Distribution

1 and 2: Coastal waters of Australia and Southeast Asia. H. maculosa in the south of Australia (including Tasmania) and H. lunulata in the north of Australia.

Biology

Within the invertebrates (Mollusca), to which snails and shellfish also belong, the cephalopods (Cephalopoda) form a distinct class.

  Fig. 4.82 Hapalochleane maculosa.

The "head" (homologous to the foot of snails or shellfish) has well-developed eyes. Eight or more arms are attached near the mouth, and these are used for grabbing and locomotion. The body is attached directly to the head and is elongated (squids) to rounded (octopuses) in shape. Only Nautilus spp. have a well-developed shell covering the entire body, which is largely absent in other cephalopods.

In the mouth region there are horny jaws in the shape of a parrot's beak, with which they can easily crack open even hard-shelled crustaceans. There are two salivary glands in the oral cavity whose secretions may contain fractions of physiologically highly active substances. These salivary secretions probably serve to aid digestion.

The salivary secretions of H. maculata and probably also H. lunulata contain the highly toxic substance maculotoxin, which is identical to tetrodotoxin (TTX), found in puffers. Along with maculotoxin, another substance, called hapalotoxin, was isolated from H. maculosa. Hapalotoxin is less dangerous for humans and is probably used in catching prey (especially crabs). Maculotoxin does not seem to have any effect on crabs and is probably used more for defence against predatory fish.

As members of the order Octopoda, H. maculata and H. lunulata possess 8 strong tentacles. Apart from body size they are morphologically hardly distinguishable from each other. H. maculosa reaches a maximum body length (including tentacles) of 12 cm, H. lunulata of up to 20 cm. The dirty-grey to yellowish-brown body is covered with luminous blue rings, which may also be broken up into lines on the body. They are generally solitary, living in caves and crevices in shallow water or in isolated pools in the intertidal zone. Humans are practically only ever bitten when they pick up these animals or allow them to crawl over their body for fun. The bite is barely noticeable, but the bleeding bite marks are clearly visible.

Risk

Accidents involving the Blue-ringed octopus are uncommon, but extremely dangerous. In cases of severe envenoming the symptoms commence within minutes. Accidents are only known to have occurred in Australia. Sutherland (1983) gives a summary of 11 case reports since 1950. 8 of these cases of envenoming were serious, and 2 (1 each caused by H. maculosa and H. lunulata) were fatal.

Bites by other species of octopuses are generally only accompanied by local pain, or possibly also local swelling and lack of sensation.

Literature (biological)

Sutherland 1983, Sutherland and Lane 1969, Halstead 1988, Cleland and Southcott 1965, Short and Potter 1987, McMichael 1971, Williamson et al. 1996, White 1995b