Cocculina methana, Betters & Cortés & Cordes, 2024

Betters, Melissa J., Cortés, Jorge & Cordes, Erik E., 2024, New species and records of limpets (Mollusca, Gastropoda) from the Pacific Costa Rica Margin, ZooKeys 1214, pp. 281-324 : 281-324

Cocculina methana sp. nov.

Fig. 10

Type material examined.

Holotype: Costa Rica • whole organism; ethanol-fixed; Original label: “ Cocculina methana holotype, 1, whole organism, AD 4924, Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158, 1408 m, from clams. ”; SIO-BIC M 22533 . Paratypes: Costa Rica • 1 specimen; same data as for holotype; Original label: “ Cocculina methana paratype, 1, whole organism, AD 4924, Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158, 1408 m, from clams. ”; MZCR 10672-01 .

Type locality.

Costa Rica • Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158; hydrocarbon seep; clams; 1,408 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg .

Other material examined.

Costa Rica • 4 specimens; Costa Rica Margin, Quepos Seep ; 9.03174, - 84.62158; 1,408 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg.; Clams; Erik Cordes Personal Collection (EC) 5752 • 2 specimen (s); Costa Rica Margin, Mound 12 ; 8.929983333, - 84.31167667; 992 m; 20 October 2018; AT 42-03 ALVIN Dive 4974 leg.; Bone, SIO-BIC M 16788 • 3 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11562, - 84.84005; 1,908 m; 28 May 2017; AT 37-13 ALVIN Dive 4913 leg.; Wood, SIO-BIC M 16149 • 15 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1193, - 84.84277; 1,854 m; 31 May 2017; AT 37-13 ALVIN Dive 4916 leg.; Tubeworm, SIO-BIC M 16171 • 30 specimen (s); Costa Rica Margin, Quepos Seep ; 9.0303, - 84.623; 1,433 m; 1 March 2009; AT 15-44 ALVIN Dive 4508 leg.; SIO-BIC M 12024 • 3 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1172, - 84.8417; 1,866 m; 3 March 2009; AT 15-44 ALVIN Dive 4509 leg.; SIO-BIC M 12037 • 6 specimen (s); Costa Rica Margin, Mound Jaguar ; 9.651755802, - 85.88211866; 2,000 m; 25 January 2019; FK 19-0106 SUBASTIAN Dive 230 leg.; Wood, SIO-BIC M 17106 • 3 specimen (s); Costa Rica Margin, Mound Jaguar ; 9.65876081, - 85.88259157; 1,896 m; 25 January 2019; FK 19-0106 SUBASTIAN Dive 230 leg.; Wood, SIO-BIC M 17105 .

Diagnosis.

Cocculina methana sp. nov. may be diagnosed by its distinct golden-brown periostracum. It may be most reliably distinguished from its sister species, Cocculina japonica , through mitochondrial CO 1 barcoding.

Description.

Shell (Fig. 10 A – C ): Specimens exhibit uncoiled, patelliform shells. Holotype measures 3.4 mm in length, 2.3 mm in width, and 1.7 mm in maximum height. Shell roundness (width ÷ length) is ~ 0.66. Fine, concentric, radial sculpturing present on shell. The aperture opening is ovate and unornamented. The aperture lip is thin, fragile, and unornamented. The shell margin is flat. Posterior shell slope is flattened while the anterior shell slope is rounded. Shell apex is posteriorly shifted. Protoconch is unknown. Shell is robust with a thick, greenish brown periostracum covering the outer shell and wrapping over the aperture lip.

Soft parts (Fig. 10 C ): Soft tissue is light yellow to white in color. Mantle margin is thin and irregular. One pair of posterior epipodial tentacles present. Posterior tentacles are thin, elongated, and do not taper in width towards their distal ends. Two, short, blunt cephalic tentacles are present that are slightly thicker than the epipodial tentacles. The mouth has well-developed oral lappets surrounding a starburst-shaped oral opening. External reproductive structures were not observed. Foot margin is ovate and slightly irregular. Operculum is absent.

