PHYLUM CHORDATA 



365 



SUBPHYLUM UROCHORDA, MOLGULA 



Subphylum Urocliorda includes a number of common represen- 

 tative marine forms, such as Salpa, Cynthia, Ciona, Clavelma, As- 

 cidia, and Molgula. The latter genus represented by M. manhatt en- 

 sis will be given particular consideration here. This animal is com- 

 monly known as sea lemon, sea peach, or sea squirt. The body 

 of the adult is saclike and averages about one inch in diameter. In 

 this condition it would be an outcast among chordates because as an 

 adult it has no notochord, and no dorsally located, tubular nerve 

 cord. However, it does present pharyngeal gill slits. 



Incurrent siphon 

 Excurrent i/phon 

 Mantle 



Tunic 



Qanqiion 



Ana5 



^ Genital duct 



Testis 



Ovary 

 r - Digestive glands 

 -- Esophagus 

 --Intestim 

 -Stomach 

 — Branchial fold 



- - End05tyle 



- /Atrium 



- - PharynK 



Fig. 212. — Diagram of Molgula manhattensis from the left side to show the struc- 

 ture with the courses of water and food through the body indicated by arrows. 



It is saved to the chordates by the presence of all three of the 

 characteristic features in the larval stage. The larva is free-swim- 

 ming and shaped like a tadpole, while the adult is globular and sessile 

 in most of the common forms. Some are brilliantly tinted with color. 

 The adult is covered externally by a cellulose coat or tunic (test), 

 which is secreted by the cells of the underlying mantle. Inside the 

 mantle is the extensive atrial cavity. On the dorsal (unattached) 

 side of the body are two funnellike siphons. The anterior one is the 

 Iranchial siphon (oral funnel, incurrent siphon or mouth) and the 

 other is the atrial siphon (atrial funnel, excurrent siphon, or atrio- 

 pore). When the tunic of Molgula is removed, one may see most of 



