NO. 3 HARTMAN : ORBINIIDAE, APISTOBRANCHIDAE, PARAONIDAE 227 



gelatinous masses but as a thin, irregular ribbon-shaped cluster invested 

 with a delicate pellicle. These irregular pieces may adhere to the stems 

 of Zostera. The fertilized egg is nearly spherical and measures about 

 250 micra across. The young pass through a modified trochophore stage. 

 In 46 hours an elongated larva has developed, with short rows of cilia 

 but no setae. Metamorphosis occurs after about two days and results 

 in a gradual loss of ciliary rows. A six-segmented stage follows ; dorsal 

 and ventral fascicles of setae appear in the third and fourth segments. 

 An alimentary tract is formed and the larva begins to feed. After one 

 or two more days setae appear in the fifth and sixth segments and the 

 larva begins to creep. Metamorphosis requires about four days and the 

 formation of the seventh setigerous segment marks its end. This is about 

 ten days after fertilization. The first two segments are asetigerous. 

 During juvenile stages the branchiae are developed and the trunk elon- 

 gates. 



The development of Haploscoloplos kerguelensis in Japan is also 

 described by Okuda (1946, pp. 139-144). Adults are mature from June 

 to July ; they occur in sandy mud bottoms. The eggs are laid in a pear- 

 shaped gelatinous mass supported by a long stalk. Hatching takes place 

 about three days after fertilization and the pelagic life lasts only one 

 or two days. There are no larval swimming setae. The development 

 resembles that of Naineris laevigata from Japan. 



The stages of development for some species from Europe are sum- 

 marized by Thorson (1946, pp. 78, 79, 140). Scoloplos armiger, Phylo 

 foetida and Orbinia cuvieri have no pelagic stages. The best studied 

 species, Phylo foetida from the Gulf of Naples, spawns from January to 

 June at four-week periods for a single individual (Schaxel, 1912, p. 

 384). Eggs are laid in a gelatinous cylindrical mass measuring 60 to 80 

 millimeters long, attached to the sand. The young hatch in six to twelve 

 days and remain larval for two to three weeks but there is no pelagic 

 stage (Lo Bianco, 1899, pp. 448-573 and Salensky, 1883, pp. 188-220). 



Scoloplos armiger spawns in spring; eggs are laid in pear-shaped 

 gelatinous cocoons measuring about 20 by 10 millimeters; they are at- 

 tached to the sand by a tough strand 15 to 50 millimeters long. A female 

 individual may spawn more than one cocoon and each cocoon may have 

 400 to 1000 eggs. The larvae remain there for as much as three weeks 

 and hatch in a creeping stage; when hatched they are about 600 micra 

 long. The stages of cell division have been described by Delsman (1916, 

 p. 409). 



