74 



ASCIDIANS 



little or no food-yolk, and the tailed larvae (Figs. 26, 42, A) are 

 of the typical form and structure descrihed in Chapter II. 



Fam. 3. Cynthiidae. — Solitary fixed Ascidians (Fig. 39), 

 sometimes occurring in aggregations, but never forming colonies ; 

 usually with leathery or fibrous, opaque test, which is sometimes 

 encrusted with sand ; branchial and atrial apertures usually both 

 four-lobed. Branchial sac longitudinally folded (Fig. 36, A); 

 tentacles simple or compound (Fig. 37); 



stigmata straight 



Br.f.7. 



B. 



-end- 



FlG. 36. — Diagrammatic transverse sections of branchial sacs of Cynthiidae. A, Cynthia ; 

 B, Styela ; C, Styelopsis ; D, Pelonaia. Br.f 1-7, First to seventh branchial fold ; 

 d.l, dorsal lamina ; end, endostyle ; mh, meshes. 



neural gland dorsal to ganglion ; gonads attached to body-wall. 

 This family is divided into three sections : — 



Sub-Fam. 1. Styelinae. — Not more than four folds (Fig. 36, 

 B) on each side of branchial sac; tentacles simple (Fig. 37, A). 

 The more important genera are — Styela, Macleay, and Polycarpa, 

 Heller (Fig. 3 9 ), with stigmata normal ; and Bathyoncus, Herd- 

 man, with stigmata absent or modified. There are a very large 

 number of species of both Styela and Polycarpa from all parts of 

 the world, including our own seas. A very abundant British 

 littoral form has been placed in an allied genus under the name 

 Styelo'psis grossidaria (Fig. 39, A). It is known in some places 

 round our coasts as " the red-currant squirter." This^ species has 

 only one well-marked fold in the branchial sac (Fig. 36, C). 

 Another exceptional British Styelid is Pelonaia corrugata, Forb. 

 and Goods. (Fig. 39, I), with no branchial folds (Fig. 36, D). 



