Haeckel, 1870
Species Overview
Ascandra falcata Haeckel, 1870 is an erect, slightly stalked pear-shaped mass of anastomosing tubes rising from a network of similar tubes on the surface. The vertical tubes each end in an apical oscule. The differences with Clathrina spp. and Guancha lacunosa are subtle: the tubes are thicker and more independent and a stalk is barely developed. It can be easily mistaken for a Leucosolenia , and study of the spicules is necessary to make a certain identification: the triactines of Ascandra are regular, those of Leucosolenia sagittal. There are important microscopical differences in the structure of the choanocyte chambers. It is a rare species reported from the west coast of France and Spain and from the Mediterranean.
Taxonomic Description
Colour: Yellowish brown in alcohol.
Shape, size, surface and consistency: Anastomosing tubes, rising from an open network encrusting the substrate, to form erect pyriform growth forms with a barely developed stalk. Size up to 3 cm high, individual tubes 3-4 mm in diameter. Erect tubes end in an apical oscule, which is "naked" (no fringe) (Ascandra falcata ?Ates). Surface of tubes slightly hispid. Consistency fragile, not contractile.
Spicules: (Ascandra falcata spics) Calcareous. Triactines, tetractines and diactines. Triactines regular: rays 120-150 x 10 µm.
Tetractines regular: rays 180-200 x 20 µm.
Diactines curved to sickle-shaped: 180-400 x 20 µm.
Skeleton: The choanoderm is folded in this genus (in contrast to that of Clathrina and Leucosolenia ), and the folds are supported by the apical rays of the tetractines. The basal rays of the tetractines and the triactines form the cortical skeleton of the tube walls; diactines are planted radially in the tubes.
Reproduction: August-September.
Ecology: Under rocky overhangs in exposed places, from the infralittoral fringe down to 40 m.
Distribution: West coast of France and Spain, Mediterranean.
Etymology: Falcatus (Latin) = sickle-shaped, referring to the diactinal spicules.
Type specimen information: No type material in BMNH; type probably lost.
Remarks
This species superficially resembles erect Clathrina , Guancha and Leucosolenia species. From the first two Ascandra falcata differs in the coarser tubes, which all have their own apical oscule. For distinction from Leucosolenia (e.g. variabilis ) microscopic examination is necessary. The triactines of Leucosolenia are sagittal while those of Ascandra are regular.
In the Mediterranean a second species of Ascandra is found, A . minchini Borojevic (1966), which differs in forming only solitary tubes.
Source: Borojevic et al., 1990.