MONOCHITON1DA. - Family SALPIDE, Forbes. Synonyms : Salpce, Auct.; Thalides, pars, and Ludes simples, Savigny ; Biphores, Brugiere ; Biphoridce, MacLeay; Tuniciers arcs, pars, Lamarck; "les isolees," pars, Cuvier; Salpacea, pars, and Salpiens simples, Blainville; Salpiens, Van Beneden. The Salpians are free, swimming in the ocean ; plentiful in the Me diterranean and the warm parts of the ocean ; occurring also occasionally in the Norwegian and North British seas. In shape they re semble a short and wide tube, sometimes oval or cylindrical, sometimes more or less square in its transverse section, and varying consi derably in size according to species, from half an inch to 8 or 10 inches in length.
The test is thin and transparent, open at the ends and often supplied with terminal and lateral processes. The mantle lines the test, and is more or less adherent throughout ; its interior constitutes the branchial cavity ; it is provided at one of the terminal openings with a more or less perfect valvular apparatus; and contains a branchial fold traversing it obliquely. Near one extremity the chief viscera are grouped together into a conspicuous mass (the " visceral nucleus" of authors), to which the brilliant tints of the liver usually impart an orange, brown, or reddish hue (fig. 772.).
This family is of considerable interest on account of their singular mode of reproduc tion, discovered by Chamisso, and on account of the philosophical generalisations partly founded thereon by Steenstrup. These ani mals occur under two distinct conditions, being at one time solitary, and at another as sociated into circular or lengthened groups termed garlands, cordons, ribands, and chains (fig. 772. ii and c). The Salpa-chains, vary ing in length from a few inches to many feet, swim through the tranquil water with a regular serpentine movement, and are often regarded by sailors as sea-serpents ; but when taken from the water the individuals of the group are easily detached. Thus, in conse quence of accidents, separate members of these chains are often met with in seas abounding with these Molluscs ; but other, separate, Sa4he are also met with that have never been united to others, and differ considerably in form from the associated ones (fig. 772. A).
Chamisso, however, discovered that such permanently solitary Salpce do not belong to species distinct from those united in chains, however dissimilar (and they are usually so dissimilar as to appear even generically dis tinct), but are either the parents or the pro geny, as the case may be, of the aggregate forms ; and that chained Sac• do not produce chained Salpce, but solitary Salpce, which in their turn do not produce solitary, but chained Salpce. Consequently, as Chamisso graphi
cally observed, "a Sa/pa-mother is not like its daughter or its own mother, but resembles its sister, its grand-daughter, and its grand mother."* This family is mainly represented by the genus Salpa, Forskahl ; synonyms Thalia, Brown ; Holothuria, Linne and Pallas ; Dagysa, Banks and Solander ; Biphora, Brugiere ; Tethis, Tilesius ; Pegea and lasis, Savigny. The characteristic features of this genus are detailed above.
Quoy and Gaimard* established for some animals nearly allied to the Salpes and inha biting the coasts of Amboina, the genus Do lioliunz, the characters of which are, its having the form of a little cask open at the ends; from two to ten lines in length ; the anterior extremity a little prominent ; marked with circles in relief on the external surface; and having internal branchia, divided into two branches; and a heart and a dorsal vessel, si tuated near the union of these branches. This name had also been previously given by Otto t to a genus established by him on a Mediterra nean Salpa, mutilated by a crustacean of the genus Phronyme, that had made it its habita tion. This form, like Salpa triangularis and S. polymorpha (by Quoy and Gaimard, and Bory de Vincent), has been erroneously regarded as belonging to the family of Diphydes. MM. Lowig and Klilliker, however, who found the tissue of Doliolium to be identical with the pe culiar substance of the test of other Tunicata, have pointed out its true affinities, and placed it with the Salpidce.
Family PELONAIAME, Forbes. — This fa mily is represented by two rare animals, both inhabitants of the Scottish seas, constituting two species of a single genus, Pelonaia, esta blished by Professor E. Forbes and Professor Goodsint We have derived our description of the general and anatomical characters of these interesting Molluscs from the detailed account given of them by the original dis coverers.
Genus Pelonaia, Forbes and Goodsir. Animal simple, unattached. Test more or less cartilaginous, smooth or wrinkled, elon gated, and cylindrical ; anterior extremity bearing two orifices, four-cleft, without ten tacles, and placed on the same plane, on two equal, approximate, papillose eminences ; posterior extremity ending in a blunt point ; mantle adherent to the test. The Pelonake live buried in mud, quite unattached to any other body, and are extremely apathetic ani mals, presenting scarcely any appearance of motion.