The evolution of the watering pot shells (Bivalvia: Anomalodesmata: Clavagellidae and Penicillidae)

Abstract

Hitherto, the bivalve watering pot shells (Subclass Anomalodesmata) have been considered to be all contained within one superfamily the Clavagelloidea -it too possessing but one family and generally comprising two functional clades: (i) the extinct Clavagella and the nestling/boring Dacosta and (ii) the endobenthic Brechites, Penicillus, Foegia, Kendrickiana and l\JipponocIava (plus the fossil Pseudobrechites and I!\!arnea), and Stirpulina. The cemented Pliocene-Recent Humphreyia can be derived from an endobenthic Brechites-like ancestor (l\JipponocJava), making a third functional entitv. The genus Dianadema also comprises species that are cemented. l{ecently, the endolithic Blyopa has been proposed as a fourth clade and a unique extension of the clavagellid line of evolution in which the anterior region of the right valve is dissolved as the animal bores deeper. The above studies, in broadening our understanding of the range of superfamilial functional diversity, however, raise questions with regard to the, as currently defined, taxonomic arrangement of the Clavagelloidea.Species of the extinct genus Clavagella and their extant allies, notably Damsta, have an internal ligament (but no lithodesma) located between chondrophores, both adductor muscles, a pallial line with a pallial sinus, and no pedal disc. Further, although Dacosta, Bryopa, Dianadema and Stirpuiina cement their left valves to the wall of their crypt or adventitious tube, the right is free inside it. Conversely, both shell valves of Brechiles and its allies, including the cemented Humphreyia, become surrounded by and united marginally with an adventitious tube and to which they are then fused by a calcareous secretion produced from the underlying mantle. Moreover, Brechiles and Humphreyia have an external ligament (the latter with a lithodesma), are functionally amyarian as adults, have no pallial sinus and develop a watering pot anteriorly, internal to which is a highly muscular pedal disc. Most important, however, flumphreyia, at least, has a distinct post-planktonic life history stage in which a free-living, typical bivalve juvenile, metamorphoses into a tube-dwelling adult. At this time, shell growth ceases and only the tube can be extended posteriorly and repaired. This is not the case with Clavagella and its allies although at some stage the juvenile does cement itself to its burrow wall but shell growth, especially of the free right valve, can continue.All watering pot bivalves possess juvenile shells that in overall form and in the possession of distinct radial striae are reminiscent of representatives of the Lyonsiidae, suggesting a possible ancestry. The clavagellid fossil record shows that Clavagella and its allies (Dacosla, Bryopa, Dianadema and Stirpulina) : 10.18195/issn.0312-3162.24(1).2007.019-064 20 between the endobenthic tube-dwelling Stirpulina (Clavagellidae) and Brechites (Penicillidae) and the cemented Dianadema (Clavagellidae) and Humphreyia (Penicillidae). Only Dacosta and Bryopa (Clavagellidae), however, ...

A new species and a new record of endobenthic Clavagellidae (Bivalvia: Anomalodesmata: Clavagelloidea) from the Oligocene and Miocene of New Zealand

“…Clavagelloidea has recently, however, been shown to comprise two families: Penicillidae Bruguie`re, 1789 and Clavagellidae d'Orbigny, 1844, both thought to have been derived independently from lyonsiid ancestors, providing a remarkable example of convergent evolution (Morton 2007).…”

“…Brechites Guettard, 1770, Nipponoclava BJ Smith, 1976, Kendrickiana Morton, 2004, Foegia Gray, 1847and Penicillus Bruguie`re, 1789(Morton 2002a, 2004a, b, c, 2006a, both valves of the juvenile shell are incorporated into the fabric of a much larger calcareous adventitious tube or, in the case of the cemented genus Humphreyia Gray, 1858, a crypt, and cannot grow any further (Morton 2002b(Morton , 2007. In representative genera of the Clavagellidae, only the juvenile left valve is incorporated into the structure of either the crypt of endolithic species of Clavagella Lamarck, 1818, Dacosta Gray, 1858, Dianadema Morton, 2002and Bryopa Gray, 1847 or the adventitious tube of Stirpulina Stoliczka, 1870 (Owen 1835; Morton 1984aMorton , 2003Morton , 2005Morton , 2006bMorton , 2009).…”

“…In representative genera of the Clavagellidae, only the juvenile left valve is incorporated into the structure of either the crypt of endolithic species of Clavagella Lamarck, 1818, Dacosta Gray, 1858, Dianadema Morton, 2002and Bryopa Gray, 1847 or the adventitious tube of Stirpulina Stoliczka, 1870 (Owen 1835; Morton 1984aMorton , 2003Morton , 2005Morton , 2006bMorton , 2009). The post-juvenile right valve is free within the tube and can continue to grow (Morton 2007). The methods of tube or crypt formation in representatives of the two families are therefore different.…”

“…As currently defined (Morton 2007), the Clavagellidae includes representatives of the extinct genera Clavagella and Ascaulocardium Pojeta & Sohl, 1987 as well as the extant Dacosta, Dianadema, Bryopa and Stirpulina. The first two genera include either boring or crevice-enlarging endolithic species, whereas representatives of the latter three are endobenthic, endolithic and epibenthic inhabitants of soft substrata, respectively.…”

“…In the Oligocene, the preserved fossil record suggests that Clavagella extended its range eastwards into the Indo-West Pacific reaching Japan, the Philippines and Australasia in the Miocene. Recent species of the Clavagellidae occur in the Mediterranean (Soliman 1971), South Africa (Kilburn 1974), Asia and Australia (Morton 1984a(Morton , 2005(Morton , 2007.…”