Largest Organisms - Animals - Invertebrates - Mollusks (Mollusca)

Mollusks (Mollusca)

Both the largest mollusks and the largest of all invertebrates are the largest squids. The colossal squid (Mesonychoteuthis hamiltoni) is projected to be the largest invertebrate. Current estimates put its maximum size at 12 to 14 m (39–46 ft) long, based on analysis of smaller specimens. On February 22, 2007, authorities in New Zealand announced the capture of the largest known colossal squid specimen. It was later measured at 10 m (33 ft) long and 495 kg (1,091 lb) in weight. The mantle alone can be 5 m (16 ft) long based on a transverse slice of the pen of one specimen.

The giant squid (Architeuthis dux) was previously thought to be the largest squid, and while it is less massive and has a smaller mantle than the colossal squid, it may exceed the colossal squid in overall length including tentacles. One giant squid specimen that washed ashore in 1878 in Newfoundland reportedly measured 18 m (60 ft) in total length (from the tip of the mantle to the end of the long tentacles), 4.6 m (15 ft) in diameter at the thickest part of mantle, and weighed about 900 kg (2,000 lb). This specimen is still often cited as the largest invertebrate that has ever been examined. However, no animals approaching this size have been scientifically documented and, according to giant squid expert Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands.

• Aplacophorans (Aplacophora)

The largest of these worm-like, shell-less mollusks are represented in the genus Epimenia, which can reach 30 cm (12 in) long. Most aplacophorans are less than 5 cm (2 in) long.

• Chitons (Polyplacophora)

The largest of the chitons is the gumboot chiton, Cryptochiton stelleri, which can reach a length of 33 cm (13 in) and weigh over 2 kg (4.4 lb).

• Bivalves (Bivalvia)

The largest of the bivalve mollusks is the giant clam, Tridacna gigas. Although even larger sizes have been reported for this passive animal, the top verified size was for a specimen from the Great Barrier Reef. This creature weighed 270 kg (600 lb), had an axial length of 1.14 m (3.7 ft) and depth of 0.75 m (2.5 ft). The largest bivalve ever was Platyceramus platinus, a Cretaceous giant that reached an axial length of up to 3 m (nearly 10 ft).

• Gastropods (Gastropoda)

The "largest" of this most diverse and successful mollusk class of slugs and snails can be defined in various ways.

The living gastropod species that has the largest (longest) shell is Syrinx aruanus with a maximum shell length of 0.91 m (3.0 ft), a weight of 18 kg (40 lb) and a width of 96 cm (38 in). Another giant species is Melo amphora, which in a 1974 specimen from West Australia, measured 0.71 m (2.3 ft) long, had a maximum girth of 0.97 m (3.2 ft) and weighed 16 kg (35 lb).

The largest shell-less gastropod is the giant black sea hare (Aplysia vaccaria) at 0.99 m (3.2 ft) in length and almost 14 kg (31 lb) in weight.

The largest of the land snails is the Giant African snail (Achatina achatina) at up to 1 kg (2.2 lb) and 35 cm (14 in) long.

• Cephalopods (Cephalopoda)

(See Cephalopod size.) While generally much smaller than the giant Architeuthis and Mesonychoteuthis, the largest of the octopuses, the Giant Pacific Octopus (Enteroctopus dofleini), can grow to be very large. The largest confirmed weight of a giant octopus is 74 kg (160 lb), with a 7 m (23 ft) arm span (with the tentacles fully extended) and a head-to-tentacle-tip length of 3.9 m (13 ft). Specimens have been reported up to 125 kg (280 lb) but are unverified.