External morphology of the eggs of Asplanchnopus multiceps (Schrank, 1793) (Rotifera): solving the 150-year-old case of mistaken identity

Abstract

This report calls into question the practice of passing along illustrations and anatomical descriptions from the literature without scrutiny. An error made by Leydig (Zeischrift fur wissenschaftliche Zoologie 6:1–120, 1854) in characterizing the egg of Asplanchnopus multiceps was perpetuated in authoritative publications (Hyman, The Invertebrates: Acanthocephala, Aschelminthes, and Entoprocta. The pseudocoelomate Bilateria, McGraw-Hill Book Company, New York, 1951; Voigt, Rotatoria: Die Radertiere Mitteleuropas, Gebruder Borntraeger, Berlin-Nikolassee, 1957; Ruttner-Kolisko, Plankton rotifers, biology and taxonomy supplementary edition of Die Binnengewasser 26, Stuttgart, 1974; Koste, Rotatoria: Die Radertiere Mitteleuropas begrundet von Max Voigt. Monogononta 2. Auflage neubearbeitet von Walter Koste, Gebruder Borntraeger, Berlin, 1978; Mikrokosmos 76:171–175, 1987) well into the twentieth century. Daily tracking of individual mictic and amictic female A. multiceps demonstrates that the structure formerly considered to be a diapausing egg is, in fact, subitaneous. It develops without arrest into a male or female rotifer. True resting eggs containing dormant embryos are characterized by a very dark interior. In the majority of these eggs, the interior is surrounded by a halo-like zone consisting of a clear space and an external layer. The correct identification of subitaneous and resting eggs in A. multiceps confirms the description of Plate (Jenaische Zeitschrift fur Naturwissenschaft 19:1–120, 1885) and firmly establishes the mode of reproduction of this species as oviparous. Mictic females lay haploid male eggs first, followed by resting eggs if fertilization has taken place. In the absence of fertilization, mictic females lay significantly more (male) eggs than amictic females lay female eggs; however, their lifespan does not differ markedly.