94 
Fig. 4. Epizoanthus leptoderma. The largest portion 
of the holotype. X 14. 
Ectoderm. That of the scapus and coenen- 
chyme containing most of the sand. That of 
the tentacles and oral disc with olive-colored 
granules at the locations of the violet markings. 
With little or no pigmentation in the column. 
Entoderm. Without zooxanthellae. 
Cnidom. Spirocysts, of the tentacles, 12 to 15 
by 2.5 to 3 p, very numerous. Basitrichs, of the 
tentacles, 12 by 2 to 2.5 p, few. Microbasic 
b-mastigophores, of the tentacles, 12 to 15 by 
3 to 3.5 p, few; of the actinopharynx, 12 to 18 
by 2 to 2.5 p, common. Microbasic p-mastigo- 
phores, of the actinopharynx, 12 by 4.5 p, few; 
of the filaments, 12 to 20 by 4.5 p, numerous. 
Holotrichs, of the actinopharynx (entoderm), 
37 to 40 by 12 to 15 p, common; of the fila- 
ments, 37 to 40 by 12 to 15 p, common. No 
nematocysts could be found in the column. 
DISCUSSION 
Superficially E. leptoderma appears to be in- 
PACIFIC SCIENCE, Vol. XIV, April I960 
termediate between E. gabrieli Carlgren and 
E. calif ornicum Carlgren. The growth form and 
dimensions of the E. leptoderma colony and 
polyps are essentially the same as those of 
E. calif ornicum. The chief external difference 
between these two species is the thinner column 
wall and weaker incrustation of E. leptoderma 
(the characteristic for which this species is 
named). Histological examination, in addition, 
reveals that the marginal sphincter of E. lepto- 
derma is much weaker and shorter than that of 
E. calif ornicum. Although there is an overlap in 
the number of mesenteries between the two 
species, it is only an occasional polyp of E. lep- 
toderma that will have the lesser mesenterial 
complement of E. calif ornicum. The mesogloea, 
especially of the column, of the latter species is 
several times as thick as that of E. leptoderma 
and, furthermore, the cells of the mesogloea of 
E. calif ornicum are larger, more numerous, and 
have a different distribution. The cells of the 
mesogloea of the column of E. leptoderma are 
concentrated near the entoderm, whereas in 
E. calif ornicum these cells are uniformly dis- 
tributed. There is close agreement in the dimen- 
FIG. 5. Transverse section of the marginal sphincter 
muscle of Epizoanthus leptoderma. Scale = .10 mm. 
