Caecum cf. strangulatum de Folin, 1867

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 cf. strangulatum de Folin, 1867

Caecum strangulatum de Folin, 1867: 82 (with variety acuta de Folin, 1867). Type locality: Iles aux Perles, dans la baie de Panama [Pearl Islands, Panama].

Material examined.

Panama • 1 juv.; Achotines; 7.6349, -79.9968; depth 10 m; 6 Mar 2016; USNM Achotines2016 exped.; Stat. PA23a; DNA voucher; GenBank: MT727072, MT731727; USNM 1618884. • 1 juv. (Fig. 7O, P, R, T ); same collection data as for preceding; ZSM-Mol-20200038. • 1 juv.; Achotines; 7.6207, -80.0013; depth 12 m; 29 Feb 2016; USNM Achotines2016 exped.; Stat. PA14; DNA voucher; GenBank: MT727068, MT704287, MT731721; USNM 1618864.

Shell morphology.

Shell fragile, color frosted translucent (Fig. 7O ). Shape and size the same as for C. cf. teres juvenile (Fig. 7M, N ). Sculpture however appears rough and annular using light microscopy, growth lines more distinct and wavy (Fig. 7T ). Septum flat, mucro narrow, finger-like (Fig. 7R ). Aperture fringed as typical for a juvenile, growing specimen (Fig. 7P ). Striped microsculpture consists of narrow longitudinal and interrupted emarginations, shifted against each other. Almost identical to C. cf. teres (Fig. 7S ).

Remarks.

We assign the examined specimen to Caecum strangulatum (in the juvenile form), which was described from Pacific Panama ( de Folin 1867) (holotype MNHN-IM-2000-4586, accessed through the online catalogue of the MNHN), due to the narrow mucro and the annular sculpture, which probably can be interpreted as the transition to a ribbed ornamentation in later life stage. The separate species status of C. strangulatum and C. teres (see below) is not supported via our molecular species delineation (see Fig. 4 ). Both are sister clades in phylogenetic analyses (see Fig. 3 ), but the monophyly of both lineages is not reflected on mitochondrial 16S rRNA (Fig. 4 ). Both species can be distinguished by morphological features (i.e., a noticeably more pronounced shell structure and a slimmer mucro), but share a unique microsculptural pattern (Fig. 7D ). We currently lack comparative data on COI to evaluate whether the results in species delineation on 16S rRNA present a case of incomplete lineage sorting in this recent split between the two sister species or both belong to one genetically and morphologically diverse species. Due to this lack of data, we currently refrain from synonymizing the two yet existing species until more data is available to text species boundaries and the degree of intraspecific variability in shell morphology.

Figures

Figure 3. Optimal ML tree of the concatenated 28 S rRNA, 16 S rRNA and COI genes partitioned by genes and COI codon positions. Bootstrap values (below nodes) of the ML analysis are shown for values> 80 % and posterior probability support (above nodes) of the BI analysis are shown for values> 0.95. Specimens previously classified as Meioceras are indicated in yellow color. Smooth, translucent specimens, lacking diagnostic features and summarized in the ' Caecum glabrum - like complex' are indicated in blue. C. = Caecum, M. = Meioceras, MOTU I / MOTU II = molecular operational taxonomic unit within the ' Caecum glabrum - like complex'. Figured specimens are all to the same scale. Scale bar: 1 mm.

Figure 4. Molecular based species delimitation of Central American Caecidae. Guide tree used for PTP and bPTP based on the optimal likelihood tree of the concatenated three-marker dataset. Color codes indicate our preliminary species hypothesis derived from the phylogenetic tree. Color bars reflect the species delimitation suggested by the four consulted species delimitation programs (including ML and Bayesian implementation for PTP and single and multiple threshold for GMYC). Bars are missing where no sequence data obtained.

Figure 7. A-F Caecum pulchellum A, C, E, F specimen ZSM-Mol- 20090485 B, D juvenile specimen ZSM-Mol- 20200118 A, B light microscopic pictures C, D SEM scans E close-up of mucro and F microsculpture H-K C. donmoorei, specimen USNM 1618844 H-K C. regulare, specimen ZSM-Mol- 20100321, juvenile H light microscopic picture I SEM scans J close-up of mucro and K microsculpture L-T C. cf. teres and C. cf. strangulatum L specimen ZSM-Mol- 20200033, juvenile specimen with larval shell still attached M, N, Q, S specimen ZSM-Mol- 20200032, juvenile M light microscopic picture N SEM scan Q close-up of mucro and S microsculpture O, P, R, T C. cf. strangulatum, specimen ZSM-Mol- 20200038, juvenile O light microscopic picture P SEM scan R close-up of mucro and T microsculpture U-X C. cf. semilaeve, specimen ZSM-Mol- 20200034 U Light microscopic picture V SEM scan W close-up of mucro and X microsculpture. Scale bars: 10 µm (F, S, T, W, X); 20 µm (J, K, Q, R); 50 µm (E); 100 µm (H, I, L-P, U, V); 200 µm (A-D).