Bathyacmaea levinae, 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

Bathyacmaea levinae sp. nov.

Fig. 3

Type material examined.

Holotype. Costa Rica • whole organism; ethanol-fixed; Original label: “ Bathyacmaea levinae holotype, 1, whole organism, AD 4971 , Costa Rica Margin, Jaco Scar , 9.11785, - 84.8407, 1800 m, from tubeworms. ”; SIO-BIC M 22535 . Paratypes: • Same data as for holotype. Original label: “ Bathyacmaea levinae paratype, 1, whole organism, AD 4971 , Costa Rica Margin, Jaco Scar , 9.11785, - 84.8407, 1800 m, from tubeworms. ”. SIO-BIC M 22536 . Costa Rica • 2 specimens; same data as for holotype; Original label: “ Bathyacmaea levinae paratype, 2, whole organisms, AD 4971 , Costa Rica Margin, Jaco Scar , 9.11785, - 84.8407, 1720–1820 m, from tubeworms. ”; MZUCR 10674-01 - 02 . Costa Rica • 2 specimens; Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158; hydrocarbon seep; mussels; 1,409 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg .; Paratype; whole organism; ethanol-fixed; Original label: “ Bathyacmaea levinae paratype, 2, whole organisms, AD 4924 , Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158, 1409 m, from mussels. ”; SIO-BIC M 22532 . Costa Rica • 2 specimens; Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158; hydrocarbon seep; mussels; 1,409 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg .; Paratype, whole organism; ethanol-fixed; Original label: “ Bathyacmaea levinae paratype, 2, whole organisms, AD 4924 , Costa Rica Margin, Quepos Seep , 9.03174, - 84.62158, 1409 m, from mussels. ”; MZUCR 10672-02 - 03 .

Type locality.

Costa Rica • Costa Rica Margin, Jaco Scar , 9.11785, - 84.8407; hydrocarbon seep; tubeworms; 1,720–1,820 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg .

Other material examined.

Costa Rica • 5 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117375, - 84.8397; 1,811 m; 26 May 2017; AT 37-13 ALVIN Dive 4911 leg.; Tubeworm, Erik Cordes Personal Collection (EC) 5739 • 5 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117375, - 84.8397; 1,794 m; 29 May 2017; AT 37-13 ALVIN Dive 4914 leg.; Mussel, EC 5760 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11753, - 84.83953; 1,886 m; 29 May 2017; AT 37-13 ALVIN Dive 4914 leg.; Mussel, Scripps Benthic Invertebrate Collection ( SIO-BIC) M 16154 • 5 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117368, - 84.839661; 1,796 m; 30 May 2017; AT 37-13 ALVIN Dive 4915 leg.; Tubeworm, EC 5815 • 10 specimen (s); Costa Rica Margin, Quepos Seep ; 9.03048, - 84.6202; 1,409 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg.; SIO-BIC M 16201 • 10 specimen (s); Costa Rica Margin, Quepos Seep ; 9.03048, - 84.6202; 1,409 m; 7 June 2017; AT 37-13 ALVIN Dive 4924 leg.; SIO-BIC M 16179 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97043, - 84.8429167; 1,724 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg.; Tubeworm, EC 7745 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97043, - 84.8429167; 1,724 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg.; Tubeworm, EC 7420 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97043, - 84.8429167; 1,724 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg.; Tubeworm, EC 7419 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117433333, - 84.83961667; 1,796 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg.; Tubeworm, SIO-BIC M 16731 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97071, - 84.8372817; 1,785 m; 18 October 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, EC 7336 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97071, - 84.8372817; 1,785 m; 18 October 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, EC 7320 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11735, - 84.83958333; 1,795 m; 18 October 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, SIO-BIC M 16795 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11785, - 84.83952833; 1,784 m; 19 October 2018; AT 42-03 ALVIN Dive 4973 leg.; Tubeworm, SIO-BIC M 16748 • 10 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97067, - 84.839533; 1,783 m; 23 10 2018; AT 42-03 ALVIN Dive 4977 leg.; Mussel, EC 7548 • 11 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117567, - 84.840718; 1,760 m; 4 November 2018; AT 42-03 ALVIN Dive 4989 leg.; Tubeworm, EC 8894 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117783333, - 84.83945; 1,783 m; 4 November 2018; AT 42-03 ALVIN Dive 4989 leg.; Rock, SIO-BIC M 16943 • 8 specimen (s); Costa Rica Margin, Quepos Seep; 9.031816667, - 84.62048333; 1,400 m; 5 November 2018; AT 42-03 ALVIN Dive 4990 leg.; Mussel, SIO-BIC M 17001 • 4 specimen (s); Costa Rica Margin, Quepos Seep; 9.031816667, - 84.62048333; 1,400 m; 5 November 2018; AT 42-03 ALVIN Dive 4990 leg.; Mussel, SIO-BIC M 16988 • 2 specimen (s); Costa Rica Margin, Quepos Seep; 9.031816667, - 84.62055; 1,401 m; 5 November 2018; AT 42-03 ALVIN Dive 4990 leg.; Combined Slurp, SIO-BIC M 16920 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1174, - 84.839855; 1,803.1 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Rock, EC 9345 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117775, - 84.839525; 1,803 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Rock, EC 9338 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1174, - 84.839855; 1,803 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Rock, EC 9337 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1174, - 84.839855; 1,812.41 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Mussel, EC 9323 .

