Lissotesta IREDALE, 1915 :442. Type species, by original designation, Cyclostrema micra TENNISON-WOODS, 1877, Tasmania (Figs 24E, 25A-B).
Intortia EGOROVA, 1972:386. Type species, by original designation/, homocostata EGOROVA, 1972, Antarctic, 15-50 m (new synonym).
Diagnosis. Very small, globular gastropods, usually with a characteristic larval shell covered by an outer coating of, usually, finely granular, calcium carbonate which makes the suture almost invisible, except by transparency. 2-3 well rounded teleoconch whorls and a deep umbilicus with internal ridges. Radula with central tooth, one small inner and a larger outer lateral tooth and about five, basally united, flagelliform marginals.
The diagnosis above covers fairly well the species included here, except that there is a variation in the spiral sculpture, from strong and consisting of several ribs all over the whorls, to almost perfectly smooth whorls. The radula is described in more detail under L. major.
The type species of Lissotesta has never been well figured . The genus was previously placed in the Skeneidae (as a synonym of Cirsonella (WENZ 1938:329)). The radula is not known for the type species, but I have examined the radulae of two of the Antarctic species (L. notilis and L. liratula). Their radulae are very similar to that of the new species described below.
In addition to the European species listed here, there are several Antarctic and southern species that belong to this genus:
Submargarita strebeli THIELE, 1912 Submargarita similis TH1ELE, 1912 Submargarita impervia STREBEL, 1909 Margarita notilis STREBEL, 1909
Submargarita mamillata THIELE, 1912 Submargarita unifilosa THIELE, 1912 Cyclostrema humile PELSENEER, 1903 Cyclostrema liratulum PELSENEER, 1903
Lapidicola EGOROVA, 1972 (type species L. gyratum EGOROVA, 1972, Antarctic, 15-40 m) has a shell very similar to the species of Lissotesta, but has a different, probably paedomorphic radula.
Four European species are here included in Lissotesta, but I have examined additional undescribed species from off western Europe. They fit well the above diagnosis, and the major differences between the various species are the development and arrangement of the spiral sculpture.
L. minima (SEGUENZA, 1876) is here included in Lissotesta although it does not fit and will probably need a new genus when this group is better known. Presently I hesitate to propose a new genus for this featureless shell, which I place in Lissotesta because it has a similar umbilicus and shape.
A very characteristic feature of the species of Lissotesta is the protoconch , which is large and swollen, dome-shaped, usually with a granular sculpture and lacking almost every trace of coiling. This type of protoconch occurs in several «skeneimorph» genera, Lissotestella POWELL, 1946; Notosetia IREDALE, 1915; Aequispirella FINLAY, 1927; and at least one undescribed species of typical seguenziid (similar to Carenzia QUINN, 1983) from off Queensland.
The invalid family name Brookulidae has previously been used (IREDALE & McMICHAEL 1962) for some genera of small, related archaeogastropods, but the shell characters of the type species of Brookula, B. stibarochila IREDALE, 1915, are more similar to certain species best included in the Eucyclinae (sensu HICKMAN & McLEAN 1990, see also discussion about Veiulonia in WAREN & BOUCHET in press). No soft parts have been available for checking the radular morphology of Brookula. The genus Benthobrookula CLARKE, 1961 (type species B. exquisita CLARKE, 1961 from off South Georgia, 3700 m depth) is probably related to Lissotesta and congeners, since it has the same type of protoconch.
I do not know if this type of protoconch is a synapomorphy of these genera, or if it has a purely functional background, i.e. it is caused by some modification in the larval development. In the latter case it is likely to appear in unrelated taxa.