Animal Diversity Web

Glass sponges occur world­wide, mostly at depths be­tween 200 and 1000 m. This group of sponges are es­pe­cially abun­dant in the Antarc­tic.

All glass sponges are up­right, and pos­sess spe­cial­ized struc­tures at their bases for hold­ing fast to the ocean floor. Most ap­pear out­wardly to be ra­di­ally sym­met­ri­cal; they are typ­i­cally cylin­dri­cal, but may also be cup-shaped, urn-shaped, or branch­ing. The av­er­age height of a hexa­ctinel­lid is be­tween 10 and 30 cm, but some can grow to be quite large. A hexa­ctinel­lid pos­sesses a cav­ernous cen­tral cav­ity (the atrium) through which water passes; a cap of tightly woven spicules cov­ers the os­cu­lum in some species. Col­oration in most is pale. Glass sponges most closely re­sem­ble syconoid sponges, but they dif­fer too much in­ter­nally from other sponges to be con­sid­ered truly syconoid.

It is upon close in­ter­nal ex­am­i­na­tion that glass sponges can be most eas­ily dis­tin­guished from other sponges. The skele­ton of an hexa­ctinel­lid is made en­tirely of sil­ica. These siliceous spicules are gen­er­ally com­posed of three per­pen­dic­u­lar rays (and there­fore six points, so they are de­scribed as hexa­c­tine), and are often fused, lend­ing hexa­ctinel­lids a struc­tural rigid­ity not typ­i­cal of other sponge taxa. Strung be­tween the spicules is a largely syn­cy­tial net­work of soft body cells. In­cur­rent water en­ters the body through spaces in the syn­cy­tial strands. Within the syn­cy­tia are units func­tion­ally sim­i­lar to the choanocytes found in other sponges but these units com­pletely lack nu­clei, and so are re­ferred to as col­lar bod­ies rather than col­lar cells. They are fla­gel­lated, and it is the beat­ing of their fla­gella that causes the cur­rent to pass through the sponge. Within the syn­cy­tia are cells func­tion­ally com­pa­ra­ble to ar­chaeo­cytes in other sponges, but these cells seem to demon­strate only lim­ited mo­bil­ity. Hexa­ctinel­lids lack my­ocytes com­pletely, and so are in­ca­pable of con­trac­tion. While hexa­ctinel­lids pos­sess no nerve struc­ture, they seem to be able to send elec­tri­cal sig­nals across the body through the syn­cy­tial soft tis­sue.

Lit­tle is known about hexa­ctinel­lid re­pro­duc­tion and de­vel­op­ment. Sperm are taken into an or­gan­ism with water, and then must make their way to eggs within the or­gan­ism. After fer­til­iza­tion, the lar­vae are in­cu­bated for a rel­a­tively long time so they even form rudi­men­tary spicules be­fore being re­leased as parenchymella lar­vae. These dif­fer from other sponge lar­vae in lack­ing fla­gella or any other method of lo­co­mo­tion. Hexa­ctinel­lids clus­ter to an un­usu­ally high de­gree, sug­gest­ing that lar­vae do not drift far be­fore set­tling. After a larva lands on the ocean floor, it meta­mor­phoses, and the adult sponge be­gins to grow. Hexa­ctinel­lids are known for pro­lific bud­ding.

Glass sponges are purely fil­ter feed­ers. Sponges sub­sist on macro­scopic de­tri­tus ma­te­r­ial, but also con­sume cel­lu­lar ma­te­r­ial, bac­te­ria, and non­liv­ing par­ti­cles so small they can­not be re­solved with a light mi­cro­scope. Small par­ti­cles of ed­i­ble ma­te­r­ial taken in by the cur­rent cre­ated by col­lar bod­ies are ab­sorbed as they pass through the chan­nels within the sponge. The col­lar bod­ies are cov­ered with mi­crovilli that trap food, and the food passes through vac­uoles through the col­lar bodes and into the syn­cy­tia. Ar­chaeo­cytes be­tween the syn­cy­tial strands are re­spon­si­ble for food dis­tri­b­u­tion and stor­age. The ar­chaeo­cytes may also be re­spon­si­ble to some ex­tent for food cap­ture. Hexa­ctinel­lids seem to lack se­lec­tive con­trol over the food they in­gest - any food small enough to pen­e­trate the syn­cytium is in­gested. Be­cause of their lack of a con­tin­u­ous outer mem­brane and their lack of de­fined ostia, hexa­ctinel­lids lack con­trol over how much water passes through them. It is be­lieved that the sta­bil­ity of deep-wa­ter en­vi­ron­ments al­lows hexa­ctinel­lids to sur­vive de­spite these short­com­ings.

