REPRODUCTION OF SPONGES 



Little is known about the embryology of 

 commercial species of sponges although con- 

 siderable work has been done with noncom- 

 mercial species closely related to commercial 

 types. Similarity of the reproduction process 

 in the various orders studied suggests that the 

 basic pattern of reproduction found applies to 

 most sponge species. The present study con- 

 centrated on the gross examination of wool 

 sponges for larvae and on the reproduction 

 cycle as related to total sponge productivity. 



With this consideration in mind, an exten- 

 sive program of examination of living sponges 

 in the field was carried out. Sponges were 

 collected and preserved every month and ex- 

 amined for larval content. This program was 

 carried on for almost the entire 2-year in- 

 vestigational period. The actual collection and 

 preservation was done by crews of sponge 

 diving boats. 



Process of Reproduction 



The spermatozoa and ova produced by 

 sponges are similar in structure to those of 

 other members of the animal kingdom. The 

 spermatozoa, about 0.05 mm. in length, are 

 produced in large numbers close to the walls 

 of the smaller excurrent canals. Spermatozoa, 

 when mature, are released into the open water. 

 To effect fertilization the spermatozoon must 

 be taken up by an egg-producing sponge in the 

 incurrent flow of water. Since spermatozoa 

 enter an egg-producing sponge by chance, 

 their concentration in the water influences the 

 number of eggs fertilized and the number of 

 larvae developed. 



Once a spermatozoon is in one of the 

 sponge's chambers it is taken in either by one 

 of the choanocytes (collared cells) or by an 

 amoebocyte. The cell picking up the sperma- 

 tozoon is termed a carrier cell, and in the 

 sponge species studied by Duboscq and Tuzet 

 (1937) this function was fulfilled by either 

 choanocytes or amoebocytes, depending on the 

 species of the sponge. If the spermatozoon is 

 taken up by a choanocyte, this carrier cell 

 loses both its collar and flagellum and takes 

 on the appearance of an amoebocyte. The cell 



picking up the spermatozoon is usually the one 

 closest to an immature ovum. Once within the 

 carrier cell the spermatozoon loses its tail 

 while the head and body enlarge two to three 

 times. 



The presence of the spermatozoon in the 

 carrier cell close by apparently triggers the 

 immature ovum (which at this stage in the 

 reproduction process is about 15 microns in 

 size (Duboscq and Tuzet, 1937) into activity. 

 The ovum fuses with two amoebocytes called 

 the nurse cells; then the ovum enlarges. The 

 actual transfer of the sperm is accomplished 

 through a canal which develops from the outer 

 part of the ovum to the nucleus. The young 

 embryo enlarges to about 0.5 mm. and becomes 

 surrounded by a hyaline capsule. Maturing 

 embryos sometimes occur singly but more 

 often are found in groups of 10 to 15 (fig. 3b). 



The color of the fertilized ovum in the early 

 stages of cleavage is whitish. As the embryo 

 matures it becomes a dark olive green with 

 one end more deeply pigmented (fig. 3c). The 

 final stage in development of the larval form 

 is the growth of a crown of cilia at one end. 

 At this point the larva is released into the 

 nearest excurrent canal and expelled into the 

 water where it continues to live as a free- 

 swimming larva for a period of from a few 

 hours to several days. 



After being released from the sponge, the 

 larva must come in "contact with clean hard 

 bottom to develop successfully into a mature 

 sponge. Some attach to sea grass, sea whips, 

 mollusk shell, bits of coral, etc., and attain 

 some size, but being poorly anchored they are 

 usually washed about and killed. 



Observation of a '•pawning sponge by W. 

 Smith, Nassau, Bahamas, (personal communi- 

 cation) showed that all the embryos in a velvet 

 sponge matured and were released within a 4- 

 week period. 



Majority of the eggs and embryos are de- 

 veloped in the lower two-thirds and toward the 

 central part of the wool sponge (fig. 3a) with 

 very few eggs developing in the peripheral 

 portion. One phenomenon associated with the 

 production of eggs is the loss of living material 



