NO. 3 HARTMAN : ORBINIIDAE, APISTOBRANCHIDAE, PARAONIDAE 233 



The early development of Haploscoloplos robustus has been studied 

 by Horn and Bookhout (1950, pp. 1-9, pis. 1-4, as H, bustoris). In 

 North Carolina individuals are mature from May through September. 

 Natural spawning was never attained in the laboratory nor were the 

 egg masses ever collected in the field. It was assumed that there are no 

 gelatinous masses in this species as are known for some others (see 

 above). Eggs and sperm were artificially removed from adult individuals. 

 When the eggs were fertilized, only about one percent developed into 

 healthy larvae. A motile trochophore was observed sixteen hours after 

 fertilization. After 40 hours the larvae had grown so that segments 3 and 

 4 each had a pair of long setae. The presence of ten ciliated bands indi- 

 cated as many segments. The 70-hour larva showed six setigerous seg- 

 ments. Metamorphosis was complete after three days; at that time the 

 larva had nine setigerous segments and most ciliary rows had disap- 

 peared. Branchiae were present on the tenth and eleventh segments and 

 the alimentary tract was differentiated. After four days a juvenile was 

 developed which resembled the adult except for its much smaller size. 

 There was presumably no planktonic stage. 



Experimental parthenogenesis was demonstrated for Aricia by 

 Kostanecki (1909, pp. 238-253). 



Geographic Distribution 



The most widely distributed species are Naineris laevigata and 

 Scoloplos armiger, each occurring in ten of the geographic categories 

 named above. If we include the closely related Naineris dendritica with 

 N. laevigata, the range covers 14 categories. In the case of Scoloplos 

 armiger, with its subspecies it occurs in 1 1 categories. The closely re- 

 lated species of Haploscoloplos (elongatus and kerguelensis with vari- 

 ties) are found in nine groups. Species of Orbinia are limited largely to 

 Europe or coastlines of the Atlantic Ocean. Those of Scoloplos (Leo- 

 damas) come chiefly from the Southern Hemisphere. Those of Haplo- 

 scoloplos and Naineris are most diversified in the vicinities of the Gulf 

 of Mexico and West Indian seas. The single species of Protoaricia has 

 been recorded from both sides of the tropical Atlantic Ocean. Those of 

 Scolaricia, Proscoloplos, Orbiniella and Califia are the most restricted 

 geographically. 



The two charts immediately above show the geographic distribution 

 for species of Orbiniidae. (See alphabetical list of species below for 

 further bibliographic citations.) 



