Paralepetopsis variabilis, 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

Paralepetopsis variabilis sp. nov.

Fig. 6

Type material examined.

Holotype. Costa Rica • whole organism; ethanol-fixed; Original label: “ Paralepetopsis variabilis holotype, 1, whole organism, AD 4987 , Costa Rica Margin, Mound 12 , 8.92982, - 84.31167, 996 m, from tubeworms. ”; SIO-BIC M 22537 . Paratypes: Costa Rica • 9 specimens; same data as for holotype; Original label: “ Paralepetopsis variabilis paratype, 9, whole organisms, AD 4987 , Costa Rica Margin, Mound 12 , 8.92982, - 84.31167, 996 m, from tubeworms. ”; SIO-BIC M 22538 . Costa Rica • 10 specimens; same data as for holotype; Original label: “ Paralepetopsis variabilis paratype, 10, whole organisms, AD 4987 , Costa Rica Margin, Mound 12 , 8.9298, - 84.31167, 996 m, from tubeworms. ”; MZCR 10675-01 - 10 .

Type locality.

Costa Rica • Costa Rica Margin, Mound 12 , 8.92982, - 84.31167; hydrocarbon seep; tubeworms; 996 m; 2 November 2018; AT 42-03 ALVIN Dive 4987 leg .

Other material examined.

Costa Rica • 11 specimen (s); Costa Rica Margin, Mound 11 ; 8.9208, - 84.3054; 1,040 m; 25 February 2009; AT 15-44 ALVIN Dive 4504 leg.; Tubeworm, SIO-BIC M 11995 • 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 • 10 specimen (s); Costa Rica Margin, Mound 12 ; 8.9305, - 84.3123; 1,001 m; 5 March 2009; AT 15-44 ALVIN Dive 4511 leg.; SIO-BIC M 12058 • 25 specimen (s); Costa Rica Margin, Mound 12 ; 8.93042, - 84.31278; 999 m; 22 May 2017; AT 37-13 ALVIN Dive 4907 leg.; SIO-BIC M 16114 • 9 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11538, - 84.83618; 1,859 m; 27 May 2017; AT 37-13 ALVIN Dive 4912 leg.; SIO-BIC M 16126 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11538, - 84.83618; 1,859 m; 27 May 2017; AT 37-13 ALVIN Dive 4912 leg.; SIO-BIC M 16122 • 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 • 3 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 5769 • 7 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 5731 • 49 specimen (s); Costa Rica Margin, Jaco Scar ; 9.118023533, - 84.84095552; 1,741 m; 31 May 2017; AT 37-13 ALVIN Dive 4916 leg.; Tubeworm, EC 5783 • 11 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1193, - 84.84277; 1,854 m; 31 May 2017; AT 37-13 ALVIN Dive 4916 leg.; SIO-BIC M 16170 • 3 specimen (s); Costa Rica Margin, Mound 12 ; 8.930395, - 84.3124245; 995 m; 1 June 2017; AT 37-13 ALVIN Dive 4917 leg.; Tubeworm, EC 5794 • 3 specimen (s); Costa Rica Margin, Mound 12 ; 8.9293, - 84.315; 1,000 m; 1 June 2017; AT 37-13 ALVIN Dive 4917 leg.; SIO-BIC M 16161 • 81 specimen (s); Costa Rica Margin, Mound 12 ; 8.93046775, - 84.31244503; 998 m; 5 June 2017; AT 37-13 ALVIN Dive 4922 leg.; Mussel, EC 5743 • 2 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 16200 • 8 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 16182 • 15 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 16181 • 5 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 7751 • 156 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 7750 • 3 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 7744 • 3 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 10486 • 16 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 10471 • 63 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117433333, - 84.83961667; 1,796 m; 17 10 2018; AT 42-03 ALVIN Dive 4971 leg.; SIO-BIC M 16752 • 3 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117433333, - 84.83961667; 1,796 m; 17 October 2018; AT 42-03 ALVIN Dive 4971 leg.; Rock, SIO-BIC M 16733 • 123 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97071, - 84.8373; 1,785 m; 18 October 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, EC 7346 • 6 specimen (s); Costa Rica Margin, Jaco Scar ; 8.97071, - 84.8373; 1,785 m; 18 10 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, EC 7343 • 25 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11785, - 84.83728; 1,785 m; 18 October 2018; AT 42-03 ALVIN Dive 4972 leg.; Tubeworm, EC 7340 • 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.; SIO-BIC M 16796 • 37 specimen (s); Costa Rica Margin, Jaco Scar ; 9.1178, - 88.839533; 1,783 m; 23 October 2018; AT 42-03 ALVIN Dive 4977 leg.; Mussel, EC 7556 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.11775, - 84.83953333; 1,783 m; 23 October 2018; AT 42-03 ALVIN Dive 4977 leg.; SIO-BIC M 16805 • 64 specimen (s); Costa Rica Margin, Mound 12 ; 8.9308, - 84.31263; 997 m; 24 October 2018; AT 42-03 ALVIN Dive 4978 leg.; Mussel, EC 10473 • 37 specimen (s); Costa Rica Margin, Mound 12 ; 8.9308, - 84.31263; 997 m; 24 October 2018; AT 42-03 ALVIN Dive 4978 leg.; Mussel, EC 10472 • 425 specimen (s); Costa Rica Margin, Mound 12 ; 8.9307, - 84.3128; 997 m; 30 October 2018; AT 42-03 ALVIN Dive 4984 leg.; Mussel, EC 8314 • 30 specimen (s); Costa Rica Margin, Mound 12 ; 8.9307, - 84.3128; 997 m; 30 October 2018; AT 42-03 ALVIN Dive 4984 leg.; Mussel, EC 10477 • 20 specimen (s); Costa Rica Margin, Mound 12 ; 8.9307, - 84.3128; 997 m; 30 October 2018; AT 42-03 ALVIN Dive 4984 leg.; Mussel, EC 10476 • 6 specimen (s); Costa Rica Margin, Mound 12 ; 8.9299, - 84.31299; 995 m; 31 October 2018; AT 42-03 ALVIN Dive 4985 leg.; Mussel, EC 10478 • 100 specimen (s); Costa Rica Margin, Mound 12 ; 8.92983, - 84.31167; 995 m; 2 November 2018; AT 42-03 ALVIN Dive 4987 leg.; Tubeworm, EC 8615 • 1 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117783333, - 84.83944667; 1,785 m; 4 November 2018; AT 42-03 ALVIN Dive 4989 leg.; SIO-BIC M 16974 • 2 specimen (s); Costa Rica Margin, Jaco Scar ; 9.117783333, - 84.83944667; 1,785 m; 4 November 2018; AT 42-03 ALVIN Dive 4989 leg.; SIO-BIC M 16973 • 2 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 16995 • 2 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 16994 • 3 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 16991 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.1174, - 84.839855; 1,074 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Mussel, EC 9348 • 10 specimen (s); Costa Rica Margin, The Thumb ; 9.1174, - 84.839855; 1,074 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Mussel, EC 9328 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.1174, - 84.839855; 1,074 m; 7 January 2019; FK 19-0106 SUBASTIAN Dive 214 leg.; Mussel, EC 9327 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.05, - 84.4; 1,074 m; 10 January 2019; FK 19-0106 SUBASTIAN Dive 217 leg.; Tubeworm, EC 9480 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.05, - 84.4; 1,074 m; 10 January 2019; FK 19-0106 SUBASTIAN Dive 217 leg.; Mussel, EC 9468 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.05, - 84.4; 1,074 m; 10 January 2019; FK 19-0106 SUBASTIAN Dive 217 leg.; Mussel, EC 9451 • 1 specimen (s); Costa Rica Margin, The Thumb ; 9.05, - 84.4; 1,074 m; 10 January 2019; FK 19-0106 SUBASTIAN Dive 217 leg.; Mussel, EC 9434 .

