Some thirty species of Balanoglossus are known, distributed among all the principal marine provinces from Greenland to New Zealand. The species which occurs in the English Channel is Ptychodera sarniensis. The Ptychoderidae and Spengelidae are predominantly tropical and subtropical, while the Balanoglossidae are predominantly arctic and temperate in their distribution. One of the most singular facts concerning the geographical distribution of Enteropneusta has recently been brought to light by Benham, who found a species of Balanoglossus, sensu stricto, on the coast of New Zealand hardly distinguishable from one occurring off Japan. Finally, Glandiceps abyssicola (Spengelidae) was dredged during the "Challenger" expedition in the Atlantic Ocean off the coast of Africa at a depth of 2500 fathoms.
W. Bateson, "Memoirs on the Direct Development of Balanoglossus," Quart. Journ. Micr. Sci. (vols. xxiv.-xxvi., 1884-1886); W. B. Benham, "Balanoglossus otagoensis, n. sp," Q. J. M. S. (vol. xlii. p. 497, 1899); Yves Delage and éd. Hérouard, Traité de zoologie concrète (t. viii.), "Les Procordés" (1898); S. F. Harmer, "Note on the Name Balanoglossus," Proc. Camb. Phil. Soc. (x. p. 190, 1900); T. H. Morgan, "Memoirs on the Indirect Development of Balanoglossus," Journ. Morph. (vol. v., 1891, and vol. ix., 1894); W. E. Ritter, "Harrimania maculosa, a new Genus and Species of Enteropneusta from Alaska," Papers from the Harriman Alaska Exhibition (ii.), Proc. Washington Ac. (ii. p. 111, 1900); J. W. Spengel, "Die Enteropneusten," Eighteenth Monograph on the Fauna und Flora des Golfes von Neapel (1893); A. Willey, "Enteropneusta from the South Pacific, with Notes on the West Indian Species," Zool. Results (Willey), part iii., 1899; see also Q. J. M. S. (vol. xlii. p. 223, 1899); J. P. Hill, "The Enteropneusta of Funafuti," Mem. Austral. Mus. (iii., 1897-1898); M. Caullery and F. Mesnil, "Balanoglossus Kochleri, n. sp.
English Channel," C. R. Soc. Biol. lii. p. 256 (1900).