Connexochiton platynomenus Kaas, 1979

Connexochiton platynomenus Kaas, 1979 View in CoL

Fig. 81 View FIGURE 81

Connexochiton platynomenus Kaas, 1979, p. 25 View in CoL , pl. 5, figs 1–18; Ferreira 1980, p. 59; Kaas & Van Belle 1988, p. 257, fig. 116, map 37; Kaas & Van Belle 1990, p. 54, figs 22.2–22.77; Bonfitto et al. 1994, p. 144; Dell’Angelo & Palazzi 1994, p. 233, 3 unnumbered figs; Kaas & Van Belle 1998, p. 146; Dell’Angelo & Smriglio 1999, p. 99; Puchalski et al. 2008 (database: chiton fossil records); Schwabe 2010, fig. 21D; Sirenko 2020b, p. 10; Sirenko 2021a, p. 84 View Cited Treatment , figs 1, 15E, 15G.

Bathychiton biondii View in CoL Dell’Angelo & Palazzi, 1988, p. 115, figs 1–26; Kaas & Van Belle 1990, p. 54, fig. 22.1; Dell’Angelo & Palazzi 1994, p. 234; Kaas & Van Belle 1998, p. 146; Dell’Angelo & Smriglio 1999, p. 91, pls 27–28, figs 37–39; Puchalski et al. 2008 (database: chiton fossil records); Sirenko 2021a, p. 85, fig. 1.

Type material. Holotype MNHN, specimen partly curled, length 2.3 mm, width 1.6 mm . Paratype RMNH K4814 About RMNH . Holotype of Bathychiton biondii Dell’Angelo & Palazzi, 1988 at MSNL, disarticulate specimen, ca. 5 x 3 mm ( Figs 81G–H View FIGURE 81 ) .

Type locality. Bay of Biscay , 800–1050 m .

Material examined. Pleistocene. Italy: Calabria: Archi : 2 valves ( BD 566 , Figs 81A–D View FIGURE 81 ), Bovetto: 1 valve ( BD 567 , broken), Musalà: 2 valves ( BD 568 ), Vallone Catrica, 1 valve ( BD 569 , Figs 81E–F View FIGURE 81 ); Sicily: Gravitelli: 3 valves ( BD 570 ). Recent . Italy: type material of Bathychiton biondii . Maximum width of the valves: 2 / 2.8 / 1.7 mm .

Description. Head valve semicircular, highly elevated, posterior margin somewhat sinuate. Intermediate valves broadly rectangular, ii–iii highly elevated (H/W = 0.67–0.75), carinate in anterior profile, rather long (W/L = 1.50– 1.90), anterior margin strongly convex, valves iv–vii less elevated (H/W = 0.43), semicarinate in anterior profile, much shorter (W/L = 2.40–3.00 or more), anterior margin straight or slightly concave, all valves with lateral areas distinctly raised. Tail valve semicircular, nearly twice as wide as long (W/L = 1.88–2.03), anterior margin almost straight, mucro subcentral, not prominent, postmucronal slope slightly concave.

Tegmentum rough, sculptured with relatively large, roundish, flat-topped granules (diameter 75 µ), neatly arranged in quincunx, as a result they are also directed in radial rows on LA; each granule with 10–12 aesthetes of equal size, irregularly distributed. Some intermediate and tail valves show a narrow “pre-central area” adjacent to anterior margin coarse without granules.

Articulamentum with apophyses somewhat triangular in shape, rectangular in tail valve, jugal sinus flat and shallow as a result of a considerable laminate extension of articulamentum, connecting apophyses, jugal plates very slightly notched, notches corresponding with faint grooves, not separated from apophyses by prominent slits, insertion plates very short, slit formula 11 / 1/ 9–10, teeth decidedly propped, especially in tail valve, eaves narrow, solid.

Remarks. Connexochiton platynomenus Kaas, 1979 has been described on a small juv. ( 3 mm long) incomplete (valves vii-viii lacking) specimen from the Bay of Biscay. Dell’Angelo & Palazzi (1998) described Bathychiton biondii on a larger specimen ( 5 mm long), on the basis of some characters not present (or not described) in C. platynomenus , among which the presence of a “pre-central area” without granules in the intermediate and tail valves and the presence of a row of spherules on the top of dorsal scales. The presence of the pre-central area seems to be quite variable in the scarce material examined, from clearly evident ( Figs 76E–G View FIGURE 76 ) to absent ( Fig. 76C View FIGURE 76 ), while subsequently Kaas & Van Belle (1990), after a careful reexamination of the girdle of the holotype of C. platynomenus , found a few girdle scales with a marginal row of spherules, and speculated that, as the holotype of C. platynomenus is 50% smaller that the holotype of B. biondii , it is possible that the spherules appear at a later stage of growth. Fossil records of these species are scarce, therefore we prefer to consider B. biondii a synonym of C. platynomenus , awaiting further material (both fossil and living) to study.

Kaas (1979) already highlighted in the original description the difference between the first two intermediate valves (ii–iii) and the subsequent ones (iv–vii), as regards shape and elevation. These differences, clearly visible by analyzing the plates of a whole specimen, are also easily recognizable in the single intermediate valves found as fossils (e.g., Figs 76C–D View FIGURE 76 for valves ii–iii and Figs 76E–F View FIGURE 76 for valves iv–vii).

Comparisons. See Tab. 11 for a comparison with the Connexochiton spp . considered in the present study.

