Photo by Hans Bertsch, 28 September 1996
Cuevitas, Bahía de los Ángeles, 12 mm long animal
Limenandra confusa Carmona, Pola, Gosliner & Cervera, 2014
A truly confusing controversy was resolved a few years ago by these authors! To quote the title of the Laurel and Hardy 1930 film, “Another Fine Mess” has been fixed. Limenandra nodosa Haefelfinger & Stamm, 1958, was originally named from specimens collected in the Mediterranean. For nearly 50 years, new records of L. nodosa were considered part of a circumtropical distribution for the species. Haefelfinger & Stamm had also placed Baeolidia fusiformis Baba, 1949, into the genus Limenandra. These were the only two species of Limenandra, one reputedly “circumtropical,” the other known with certainty only from Japan.
The DNA and morphological study of Carmona et al., 2014, completely changed our understanding of the biogeography and taxonomy of Limenandra. They named two new species from the Indo-Pacific, L. barnosii and L. rosanae. They restricted the distribution of true L. nodosa to the Mediterranean and both coasts of the Atlantic. Central and eastern Pacific specimens previously identified as L. nodosa were named as the new species L. confusa.
Limenandra confusa has a variable body color, from gray-green to pale brown. The central dorsum is marked with white patches and concentric rings within them. The outermost ring is yellow, with an inner reddish-pink ring and a white center. The intensity and distinctness of the rings vary, as do the size and shape of the white patches. It is basically the same coloration as found in L. nodosa. In fact, Carmona et al. (2014) comment that “no external differences were found between them.”
The cerata of both Limenandra confusa and L. nodosa are papillate, whereas the cerata of L. fusiformis, L. barnosii, and L. rosanae are smooth, fusiform and rounded.
Based on DNA evidence, L. confusa and L. nodosa are considered two separate species. What are the morphological differences? As commented above, there are no consistent external differences. The presence or absence of salivary glands needs further examination. Carmona et al. (2016) wrote that the main morphological difference between the two species is the size of the receptaculum seminis, being much larger in L. confusa. An organ of the reproductive system is the distinguishing feature! Carmona et al. (2016: 45) wrote, “Thus, in view of the genetic, anatomical and biogeographic differences, we consider L. nodosa and L. confusa to be two sibling cryptic species.” This is the same evidentiary assemblage used to identify/separate the four Pacific basin species of Glaucus Forster, 1777 (see Churchill, Valdés & Foighil, 2014). DNA, structure of the reproductive system, and allopatric distributions distinguish these species clades.
Which presents me with the chance for a “philosophical-biological” detour. The biological definition of a species is reproductive isolation. In this age of computer-analyzed mathematical formulae to “call” a species a species, it is well to remember the biology of living beings (at least the multicellular animals). The biological species concept “stresses the fact that species consist of populations and that species have reality and an internal genetic cohesion owing to the historically evolved genetic program that is shared by all members of the species. According to this concept, then, the members of a species constitute (1) a reproductive community,...(2) an ecological unit , [and] (3) a genetic unit consisting of a large intercommunicating gene pool...The species definition that results from this theoretical species concept is: Species are groups of interbreeding natural populations that are reproductively isolated from other such groups” (Mayr, 1971). Today’s DNA analyses allow us to view the genetic homogeneity of a species that is different from other species. Field testing of reproductive isolation (versus or including hybridization) has always been difficult for marine invertebrates, especially widely-distributed rare species. We should use this molecular tool to understand the biology, remembering that the biology should drive the understanding, not the other way around.
Which presents us with a real world question. Is this variation in the reproductive system a “mechanism” that prevents interbreeding? Or is the allopatric occurrence sufficient? How are they related. I’m reminded of the lock-and-key mechanism among beetles, which prevent two different species (usually sympatric) from interbreeding (e.g., Sasabe, Takami & Sota, 2007).
Back to what we know about Limenandra confusa.
