Re-plumbing in a Mediterranean sponge

Abstract

Observations are reported for Dysidea avara sponges where once functioning oscula (outlets) are converted through internal re-plumbing into functioning oversized ostia (OSO; inlets). Flow tank studies employed high-speed photography and particle tracking of laser-illuminated 0.5-6.0 microm diameter glass beads to trace particles streaming into OSO. A fluorescein dye/glass bead uptake experiment showed that an oversized ostium was connected through internal structures to the lone osculum. Beginning 30 s after uptake and continuing over a 20 min period, dye streamed from the osculum, but no beads emerged. Scanning electron microscopy revealed that beads were deposited only on the inhalant side of particle filtering choanocyte chambers and not on the exhalant side, suggesting that internal re-plumbing had occurred. Functioning OSO were also found on freshly collected specimens in the field, making it highly unlikely that formation of OSO was only an artefact of sponges being held in a laboratory tank.

Figure 1

(a) Normal light photograph of D. avara sponge showing three OSO (1–3) superimposed onto a high-speed video image showing laser-illuminated glass beads in the background. (b) Computed speed distributions (colours) and streamlines (white) around sponge which is superimposed semi-transparently onto calculated speed distributions. Inflow is visible only for ostia 1 and 2, given that ostium 3 was not illuminated by the laser light sheet. Scale bar, 2 mm (movie in the electronic supplementary material shows beads entering OSO).

Figure 2

(a) Fluorescein dye experiment. Normal light digital photograph of sponge DA-7 as fluorescein dye began to exit the osculum. (b) SEM digital image of internal anatomy of sponge DA-7. (c) Inhalant canal and prosopyles (inlets to choanocyte chambers); see enlarged image of beads in the electronic supplementary material figure 2c. (d) Glass beads deposited on inhalant side of choanocyte chamber. Note. Partially torn prosopyle (artefact of cryofracture) with glass beads deposited onto the prosopyle wall and at the base (inhalant side) of choanocyte collars; a, apopyle (exit of choanocyte chamber); ch, typical cryofractured choanocyte chamber showing mass of tangled flagella; ec, exhalant canal; fm, flagellar mass; ic₁, inhalant canal; ic₂, inhalant canal leading to prosopyle; m, streams of dye which escaped the suction of the ostium; n, hypodermic needle; o, osculum; p, phagosomes with ingested glass beads; arrow heads, prosopyle openings that lead into the choanocyte chambers; arrows, glass beads.