Diagnosis.

From tubeworms, Bathyacmaea levinae sp. nov. may be diagnosed by their flat, serrated radular teeth and high, conical shells lacking any obvious axial sculpturing. On mussels, Bathyacmaea levinae sp. nov. may be diagnosed through the combination of their ovate, evenly sloped, flattened shells lacking any obvious axial sculpturing with their radular characteristics. At the time of publication, these are the only Bathyacmaea species known from the Eastern Pacific Ocean.

Description.

Shell (Figs 3 A, B , 5 ): Specimens exhibit uncoiled, patelliform shells. Holotype measures 8.1 mm in length, 5.2 mm in width, and 4.7 mm in maximum height. Shell roundness (width ÷ length) is 0.65. Shell sculpturing and ornamentation lacking but fine radial growth lines are present. Very fine axial striations present but not raised. Aperture opening is ovate and aperture lip is thick and unornamented. Shell slope is flattened to mildly convex. Shell apex is degraded and centrally located. Protoconch is unknown. Shell is thick, white, and semi-translucent. Shell microstructures are (in order from the outermost shell layer to the innermost): irregular spherulitic prismatic type-A, semi-foliated, concentric crossed lamellar structures, and radial crossed lamellar structures (Fig. 5 ).

Soft parts (Fig. 3 C ): Soft tissue is white-to-yellowish in color. Mantle is thick with a flat margin. Foot follows the shape of the shell aperture in terms of its roundness. Margin of the foot sole is flat. Pallial tentacles are lacking. Operculum is absent. Two cephalic tentacles are present which are short, thick, and placed low on the head. Bipectinate gill extends from behind animal’s right cephalic tentacle. Eyes are absent. Oral lappets are absent but the oral opening is lined with thickened tissue ornamented with very fine frilling.

Radula (Fig. 3 P – R ): Radula was obtained from the sequenced specimen (Fig. 3 G – I ), whose shell measured 10 mm in length, 7.0 mm in width, and 6.8 mm in height. Docoglossate radula with formula 0 + 1 + 0 + 1 + 0. Radular ribbon measures ~ 240 µm across. Rachidian teeth highly diminished and obscured by laterals. Lateral teeth are long, robust, and consisting of three distinct cusps that appear to be fused together. Lateral teeth may measure up to 400 µm in length. The first, most anterior, cusp forms a single sharp hook lacking denticle. The second cusp is longer than the first and falls in line with the third cusp such that it creates one continuous ridge. Eight or nine short, sharp denticles are present on this second cusp. The third, most posterior, cusp is the longest (~ 3 × the length of the second cusp) and forms a robust, serrated ridge with 25 or more short, sharp denticles that are indistinguishable from those on the second cusp. The third cusp’s posterior end curves inward towards the radular ribbon. The connecting point of the lateral teeth to the radular ribbon is located near the posterior end of the third cusp. Marginal teeth lacking.

Variation.

Two distinct morphotypes of Bathyacmaea levinae sp. nov. are herein identified: One inhabiting tubeworms (Fig. 3 A – I ), and one inhabiting mussel shells (Fig. 3 J – O ). Holotype description applies to specimens found on tubeworms. Bathyacmaea levinae sp. nov. found on mussel shells differ in that they exhibit rounder apertures, flatter shell margins, lower shell profiles, and greater apex erosion (Fig. 3 J – N ). Paratype specimens from mussel shells measure between 7.9–11.0 mm in length, 6.4–9.0 mm in width, and 3.0– 4.5 mm in height. Measures of shell roundness (width ÷ length) for these paratypes are all between 0.81–0.85, distinguishing them from the roundness of the holotype (0.65).

Radulae of specimens found on mussels also differ (Fig. 3 S – U ). Formula remains 0 + 1 + 0 + 1 + 0 with tricuspid laterals, reduced rachidian teeth, and no marginals. All cusps of the lateral teeth are located at the very anterior end of a long, thin tooth shaft which connects to the radular ribbon at its far posterior end (Fig. 3 S ). The first, most anterior cusp of the lateral teeth is similar between morphotypes, being sharp, hooked, and lacking denticles. The second cusp of specimens found on mussels resembles the first cusp in terms of thickness, but with a blunt outer edge that lacks denticles and points forward (perpendicular to the radular ribbon). The third, most posterior cusp is short, thick, lacking denticles, and is fused with the second cusp. This third cusp is truncated and forms a sharp barb which faces outwards when situated on the radular ribbon. Under-developed teeth of this species (Fig. 3 V ) further differ. Rachidian and minor lateral teeth are highly reduced; Reduced minor lateral teeth present as thin and strand-like with pointed anterior ends. Major laterals exhibit broad, un-serrated cusps whose outermost end is twisted backwards, forming a lemniscate shape. The first tooth cusp forms a sharp barb, similar to the mature radular tooth (Fig. 3 S ).

