8 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



Order CYDIPPIDiE Gegenbaur, 1856. 



Cydippidas, Gegenbaur, 1856, Archiv fiir Naturgesch.. Jahrg. 22, p. 196. — Chun, 

 1880, Ctenophoren des Golfes von Neapel, pp. 30, 273, 275. — Moser, 1903, 

 Ctenophoren der 5i6oga-Expedition, p. 4. — Vanhoffen, 1906, Nordisches 

 Plankton, Ctenophoren, xi, p. 2. 



PleurobrachiidcB, Ghigi, 1909, Ctenofori, Firenze, vol. 2, fasc, i, p. 7. 



CHARACTERS OF THE CYDIPPID.^. 



Ctenophorae with 2 tentacles in the funnel diameter which arise 

 from sheath-Uke clefts in the sides of the body. The body is usually 

 laterally compressed, the tentacular diameter being the wider, although 

 it may be spherical or cylindrical. There are neither oral lobes nor 

 auricles. The meridional and paragastric canals end blindly. The 

 tentacles may be simple or with side branches. The axis of the tentacle 

 is mesodermal as in other ctenophores. 



Genus MERTENSIA Lesson, 1836. 



Mertensia, Lesson, 1836, Annals des Sci. Nat., s^r. 2, tome 5, p. 253; 1843, Hist. 

 Zooph. Acal., p. 100. — M5RCH, 1857, Nat. Bid. til en Beskriv. af Gronland, 

 p. 97. — Agassiz, a., 1865, North Amer. Acal., p. 26. — Chun, 1898, Ergeb. der 

 Plankton-Expedition, Ctenophoren, p. 10. — VanhSffen, 1906, Nordisches 

 Plankton, 11, Ctenophoren, p. 2. — Moser, 1909, Ctenophoren der deutsch. 

 Siidpolar-Exped., Bd. 11, Zool. 3, p. 123. 



GENERIC CHARACTERS. 



Cydippidae in which the body is laterally' compressed, the tentacular 

 axis being wider than the axis through the plane of the stomodaeum. The 

 4 subtentacular rows of cilia are longer than the 4 subventral rows and 

 arise at a higher level, and are farther removed from the apical sense- 

 organ than the latter. There are no wing-like protuberances upon the 

 sensory pole-plate. 



The type species is Mertensia ovum of the Arctic Ocean. It was 

 first described by Fabricius, 1780, as Beroe ovum. 



Mertensia ovum Lesson. (Fig. i, plate i.) 



Beroe ovum, Fabricius, 1780, Fauna Gronlandica, p. 362, No. 355. 



Cydippe ovum, C. ciwullus, Eschscholtz, 1829, Syst. der Acal., p. 25. 



Beroe pileus, Scoresby, 1820, Arct. Reg., 2, plate 16, fig. 4. 



Mertensia ovum, Lesson, 1836, Annales des Sci. Nat., s6v. 2, tome 5, p. 254. 



Cydippe {Mertensia) ovum, Morch, 1857, Beskriv. af Gronland, p. 97. 



Mertensia scoresbyi, Lesson, 1843, Hist. Zooph. Acal., p. 100. 



Cydippe cucumis. Lesson, 1843, Hist. Zooph. Acal., p. 105. 



Mertensia cucullus, Agassiz, L., i860, Cont. Nat. Hist. U. S., vol. 3, p. 293. 



Mertensia ovum, Agassiz, A., 1865, North Amer. Acalephas, p. 26, figs. 29 to 37; 

 1874, Mem. American Acad., vol. 10, No. 3, p. 375, figs, i, 2. — Vanhoffen, 

 1895, Bibliotheca Zoologica, Heft 20, Lfg. i, p. 21. — Chun, 1898, Cteno- 

 phoren der Plankton-Expedition, p. 10 — Romer, 1903, Fauna Arctica, Cteno- 

 phoren, Bd. 3, p. 72 (full list of Hterature). — Vanhoffen, 1906, Nordisches 

 Plankton, xi, Ctenophoren, p. 2, figs, i to 3. — Bigelow, 1909, Proc. U. S. Nat. 

 Mus., Washington, vol. 37, p. 316. 



M. ovum is larger than Pleurobrachia pileus, becoming 55 mm. long. 

 Body egg-shaped in outline, the mouth being at the pointed pole and the 

 apical sense-organ at the broad end. The body is strongly compressed 

 in the plane perpendicular to the tentacular radii, and thus the creature 

 superficially resembles a much-flattened Pleurobrachia. The apical 

 sense-organ contains a mass of small concretions and is surrounded by a 



