Sexes are separate in temperate-dwelling sea cucumbers. Gonads are single and mop-like in form. Gametes are released from one or several gonopores that are mostly located on the membrane between mouth and tentacle ring.

In Indian Arm, British Columbia gonads of Parastichopus californicus develop through the summer and spawning is in late summer/early autumn. Sex ratios are not significantly different from a 1:1 ratio, and spawning is partially synchronous. Gonad indices are similar in the two sexes. Cameron & Fankboner 1986 Can J Zool 64: 168; for a detailed study on oogenesis in P. californicus see Smiley 1988 Biol Bull 175: 79.

NOTE  calculated as volume of gonad/fresh body mass (minus gonad and coelomic fluid) X 100. This is an unusual method of calculating a gonad index (for the more usual method, see Research Study 2 below) and makes it all but impossible to compare these results with those of other studies

Around Sonoma County, California the black sea cucumber Cucumaria pseudocurata lives among sea mussels and on partially protected, vertical rock surfaces from the lower part of the mussel-bed to zero tide-mark. It is a brooding species.  Gonadal indices are highest in winter and lowest in summer. Spawning by males and females is synchronous, and occurs Jan-Mar.  Egg numbers per individual are dependent on size, and can reach over 300 in the largest females (>70mg live mass). Following their release, the eggs are held under the female’s body for about a month until they hatch.  Rutherford 1973 Mar Biol 22: 167.

NOTE  calculated as dry mass of gonad/dry body mass (including gonad) X 100. There are 2 lines on the graph representing the 2 sexes but, as the sexes do not differ significantly from one another, they are replaced here by a single combined blue line