Iotroata spinosa (Lundbeck, 1905) is a thickly flabellate deep-water sponge with opposite pore-bearing and oscule-bearing sides. Its consistency is rather soft and fragile. It is recorded from several northern North Atlantic sites.
Colour: Grey brown in alcohol.
Shape, size, surface and consistency: Thickly flabellate or cup-shaped sponge of considerable size: fragments are up to 8 x 10 x 2 cm with distinct oscular and poral surfaces on opposite sides. Surface smooth with detachable skin. Consistency, crumbly, soft.
Spicules: Megascleres: Ectosomal tylotes, smooth with distinct tyles: 260-340 x 2-4 µm; acanthostyles spined all over: 450-580 x 6-10 µm.
Microscleres: Birotulates (Iotroata spinosa birotulates) in two distinct size categories: 19-22 µm and 26-41 µm.
Skeleton: Ectosomal skeleton a tangential crust of loose megascleres (both tylotes and acanthostyles). Choanosomal skeleton an irregular isotropic reticulation of 1-5 spicules each side.
Ecology: Deep water.
Distribution: Subarctic North Atlantic, 69°-66°N 07° W-02°E.
Etymology: The name refers to the possession of acanthostyles.
Type specimen information: The type is in the Copenhagen Museum.
Iotroata erected for the species Iotrochota acanthostylifera Stephens (1916) is a typical Myxillina genus, with isotropic skeleton of (acantho-) styles, ectosomal tylotes, and isochelae (including birotulates) derived from anchorates. The present species, although it lacks the isochelae, fits perfectly into this genus. Other North Atlantic species cited under Iotrochota by Lundbeck (1905) are: I. varidens (smooth styles), I. oxeata (smooth oxeas instead of styles), I. dubia (close to I. acanthostylifera), I. intermedia (smooth styles), I. rotulancora (with peculiar unguiferate chelae resembling birotulates), I. polydentata (smooth styles, no unguiferates) and I. affinis (with acanthose birotulates).
Halichondria abyssi Carter (1874), also from the North Atlantic, was made the type of the genus Iotaota De Laubenfels (1936), on account of the alleged absence of unguiferates and the possession of smooth styles (I. polydentata would fit this "genus", too). However, Lundbeck (1905) claims to have found unguiferates in Carter's type. Aside from this, we do not think the loss of unguiferates is sufficient evidence of generic distinctness in view of the variation in these closely related forms.
Other birotulate bearing genera in the area are Hymetrochota (with type species H. rotula Topsent, 1904); this has a hymedesmoid skeleton, with acanthostyles erect on the substrate and ectosomal anisotornotes. A possible synonym is Hymenotrocha (with type species H. topsenti Burton, 1930a), which has in addition to the above-mentioned spicules also smooth styles and allegedly arcuate chelae. In view of the similarity of all birotulates in the various genera bearing them, it has been proposed recently to unite them in a new family Iotrochotidae, sister group of a restricted family Myxillidae.
Source: Van Soest, 1987