Caecum invisibile Egger & Joerger, 2020

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 invisibile Egger & Joerger sp. nov.

Material examined.

Holotype Belize • 1 (Fig. 5O-R ); Carrie Bow Cay; 16.8015, -88.0790; depth 10 m; 14 Jan 2010; USNM Belize2010 exped.; Stat. CBC1b; DNA voucher; DNA bank: r462p15f2t91; GenBank: MT727055, MT704268, MT731697; ZSM-Mol-20100320. Paratypes Belize • 1; same data as for holotype; DNA voucher; DNA bank: r462p14f2t91; GenBank: MT727054, MT704267, MT731696; ZSM-Mol-20200109. Belize • 2; same data as for holotype; ZSM-Mol-20200111, ZSM-Mol-20200112. Other material Belize • 10; same data as for holotype; DNA voucher; GenBank: MT727056-MT727065, MT704269-MT704279, MT731698-MT731707; USNM 1618839, USNM 1618840, USNM 1618841, USNM 1618842, USNM 1618843, USNM 1618846, USNM 1618847, USNM 1618848, USNM 1618849. Panama • 1; Bocas del Toro; 9.2140, -81.9318; depth 8.5 m; 5 Jun 2010; USNM BRS2010 exped.; Stat. BRS104; DNA voucher; GenBank: MT727049, MT704264, MT731689; USNM 1618856. • 1; Bocas del Toro; 9.3507, -82.1724; depth 3 m; 13 Jun 2010; USNM BRS2010 exped.; Stat. BRS200; DNA voucher; GenBank: MT727052, MT731694; USNM 1618859.

Molecular diagnostic characters.

see Table 4 .

Morphological description.

All investigated specimens were very similar in appearance, with little or no variation in shell morphology. Shell completely translucent. Length 0.8 mm long, width 0.2 mm (holotype, Fig. 5O ). Tube regularly curved, shape equal in width but bears prominent edge at transition to septum, edge with smaller diameter. Septum round and blistered lacking a distinct mucro. Septum slightly inclining towards the left, dorsal side in holotype with slight variation between the specimens. Aperture equally wide as tube with straight edge. Sculpture appears smooth, only with faint growth lines (Fig. 5R ). Whitish translucent body visible through translucent shell. Operculum translucent, slightly tinted yellowish. Radula formula shows taenioglossate pattern 2.1.1.1.2. with very small central rhachidian tooth. Large lateral teeth oriented towards the rhachidian tooth. Marginal teeth finer, outer marginal teeth are scoop-like curved. All the specimens investigated are adults based on the cylindrical shape of the tube and the shape of the aperture showing a reflected lip without cutting edge, which is normally present in immature specimens.

Etymology.

The Latin adjective invisibile (invisible, unable to be seen) refers to the minute size of specimens, the translucent color of its shell, its hidden lifestyle between sand grains, and its taxonomic crypsis.

Distribution.

Type locality: Carrie Bow Cay, Belize. (16.8015°N, - 88.0790°W, -10 m). Distributed in Central American Atlantic from Carrie Bow Cay, Belize to Bocas del Toro, Panama. Interstitial in coarse biogenic sediments (calcareous sand and shell hash), shallow subtidal at ten meters’ depth.

Remarks.

Caecum invisibile sp. nov. is described as a new species based on molecular diagnostic characters, which show it as distinct from the European C. glabrum (Fig. 5M ), as well as the morphologically similar C. corrugulatum (Fig. 5F, G ) from the Central American Pacific and C. glabellum from Japan (Fig. 5N ).

MOTU I

Material examined. Panama • 1 (Fig. 5I-L ); Bocas del Toro; 2010; USNM BRS2010 exped.; DNA voucher; DNA bank: r462p13f2t91; GenBank: MT704263, MT731688; ZSM-Mol-20200039.

Morphological characterization. Shell size 1.3 mm long, 0.3 mm wide. Translucent, with whitish body. Tube regularly curved and equal width. Septum hemispherical (Fig. 5K ). Aperture straight, with lip indicating an adult specimen. Operculum brownish. No sculpture or microsculpture diagnostic features (compare Fig. 5L ).

Remarks. MOTU I is highly similar to the European C. glabrum (Fig. 5M ) and Caecum invisibile sp. nov. (Fig. 5O-R ). However, MOTU I shows some small morphological differences such as a bigger shell size and a tiny rim at the aperture (Fig. 5L ) which is absent in C. glabrum . The septum is further completely round and blistered (Fig. 5K ), whereas the one of Caecum invisibile sp. nov. slightly inclines (Fig. 5Q ). MOTU I is based on a singleton and an incomplete molecular dataset, lacking COI sequence data. Additional material from the same locality is necessary to justify proper species description in future research.

MOTU II

Material examined. Panama • 1 (Fig. 5H ); Bocas del Toro; 9.4333, -82.347; depth 3 m; 5 Jun 2010; USNM BRS2010 exped.; Stat. BRS101; DNA voucher; GenBank: MT727046, MT704262, MT731687; USNM 1618853. • 1; Bocas del Toro; 9.3507, -82.1724; depth 15 m; 13 Jun 2010; USNM BRS2010 exped.; Stat. BRS110; DNA voucher; GenBank: MT727051, MT731693; USNM 1618852. • 1; Bocas del Toro; 9.3507, -82.1724; depth 3 m; 13 Jun 2010; USNM BRS2010 exped.; Stat. BRS200; DNA voucher; GenBank: MT727053, MT731695; USNM 1618860.

Morphological characterization. Shell size unknown. Translucent, with translucent body. Tube regularly curved, slightly increasing in diameter towards aperture. Septum round, slightly flattened (Fig. 5H ). Aperture straight. No sculpture visible, microsculptural data missing.

Remarks. MOTU II is based on the molecular data of three specimens; however, we unfortunately lack SEM scans and thus microsculptural data of the shell and light microscopic images are only available for one specimen (Fig. 5H ). This specimen is a juvenile, and due to uncertainty with regards to adult ornamentation of the shell, and its possible identity with an already described species, we refrain from providing a formal description based on the available material only.

Figures

Figure 5. A-D Meioceras nitidum, specimen MNHN-IM- 2013 - 72087 A light microscopic picture B SEM scan C SEM close-up of mucro and D microsculpture E M. cubitatum, specimen USNM 1618851 F, G C. cf. corrugulatum, specimen USNM 1618861 F light microscopic picture G light microscopic close-up of microstructure H MOTU II, specimen USNM 1618853 I-L MOTU I, specimen ZSM-Mol- 20200039 I light microscopic picture J SEM scan K SEM close-up of mucro and L microsculpture M C. glabrum, specimen ZSM-Mol- 20200096 N C. glabellum auctt. non Adams, specimen ZSM-Mol- 20200074 O-R C. invisibile sp. nov., holotype ZSM-Mol- 20100320 O light microscopic picture P SEM scan Q SEM close-up of mucro and R microsculpture. Scale bars: 10 µm (R); 20 µm (C, K, L, Q); 50 µm (D, E) 100 µm (I, J, O, P); 200 µm (A, B, M, N).