Bertsch (1972: 105) describes the locomotory actions: “The crawling behavior was by the extension-contraction method. with simultaneous forward and backward pumping of the cerata. All the cerata were jerked uniformly backward, pivoting at the base where the cerata are attached to the body. Then they were jerked upward, and the animal's body was extended forward longitudinally. The backward stroke was repeated, the animal contracted; then the forward jerk, extension, and animal's progression. The forward movement of the animal was in a regular rhythm with the ceratal pumping. It is not known whether the ceratal movement assisted or caused the animal's forward progression, or was just a side effect of the extension-contraction locomotory method.”
Limenandra nodosa occurs widely in the Atlantic and Mediterranean.
Limenandra confusa occurs across the Pacific basin. It has been reported from the Philippines, in the far western Pacific (Carmona et al., 2014) Reports from the Hawaiian Island chain in the central Pacific are from the Midway Islands (type locality), and from Wailua (Bertsch & Johnson, 1980) and Kaneohe Bay, Oahu (Gosliner, 1980). Its first report in the eastern Pacific was from Las Cruces, [ Baja California Sur (Bertsch, 1972). It has since been reported from Bahía de los Ángeles (Bertsch, 2014)(1) and (2) and Bahía Concepcion (González Cibrián, 2012) in the Gulf of California, from Bahía de Banderas in southern México (Hermosillo González, 2006), from Costa Rica (Camacho-García et al., 2005) and from Colombia (Londoño-Cruz, in press).
Bertsch, Hans. 1972. Two Additions to the Opisthobranch Fauna of the Southern Gulf of
California. The Veliger 51(2): 103-106.
Bertsch, Hans & Scott Johnson. 1980. Hawaiian Nudibranchs: A Guide for Scuba Divers, Snorkelers, Tidepoolers and Aquarists. The Oriental Publishing Company, Honolulu. 112 pp.
Camacho-García, Yolanda, Terrence M. Gosliner & Ángel Valdés. 2005. Guía de Campo de las Babosas Marinas del Pacífico Este Tropical / Field Guide to the Sea Slugs of the Tropical Eastern Pacific. California Academy of Sciences, San Francisco. 129 pp.
Carmona, Leila, Marta Pola, Terrence M. Gosliner & Juan Lucas Cervera. 2014. The end of a long controversy: systematics of the genus Limenandra (Mollusca: Nudibranchia: Aeolidiidae). Helgol Mar. Res. 68: 37-48.
Churchill, Celia K. C., Ángel Valdés & Diarmard Ó Foighil. 2014. Molecular and morphological systematics of neustonic nudibranchs (Mollusca : Gastropoda: Glaucidae: Glaucus), with descriptions of three new cryptic species. Invertebrate Systematics 28(2):174-195.
González Cibrián, Afelandra Victoria Rosalia. 2012. Opistobranqios (Mollusca: Opisthobranchia) de Bahía Concepción, Baja California Sur. Tesis de Licenciatura, Universidad Autónoma de Baja California Sur, La Paz. vii + 200 pp.
Gosliner, Terrence M. 1980. The systematics of the Aeolidacea (Nudibranchia: Mollusca) of the Hawaiian Islands, with descriptions of two new species. Pacific Science 33(1): 37-77.
Haefelfinger, H.-R. & Roger A. Stamm. 1958. Limenandra nodosa gen. et spec. nov. (Nudibranch, Aeolidiidae propr.), (I) un opisthobranche nouveau de la Méditerranée. Vie et Milieu 9(4):418-423.
Hermosillo González, Alicia. 2006. Ecología de los opistobranquios (Mollusca) de Bahía de Banderas, Jalisco-Nayarit, México. Tesis de Doctorado, Universidad de Guadalajara, Centro Universitario de Ciencias Biológicas y Agropecuarias. viii + 151 pp.
Londoño-Cruz, Edgardo. In press. The contribution of Heterobranchia (Mollusca: Gastropoda) to the biodiversity of the Colombian tropical eastern Pacific. Marine Biodiversity.
Mayr, Ernst. 1970. Populations, Species, and Evolution: An Abridgement of Animal Species and Evolution. The Belknap Press of Harvard University Press, Cambridge, Massachusetts. xv + 453 pp.
Sasabe, M., Y. Takami & T. Sota. 2007. The genetic basis of interspecific differences in genital morphology of closely related carabid beetles. Heredity 98: 385-391.