A new species and genus of the Aglajidae and the evolution of the philinacean opisthobranch molluscs

Abstract

A new genus and species of the Aglajidae is described. It differs from the other members of the family in having a radula and a rudimentary gizzard, but has sensory bristles and the Yellow Gland, features unique to the Aglajidae. From all the evidence available it is suggested that the families Scaphandridae, Gastro‐pteridae, Philinidae and Aglajidae arose separately from a Cylichna‐wke ancestor with an oodiaulic reproductive system. It is possible that the first three families arose from a common ancestor that had developed a monaulic reproductive system, but it is equally likely that monaulism occurred independently in each family, as it has in the Aglajidae. A new family for Cylichna is proposed. Summary. Cylichna fills many of the requirements of an hypothetical common ancestor of the Philinaceae. From such an ancestor, five distinct lines have evolved, each separately specializing different aspects of their anatomy (Fig. 6). In the Tomatina‐Cylichnella group, the development of a monaulic reproductive system and calcification and elaboration of the gizzard plates, seems to be the only major advances. In the Scaphander‐Paracteocina group we see a tendency to detort with accompanying degeneration of the shell. Monaulism and the calcification and elaboration of the gizzard plates has also occurred. In Philine, bilateral symmetry of the body has evolved, the shell is internal and the reproductive system is monaulic. The alimentary canal in advanced forms shows great elaboration. We find species showing all stages in the evolution of the P. aperta‐type gut from the primitive P. falklandica‐type. In the Gastropteridae, jaw‐plates have been retained, but the gizzard has been lost. The greatest development has been in external body form, with loss of the mantle cavity and presence of an external gill and large wing‐like parapodia for swimming. In the Aglajidae we find the greatest degree of modification. In all but Odontoglaja the radula and gizzard have been lost, and in all cases the body is very stream‐lined, the shell being reduced and internal. Aglajids are capable of infaunal burrowing, but most species are usually epifaunal. Unlike the other families there is a diversity in the structure of the reproductive system.

Phylogeny of the family Aglajidae (Pilsbry, 1895) (Heterobranchia: Cephalaspidea) inferred from mtDNA and nDNA

“…The systematics and taxonomy of Aglajidae have been reviewed by Rudman (1972aRudman ( ,b,c, 1974Rudman ( , 1978, Gosliner (1980), and Baba (1985) based on morphological data. However, difficulties in phylogenetic reconstruction and identification of aglajids using morphological traits, has resulted in complex and often conflicting classification schemes.…”

“…Emphasis of one set of characters over another has often produced contradictory classifications. Additionally, establishing generic boundaries based on morphological differences have led to some disagreement over the composition of the various genera (Rudman, 1978;Gosliner, 1980). Rudman (1978) and Gosliner (1980) made the first attempts to reconstruct the evolutionary history of Aglajidae using different approaches.…”

Diet preferences of the Aglajidae: a family of cephalaspidean gastropod predators on tropical and temperate shores

“…P. taronga, P. orientalis) that is also present in Aglaja, Melanochlamys and Navanax; and a tubular variation (e.g. P. depicta, P. pilsbryi) (Rudman, 1971(Rudman, , 1972a(Rudman, , b, c, 1974(Rudman, , 1978 (Figure 1A-C). The buccal bulb in Aglaja and Navanax can evert completely, whereas this ability is absent in Chelidonura, Nakamigawaia, Melanochlamys and Philinopsis (Rudman, 1971(Rudman, , 1974Gosliner, 1980Gosliner, , 1994.…”

“…The genus Navanax feed upon other cephalaspideans including conspecifics, sacoglosans, anaspideans, nudibranchs, caenogastropods, polychaetes, crustaceans and small fish (Paine, 1963(Paine, , 1965Blair & Seapy, 1972;Gosliner, 1980;Leonard & Lukowiak, 1984;Pennings, 1990;Pennings et al, 2001;Korb, 2003); Philinopsis and Melanochlamys feed upon cephalaspideans and polychaetes (Rudman, 1972a, b, Göbbeler & Klussmann-Kolb, 2009); Chelidonura upon flatworms (Gosliner, 1987(Gosliner, , 1994Yonow, 1992;Mangubhai, 2007); while Odontoglaja feeds on polychaetes and bivalves (Rudman, 1978;Wägele & Klussmann-Kolb, 2005;Lobo-da-Cunha et al, 2009). No data are available on the diet of Aglaja and Nakamigawaia.…”

“…Aglajidae is a diverse group of predominantly shallow-water cephalaspidean gastropods with an extensive degree of morphological and colour variation (Rudman, 1971(Rudman, , 1972a(Rudman, , b, c, 1974(Rudman, , 1978Gosliner, 1980Gosliner, , 2008. The family contains seven recognized genera and approximately 80 species worldwide distributed in tropical, sub-tropical and temperate shores.…”