248 DISCOVERY REPORTS 



VERETILLIDAE 



Some general remarks on the family 

 Hickson (1916) emended the definition of this family to include the genus Actinoptilum, which 

 Kiikenthal and Broch (191 1) had united with Echinoptihim in the family Echinoptilidae, the zooids 

 having more or less distinctly developed calices. Hickson maintained that the 'calices ' mentioned by 

 Kiikenthal and Broch in Actinoptilum were verrucae not calices. It is not clear, where we ought to 

 draw the line between a calix and a verruca; in Actinoptilum these structures are quite rudimentary 

 and consist only of two rather small, low teeth. Two corresponding teeth have been developed in 

 Echinoptihim ; indeed in E. echinatum they are remarkably large, and in this species Hickson did 

 acknowledge them to be part of a calix. But it is impossible to tell whether the smaller teeth of Acti- 

 noptilum are a commencement (oriment) or the remnants (rudiments) of a calix or a verruca. 



Much more stress must be laid on the external symmetry. Hickson quite correctly pointed out that 

 the external features of Actinoptilum show no hint of bilateral symmetry and that accordingly the 

 right place for the genus was among the Veretillidae. He also maintained that the Veretillidae are 

 'sea-pens in which the autozooids and siphonozooids are distributed without any definite arrange- 

 ment in horizontal or longitudinal rows'. This statement, however, cannot be accepted. Both in 

 Veretilhwi and in Actinoptilutn longitudinal furrows divide the surface of the rachis into obvious 

 longitudinal ribbon-like fields, each of which generally shows a single row of autozooids placed at 

 somewhat varying intervals, so that they do not form regular transverse rows. Drawings of living 

 specimens of Veretillum cynomorium (Kiikenthal and Broch 191 1, pi. XHI, fig. i) show that in this 

 species the siphonozooids form a single longitudinal row in the middle of the ribbon-like field, where- 

 as in Actinoptilum molle they are irregularly placed, crowded on the ' ribbon ', and generally arranged 

 side by side. 



Hickson (191 6) agreed with Kiikenthal and Broch (191 1) that the Veretillidae probably stand near 

 the ancestral sea-pens. After examination of specimens from the 'John Murray Expedition' and 

 comparison with specimens from other collections, Hickson (1937) wrote: 'The consideration of 

 these specimens confirms the view that I ventured to put forward in 1918 (p. 131) that in these 

 radially symmetrical Veretillidae we have the most primitive forms of the Pennatulacea.' However, 

 it is not clear, whether in this case he was referring to the genus Cavernularia, or the Veretillidae as 

 a whole. 



It is impossible to tell which form of spicules is the most primitive. But it is obvious that the 

 spicules of the radially symmetrical Veretillidae in general are much more variable than those of the 

 externally bilateral sea-pens. The development of the spicules has not yet been determined in the 

 Veretillidae ; nevertheless, there is much to be said for regarding the flat biscuit-shaped spicules as 

 the most primitive. They occur in Veretillum and Actinoptilum, where an axis is wanting, as well as 

 in the axiferous genus Lituaria. In Actinoptilum, however, the biscuit-shaped spicules are restricted 

 to the stalk, whereas the rachis has three-flanged, rod- or needle-shaped spicules similar to the 

 dominant type in the bilaterally symmetrical groups. The genus Cavernularia, in the wide sense of 

 Hickson (1937), on the other hand, displays a great variation both in form and disposition of the 

 spicules. In some species they are restricted to the surface layer, in others they also occur in great 

 numbers in the inner tissues of the stalk. The spicules may be of uniform shape throughout, or they 

 may have one shape in the surface tissues and another in the interior of the specimen. In one species 

 the spicules are knobbed or branched at their ends, in others oval, slender spindles or needle-shaped. 

 A revision of this genus is indeed needed, but must be based on extensive investigation of the varia- 

 tions and behaviour in living specimens. 



