Caecum heptagonum Carpenter, 1857

Egger, Christina, Neusser, Timea P., Norenburg, Jon, Leasi, Francesca, Buge, Barbara, Vannozzi, Angelo, Cunha, Regina L., Cox, Cymon J. & Joerger, Katharina M., 2020, Uncovering the shell game with barcodes: diversity of meiofaunal Caecidae snails (Truncatelloidea, Caenogastropoda) from Central America, ZooKeys 968, pp. 1-42 : 1

Caecum heptagonum Carpenter, 1857

Caecum heptagonum Carpenter, 1857: 319, t. 1524. Type locality: Mazatlán [Mexico].

Material examined.

Panama • 1 juv. (Fig. 6B-E ); Achotines; 7.6349, -79.9968; depth 10 m; 6 Mar 2016; USNM Achotines2016 exped.; Stat. PA23a; DNA voucher; DNA bank: r462p4f2t91, GenBank: MT704283, MT731717; ZSM-Mol-20200030. • 1 juv. (Fig. 6A ); same collection data as for preceding; DNA voucher; GenBank: MT704291, MT731726; USNM 1618866. • 1 juv.; same collection data as for preceding; ZSM-Mol-20200116. • 1 juv.; same collection data as for preceding; ZSM-Mol-20200117. • 1 juv.; Achotines; 7.6346, -79.9965; depth 10 m; 6 Mar 2016; USNM Achotines2016 exped.; Stat. PA23b; ZSM-Mol-20200115.

Shell morphology.

In juvenile specimens, shell fragile, translucent brownish color. Tube doubles diameter towards aperture, with a moderate curvature in anterior half, increasing distally in curvature. Septum level beneath cutting plane, slightly rising towards mucro (Fig. 6D ). Mucro slender finger-like shape (Fig. 6D ). Aperture fragile and partly broken. Shell sculptured by seven longitudinal ridges with transverse ribs crossing, knobs at intersections, ridges less prominent towards posterior. Microsculpture of fine rugose longitudinal stripes, noticeably increasing in width on transversal rings in comparison to interspaces (Fig. 6E ).

Remarks.

Due to the characteristics of the heptagonal tube with the transversal rings, considered unique among caecids ( Lightfoot 1993a), the investigated specimen could be unambiguously assigned to C. heptagonum . However, illustrations of C. heptagonum indicate a very thick shell with distinct differentiated aperture with inner bulge forming a round opening instead of the outer polygonal shape ( Keen 1974; Pizzini et al. 1998: 142, figs 1-13) including an inner bulge in the aperture, forming a round opening instead of the outer polygonal shape which is absent in the rather thin and fragile investigated specimens. As our samples only comprised juvenile specimen, however, we can attribute this variation to the unfinished shell state.

Figures

Figure 6. A-E Caecum heptagonum A specimen USNM 1618866 juvenile specimen with larval shell still attached B-E specimen ZSM-Mol- 20200030, juvenile specimen already resembling closely the adult form B light microscopic picture C SEM scan D close-up of mucro and E microsculpture F-I C. cooperi, specimen MNHN-IM- 2019 - 32 F light microscopic picture G SEM scan H close-up of mucro and I microsculpture whole specimen and close-up of mucro and microsculpture J-M C. debile, specimen MNHN-IM- 2019 - 27 J light microscopic picture K SEM scan L close-up of mucro and M microsculpture N-Q C. striatum, specimen ZSM-Mol- 20100322 N light microscopic picture O SEM scan P close-up of mucro and Q microsculpture R-U C. clathratum, specimen MNHN-IM- 2019 - 17 R light microscopic picture S SEM scan T close-up of mucro and U microsculpture. Scale bars: 10 µm (D, E, I, Q); 20 µm (H, M, P, U); 100 µm (A, B, C, L, N, O, T); 200 µm (F, G, J, K whole specimen); 300 µm (R, S).