Evidence for convergent evolution of brooding in a unique gastropod from Lake Tanganyika: anatomy and affinity ofTanganyicia rufofilosa(Caenogastropoda, Cerithioidea, Paludomidae)

Abstract

Tanganyicia rufofilosa is an enigmatic gastropod endemic to Lake Tanganyika and unique among lake species in possessing a brood pouch within the head‐foot. However, the only existing anatomic studies of the species are incomplete. Hence, the affinity of this species to other Tanganyikan gastropods and the evolution of viviparity among limnic Cerithioidea are unclear. The anatomic redescription and reinterpretation of reproductive homologies presented here revealed several features from the midgut and kidney that are informative concerning the phylogeny of Lake Tanganyika gastropods. In addition, the complex reproductive anatomy of both sexes is described. A rare accessory gland is present in males that is hypothesized to function in spermatophore formation and to be homologous to the ‘penis’ of some cerithioideans, an otherwise predominantly aphallic group. The structurally unique brood pouch, restricted to the mesopodial portion of the foot, is described and demonstrated to be unknown among viviparous cerithioideans. In contrast to the view that the cerithioideans of Lake Tanganyika represent an endemic radiation of Thiaridae, based on these new data T. rufofilosa appears to be allied to the Paludomidae.

The morphology and independent origin of ovoviviparity in Tiphobia and Lavigeria (Caenogastropoda: Cerithioidea: Paludomidae) from Lake Tanganyika

“…(7) Moore assumed presence of a muscular introvertible penis, based on the presence of an outgrowth from the male pallial gonoduct. The structure, function and homologies of this structure have been discussed by Strong and Glaubrecht (2002) and Glaubrecht and Strong (2004); it is here confirmed to represent a glandular spermatophore-forming organ.…”

“…(3) Delayed calcification in conjunction with shrinking of the large yolk mass, producing a characteristically wrinkled embryonic cap, is evident in many brooding cerithioideans, including members of the Paludomidae, Pachychilidae, Planaxidae, and Thiaridae s.s. (e.g. Houbrick 1990;Riedel 1993;Glaubrecht 1996;Rintelen and Glaubrecht 1999;Kohler andGlaubrecht 2001, 2003;Strong and Glaubrecht 2002;Glaubrecht and Rintelen 2003; current study). As noted by Riedel (1993), the precise mode of calcification varies, producing distinct shell textures in various taxa.…”

“…This represents a third independent origin of this life history strategy in the lake, as well as a unique brooding structure in the Cerithioidea (Strong and Glaubrecht 2002) (see Fig. 17).…”

“…An additional species, Tanganyicia rufofilosa possesses a brood pouch within the foot -a so-called mesopodial brood pouch (Strong and Glaubrecht 2002). This represents a third independent origin of this life history strategy in the lake, as well as a unique brooding structure in the Cerithioidea (Strong and Glaubrecht 2002) (see Fig.…”

“…This resemblance, as well as their alleged morphological affinity with various marine families, particularly in features of the alimentary and nervous systems, formed the basis for Moore's (1898cMoore's ( , 1903 hypothesis that Lake Tanganyika represents a relictual Jurassic sea. Although that notion has long been dismissed, the origin and evolution of Lake Tanganyika's distinctive thalassoid fauna have been the focus of intense debate (see Glaubrecht 1996Glaubrecht , 2001Strong and Glaubrecht 2002; and the references cited in those works).…”