38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



however, is a typical cirriped cypris, much resembling the adult of 

 Synagoga (A). A species figured by Fisher (1911) as Dendrogaster 

 arbuscuhis, found in a Calif ornian starfish, has an elaborately branched 

 structure. 



The known nauplii of the Ascothoracica, according to Okada, differ 

 from the nauplii of other cirripeds in the absence of the usual frontal 

 horns, another feature that sets the ascothoracicans ofT as a primitive 

 branch of the cirripeds. Some species hatch as nauplii, others as meta- 

 nauplii, and still others in the cypris stage. 



The Thoracica. — To this suborder belong the barnacles, which in 

 the adult stage are enclosed in calcareous shells. Some are conical and 

 sit flat on the substrate (fig. 14 F), others are flattened and sup- 

 ported on stalks (H). When either kind is broken open, however, 

 there is exposed within the shell a shrimplike creature (G) lying on 

 its back or standing on its head with its cirruslike feet, when active, 

 sticking out of the top or side ( H ) with a waving movement. 



The nauplius of a common barnacle such as Balanus, described by 

 Runnstrom (1924-1925), has the typical naupliar structure (fig. 14 A) 

 except for the pair of small horns {B,fh) on the anterior part of 

 its body. Runnstrom describes two naupliar stages, but since the sec- 

 ond becomes elongate and acquires rudiments of three postmandibular 

 appendages it would ordinarily be called a metanauplius. After a few 

 hours of swimming, the metanauplius abruptly transforms into a 

 cypris (C) with a bivalve shell and long seta-bearing legs, wherewith 

 it is better equipped for a pelagic life. Eventually the cypris fixes 

 itself to a support by its first antennae (lAnt), each of which (E) 

 is provided with an adhesive cup on the third segment. A cementing 

 substance discharged through the antennae from glands in the head 

 gives the cypris a permanent attachment. Then the cypris withdraws 

 the hind part of its body and its legs into the shell, and now begins 

 the formation of the plates of the adult barnacle. According to 

 Runnstrom, the plates are first formed as chitinizations of the mantle 

 and only later become calcified. When the plates have the essential 

 adult pattern (D) the cypris shell is cast off, and with the moult the 

 legs of the cypris are replaced by the cirri of the barnacle. 



The metamorphosis of the cypris into the barnacle is not excessive. 

 It is a structural adaptation to the permanently sessile condition within 

 the shell, and the eyes are absorbed as now useless organs. The 

 changes that take place in the body have been described by Doochin 

 (1951). The shell-closing muscle of the cypris is retained (fig. 14 G, 

 mcl), and the mantle supporting the plates of the shell is attached to 