Radula (Fig. 10 I – K ): Radula is rhipidoglossate. Rachidian teeth are highly diminished, lacking cusps; The rachidian teeth form a continuous, raised ridge down the center of the radula. Rachidian are flanked by three major lateral teeth on each side. Lateral teeth have spatulate cusps that decrease in size from the first to third tooth. First major lateral teeth are the broadest, having 6–8 rounded denticles on their cusps. Second major lateral teeth are slightly thinner, having 3–5 denticles on their cusps. Finally, the third major laterals are thinner than the other two, and have two or fewer denticles on their cusps. These three major laterals are followed by one minor lateral tooth, which is broader than any of the other teeth preceding it. This minor lateral tooth has a short cusp that is angled outwards with four or five blunt, rounded denticles. Each minor lateral tooth has one or two short denticles on their innermost side (raised the highest), followed by one broad, elongated denticle, and finally followed by another short denticle on its outermost, lowest side. Two sets of numerous, marginal teeth follow, set at different angles. Sets of inner marginal teeth are more or less parallel to the radular ribbon, and number 10–12 teeth. Each tooth has a very thin and long tooth shaft (thinner than any of the preceding teeth) and a spatulate cusp with 5–7 short, rounded denticles. Sets of outer marginals are set at ~ 45 ° angle to the radular ribbon, and number between 15–20 teeth. These outer marginals also have a thin and long tooth shaft with spatulate cusps. These cusps, however, are decorated with ~ 24 thin, bristle-like denticles (~ 12 on each side of the cusp).

Distribution.

Cocculina methana sp. nov. is confirmed from the hydrocarbon seep sites Quepos Seep (9.03, - 84.62), Mound 12 (8.93, - 84.31), Jaco Scar (9.12, - 84.84), and Mound Jaguar (9.66, - 85.88) at the Pacific Costa Rica Margin. This species was sampled from clam shells, wood, tubeworms, and bone between 1,408 –2,000 m depth. These are among the deepest-known Cocculina .

Remarks.

The shells of Cocculina methana sp. nov. most closely resemble those of C. japonica ( Dall 1907) . Radulae of these specimens most closely resembled that of C. cowani ( McLean 1987) but with distinct central teeth that form a narrow, defined ridge down the center of the radula (Fig. 9 J ). The shell apex of this species notably lacks the hooked “ sail fin ” appearance of other Cocculina species. The periostracum of these specimens was observed to significantly corrode with prolonged ethanol preservation (Fig. 10 G, H ). This should be considered when examining museum specimens.

Etymology.

The species name methana refers to the occurrence of this species at a hydrocarbon seep site. This habitat type is notable, as all other known species of Cocculina occur at either inactive hydrothermal vents or organic falls.

Figures

Figure 9. Specimens of Lepetodrilus guaymasensis and Pseudolepetodrilus costaricensis gen. et sp. nov. A – C sequenced L. guaymasensis specimen (GenBank Accession # OQ 644591) from Mound 12, 998 m, AD 4917, 1 June 2017 D – F additional L. guaymasensis specimen from Jaco Scar, 1,811 m, AD 4912, 27 May 2017 G – I Pseudolepetodrilus costaricensis sp. nov. holotype (G – I) and sequenced specimen (J – L) (GenBank Accession # OQ 644586), both from tubeworms, Jaco Scar, 1,760 m, AD 4989, 4 November 2018 M close up view of P. costaricensis epipodial tentacles, with tracing N – P radula morphology representative of this new genus O isolated marginal lateral tooth. Scale bars: 1 mm (A – M); 300 µm (N); 50 µm (O); 30 µm (P).

Figure 10. Specimens of Cocculina methana sp. nov. A, B holotype from clam shells, Quepos Seep, 1,408 m, AD 4924, 7 June 2017 C holotype soft tissue with tracing D – F paratype from tubeworms, Quepos Seep, 1064 m, AD 4923, 7 June 2017 G, H sequenced specimen (GenBank Accession # OQ 644629) from same location as previous showing intact periostracum prior to erosion with ethanol preservation. White dotted line denotes obstruction of image by forceps used to position the specimen I – K details of radula K details of marginal teeth. Scale bars: 1 mm (A – H); 150 µm (I); 50 µm (J); 20 µm (K).