Sponge forming a shallow sheet, hard, not very strong, of a pale brownish colour; the surface irregularly spiny; the oscula small but conspicuous, circular, raised on little turret-like eminences; the external membrane adhering closely to the sponge.
Skeleton dense but by no means regular; the network composed largely of single spines; thick radiating fibres distinguishable in the upper part of the sponge.
Spicules. Skeleton-spicules smooth, not very stout, amphistrongylous, occasionally a little swollen at the ends, often with one or more fusiform swellings, measuring on an average about 0.27 × 0.0195 mm. Flesh-spicules with distinct rotules, the recurved spines numbering 4 to 6, measuring about 1/7 the length of the spicules; the shaft by no means strongly curved; their length from 0.03-0.045 mm. Gemmule-spicules amphioxous, as a rule distinctly curved, sometimes swollen at the ends, covered regularly but somewhat sparsely with fine spines, not measuring more than 0.49 × 0.078 mm.
Gemmules strongly adherent, arranged in small groups, either single or double; when single spherical, when double oval; each gemmule or pair of gemmules covered by two layers of gemmule-spicules bound together in chitinous substance; the inner layer on the inner coat of the gemmule, the outer one separated from it by a space and in contact with the outer cage of skeleton-spicules; the size of the gemmule-spicules variable in both layers; external to the outer layer a dense cage of skeleton-spicules; foraminal tubule short, cylindrical.
This sponge is closely related to S. loricata, Weltner, of which Kirkpatrick regards it as a variety. "The main difference," he writes, "between the typical African form and the Burmese variety consists in the former having much larger microstrongyles (83 × 15.7 µ [0.83 × 0.157 mm.]) with larger and coarser spines;... Judging from Prof. Weltner's sections of gemmules, these bodies lack the definite outer shell of smooth macrostrongyles [blunt skeleton-spicules], though this may not improbably be due to the breaking down and removal of this layer. A further difference consists in the presence, in the African specimen, of slender, finely spined strongyles [amphistrongyli], these being absent in the Burmese form, though perhaps this fact is not of much importance."
Type in the British Museum; a piece in the Indian Museum.
Habitat.—Myitkyo, head of the Pegu-Sittang canal, Lower Burma (E. W. Oates).
Biology.—The sponge had grown over a sheet of the polyzoon Hislopia lacustris, Carter (see p. 204), remains of which can be detected on its lower surface.
"Mr. E. W. Oates, who collected and presented the sponge, writes that the specimen was found encrusting the vertical and horizontal surfaces of the bottom beam of a lock gate, where it covered an area of six square feet. The beam had been tarred several times before the sponge was discovered. The portion of the gate on which the sponge was growing was submerged from November to May for eight hours a day at spring tides, but was entirely dry during the six days of neap tides. From May to October it was constantly submerged. The sponge was found in April. Although the canal is subject to the tides, the water at the lock is always fresh. The colour of the sponge during life was the same as in its present condition."
23. Corvospongilla lapidosa* (Annandale).