Siphonodictyon siphonum (de Laubenfels 1949)

Siphonodictyon siphonum (Laubenfels)

Siphonochalina siphona Laubenfels, 1949, pp. 11–13.

HOLOTYPE.—AMNH 468; Bimini, Bahamas; less than 1 m; 1 July 1948.

MATERIAL.—USNM 24106, USNM 24107; East of Turtle-Rocks, Bimini, Bahamas; 1 m; 7 August 1967.

DESCRIPTION.—Shape and size: Clusters of tubes and hollow processes protrude from the sand substratum. They are irregular oval in cross section, 6–18 mm in diameter, and up to 70 mm high (from substrate level). The walls are 1–3 mm thick. Two to seven processes are fused together along their sides. The largest of the collected clusters extended over an area of 20 cm2, up to 20 were observed per m2 of sand bottom. Most of the basal mass of the choanosome is buried in the sand, only fragments were recovered.

Color: The exposed parts are chestnut brown, sometimes with a reddish tinge, the choanosome is greyish brown in life. They turn blackish brown in alcohol.

Consistency: The tubes are stiff but elastic, the choanosome is soft, compressible, and mucous.

Surface: Smooth to microhispid, particularly on top of the finger-shaped processes. Numerous wart-like swellings bearing a single pore (ostium?) can be noted.

Apertures: The oscula are more or less circular with irregular brush-like rims. They measure 5–12 mm in diameter. The ostia measure 150–300 μm.

Skeleton: A discontinuous surface reticulation is present. The tracts of spicules embedded in some spongin are 30–150 μm in diameter; they form meshes of 250–600 μm. Below, the ectosomal reticulation consists of radiating primary fibers, brushing out at the surface; these are connected by secondaries to form rectangular meshes. Fiber diameter, 75–125 μm; mesh diameter, 150–250 × 75–120 μm. In the choanosome the spiculation is in confusion, with the exception of some irregular strands.

Spicules: The slender oxea are usually bent, with a tendency to being flexuous. A second size category is not distinct. In the ectosome they are frequently broken. The tips are rough to acuminate, sometimes modified to styles or strongyles sometimes degenerated.

Measurements (of the present specimens and of the holotype): Given in Table 2.