896 THE VOYAGE OF H.M.S. CHALLENGER. 



Family XLV. NASSELLIDA, Haeckel. 



Cystidina, Haeckel, 1883, Sitzungsb. Jena Ges. fur Naturw., Februar 16. 



Definition. NASSELLARIA without skeleton. The soft body composed of a 

 monopylean central capsule (with porochora and podoconus) and of a surrounding 

 jelly- veil or calymma. 



The family Nassellida comprises the simplest and most primitive forms of 

 NASSELLARIA, the only group which is entirely without a skeleton. The central capsule 

 is therefore perfectly free and naked, enveloped by the calymma only, as in the 

 Colloidea among the SPUMELLARIA, in the Phseodinida among the PH^EODARIA. 

 Probably these naked and skeletonless MONOPYLEA must be regarded as surviving 

 remnants of the common ancestral group of this legion ; but the possibility is not 

 excluded that the few observed forms are either young NASSELLARIA which have not yet 

 secreted a skeleton, or older NASSELLARIA which have lost their original skeleton. 



We distinguish in this small family two genera only : Cystidium with hyaline, not 

 foamy calymma, without extracapsular alveoles, and Nassella, with a very voluminous 

 foamy calymma, including numerous large alveoles ; the former corresponds to Actissa 

 and the latter to Thalassicolla among the Colloidea or the skeletonless SPUMELLARIA. 

 But in these two latter genera, as in all PERIPYLEA, the central capsule is perforated 

 everywhere by innumerable small pores ; the two former genera, however, exhibit the 

 same characteristic podoconus in the central capsule, and the same porochora at its 

 base, as all the other MONOPYLEA. The pseudopodia are protruded from the central 

 capsule through the porochora only. 



TJie Central Capsule is in the two observed genera either ovate or nearly spherical, 

 usually slightly tapering towards the basal mouth. Its transverse section is constantly 

 circular. The membrane of the capsule is usually rather thick and double-contoured, 

 and bears on the truncate basal pole a circular " porochora " or area porosa, through 

 which the pseudopodia are protruded. The porochora is either quite simple, circular, or 

 in some species trilobed, with three equal circular lobes, each of which is surrounded by 

 a girdle of small granules. The >odoconus, or " pseudopodial-cone," arising vertically 

 from the horizontal basal porochora, is half as long as the central capsule, or longer, 

 simply conical and finely striped longitudinally. The nucleus lies usually in the upper- 

 most part of the central capsule, above or behind the podoconus, and is either spherical 

 or ovate, sometimes kidney-shaped. It includes one or more nucleoli. 



Synopsis of the Genera of Nassellida. 



Calymma hyaline, without alveoles, ....... 382. Cystidium. 



Calymma foamy, with numerous large alveoles, ..... 383. Nassella. 