Distribution. Pleistocene: central Mediterranean, S. Italy: Archi, Bovetto, Gravitelli, Musalà, Vallone Catrica ( Dell’Angelo & Palazzi 1988, 1994; this study). Recent: Atlantic Ocean: Atlantic side of Strait of Gibraltar: Bay of Biscay; Canary Islands: SW of Hierro Island ( Kaas 1979; Kaas & Van Belle 1988); Mediterranean Sea: S. Lucia Bank, Tuscan Archipelago ( Dell’Angelo & Palazzi 1988).

“ Connexochiton ” roccai Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013

Fig. 82 View FIGURE 82

Connexochiton roccai View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013, p. 82, pl. 5, figs J–M; Dell’Angelo et al. 2021b, p. 416, figs 78–81; Sirenko 2021a, p. 99.

Type material. Holotype MZB 49980, tail valve, width 1.7 mm, Figs 82A–D View FIGURE 82 .

Type locality. Borzoli ( Liguria, ltaly) .

Type stage. Lower Pliocene (Zanclean) .

Material examined. Lower Pliocene: Italy: Borzoli : type material .

Description. Head and intermediate valves unknown. Tail valve small, semicircular, rather flat, mucro situated anteriorly, not prominent, antemucronal and postmucronal slopes almost straight.

Tegmentum rather coarsely granulose. PMA sculptured with roundish granules united with each other (diameter 48–53 µm), forming fine network. AMA sculptured with granules arranged in segments of various size and shape, slightly overlapping each other to form very irregular longitudinal rugosities, obliquely oriented with respect to anterior-posterior axis.

Apophyses rounded, wide, connected across jugal portion, insertion plate thick, eaves solid, teeth rough, irregular, 10 slits visible, total number estimated at 12.

Remarks. “ Connexochiton ” roccai Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013 is a very rare taxon, known only from a single tail valve found in the Lower Pliocene of Borzoli. The valve’s characters are very distinctive and well defined, to justify the description of a new species. Until more material is discovered, variability remains unknown.

The generic attribution is difficult, and the emended diagnosis of the genus Connexochiton by Sirenko (2021a) does not fully meet the characteristics of the valve of “ Connexochiton ” roccai , as regards the sculpture of the tegmentum. This species is provisionally referred to Connexochiton based on articulamentum characters, though the tegmentum sculpture deviates from the genus diagnosis.

According to Sirenko (2021a), the genus Connexochiton superficially resembles five genera: Subterenochiton Iredale & Hull, 1924 , Thermochiton Saito & Okutani, 1990 , Callistochiton Carpenter MS, Dall, 1879 , Stenosemus Middendorff, 1847 and Lepidozona Pilsbry, 1892 . We provisionally attribute the material studied to Connexochiton , pending the avalability further material.

Comparisons. See Tab. 11 for a comparison with the Connexochiton spp . considered in the present study.

Distribution. Lower Pliocene: central Mediterranean, Italy: Borzoli ( Dell’Angelo et al. 2013, 2021b).

“ Connexochiton ” vivesi Dell’Angelo, Lesport, Cluzaud & Sosso, 2018

Fig. 83 View FIGURE 83

Connexochiton vivesi View in CoL Dell’Angelo, Lesport, Cluzaud & Sosso, 2018a, p. 28, figs 6G–L; Dell’Angelo et al. 2021b, p. 52, tab. 9; Sirenko 2021a, p. 99.

Type material. Holotype: MHNBx 2017.6.1, tail valve, width 4 mm ( Figs 83A–D View FIGURE 83 ).

Type locality. Meilhan , Carriere Vives ( France) .

Type stage. Lower Miocene (Burdigalian) .

Material examined. Lower Miocene: France: Meilhan : type material .

Description. Head and intermediate valves unknown. Tail valve small, semicircular, length about half width, rather flat, anterior margin slightly convex, mucro situated anteriorly, not prominent, antemucronal slope almost straight, postmucronal slope slightly concave just underneath mucro and quite straight posterior from there.

Tegmentum rather coarsely granulose. PMA sculptured with granules arranged in segments of various size and orientation, slightly overlapping each other forming rugosities. AMA sculptured with roundish granules fused forming fine network.

Apophyses rounded, wide, connected across jugal portion, insertion plate thick, eaves solid, central depression with numerous transverse slits in jugal tract, teeth eroded and scarcely visible, but 28 well marked slits rays are present.

Remarks. “ Connexochiton ” vivesi Dell’Angelo, Lesport, Cluzaud & Sosso, 2018 is known only for a single tail valve from the Lower Miocene of Meilhan. The valve is partly eroded, also the apophyses are not complete, but the connection by a lamina is still visible. Also the posterior margin is eroded, the incisions are barely outlined and hardly visible. Nevertheless, the valve’s characters are very distinctive and well defined, and justify the description of a new species. Until more material is discovered, variability remains unknown.

The generic attribution is difficult, since the emended diagnosis of the genus Connexochiton by Sirenko (2021a) does not fully meet the characteristics of the valve of “ Connexochiton ” vivesi , as regards the sculpture of the tegmentum. This species is provisionally referred to Connexochiton based on articulamentum characters, though the tegmentum sculpture deviates from the genus diagnosis.

Comparisons. “ Connexochiton roccai ” Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013 has a granulose sculpture with some resemblance to C. vivesi , but the pattern is opposite, with the network in postmucronal area and the irregular concentric wrinkles in antemucronal one (see Tab. 11).

Distribution. Lower Miocene: northeastern Atlantic (early Burdigalian): Aquitaine Basin, France: Meilhan ( Dell’Angelo et al. 2018a).