Patinapta edentatus, Yamana & Hirashima & Sato & Yamamori, 2025

Patinapta edentatus sp. nov.

[New Japanese name: Hanashi-himo-ikari-namako]

( Figs 21–23 View FIGURE 21 View FIGURE 22 View FIGURE 23 , Tables 1 View TABLE 1 ; 13 View TABLE 13 ; 14)

Three specimens from Kabira Bay , Ishigaki-jima Island (WMNH-2021-INV-972, 973, 974) were identified as new to science .

Diagnosis. Outer edge of anchor plate ossicles and inner edge of their perforations lacking teeth anywhere, with large seven perforations arranged in symmetrical order in the distal part, while minute perforations sporadically scattered in basal part. Tentacles possess small numbers of simple rod ossicles and large numbers of simple elongated C-shaped granule ossicles. Mostly elongated C-shaped granules equipped in longitudinal muscles, rarely with Oshaped granules among them. Ciliated funnels attached to inner side body wall along midline of right dorso-lateral interradius (IR4).

Type series. Holotype, WMNH-2021-INV-973; two paratypes, WMNH-2021-INV-972, 974.

Description of holotype (WMNH-2021-INV-973: middle-size complete specimen). External and internal morphologies as follows ( Table 1 View TABLE 1 ): Specimen preserved for20 years; pale misty-rose ( Fig. 21A View FIGURE 21 ), based on information from the collector color was transparent rose in living state ( Fig. 21 View FIGURE 21 A’). Tentacles 12, each with 9 digits, including four pairs of smaller digits equipped along lateral-stem of tentacle and large one digit equipped on distal end of tentacle. On the oral side of tentacle stem, about 10–20 sensory cups sporadically arranged in a U-shape.

Polian vesicle single, fusiform with thread-like tip, 4.12 mm ( Table 1 View TABLE 1 ). Ciliated funnels occur sporadically in one row along right dorso-lateral interradius (IR4). Stone canal undetected, lacking or too small to detect.

Inside body, two tufts of gonad tubules attached to both sides of anterior dorsal mesentery, none of the whitish tubule organs adhered to intestine canal. Intestine canal lacking loop.

Body wall coarse surface, rigid and thin, densely packed with ossicles arranging latitudinal layout of all as sets of anchor and plate. Both sides along five longitudinal muscles with distal ends of anchor ossicles facing towards interradial area, however ossicles on radial body walls upon longitudinal muscles and interradial body walls have distal ends randomly facing either direction.

Etymology. The species name edentatus alluding their teeth-less anchor plate ossicle.

The present results of ossicle morphologies

Body wall ossicles anchors and anchor plates ( Fig. 22 View FIGURE 22 , Table 13 View TABLE 13 ). Anchor plates ranged within 97–112 μm in length. Size of perforations not noticeably variable between central area and marginal area, but almost constant between central area. Perforations of anchor plate ossicles toothless, seven ovoid form, central one and marginal six, arranged by symmetrical hexagonal layout, without marginal teeth around outer rim of plates. Two calculated indicators for anchor plates and a parameter were variated within APS =0–2.7; Ntp =0; APT =0% ( Fig. 22 View FIGURE 22 , Table 13 View TABLE 13 ).

Anchor ossicles ranged within 143–165 μm in length ( Fig. 22 View FIGURE 22 , Table 19). All the anchor arms (bills) equipped with minute teeth on their outer tips, numbers of teeth variable within 3–7 (mostly 2–3 in one arm of the anchor ossicle), and anchor ossicles of this specimen possess stem broad also relatively narrow anchor arms width, with ASW =21.8–29.5%; AEW =41.2–60.7%. T-shaped basal end of the anchor ossicle of this species crescent-shaped ( Fig. 22B; D View FIGURE 22 ).

Body longitudinal muscle, all elongated C-shaped granule ossicles of this specimen ranged within 47–106 μm in length ( Fig. 22 View FIGURE 22 , Table 13 View TABLE 13 ). The calculated indicator for granule proportions was variated within GP =29.2–62.5%; GCO =0%, no O-shape granules were present.

Tentacle ossicles ranged within 23–63 μm in length ( Fig. 22 View FIGURE 22 , Table 10), mostly elongated C-shaped granule ossicles with few simple rod ossicles. Two calculated indicators for rod proportions and complexities were variated within RP =9.5–53.8%; RC =4.8–8.7 ( Table 10).

Observation on the morphologies of calcareous ring

Calcareous plates 12 ( Fig. 23 View FIGURE 23 ), thin and plate-like, with posterior depression on every plate other than the 4 plates situated in right and left dorso-lateral positions (IR4’; RIII; IR3’; RII), where additional interradial plates (IR4’; IR3’) and adjacent radial plates (RIII; RII) construct a wide space (like a “interradial perforation”) between their lateral ends. Three radial plates (RI; RIV; RV) with slight anterior projection and perforation, also interradial plates with slight anterior projection, however medio-dorsal plate (IR5) with only posterior depression, lacking anterior projection.

Ossicle variation among the three specimens

The three specimens examined were chosen as largest specimens of this species housed in the WMNH-INV collection, approximately 45–70 mm in length ( Table 1 View TABLE 1 ), and all three specimens well-matured possessing fully equipped gonad tubules in their body cavities. Their bodies were extremely contracted by shrunken latitudinal muscle caused by unanesthetized fixiation, and resulting in the largest specimen autotomized on the anterior part. Their external and internal morphologies well agreed with each other’s ( Table 1 View TABLE 1 ).

