A RESTUDY OF THE BYSSAL NOTCH OF THE SPECIES CLARAIA TUMIDA (PATTE,1935)(BIVALVIA:CLARAIIDAE)
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Abstract:
The original photo of the species Claraia tumida published by Patte(1935, p. 22, pl. 2, fig. 4 b, accession number: NIGP 6442) has clearly shown the typical Claraia-type byssal notch(also see text-fig. 1-1 a—1-1 d, 1-1 f of this paper). But Gu Zhi-wei et al.(Editorial Group on "The Lamellibranch Fossils of China", 1976, p. 201, pl. 33, fig. 13, also see text-fig. 1-1 e of this paper) cut the photo according to the crevasse traces(please compare with black arrows in text-fig. 1-1 b, 1-1 d and 1-1 f for confirming their positional relationship), so that they got a false "byssal notch" of a half wheel shape in ‘The Lamellibranch Fossils of China". This so-called "byssal notch" has been widely cited in recent years as a "real" Claraioides-type byssal notch(Yang et al., 2001; Gao et al., 2004, 2009; He et al., 2007, 2014). However, this "byssal notch" has been turn out to be false herein and it has nothing to do with the real byssal notch. The species of Claraia tumida does not develop the Claraioides-type byssal notch. Therefore, all the views and inferences derived from the false "byssal notch" of Claraia tumida may not be valid, such as the "Scatter plot of measured characters" of He et al.(2007, p. 1013, Fig. 4) using the measurement data of the false "byssal notch" of Claraia tumida, and their related conclusion on "progressive morphological changes" in Claraia(also including Claraioides) from the early Changhsingian to the Induan(He et al., 2007, p. 1017, Fig. 6; 2014; Ros-Franch et al., 2014), losing their necessary basis too. There is no so-called intermediate transition type has been found between Claraia-type and Claraioides-type byssal notches so far, which represent two different mode of byssal notch development in Claraia-like species, indicating that they are two separate and parallel evolutionary lineages. In addition, the genera Claraia and Claraioides had never coexisted in geological and geographical distribution, and there is no possibility of establishing an evolutionary relationship between them(Fang, 2003, 2004, 2010; Fang in Fang et al., 2009).
