Arturia (sponge)

The skeleton is composed primarily of straight, conical and sharp spicule with two or three pointed arms but in rare instances may have four. The spicules with three and four pointed arms have no special organisation (they have equal angles and radiate equally) but the apical spicule (of the three pointed arms) is projected inside the tubes. The spicules with two sharp pointed arms are slightly spindle-shaped, and have the spines perpendicular to the surface. The size of the diactines is very variable. Several three-pronged oxeas are present on the surface.[9]

It is usually found at depths between 8 and 23 metres (26 and 75 ft).[12] It grows on shady rock substrates and in caves but its preferred location is the underside of ledges formed by horizontal, plate-like layers of coral. It is often found growing in these locations with coralline algae and bryozoans in a rich, diverse community.[11] In a 2007 survey of sponges off the coast of Georgia, Arturia canariensis was discovered in cryptic locations under rocks, in crevices and overgrown by other organisms. This was an extension of its previous known range.[13]

Cells with yellow granules are present in the mesohyl, as are embryos, which are always found near choanocytes. The cells with yellow granules are distributed homogeneously, throughout the mesohyl.

The skeleton consists of equiangular and equiradiate triactines. Tetractines are also present, but they are rare. Actines are conical or cylindrical, but they always have sharp tips. Sometimes, they are slightly undulated. Diactines are abundant on the external tubes; they are curved or straight, vary in size and have sharp tips, one of which is club-shaped. The largest diactines are curved at the tip. They project through the surface in some parts of the cormus only, and the club-shaped portion of the spicule lies inside the tube.[17]

smooth and sharp. Trichoxeas are also present but there are very few.[21]

The regular triradiates have rather stout, slightly fusiform rays, bluntly and rather abruptly pointed at the apex, which is often somewhat irregular. The rays measure about 0.1 mm in length by 0.012 mm in diameter at the thickest part.

The quadriradiates are abundant and resemble the triradiates, but with an apical ray projecting at right angles into the gastral cavity. This ray is somewhat variable in form and size; typically it is long and slender, gradually and sharply pointed, and slightly undulated towards the extremity; in the type specimen it attains a length of about 0.14 mm.

The very slender, hair-like oxea sparsely hispidate the surface of the tubes. These may attain a length of more than 0.4 mm, with an average diameter of only about 0.002 mm. They taper very gradually from the proximal extremity, which is somewhat hastately sharp-pointed and may be as much as 0.004 mm thick, to the distal, which is hair-like and apparently nearly always broken off.[23]