Diagnosis.

Paralepetopsis variabilis sp. nov. may be diagnosed by their ovate, white, semi-translucent shells showing fine, radial growth rings. This species also exhibits two cephalic tentacles which are short (they do not extend past the outer shell margin) and placed low on the head. Soft tissue is whiteish-yellow in color. However, the most reliable way to diagnose Paralepetopsis variabilis sp. nov. is through DNA characterization, as morphology is highly variable within this species and intersects with other known species in the genus.

Description.

Shell (Fig. 6 A, B ): Specimen exhibits uncoiled, patelliform shell. Holotype measures 6.8 mm in length, 4.1 mm in width, and 2.9 mm in maximum height. Shell roundness (width ÷ length) is ~ 0.61. Shell sculpturing and ornamentation lacking but fine radial growth lines are present. Aperture opening is ovate and aperture lip is thin and unornamented. Shell apex is degraded and anteriorly shifted. Anterior and posterior shell slopes are flattened to mildly convex. Shell is very thin, white, and semi-translucent.

Soft parts (Fig. 6 C ): Soft tissue is white to yellowish in color. Mantle is thick with a mildly crumpled 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. Eyes are absent. Very reduced oral lappets are present, as well as thickened tissue around the mouth ornamented with very fine frilling. The animal’s head has a slight brownish coloration and a high profile.

Radula (Fig. 6 S ): Docoglossate radula with formula 2 + 1 + 2 + 1 + 2 + 1 + 2. Rachidian teeth have long shapes, with large triangular cusps at their anterior ends lacking serration. Rachidian teeth are flanked on either side by a pair of minor lateral teeth that are similar in shape to the rachidian. These two minor laterals also have triangular cusps lacking serrations and are slightly rotated inwards. The third (major) lateral tooth is distinct from the other two laterals, in that its cusp is very broad, flat, and perpendicular to the radular ribbon with 9–13 small serrations along its edge. These serrations become less pronounced near the tooth’s outer end. These major laterals are not in line with the others, being set slightly lower, approximately midway between the rows of rachidian and minor lateral teeth. There are two marginal teeth set on the outer edge and just below the major laterals. Marginals have very short, semi-lunate cusps that lack serrations. First outer marginals are ~ 2 × the size of the second outer marginals.