Hexa­ctinel­lids are com­pletely ses­sile. Even lar­vae seem to dis­play no move­ment, out­side of their abil­ity to dis­perse small dis­tances in cur­rents. Fur­ther­more, un­like other sponges, hexa­ctinel­lids do not con­tract when stim­u­lated.

As with other sponges, hexa­ctinel­lids may be sources of phar­ma­ceu­ti­cals, al­though their eco­nomic po­ten­tial is largely un­ex­ploited. Hu­mans rarely come into con­tact with glass sponges, and are mostly un­af­fected by them. In Japan, how­ever, they are given as wed­ding pre­sents. Hexa­ctinel­lids of a par­tic­u­lar species en­gage in a sym­bi­otic re­la­tion­ship with shrimp. When small, two shrimp of op­po­site sexes enter the sponge atrium, and, after grow­ing to a cer­tain size, can­not leave. They feed on ma­te­r­ial brought in by the cur­rents pro­duced by the sponge, and even­tu­ally re­pro­duce. A skele­ton of a sponge con­tain­ing the two shrimp is given as a wed­ding pre­sent in Japan.

Lit­tle ef­fort is being made to pre­serve hexa­ctinel­lid species, but there may be great value in keep­ing glass sponge pop­u­la­tions healthy, as they may hold the se­crets of hun­dreds of mil­lions of years of evo­lu­tion, and may have evolved chem­i­cals of po­ten­tial value to hu­man­ity.

Hexa­ctinel­lids are con­sid­ered close rel­a­tives of Demo­spon­giae.

Ref­er­ences:

Ax. 1996. Mul­ti­cel­lu­lar An­i­mals: A New Ap­proach to the Phy­lo­ge­netic Order in Na­ture; Springer, Berlin.

Bergquist, P. R. 1978. Sponges. Uni­ver­sity of Cal­i­for­nia Press, Berke­ley and Los An­ge­les. 268 pages.

Dohrmann, M., J. Dorte, J. Re­it­ner, A.G. Collins, and G. Wörheide. 2008. Phy­logeny and Evo­lu­tion of Glass Sponges (Porifera, Hexa­ctinel­l­ida). Sys­tem­atic Bi­ol­ogy, 57:388.

Ko­zloff, E. N. 1990. In­ver­te­brates. Saun­ders Col­lege Pub­lish­ing, Philadel­phia and other cities. 866 pages.

Levin, H. L. 1999. An­cient In­ver­te­brates and Their Liv­ing Rel­a­tives. Pren­tice Hall, Upper Sad­dle River. 358 pages.

Leys, S.P., Mackie, G.O., Reiswig, H.M. 2007. The bi­ol­ogy of glass sponges. Ad­vances in Ma­rine Bi­ol­ogy. 52:1¬145.

Philippe et al. 2009. Phy­loge­nomics re­vives tra­di­tional views on deep an­i­mal re­la­tion­ships. Cur­rent Bi­ol­ogy, 19:706.

Rup­pert, E. E. and R. D. Barnes. 1994. In­ver­te­brate Zo­ol­ogy: Sixth Edi­tion. Saun­ders Col­lege Pub­lish­ing. Fort Worth and other cities. 1040 pages.

Sper­ling, E.A., J.M. Robin­son, D. Pisani, and K.J. Pe­ter­son. 2010. Where's the glass? Bio­mark­ers, mol­e­c­u­lar clocks, and mi­croR­NAs sug­gest a 200-Myr miss­ing Pre­cam­brian fos­sil record of siliceous sponge spicules. Geo­bi­ol­ogy 8:24.

Thiel, V., M. Blu­men­berg, J. Hefter, T. Paper, S. Pom­poni, J. Reed, J. Re­it­ner, G. Wörheide, and W. Michaelis. 2002. A chem­i­cal view of the most an­cient meta­zoa--bio­marker chemo­tax­on­omy of hexa­ctinel­lid sponges. Natur­wis­senschaften 89:60.

Con­trib­u­tors

Dan At­wa­ter (au­thor), Daphne G. Fautin (au­thor).