Body wall ossicles are anchors and anchor plates.Anchor plate ossicle lengths and calculated indicators of three specimens ranged within: 79–124 μm in length, APS =0–2.7, Ntp = 0, APT =0% ( Table 13 View TABLE 13 ). Among these values, length and the parameter Ntp of anchor plate ossicles (both ventrally and dorsally) were not significantly different (Ps>0.05, Kruskal-Wallis’ test), and non-size dependance indicator of plate skewness APS was also not significantly different (Ps>0. 05, Kruskal-Wallis’ test). All three specimens did not possess teethed perforations of anchor plate ossicles. From these results, the anchor plate ossicles in the body wall of the present three specimens were not different in length or skewness of anchor plate ossicles, and the critical feature of lacking teethed perforations can be the accurate key.

Anchor ossicle lengths and calculated indicators ranged within: 133–184 μm in length, ASW =19.3–27.8%, AEW =39.5–57.9% ( Table 13 View TABLE 13 ). Among these values, length of anchor ossicles (both ventrally and dorsally) was significantly different (Ps <0.005, Kruskal-Wallis’ test), while the indicator for anchor stem breadth ASW and for basal / distal ends width AEW were not significantly different (Ps>0. 05, Kruskal-Wallis’ test). From these results, the anchor ossicles in the body wall of the present three specimens were different in ossicle lengths, while their shapes were not different. Therefore, length cannot be the accurate key, but the shape of the anchor ossicles can be the accurate key.

Longitudinal muscles had only elongated C-shaped granule ossicles, and length and calculated indicators ranged within: 24–106 μm in length, GP =29.2–74.1%, GCO =0% ( Table 13 View TABLE 13 ). Among these values, length of granule ossicles was significantly different (Ps <0.005, Kruskal-Wallis’ test, both in ventrally and dorsally), while the two calculated indicators GP and GCO were not significantly different in GP (Ps>0.05, Kruskal-Wallis’ test). Therefore, length of the granule ossicles cannot be the accurate key. However, the complete unbalance of O-shaped (0%) or C-shaped (100%) granules can be a useful key.

Tentacle ossicles consisted of many elongated C-shaped granules and rare rods, length and calculated indicators of three specimens ranged within: 22–63 μm in length, RP =9.5–55.2%, and RC =4.1–11.1 ( Table 13 View TABLE 13 ). Among these values, length of granule ossicles was not significantly different (P>0. 05, Kruskal-Wallis’ test) among specimens, and non--sizeependence indicator for proportion (RP) and non--sizeependence complexities (RC) were also not significantly different (P>0. 05, Kruskal-Wallis’ test). Therefore, the morphologies of the granule ossicles of this species can be a critical accurate key.

Remarks

Previously, in a report of the Ministry of the Environment Japan (2007), this species was preliminarily identified as Patinapta sp. (and misidentified in their distribution map as P. ooplax ). However, it was revealed that this species can be easily distinguished from other species by their elongated C-shaped granule ossicles (lacking perforations) with highest concentrations in the tentacles, different from all congeners (Table 7-2).

Distribution

Presently, only two localities are known for this species. In the type locality Kabira Bay, Ishigaki-jima Island, 20 specimens including the three type specimens were collected from the coarse-sandy intertidal flats, where most of specimens had been infested with co-existing bivalves Anisodevonia ohshimai . In Nagura Bay, the smaller specimens were collected from the coarse-sandy intertidal shore and the muddy-sand intertidal flats with mangrove woods ( Table 14).

Discussion

We illustrate herein all twelve plates of the calcareous ring for the first time (see, Table 7-3). As a result, the present calcareous rings of two species previously described from Japan agree to the original descriptions based on type materials. Specifically, agreement is found in the points of “interradial plates with semicircular perforation” reported for P. ooplax ( Fig. 8 View FIGURE 8 ), and “same compose to P. ooplax , but the anterior tips not undulated at all ( Chao et al, 1988)” reported for P. taiwaniensis ( Fig. 11 View FIGURE 11 ). Both characters of the calcareous ring were also detected in the present four new species from Japanese waters. Regardless of the mostly separated distributions of P. ooplax and P. edentatus , both species possess the same type of calcareous ring compositions, namely inter-radial perforated type ( Figs 8 View FIGURE 8 , 23 View FIGURE 23 ), while P. taiwaniensis , P. deformis and P. parvaspiculus possess another type of composition, namely radial perforated type ( Figs 11 View FIGURE 11 , 14 View FIGURE 14 , 17 View FIGURE 17 ). In addition to these, between the “separated distributions of P. ooplax and P. edentatus ,” another type of calcareous ring, namely inter-radial creviced type of P. neglectus , was described in the present study ( Fig. 20 View FIGURE 20 ). This result of morphologies of calcareous rings naturally leads us to speculate that the phylogeny of this genus may be more interesting than previously expected, and molecular analyses are needed in the future.

From the present observations for the six species described above, only the latitudinal layouts of ossicles (anchor and plate) were generated in the present materials, however, this information can be useful in field observations, or future studies of phylogenetic taxonomy.

To achieve accurate species identification, keys for the present six species described above are given below, using the present results of ossicle morphologies. Simultaneous use of Table 15 (Appendix tables attached to the last of this article) with the below key will lead to more convenient identification.