Variation.

Paralepetopsis variabilis sp. nov. exhibits significant shell variation across specimens which makes distinguishing species based on morphology alone difficult. Shells may measure 5–10 mm with shell roundness varying between 0.6 and 0.8. While all specimens exhibit uncoiled, patelliform shells, specimens may exhibit axial sculpturing, radial sculpturing, both, or neither. Shell margins may vary in that they may be flat, convex, or rounded. Shell apexes were unanimously degraded and anteriorly shifted, but the degree of this erosion varies; Some shells have only the protoconch degraded, while others have the majority of their outer shell degraded. Anterior and posterior shell slopes may be flat or mildly rounded. Shells may be thickened, very thin, yellowish, white, or semi-translucent.

Radulae of this species are somewhat variable, with the third major lateral teeth being at noticeably different angles depending on the individual and, potentially, the substrate (Fig. 6 S – V ). The first major lateral teeth imaged from a specimen collected from tubeworms were perpendicular to the radular ribbon (Fig. 6 S ), those collected from plastic were comparatively rotated outwards (Fig. 6 U ), and those collected from mussels were comparatively rotated inwards (Fig. 6 V ). The presence or absence of marginal teeth also varies (Fig. 6 T ), which may be dependent on the amount of wear on the radula or the stage of radular tooth development. This hypothesis, however, requires further testing to validate.

The mantle and foot margins of specimens may vary from flat to crumpled. Coloration of soft tissues varies between specimens, with some exhibiting a distinct blue-to-purple pigmentation around the oral lappets, while others do not.

Distribution.

Paralepetopsis variabilis sp. nov. has been collected from the hydrocarbon seep sites “ Jaco Scar ” (9.12, - 84.84), “ Quepos Seep ” (9.03, - 84.62), “ Mound 11 ” (8.92, - 84.31), and “ Mound 12 ” (8.93, - 84.31) from the Pacific Costa Rica Margin. This species was sampled from mussels, tubeworms, and rocks between 995–1,860 m depth. Specimens have also been found and genetically characterized from a Pescadero Basin hydrocarbon seep site (23.64, - 108.39), collected by the ROV Tiburon during dive # 756 from below 2000 meters depth.

Remarks.

Paralepetopsis variabilis sp. nov. clade 1 shells resemble most closely those of P. clementensis ( McLean 2008) but could be distinguished from them by having flat, rather than rounded, shell margins and flat, rather than convex, shell slopes. At least one specimen of clade 1 exhibited shell structuring that fits the description of the closely related genus Neolepetopsis (Fig. 6 J, K ; McLean 1990). However, such specimens occurring within the genus Paralepetopsis indicates that shell sculpturing may not be as taxonomically informative as previously thought. Paralepetopsis variabilis sp. nov. clade 2 specimens most closely resembled P. clementensis ( McLean 2008) ; however, the axial striations exhibited by these individuals are distinct and are instead most like P. tunnicliffae ( McLean 2008) . Clade 2 specimens may be distinguished from P. tunnicliffae in that their shell margins are rounded, rather than flat. Radulae obtained from Paralepetopsis clade 2 appears most like P. tunnicliffae in their reduced lateral marginal teeth. Paralepetopsis variabilis sp. nov. clade 3 specimens most closely resembled P. clementensis ( McLean 2008) ; however, they lack the convex shell slopes typical of this species. Radulae of this species, overall, resembled those of P. ferrugivora , but have a distinct major lateral tooth shape ( Warén and Bouchet 2001).

Etymology.

The species name variabilis is Latin for variable, referring to the notable and confounding shell variation observed in this species.

Figures

Figure 6. Paralepetopsis variabilis sp. nov. A – C holotype from tubeworms at Mound 12, 995 m, AD 4987, 2 November 2018 D – F sequenced clade 3 specimen (GenBank Accession # OQ 644613) from plastic chip deployment, Jaco Scar, 1,796 m, AD 4915, 17 October 2018 G – I sequenced clade 1 specimen (GenBank Accession # OQ 644624) from mussels at Mound 12, 997 m, AD 4978, 24 October 2018 J – L sequenced clade 1 specimen (GenBank Accession # OQ 644614) from unknown substrate at Mound 12, 1,008 m, AD 4501, 22 February 2009 M – O sequenced clade 2 specimen (GenBank Accession # OQ 644619) from tubeworms, Jaco Scar, 1,724 m, AD 4971, 17 October 2018 P – R sequenced clade 1 specimen (GenBank Accession # OQ 644571) from mussels at Mound 12, 995 m, AD 4985, 31 October 2018 S – V details of radular ribbons. Scale bars: 1 mm (A – R); 40 µm (S); 20 µm (T); 40 µm (U); 50 µm (V).