Bigfin Reef Squid

Sepioteuthis lessoniana, commonly referred to as the bigfin reef squid or northern calamari, is a notable species within the loliginid squid family, presently one of the three established species within the Sepioteuthis genus. Research conducted in 1993 suggests that this species may represent a cryptic species complex, potentially encompassing several closely related species.

Physical Characteristics and Behavior

Characterized by an expansive oval fin encircling its mantle, akin to the cuttlefish, the bigfin reef squid is a small to medium-sized marine invertebrate ranging from approximately 3.8 to 33 centimeters in length. Noteworthy for their intricate mating displays, these squids primarily spawn in May, with variations depending on geographical locations. Upon hatching, their paralarvae exhibit the capacity for pigmentation change, a trait unusual for newly hatched squids. Remarkably, bigfin reef squids boast the swiftest documented growth rate among large marine invertebrates, achieving up to 600 grams within a span of four months, and have a lifespan reaching up to 315 days.

Habitat and Distribution

Found predominantly within temperate and tropical waters of the Pacific and 🌊 Indian Oceans, their presence has also been recorded in the Mediterranean as Lessepsian migrants. Typically, these squids remain near shorelines, amidst rocks and coral reefs, and are extensively utilized for human consumption across Asia. Due to their rapid growth, short lifespan, and adaptability to captivity, they are considered highly viable for mariculture. Additionally, they provide crucial resources for medical research, particularly giant axons.

Morphological Features

Distinguished by thick, muscular oval fins extending nearly the entire length of their mantle, these squids can often be mistaken for cuttlefish. Observers will note thick, cylindrical mantles tapering to a blunt posterior and significant weight variability with maximum documented lengths of 38 cm in both sexes. Their vision is complemented by large, transparent corneas, with distinct olfactory crests located at the perimeter of the eyes. The species exhibits precise adaptations such as hectocotylus in males for reproduction and a range of teeth patterns within its tentacles.

Coloration and Camouflage

Bigfin reef squids possess metachrosis capabilities, enabling them to alter their body coloration and patterns rapidly through chromatophore control. Possessing iridophores and potentially leucophores, they can exhibit a spectrum of vivid body patterns from birth, a rarity among similar squid species. Their absence of photophores excludes bioluminescent properties.

Dietary Habits and Expansion

Primarily carnivorous, these squids subsist on crustaceans, including prawns, and fish. Captivity studies show their feeding frequency typically spans every 2 to 25 hours. Meanwhile, predator fish and some groundfish pose predatory threats to them.

Interaction with Other Marine Species

The squids host several parasites, including the copepod ectoparasite Doridicola similis and the endoparasites Dicyema koshidai and Dicyema orientale. Bigfin reef squids also exhibit positive phototactic behavior, readily moving towards light sources, indicating a possible involuntary stimulus response potentially beneficial for research into sensory and behavioral patterns.

Ecological and Research Importance

Given their adaptability and physiological features, bigfin reef squids represent significant ecological and commercial value, offering insights into cephalopod growth rates, behavior, and physiological adaptations. Their widespread distribution and interactions within marine ecosystems underscore their vital role in comparative anatomy and marine biology studies.