Distribution.

Bathyacmaea levinae sp. nov. has been collected from the hydrocarbon seep sites “ Jaco Scar ” (9.12, - 84.84) and “ Quepos Seep ” (9.03, - 84.62) at the Pacific Costa Rica Margin. This species was sampled from both mussels and tubeworms between 1,400 –1,890 m depth.

Remarks.

Measurements of Bathyacmaea levinae sp. nov. across the entire, sampled size range at the CRM found divergent trends in growth between substrates culminating in the morphological differences observed (Fig. 4 ). These substrate-determined differences support previous studies that demonstrate radula and shell variability in Bathyacmaea ( Chen et al. 2019) . Bathyacmaea levinae sp. nov. found on mussels at the CRM most closely resemble the species Bathyacmaea nipponica Okutani, Tsuchida & Fujikura, 1992 . However, Bathyacmaea levinae sp. nov. are genetically distinct from this species for both the mitochondrial CO 1 gene and the nuclear histone- 3 gene. Furthermore, the inner shell layers of Bathyacmaea levinae sp. nov. are comprised of concentric and radial crossed lamellar microstructures only, distinguishing them from Bathyacmaea nipponica , whose inner shell layers display an interspersion of semi-foliated microstructures and crossed lamellar structures ( Sato et al. 2020). Bathyacmaea levinae sp. nov. from mussel shells also closely resemble Bathyacmaea subnipponica Sasaki, 2003 , but lack its cancellated shell sculpture. Bathyacmaea levinae sp. nov. found on tubeworms most closely resemble Bathyacmaea kanesunosensis Sasaki, 2003 , though its distribution is highly distinct from our specimens. Due to a lack of sequences published for B. kanesunosensis , their genetic distinction remains unknown. At the time of publication, Bathyacmaea levinae sp. nov. is the only Bathyacmaea species found in the Eastern Pacific.

Etymology.

This species is named for Dr. Lisa A. Levin from Scripps Institute of Oceanography for her significant contribution to deep-sea knowledge, especially in regard to hydrocarbon seeps.

Figures

Figure 3. Bathyacmaea levinae sp. nov. A – C holotype from tubeworms at Jaco Scar, 1,724 m, AD 4971, 17 October 2018 D – F paratype from tubeworms at Jaco Scar, 1,724 m, AD 4971, 17 October 2018 G – I Sequenced specimen (GenBank Accession # OQ 644578) from tubeworms at Jaco Scar, 1,760 m, AD 4989, 4 November 2018 J – L paratype from mussels at Quepos Seep, 1,409 m, AD 4924, 7 June 2017 M – O sequenced specimen (GenBank Accession # OQ 644573) from mussels at Jaco Scar, 1,783 m, AD 4977, 23 October 2018 P radula from specimen sampled from tubeworms Q closer view of the same radula R isolated radular tooth S isolated radular tooth from specimen sampled from mussels T, U radula from specimen sampled from mussels V under-developed (young) section of radula from the same specimen. Scale bars: 1 mm (A – O); 250 µm (P); 100 µm (Q – T); 50 µm (U); 100 µm (V).

Figure 4. Divergent trends in growth among Bathyacmaea levinae sp. nov. Data from 52 individuals (Tubeworm, n = 33; Mussel, n = 19) are shown A specimens found on tubeworms become taller than those found on mussels as they grow, despite being similar in height at smaller sizes B specimens found on tubeworms become less round as they grow (m = - 0.015, p < 0.001), while specimens found on mussels remain approximately the same roundness regardless of size (p > 0.1).

Figure 5. Shell microstructures of Bathyacmaea levinae sp. nov. from tubeworms at Jaco Scar, 1,785, October 2018. For all images, the outer shell is oriented to be at the top of the image, and the inner shell is at the bottom A cross section of newer shell (closer to the shell margin). Outermost layer shows semi-foliated structure, followed by alternating bands of crossed lamellar structure in concentric and radial orientations B – D close-up views of A E cross section of older shell (closer to the apex). Outermost layer shows irregular spherulitic prismatic type-A structure, followed by semi-foliated and concentric crossed lamellar structures F – H close-up views of E. Abbreviations: SF = semi-foliated structure, cCL = concentric crossed lamellar structure, rCL = radial crossed lamellar structure, ISP-A = spherulitic prismatic type-A structure. Scale bars: 300 µm (A); 50 µm (B); 20 µm (C); 10 µm (D); 300 µm (E); 40 µm (F, G); 5 µm (H).