Fredericellidæ, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 168 (1887).
Zoaria dendritic; zoœcia distinctly tubular, with the ectocyst well developed; statoblasts of one kind only, each surrounded by a chitinous ring devoid of air-spaces; polypides with the lophophore circular or oval when expanded.
The Fredericellidæ consist of a single genus (Fredericella) which includes several closely-allied forms and has a wide geographical distribution.
Genus FREDERICELLA, Gervais (1838).
Fredericella, Allman, Mon. Fresh-Water Polyzoa, p. 110 (1857). Plumatella, ("arrêt de développement") Jullien, Bull. Soc. zool. France, x, p. 121 (1885). Fredericella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 99 (1887). Fredericella, Goddard, Proc. Linn. Soc. N. S. Wales, xxxiv, p. 489 (1909).
This genus has the characters of the family. Its status has been much disputed, some authors regarding the shape of the lophophore as of great morphological importance, while Jullien believed that Fredericella was merely an abnormal or monstrous form of Plumatella. The latter belief was doubtless due to the fact that the zoaria of the two genera bear a very close external resemblance to one another and are sometimes found entangled together. The importance of the shape of the lophophore may, however, easily be exaggerated, for, as both Jullien and Goddard have pointed out, it assumes an emarginate form when retracted.
The best known species is the European and N. American F. sultana (Blumenbach), of which several varieties or phases have been described as distinct. This form is stated to occur also in S. Africa. F. australiensis, Goddard[[BC]] from N. S. Wales is said to differ from this species in having an oval instead of a circular lophophore and in other small anatomical characters; but it is doubtful how far these characters are valid, for the lophophore appears to be capable of changing its shape to some slight extent and has been stated by Jullien to be habitually oval in specimens from France. F. cunningtoni, Rousselet[[BD]] from Lake Tanganyika has stout zoœcia encrusted with relatively large sand-grains.
The zoaria of Fredericella are usually found attached to solid objects in shallow water, but a form described as F. duplessisi, Ford has been found at a depth of 40 fathoms embedded in mud at the bottom of the Lake of Geneva. F. cunningtoni was dredged from depths of about 10 and about 25 fathoms.
The statoblasts of this genus do not float and often germinate in the parent zoœcium after its polypides have died. They are produced in smaller numbers than is usually the case in other genera of the order. The polypides sometimes undergo a process of regeneration, but without the formation of brown bodies.