Smeagol is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of small air-breathing sea slug

Slug

Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...

s of the upper intertidal zone

Intertidal zone

The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...

, pulmonate gastropod mollusks in the superfamily Otinoidea

Otinoidea

Otinoidea is a superfamily of small, air-breathing sea snail and sea slugs, marine pulmonate gastropod mollusks....

.

Smeagol is the only genus in the family Smeagolidae. This family has no subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005

Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)

The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...

).

Etymology

The name of the genus is in honour of Tolkien's fictional character Gollum

Gollum

Gollum is a fictional character from J. R. R. Tolkien's legendarium. He was introduced in the author's fantasy novel The Hobbit, and became an important supporting character in its sequel, The Lord of the Rings....

, originally known as Sméagol.

Species

There are five described species and potentially one undescribed species from Tasmania

Tasmania

Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

 in the genus Smeagol:

• Smeagol climoi Tillier & Ponder, 1992
• Smeagol hilaris Tillier & Ponder, 1992
• Smeagol manneringi Climo, 1980
• Smeagol parvulus Tillier & Ponder, 1992
• Smeagol phillipensis Tillier & Ponder, 1992

Anatomy

Smeagol manneringi has no tentacles and is a very active blind animal with a size of up to 10 mm.

Smeagol species have no shell. The have a weakly developed snout

Snout

The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...

. The radula

Radula

The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...

 is unicuspid and the radular dentition is of the rhipidoglossate type. They have a radular membrane of flexoglossate type. They have no jaw. They have salivary glands with salivary ducts.

The Excretory organs

Excretory system of gastropods

The excretory system of gastropods removes nitrogenous waste and maintains the internal water balance of these creatures, commonly referred to as snails and slugs...

 are only the left ones, in the pallial cavity. In the circulatory system

Circulatory system of gastropods

As in other molluscs, the circulatory system of gastropods is open, with the fluid, or haemolymph, flowing through sinuses and bathing the tissues directly. The haemolymph typically contains haemocyanin, and is blue in colour.-Circulation:...

 the haemolymph circulates as follows: mantle

Mantle (mollusc)

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...

 → nephridium

Nephridium

A Nephridium is an invertebrate organ which occurs in pairs and function similar to kidneys. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other...

 or nephridia → heart.

These slugs breathe using a pallial lung. They have a contractile pneumostome

Pneumostome

The pneumostome is a feature of the external body anatomy of an air-breathing land slug or land snail. It is a part of the respiratory system of gastropods....

.

They have a suprapedal gland

Suprapedal gland

The suprapedal gland or mucous pedal gland is an anatomical feature found in some snails and slugs. It is a gland located inside the front end of the foot of gastropods.The term suprapedal means "above the foot"....

.

The number of chromosomes is unknown. They have no sex chromosomes.

Ecology

These slugs inhabit the upper intertidal zone

Intertidal zone

The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...

 on gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

 substrate

Substrate (biology)

In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...

 in New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 and Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

.

The development of the veliger

Veliger

A veliger is the planktonic larva of many kinds of marine and freshwater gastropod molluscs, as well as most bivalve mollusks.- Description :...

 is completed in the egg (they do not have a trochophore

Trochophore

A trochophore is a type of free-swimming planktonic marine larva with several bands of cilia.By moving their cilia rapidly, a water eddy is created. In this way they control the direction of their movement...

 larval stage).

Further reading

• Haszprunar G. & Huber G. (1990). "On the central nervous system of Smeagolidae and Rhodopidae, two families questionably allied with the Gymnomorpha (Gastropoda: Euthyneura)". Journal of Zoology 220: 185–199. doi:10.1111/j.1469-7998.1990.tb04302.x

External links