Patinapta ooplax ( von Marenzeller, 1882 )

Patinapta ooplax ( von Marenzeller, 1882) View in CoL

[Japanese name: Himo-ikari-namako]

( Figs 4–8 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 ; Tables 1–3 View TABLE 1 View TABLE 2 View TABLE 3 )

Synapta ooplax Von Marenzeller, 1882: 122–123 View in CoL +Taf. IV fig. 1.)

Leptosynapta ooplax : Ohshima 1914: 469–470; Clark 1908: 90–91.

Patinapta ooplax ( von Marenzeller, 1882) View in CoL : Heding 1928: 238–241, accepted after Liao 1997: 263 + textfig. 156a–d.

Original species description (as Synapta ooplax in von Marenzeller, 1882: 122–123 +pl. IV fig. 1. Translated and simplified from original deutsche).

Type locality, Japan. Three specimens examined in von Marenzeller’s (1882) study. Tentacles 12 short, body vermiform up to 70 mm, color receding reddish, skin wavy but not rough. Each tentacle possesses 4–5 pairs of digits. Calcareous ring composed of 12 plates weakly bound, one additional interradial plate inserted between in left dorsal RIV and RII, also the same in right dorsal RV and RIII. Radial plates with sharp anterior point, interradial plates with semicircular perforation on their anterior tip. Polian vesicle single, 4–12 mm long, stone canal single, gonad tubules branched.

Body wall ossicles consisted of anchors and anchor plates. Anchor plates ranged within 94–109 μm length, perforations centrally larger than those of marginal. Positions of perforations were irregular, only large perforations equipped with teeth arraign along with inner rim. Anchor ossicles ranged within 113–119 μm length, all anchor arms (bills) equipped with 2 or 3 minute teeth on their outer tips. Longitudinal muscle granule ossicles consisted of minute curved rods or ovoid perforated plates ranged within 28–40 μm length and about 15.7 μm width. Tentacle ossicles only rod ossicles, weakly curved and often branched or perforated at distal ends. Rod ossicles ranged within 52–87 μm length and 6–12 μm breadth.

Description of the present result

The largest specimen from Otsuchi Bay (WMNH-2014-INV- 239) was identified as this species. External and internal morphologies as follows ( Table 1 View TABLE 1 ): The preserved body color, pale peanut after fixation for about 10 years ( Fig. 4 View FIGURE 4 ). 12 tentacles, each with up to 6 pairs of digits. On the oral side of the tentacle stem about 5–18 sensory cups, sporadically arranged within the 10 tentacles of the ventral side; the medio-dorsal 2 tentacles without sensory cups.

Polian vesicle single, narrow, fusiform, 7.63 mm length, attached with posterior end of the water brood circle just behind of calcareous ring at medio-ventral position (RI). Tentacles ampullae12 attached with outer circle of calcareous ring, each ampullae narrower and shorter than Polian vesicle. Stone canal single, thread-like, attached to narrow space of anterior end of left side of dorsal mesentery between basal parts of tentacle ampullae at mediodorsal (IR5), suddenly turned to upward and forward, resulted in facing forward, distally with mold-like madreporite. Ciliated funnels are attached along midline of left dorsal interradial (IR3) inner-side body wall, forming crowded one band in this specimen.

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 sticky surface, soft but thick, with ossicle sporadically arranging latitudinal layout of all as sets of anchor and plate, their direction disordered, lacking in body wall upon longitudinal muscles.

Variation of external and internal morphologies

All external morphologies well-agreeing to those as represented above, however, internally several differences were observed. In the small specimen (WMNH-2020-INV-62), whitish tubule organ adhered to underside of intestine canal, and lacking dorsal gonad tubules ( Fig. 5B View FIGURE 5 ). In the middle-size specimen (WMNH-2014-INV-238), whitish tubule organ adhered to underside of intestine canal and also equipped with dorsal gonad tubules ( Fig. 5A View FIGURE 5 ). From these whitish tubule, narrow canal bound to basal part of gonad tubules, but none of the genital cells were observed in the whitish tubule, which was fully filled with non-staining cells (anucleate cells) ( Fig. 6A, B View FIGURE 6 ).

