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

Patinapta parvaspiculus sp. nov.

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

( Figs 15–17 View FIGURE 15 View FIGURE 16 View FIGURE 17 ; Tables 1 View TABLE 1 , 9 View TABLE 9 , 10)

Two specimens from Yoron-jima Island (WMNH-2015-INV-107; 2023-INV-157) and one specimen from Imari Bay (WMNH-2024-INV-156) were identified as new to science. We herein describe the morphological characters of this new species .

Diagnosis. Anchor and anchor plate ossicles small. Anchor plate ossicles smaller than 100 μm, while anchor ossicles up to 150 μm, resulting in unbalanced size combinations of bounded ossicles. Total shapes of anchor plates strongly distorted (because of small total numbers of perforations), basally with a concave shallow or deep, resulting in a two-tipped ovoid shape. Perforations of anchor plate ossicles mostly without teeth, while outer edge of anchor plate ossicles equipped with minute teeth in small numbers. Ciliated funnels attached to inner side body wall along midline of left dorso-lateral interradius (IR3).

Type series. Holotype, WMNH-2023-INV-157; two paratypes, WMNH-2015-INV-107; WMNH-2024-INV-156.

Description of holotype (WMNH-2023-INV-157: middle-size damaged specimen). External and internal morphologies as follows ( Table 1 View TABLE 1 ): 30 year-old preserved well-matured specimen pale peanut color, body large about 100 mm length ( Fig. 15 View FIGURE 15 ). Tentacles 12, each with 10 digits of 5 pairs. On oral-side of tentacle stem, about 10–16 sensory cups sporadically arranged in a U-shape.

Polian vesicle in medio-ventral position, fusiform, triple ( Table 1 View TABLE 1 ), stone canal single and thread-like, attached to narrow space between basal parts of tentacle ampullae at mediodorsal (IR5), suddenly turned upward and forward, resulted in it facing forward, distally with moldy surface madreporite. Ciliated funnels in one crowded band along left dorsal interradius (IR3).

Inside body, two tufts of gonad tubules attached to both sides of anterior dorsal mesentery, also two whitish tubule organs adhered to upper and under sides of intestine canal. Intestine canal lacking loop.

Body wall smooth surface, hard but thin, with ossicle 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 parvaspiculus , alluding to the ossicles’ small size.

The present results of ossicle morphologies

Body wall ossicles anchors and anchor plates ( Fig. 16B, D View FIGURE 16 ; Table 9 View TABLE 9 ). Anchor plates ranged within 75–98 μm in length. Size of perforations not noticeably variable between central area and marginal area, and instead almost constant between central area and marginal area, because of only few marginal perforations rarely equipped. Plates showed slight distortion, with small total numbers of perforations arranged more or less in two rows as holothuroid button ossicles, and basally with a concave shallow or deep, resulting in a two-tipped ovoid shape. Perforations of anchor plate ossicles mostly toothless, while outer edge of all anchor plate ossicles equipped with small numbers of sharp minute teeth. Two calculated indicators for anchor plates and a parameter were variated within APS =0–0.7; Nt =0–3; APT =0–27.3% ( Fig. 16B, D View FIGURE 16 ; Table 9 View TABLE 9 ).

Anchor ossicles ranged within 144–173 μm in length ( Fig. 16B, D View FIGURE 16 ; Table 9 View TABLE 9 ). All anchor arms (bills) equipped with minute teeth on their outer tips, numbers of teeth variable within 0–6 (mostly 1–2 in one arm of the anchor ossicle), and anchor ossicles of this specimen possessed narrow stem and also relatively narrow anchor arm 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. 16B; D View FIGURE 16 ).

Body longitudinal muscle, granule ossicles of this specimen ranged within 21–34 μm in length ( Fig. 16C, E View FIGURE 16 ; Table 9 View TABLE 9 ). The calculated indicator for granule proportions were variated within GP =35.3–64.3%; GCO =36.4–78.6% did not have noticeable differences in amounts between the O-shape and C-shape granules.

Tentacle ossicles rods, ranged within 53–102 μm in length ( Fig. 16A View FIGURE 16 , Table 9 View TABLE 9 ). Two calculated indicators for rod proportions and complexities were variated within RP = 7.1–16.9%; RC =2.7–11.7 ( Table 9 View TABLE 9 ).

Observation on the morphologies of calcareous ring

Calcareous plates 12, mostly firmly bound ( Fig. 17 View FIGURE 17 ), with slight anterior projection and deep posterior depression in interradial plates, while only posterior depression in radial plates. All radial plates perforated in each anterior half. The connections between 4 plates situated in right and left dorso-lateral positions (IR4; RIII; IR3; RII), where additional interradial plate (IR4’; IR3’) and adjacent radial plate (RIII; RII) form triangular shapes and weakly bound by their apical ends.

