Patellogastropoda Lindberg, 1986
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publication ID |
https://doi.org/ 10.6620/ZS.2023.62-26 |
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persistent identifier |
https://treatment.plazi.org/id/03D95613-FFED-4B72-FC83-FD9F13413B28 |
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treatment provided by |
Felipe |
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scientific name |
Patellogastropoda Lindberg, 1986 |
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Subclass Patellogastropoda Lindberg, 1986 View in CoL Family Neolepetopsidae McLean, 1990 Genus Paralepetopsis McLean, 1990
Type species: Paralepetopsis floridensis McLean,
1990 (by original designation).
Paralepetopsis polita sp. nov. ( Figs. 2–4 View Fig View Fig View Fig ) urn:lsid:zoobank.org:act:B202762C-E2B1-42E1-8644-7B7DFCC556BF
Type locality: On the shell of Archivesica marissinica, Haima methane seep (16°41.6561'N, 110°23.8165'E, 1361 m depth) in the South China Sea ( Fig. 1B View Fig ).
Type material: Holotype ( TMBC031004 ; Fig. 2A View Fig ); SL 7.9 mm, SW 5.6 mm, SH 2.4 mm; a piece of mantle removed for DNA sequencing . Paratype 1 ( NSMT Mo- 79367; Fig. 2B View Fig ); SL 7.0 mm, SW 4.7 mm, SH 2.8 mm. Paratype 2 ( NSMT Mo-79368; Fig. 2C View Fig ); SL 6.4 mm, SW 4.3 mm, SH 2.3 mm. Paratype 3 ( NSMT Mo- 79369; Fig. 2D View Fig ); SL 5.6 mm, SW 4.0 mm, SH 2.0 mm. Paratype 4 ( TMBC 031005; Fig. 3 View Fig ); SL 5.7 mm, SW 4.0 mm, SH 1.6 mm; a piece of foot used for DNA sequencing, shell and radula used for SEM. All collected from the type locality, taken using a scoop-net by ROV Haima II in September 2020 on-board R / V Haiyang #6 during cruise HYDZ 6-202005. They were originally frozen in -80°C while still attached to Archivesica clams and later transferred into 99% ethanol.
Etymology: ‘ Politus ’ (Latin), polished or smooth, named for its smooth teleoconch surface devoid of major concentric or radial sculpture.
Diagnosis: A medium-sized Paralepetopsis (SL up to 7.9 mm) with semi-transparent shell lacking any significant sculpture except very fine concentric growth lines, apex located on the mid-line at the anterior third of the shell. Central tooth with finely pointed cusp, other teeth with quadrangular cusps. All teeth exhibiting sturdy, well-developed shaft; each teeth significantly descend in position relative to the central tooth.
Description: Shell ( Figs. 2 View Fig , 3A–B View Fig ) thin, semi-transparent, with a very thin layer of transparent periostracum where not corroded. Maximum shell length among specimens available 7.9 mm (holotype). Elliptic in outline, narrower at anterior end than posterior end, especially obvious in large specimens ( Fig. 2A View Fig ). Apex on midline, located at approximately one-third from anterior edge. Apex strongly corroded, inner surface of protoconch sealed. Protoconch unknown. Shell profile moderately high, margin aligned along one plane in specimens examined. Anterior margin straight to concave ( Fig. 2A–B View Fig ), posterior margin convex. Shell surface nearly completely smooth except very fine concentric growth lines. Muscle scars indistinct.
Radula ( Fig. 3C–D View Fig ) with two laterals, pluricuspid tooth, two marginals on either side of rachidian, no clear evidence of significant mineralisation. Each tooth from rachidian outwards descent significantly in position, each outer tooth diverging posteriorly, resulting in teeth on each row aligned like inverted ‘V’. Rachidian narrow but sturdy, well-developed, with finely pointed cusp. Shaft of rachidian slender with narrow lateral ridge on each side, narrower than cusp where they connect. First inners lateral twice as broad as rachidian, with broad, overhanging, truncated quadrangular cutting edge. Shaft of first inner lateral sigmoidal in outline on outer side. Second inner lateral similar but with strong lateral ridge near base to accommodate base of first inner lateral. Pluricuspid robust, twice as broad as inner laterals, with one very broad, overhanging rounded inner cusp plus one small, narrow, poorly formed outer cusp. Shaft with lateral mid-shaft projection from where shaft tapers towards base. Inner marginals with narrow shaft, broadening apically to form rounded, spoon-like overhanging cusps. Shaft of inner marginals most narrow at centre, with lateral projection near base. Outer marginals two-thirds as long as inner marginals, with broader shafts. Cusps spoon-like, less developed than inner marginals.