The present results of ossicle morphologies

Body wall ossicles are anchors and anchor plates ( Fig. 7 View FIGURE 7 ; Table 2 View TABLE 2 ). Anchor plates ranged within: 93–117 μm length (mean±SD=106.6±2.9 μm in ventrally, 101.3±7.4 μm in dorsally). Perforations on anchor plates centrally larger than those of marginal, relatively larger seven perforations arranged in each six apex and one center positions of slightly distorted hexagon. Larger perforations equipped with sharpened triangle teeth, closely and continuously standing along with their peripheral edge, some perforations filled up by teeth and resulting in asterisk-like form. Two calculated indicators for anchor plates and parameters varies within APS =0–11.2 (mean±SD= 2.6 ± 4.8 in ventrally, 1.3± 1.3 in dorsally); Ntp =7–10 (mean±SD=7.6 ± 0.5 in ventrally, 7.5± 1.77 in dorsally); APT =22.2–47.4% (mean±SD=29.8 ± 2.2% in ventrally, 39.1±8.0% in dorsally), thus this specimen had values of “ APS =0 (n =1), Ntp =7 (n =1)”and “ APT =23% (n =1)” close to those from von Marenzeller’s work (1882) based on the syntype.

Anchor ossicles ranged within 144–164 μm length (mean±SD=152.4± 8.6 μm in ventrally, 154.3±7.0 μm in dorsally). All the anchor arms (bills) equipped with minute teeth on their outer tips, numbers of teeth ranged within 3–8 (mean±SD=6.2± 0.4 in ventrally, 6.1± 1.6 in dorsally): about 3 teeth on each anchor arms. Two calculated indicators for anchors were ranged within ASW =20.3–24.3% (mean±SD=21.5 ± 0.7% in ventrally, 22.4±1.4% in dorsally); AEW =47.3–58.8% (mean±SD=53.9±3.4% in ventrally, 52.0±2.4% in dorsally), thus this specimen had values of “ ASW =21.9% (n = 1) and AEW =55% (n =1)” that were close to those calculated from von Marenzeller’s work (1882) based on the syntype.

Body longitudinal muscle ossicles are granule ossicles ( Fig. 7C,E View FIGURE 7 , Table2 View TABLE 2 ), both O-shaped and C-shaped granules ossicles observed, ranging within 27–59 μm length (mean±SD=36.8±7.7 μm in ventrally, 35.8±6.5 μm in dorsally). The calculated indicator for granule proportions was variated within GP =27.1–79.4% (mean±SD=47.3±12.5% in ventrally, 47.5±9.4% in dorsally) and GCO =69.2% in ventrally, 76.5% in dorsally, thus this specimen had a value of “ GP =44.3% (n =6)” that was close to that calculated from von Marenzeller’s work (1882) based on the syntype. However, another indicator of all three specimens were noticeably larger values than“ GCO =50% (n =6, presumably selected as typical two shapes of O-shaped and C-shaped granules ossicles)” that was calculated from von Marenzeller’s work (1882) based on the syntype.

Tentacle ossicles were rods ( Fig. 7 View FIGURE 7 , Table 2 View TABLE 2 ), their length and calculated indicator for rod proportions (RP) and complexities (RC) ranged within: 69–97 μm length (mean±SD=83.4 ±9.0 μm), RP =7.2–13.6% (mean±SD=9.8 ± 2.2%), and R =8.9 (mean±SD=8.9 ± 3.3), thus this specimen had values “ RP =13.1% (n =3) and RC =11.2 (n =3)” close to those from von Marenzeller’s work (1882) based on the syntype.

Observation on the morphology of calcareous ring

Calcareous plates 12, weakly bound ( Fig. 8A View FIGURE 8 ), 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 plate (IR4’; IR3’) and adjacent radial plate (RIII; RII) construct a wide space (like a “interradial perforation”) between their lateral ends. Three radial plates of the calcareous ring (RI; RIV; RV) with a slight anterior projection and a perforation; the interradial calcareous ring plates also with a slight anterior projection; the medio-dorsal plate (IR5) with indentations, one at the anterior margin and one at the posterior margin.

Ossicles variation among three specimens

Three specimens were chosen as specimens with different body sizes ( Table 1 View TABLE 1 ) to investigate if morphological changes of ossicles occur in different body sizes.

