How features of the hinge plate aid in discriminating among three Yoldiella (Pelecypoda, Protobranchia) species from the Campos Basin, Brazil

Abstract

Subjectivity is a common problem in most taxonomic studies that deal with gradual changes in shape. An example is the systematics of the genus Yoldiella, which has been a matter of debate for over 40 years. However, hinge plate features have never been examined as a significant diagnostic feature in descriptions of Yoldiella species. We tested how hinge plate characters perform in discriminating among three species of this genus from the Campos Basin, Brazil. We tested the efficacy of traditional shell shape features alone, and contrasted this with a general analysis that included the hinge plate features; and also with an analysis based solely on the hinge plate. Some information on the hinge plate is used here for the first time, such as the distance between the highest teeth to the umbo and the distance between the highest teeth to the margin. The hinge plate analysis and a general analysis, including both shell shape and hinge plate variables, were more effective (87.5% of cases assigned correctly) than the analysis that included only shell shape variables (73.3% cases assigned correctly). The variables related to the highest teeth and the width of the hinge teeth stood out as major contributors in discriminating among these three species.

Microgloma Sanders & Allen, 1973 (Nuculanidae) and Pristigloma Dall, 1900 (Pristiglomidae) (Pelecypoda) in the Campos Basin of Brazil

“…The species were characterized considering traditional criteria used in pelecypod orientation and terminology ( Figs 1–2 ) ( Fischer 1886 , Sanders and Allen 1973 , Mikkelsen and Bieler 2008 , Baylei 2009 ). In view of the importance of the features of the hinge plate for the discrimination of other protobranch species (Benaim and Absalão 2011, Benaim et al 2011 ), and also some subjective concepts in taxonomy (e.g., ‘thin’ or ‘thick’), we described the species using certain quantitative criteria such as the ratios of the hinge teeth (wht) and hinge plate (whp) measurements ( Figs 1–2 ), which are described as follows: ‘thin’ for width of hinge plate/total height ratio < 0.1; ‘thick’ for width of hinge plate/total height ratio ≥ 0.1. The width of the hinge teeth was measured just above (dorsal) and below (ventral) the limit of the big ger teeth.…”

Treatise Online no. 61: Part N, Revised, Volume 1, Chapter 4: The early shell: Ontogeny, features, and evolution

“…alleN, 2008). All protobranchs are presumably lecithotrophic-hence, excluding matrotrophy and feeding on dissolved organic matter-but descriptions of their development and larval shells are anecdotal (e.g., alleN, 1993;ockelMaNN & WaréN, 1998;schelteMa & WilliaMs, 2009;BeNaiM, vieGas, & aBsalão, 2011). Protobranch dominance in the deep sea may simply reflect the vastness of organic-rich bottom sediments that favor deposit-feeding bivalves, or their hemocyanin or hemoglobin may have preadapted them to oxygendepleted environments (MaNGuM & others, 1987;alleN, 1993;taylor, daveNPort, & alleN, 1995;aNGeliNi & others, 1998;saNders, childress, & McMahoN, 1998).…”