Soft parts ( Fig. 4 View Fig ). Cephalic tentacles simple, conical, tapered, lacking appendages. Eyes appear lacking from external examination. Oral disc with muscular outer lip, labial lobe poorly developed. Clear groove separates oral disc from foot. Foot sole oval, large, with unciliated rim, epipodium lacking. Shell muscle U-shaped, comprising numerous muscle bundles along posterior third of body, length of bundles increases posteriorly. Mantle edge with numerous papillae, presumably sensory. Mantle cavity extending to just over one-third of body length. Gonad located along mid-body ventrally posterior or pericardium, partly visible through mantle roof. Ctenidium lacking. Intestine and stomach embedded within digestive glad which extends extensively as seen through mantle roof. Intestine loops twice prior to emerging as rectum. Anus located on right side of mantle roof, just left of urogenital papillae. Right kidney sizeable, at posterior end near shell muscles.
Distribution: Only known from the Haima methane seep area in the South China Sea.
Remarks: The shell lacking cancellate sculpture, as well as a radula with broad, overhanging lateral cusps lacking noticeable mineralisation places P. polita sp. nov. in Paralepetopsis rather than Neolepetopsis . Two features together separate P. polita sp. nov. from all other described Paralepetopsis species, including the semi-transparent shell lacking any significant sculpture and the pluricuspid tooth with two cusps. Although species such as P. tunnicliffae and P. rosemariae also exhibit little shell sculpture, they still show weak radial striae ( Beck 1996; McLean 2008) which are lacking in P. polita sp. nov. Paralepetopsis clementensis is the only described congener lacking radial sculpture, but that species has a clearly convex anterior margin ( McLean 2008) as opposed to straight to concave in P. polita sp. nov. The only other neolepetopsid exhibiting a pluricuspid with two clearly separated cusps is Neolepetopsis gordensis McLean, 1990 which also has a much larger, major inner cusp and a smaller outer cusp ( McLean 1990 2008). Although the cutting edge of the pluricuspid tooth in P. ferrugivora also exhibits two to three blunt tubercles, they are not separated out to form individual cusps ( Warén and Bouchet 2001). A key to the described Paralepetopsis species, with information on the known distribution of each, is shown in table 1.
Molecular Phylogeny
We used the first and second codon positions of the COI gene to reconstruct the phylogeny of Patellogastropoda and to assess the systematic position of Paralepetopsis polita sp. nov., with the consensus tree shown in figure 5. In our tree, the two sequences of P. polita sp. nov. included (from the holotype and paratype 4) were recovered together with full support (Bayesian posterior probability, BPP = 1). They were, however, not clustered with other sequences assigned to Neolepetopsidae which formed a weakly supported clade ( BPP = 0.6) – including two described species of Neolepetopsis and two described species of Eulepetopsis , as well as two sequences of undescribed preliminarily assigned to Paralepetopsis but without published data on their morphology ( Aktipis and Giribet 2010; Goffredi et al. 2017). Within this clade, the two Neolepetopsis species formed a strongly supported clade ( BPP = 0.98), as did the two Eulepetopsis species ( BPP = 0.97); these two genera were recovered as sisters with weak support ( BPP = 0.43). This clade was in turn sister to a moderately supported clade ( BPP = 0.66) containing the two undescribed species assigned to Paralepetopsis , but only with moderate support ( BPP = 0.66).
Surprisingly, we found P. polita sp. nov. nested within two sequences of species in Lepetidae , where it was sister to Lepeta caeca (Müller, 1776) with moderate support ( BPP = 0.63). These two species were in turn found to be closely related to Lepeta kuragiensis ( Yokoyama, 1920) with strong support ( BPP = 0.93). The clade containing these three species was found to be sister of the clade containing the abovementioned six neolepetopsid species, a relationship that was moderately supported ( BPP = 0.65). The other six currently accepted patellogastropod families were all recovered as monophyletic with various levels of support ( BPP = 0.69–1), the relationships among which were the same as a previously published phylogeny by Chen et al. (2021).
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