Body wall ossicles are anchors and anchor plates. Anchor plate ossicle length and calculated indicators ranged within: 88–109 μm length, APS =0–11.4, Ntp =3–9, APT =8.8–55.9% (in small specimen WMNH-2020-INV-62, Table 2 View TABLE 2 ); 94–113 μm length, APS =0–6.4, Ntp =5–8, APT =17.2–32.0% (in middle-size specimen WMNH-2014-INV-238, Table 2 View TABLE 2 ); and 93–117 μm length, APS =0–11.2, Ntp =4–10, APT =22.2–47.4% (in large-size specimen WMNH-2014- INV-239, Table 2 View TABLE 2 ). Among these values, length of anchor plate ossicles and the numbers of teethed perforations Ntp were not significantly different (Ps>0.05, Kruskal-Wallis’ test, both in ventrally and dorsally), while the frequency of teethed perforations APT was significantly different (Ps <0.005, Kruskal-Wallis’ test), and non-size dependance indicator of plate skewness APS were 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 not different in ossicle lengths, but different in the frequencies of the teethed perforations in total perforations different among body size (large specimen possess many teeth-less perforations on the anchor plate ossicles). Therefore, length of the anchor plate ossicles (average about 100–110 μm), numbers of teethed perforations (4–10), and skewness (distorted slightly caused by disorderly scattered basal small perforations) of this species can be the appropriate (accurate) diagnostic keys, while the indicator of the frequency of teethed perforations APT will change during individual growth, and is not an appropriate key.

Anchor ossicles length and calculated indicators ranged within: 135–185 μm length, ASW =18.3–23.9%, AEW =47.9–60.3% (in small specimen WMNH-2020-INV-62, Table 2 View TABLE 2 ); 145–168 μm length, ASW =24.4–31.3%, AEW =51.4–63.0% (in middle-size specimen WMNH-2014-INV-238, Table 2 View TABLE 2 ); and 144–164 μm length, ASW =20.3– 24.3%, AEW =47.3–58.8% (in large-size specimen WMNH-2014-INV-239, Table 2 View TABLE 2 ). Among these values, lengths of anchor ossicles were not significantly different (Ps>0.05, Kruskal-Wallis’ test), while the indicator for anchor stem breadth ASW and AEW for basal / distal ends width were significantly different (Ps <0.005, Kruskal-Wallis’ test, both in ventrally and dorsally). From these results, the anchor ossicles in the body wall of the present three specimens were not different in ossicle length, but different in stem breadths and basal / distal ends balances in different body sizes (small specimen possessing narrower anchor stems and narrower distal end widths between one arm and other arm, resulting in close values of basal/distal ends width). Therefore, length of the anchor ossicles of this species is an appropriate diagnostic key, while their ossicle shape indicated in ASW and AEW changes across individual body growth, and thus are not appropriate keys.

Longitudinal muscle involved both O-shaped and C-shaped granule ossicles, length and calculated indicators ranged within: 27–45 μm length, GP =36.6–53.2%, GCO =77.8–80.0% (in small specimen WMNH-2020-INV-62, Table 2 View TABLE 2 ); 24–45 μm length, GP =42.9–77.8%, GCO =62.5–100% (in middle-size specimen WMNH-2014-INV-238, Table 2 View TABLE 2 ); and 27–59 μm length, GP =27.1–79.4%, GCO =69.2–76.5% (in large-size specimen WMNH-2014-INV-239, Table 2 View TABLE 2 ). Among these values, length and their ratio of C- or O-shape GCO of granule ossicles were not significantly different (Ps>0.05, Kruskal-Wallis’ test and Ps>0.05, χ 2 -multiple test, respectively, both in ventrally and dorsally), while another calculated indicator for proportion GP was significantly different (Ps <0.005, Kruskal-Wallis’ test). Therefore, the length (average about 30–40 μm) of granule ossicles and their ratio of C- or O-shaped granule ossicles (ratio O-shaped granule ossicles about twice larger than the other) are appropriate keys.

Tentacle ossicles were rods, their length and calculated indicators ranged within: 51–74 μm length, RP =7– 14%, and RC =6.8 (in small specimen WMNH-2020-INV-62, Table 2 View TABLE 2 ); 62–83 μm length, RP =11–20%, and RC =7.5 (in middle-size specimen WMNH-2014-INV-238, Table 2 View TABLE 2 ); and 69–97 μm length, RP =7–14%, and RC =8.9 (in large-size specimen WMNH-2014-INV-239, Table 2 View TABLE 2 ). Among these values, length of rod ossicles and non-size dependence indicator for proportion (RP) were different significantly (Ps<0.005, Kruskal-Wallis’ test), while non-size dependence complexities (RC) were not different significantly (P>0.05, Kruskal-Wallis’ test). From these results, the rod ossicles in the tentacles of the present three specimens were different in their length, proportions and complexities in different body sizes (large specimen possessing more complex shapes of rod ossicles). Therefore, the morphologies of tentacle rod ossicles of this species cannot be good diagnostic characters as their values change over an individual’s growth.

