240 



THE VOYAGE OF H.M.S. CHALLENGER. 



Ecteinascidia has its nearest ally in Clavelina, and is intermediate in its characters 

 betweep that genus and Ciona, thus leading towards the Ascidiidas. The three species 

 differ considerably in external appearance, and are also easily distinguished by the structure 

 of their branchial sac and other internal organs. 



They may be separated, according to the conditions of their tests, by the following 



table : — 



Ecteinascidia. 



Test membranous. 



Ecteinascidia turbinala. 



Test cartilaginous. 



Test thin in the upper 

 part, of a dark colour. 



Ecteinascidia fusca. 



Test thick all over, of a 

 light grey colour. 



Ecteinascidia crassa. 



Ecteinascidia crassa, Herdman (PI. XXXVI. figs. 12-14). 



Ecteinascidia crassa, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1879-80, p. 723. 



External Appearance. — The body is irregular in shape, it is rudely triangular, or rather 

 of a flattened pyramidal form, and is attached by an extended base to a clump of sponge 

 spicules. The anterior end is narrow but more or less rounded. The sides are irregular ; 

 the posterior end is wide and expanded. The apertures are both near or at the anterior 

 end, they are sessile and inconspicuous, and no lobes are visible. 



The surface is rather irregular, but not rough. The colour is a warm grey, slightly 

 yellowish in places. 



Length of the body, 1*6 cm. ; breadth of the body (at the posterior end), 1*5 cm. 



Hie Test is strong, cartilaginous, and very thick. 



TJie Mantle is strongly developed, and the muscle bands are thick. 



The Branchial Sac has delicate but distinctly marked undulating internal longitudinal 

 bars, borne on large triangular connecting ducts. No papillae are present. The transverse 

 vessels are all of one size, and are rather wide. The stigmata are elongate-elliptical in 

 shape, and are very regular. The meshes are nearly square, and contain generally three 

 stigmata each. 



The Dorsal Lamina is in the form of lanmiets. 



The Viscera extend considerably beyond the branchial sac, and form a distinct 

 abdomen. 



This is a small and rather irregular species, which differs notably in external appear- 

 ance from the other two species, inasmuch as its posterior end is wide, and expands into 

 a broad base in place of tapering to form a short stalk. 



