When size matters: the first comprehensive anatomical study of a species of ``Condylocardiidae{''}, an extremely miniaturized bivalve

Author(s)

Passos, Flavio Dias ^[1] ; Batistao, Alan Rodrigo ^[1] ; Bieler, Rudiger ^[2]

Affiliation

^[1] Univ Estadual Campinas, Inst Biol, Dept Anim Biol, Sao Paulo, SP - Brazil

^[2] Field Museum Nat Hist, Negaunee Integrat Res Ctr, Chicago, IL - USA

• Document type: Journal article
• Source: PEERJ COMPUTER SCIENCE; v. 9, AUG 30 2021.
• Web of Science Citations: 0

Abstract

`Miniaturization' is a widespread phenomenon among the Metazoa. In the molluscan class Bivalvia, records of miniaturization are numerous. Among the Archiheterodonta, Warrana besnardi (Klappenbach, 1963) has attracted attention for its tiny size, which does not exceed 1.5 mm in shell length, and because it belongs to a group with limited anatomical information and often-debated status, the ``Condylocardiidae{''} (which recent molecular studies place deeply nested within the family Carditidae). All species of Warrana Laseron, 1953 are small-bodied, and so miniaturization presumably occurred from a large-bodied ancestor within the Carditidae sensu lato. South American W. besnardi is here studied in detail. Its small size and the enlargement of the anterodorsal region during growth, reflects (and likely led) to infaunal habit, living as a burrowing bivalve that passively feeds on deposit particles entering the pallial cavity anteriorly. Mantle glands, previously reported as a common feature of other archiheterodonts, are missing in W. besnardi, but spongiform tissue in the antero-ventral portion of the mantle lobes presumably represents a blood sinus that might compensate for the great reduction of the ctenidia. Lecithotrophy is reported, with yolky oocytes bearing a thick non-cellular capsule layer; brooding was not observed, and it is here hypothesized that the extreme miniaturization, with the great reduction of ctenidia, is responsible for a shift in the reproductive mode of condylocardiids, contrasting with the commonly reported ovoviviparity of the carditids. (AU)

• FAPESP's process: 18/11431-6 - Unravelling the Condylocardiidae family (Mollusca, Bivalvia): an anatomical and taxonomic study of Warrana besnardi (Klappenbach, 1963)
• Grantee: Alan Rodrigo Batistão
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 18/10313-0 - Build-up of scientific collections of marine invertebrates: strategies for biodiversity conservation
• Grantee: Antonia Cecília Zacagnini Amaral
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 18/06347-6 - Biodiversity and biogeography of benthonic animals from the deep-sea: a study of the Brazilian Caudofoveata (Mollusca, Aplacophora)
• Grantee: Flávio Dias Passos
• Support Opportunities: Regular Research Grants