Calcareous ring variation among three specimens

Three specimens were chosen as specimens collected only from Otsuchi Bay, with a large-size specimen, WMNH-2014-INV-239 (90.5 mm length) ( Fig. 8A View FIGURE 8 ); small specimen, WMNH-2014-INV-240 (56.1 mm length) ( Fig. 8C View FIGURE 8 ); and middle-size specimen WMNH-2014-INV-241 (75.3 mm length) ( Fig. 8B View FIGURE 8 ). Calcareous plates 12, weakly bound ( Fig. 8A View FIGURE 8 ), 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 plate (IR4’; IR3’) and adjacent radial plate (RIII; RII) made a wide space like an “interradial perforation” between their lateral ends of the large-size and the middle-size specimens, with a wide space and a narrow space, respectively, however, only deep posterior depression instead of “interradial perforation” in the calcareous plates of small specimen. Three radial plates of the calcareous ring (RI; RIV; RV) with a slight anterior projection and a perforation, very short projection and small perforation in small specimen; the interradial calcareous ring plates also with a slight anterior projection; the medio-dorsal plate (IR5) with indentations, one at the anterior margin and one at the posterior margin, while only medio-ventral plate (RI) possess posterior depression and other plates possess only posterior expanding in small specimen.

Supplemental note

In the observation of one syntype specimen of Synapta ooplax by Y.Y., all of ossicles were eroded and could not be confirmed, as they had been drying for long time, as has previously been reported in an accident of the syntype of Chiridota japonica (see Yamana et al. 2022). Through von Marenzeller’s dissection opening, we could confirm that a radial plate of the calcareous ring at medio-ventral position (RI) was perforated, and at least one band of crowded ciliated funnels aligned at along midline of the left dorsal interradius (IR3).

Remarks

From the investigation on three different-size specimens, several morphological trends on ossicles of this species can be expected: i) rod ossicles of tentacles change their length small to large, also their shapes change from simple to complex as it grows; ii) anchor plate ossicles and anchor ossicles do not change their length during growth from young to mature adult, iii) in the body wall in young specimens, anchor plate ossicles show more distortion than in mature adults, at least in the type species of the genus Patinapta .

Morphologies of calcareous plates of three specimens all from Otsuchi Bay different among specimens. Fully matured large and middle animals possess a calcareous ring with “interradial perforation,” while young immature animals possess a calcareous ring without “interradial perforation.” It is strongly considered that such morphological changes may be a result of individual growth, thus some intermediate forms must be expected.

Distribution

The present three specimens were collected from mid-intertidal sandy boulder shore, closely situated to a small river mouth. Basing on the identifying features suggested from the present results, WMNH-INV accommodates total 584 specimens of this species preserved in 36 bottles (Honshu island 25; Shikoku island 3; Kyushu island 7; Ryukyu islands 1) ( Table 3 View TABLE 3 ), ranging from Mutsu Bay, Aomori (40°N) to Tatsugo Bay, Amami island, Kagoshima (28°N). Throughout this latitudinal range (ca. 28– 40°N) this species must be inhabiting everywhere in the intertidal zone and shallow waters (ca. 0–10 m deep), encircling Japanese islands, while previous distributional reports about outside Japanese waters, lately Liao (1997: 263–264) noted distribution of this species as: Chinese coastal waters, southernmost of Haimen town, Guangdong province (23°N) to northernmost of Dalian City, Liaoning province (38°N), however in the figures for ossicles, anchor plate are lacking with bilateral symmetrical shape and all the perforations without teeth, thus strongly implies Liao (1997) made a misidentification for this species. The Aomori specimens represent a northernmost extension of the distribution of this species, which had previously been considered to be Sagami Bay ( Utinomi 1965). In our observations of the specimens in WMNH-INV, Hokkaido and the South-western islands of Tokara, Ryukyu and Yaeyama did not have specimens of this species, and it is likely this species is not distributed in these regions. It has not yet been investigated whether this species inhabits the Ogasawara (Bonin) Islands (around 27°N) or not.