: 65-80. Accessed January 08, 2011 at http://www3.interscience.wiley.com/journal/97516237/abstract?CRETRY=1&SRETRY=0 .

Stowasser, G., G. Pierce, J. Wang, M. Santos. 2007. "An Overview of Cephalopods Relevant to the SEA 5 Area" (On-line). Accessed January 08, 2011 at http://www.offshore-sea.org.uk/consultations/SEA_5/SEA5_TR_Cephalopods_UOA.pdf .

Young, R., M. Vecchione, K. Mangold. 2008. "Decapodiformes Leach, 1817. Squids, cuttlefishes and their relatives" (On-line). Tree of Life Project. Accessed February 28, 2011 at http://www.tolweb.org/Decapodiformes/19404 .