Ossicle variation among three specimens

Three specimens approximately 50–100 mm in length ( Table 1 View TABLE 1 ), two specimens (WMNH-2015-INV-107; 2023- INV-157) well-matured and possessing fully equipped gonad tubules in their body cavities, while one specimen (WMNH-2024-INV-187) immature and extended by strong contraction of latitudinal muscle. Their external and internal morphologies agreed with each other’s in many parts ( Table 1 View TABLE 1 ).

Body wall ossicles anchors and anchor plates. Anchor plate ossicle length and calculated indicators of three specimens ranged within: 75–123 μm in length, APS =0–11.3, Ntp =0–4, APT =0–27.3%. Among these values, length of anchor plate ossicles (both ventrally and dorsally) was significantly different (Ps <0.005, Kruskal-Wallis’ test), while non-size dependance indicator of plate skewness APS was not significantly different (Ps>0.05, Kruskal-Wallis’ test). However, the frequency of teethed perforations APT was significantly different (Ps <0.005, Kruskal-Wallis’ test), while contrary to this parameter Ntp was not significantly different (Ps>0.05, Kruskal-Wallis’ test). From these results, the anchor plate ossicles in the body wall of the present three specimens were different in ossicle length and frequency (APT) of teethed perforations (P s<0.005, Kruskal-Wallis’ test), while the numbers of teethed perforations (Ntp) were not significantly different. Therefore, other than the number of teethed perforations (0–4) and noticeable plate skewness (APS =0–11.3), all the other morphological characters of the anchor plate ossicles cannot be the accurate keys.

Anchor ossicle lengths and calculated indicators ranged within: 140–178 μm in length, ASW =21.8–32.5%, AEW =38.5–64.9% ( Table 9 View TABLE 9 ). Among these values, lengths of anchor ossicles (both ventrally and dorsally) were not significantly different (Ps>0.05, Kruskal-Wallis’ test), also 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 not different in ossicle length or shape. Therefore, proportion and shape of the anchor ossicles can be the accurate keys.

Longitudinal muscle had both O-shaped and C-shaped granule ossicles, length and calculated indicators ranged within: 21–54 μm in length, GP =28.2–80.8%, GCO =33.3–78.6% ( Table 9 View TABLE 9 ). Among these values, lengths of granule ossicles (both ventrally and dorsally) were significantly different (Ps <0.005, Kruskal-Wallis’ test), also calculated indicator GP was significantly different (Ps <0.005, Kruskal-Wallis’ test), but GCO was not different significantly (Ps>0.05, χ 2 -multiple test). Therefore, the length and proportion of the granule ossicles cannot be the accurate keys, while the ratio C- or O-shaped granule ossicles of this species can be the accurate key.

Tentacle ossicles rods. Lengths and calculated indicators of three specimens ranged within: 53–102 μm in length, RP =7.1–21.5%, and RC =2.7–17.8. Among these values, length and non-size dependence complexities (RC) of rod ossicles were not significantly different (P>0.05, Kruskal-Wallis’ test), while non-size dependence indicator for proportion (RP) was significantly different (P <0.005, Kruskal-Wallis’ test). From these results, the rod ossicles in the tentacles of the present three specimens have similar length, however their proportion was noticeably variable. Therefore, the length (about 50–100 μm) and the high complexity of the rod ossicles shown by RC =2.7–17.8 of this species can be accurate keys, however their proportions cannot be the accurate key.

Remarks

Among the present three specimens, the smallest specimen (WMNH-2024-INV-156) had no " two-tipped anchor plate" in the body wall, that was deviation for one diagnostic character noted above, however, that simultaneously had other two diagnostic characters "perforations of anchor plate ossicles mostly without teeth" and "outer edge of anchor plate equipped with minute teeth in small numbers, "therefore, we concluded that the anchor plate of immature animals would be underdeveloped and without basal concave which divide the "two-tips". Among the previously nominated six species of the genus Patinapta Heding, 1928 (WoRMS 2024, listed in Table 7), only one species, P. laevis ( Bedford, 1899) , was reported as a species possessing toothless perforations on anchor plate ossicles (Table 7-2), which showed a concave on basal tip resulting in two tips basal end, also resembling the present new species parvaspiculus sp. nov. However, P. laevis also possesses unique ossicles in its longitudinal muscles, mostly two perforated oval granule ossicles, and thus is easily distinguishable from the present new species.

Distribution

Southern Japan (Kyushu Island, Shikoku Island and the Ryukyu Islands). In Yoron-jima Island (type locality), the specimens were collected from intertidal sandy beach with boulders originated from dead corals. Among the specimens housed in WMNH-INV, including the present specimens, 5 bottles including 8 specimens were identified as this species ( Table 10). Other than the type locality, 6 young specimens collected from Oita and Saga of Kyushu Island, from Kochi of Shikoku Island, and from two islands of Kagoshima in Ryukyu Islands, Japan were identified as this species. All the specimens were collected from estuarine intertidal flats.