Family XXXIV. Litholophida, Haeckel.
Litholophida, Haeckel, 1862, Monogr. d. Radiol., p. 401.
Definition.—Acantharia with a variable number of simple radial spines radiating within a conical space (or within the quadrant of a sphere) from one common central point, which is the apex of the conical central capsule. No lattice-shell.
The family Litholophida, represented only by a single genus, Litholophus, differs from all other Acantharia in the remarkable fact that the common point, from which the radial spines arise, is not the geometrical central point of the whole body, but is quite excentric in position, the apex of the conical or pyramidal central capsule. Therefore the spines form together a kind of brush or broom.
When I founded the family Litholophida in my Monograph (1862, p. 401) I knew only a single species, Litholophus rhipidium, observed very frequently in Messina. Another species, Litholophus ligurinus, was afterwards (1864) found by me at Nice. Six other species were detected in the preparations of the Challenger, some of them very frequent. All these eight species of Litholophus are very nearly allied, and exhibit only slight differences in the form and number of the radial spines; their mode of excentric connection and the structure of the peculiar soft body is everywhere the same.
The radial spines in all observed Litholophida possess the form of the genus Acanthonia, i.e., they are quite simple, four-sided prismatic or quadrangular, with square transverse section; their four edges are sometimes smooth, at other times elegantly denticulate, commonly more or less prominent or wing-shaped. In the greater number of species they are very long and of nearly equal breadth, prismatic; in some species they are more pyramidal, thinned towards the distal end; the latter is commonly truncated or broken off, sometimes pyramidal. The central end is everywhere thinned, more or less pyramidal, and the neighbouring spines are propped one upon another by the triangular faces of their small basal pyramids. A slight pressure is sufficient to destroy their connection.
The number and disposition of the radial spines seem to be variable and irregular, but require further researches. In four of the observed eight species I found constantly ten spines, in two other species from ten to twenty (commonly twelve or sixteen), and in two species twenty or more. A certain order or disposition of the spines within the conical space in which they radiate could nowhere be ascertained.
When I first observed Litholophus, I supposed that it might only be a mutilated or altered form of an Acanthonia. Afterwards, observing many specimens with ten spines, I was led to the suggestion that they were produced by self-division of an Acanthonia, and that the number of the spines in each half of the body might be afterwards doubled. But this suggestion seems to be refuted by the fact that in no other genus of the numerous Acantharia is self-division observed, and that many hundreds of Litholophus which I observed exhibit quite constantly only a single form of radial spines, that of Acanthonia—simple quadrangular spines without any apophyses.
Genus 320. Litholophus,[[360]] Haeckel, 1862, Monogr. d. Radiol., p. 401.
Definition.—Litholophida with a variable number of quadrangular diverging radial spines, united with pyramidal bases in the apex of the conical central capsule.