Punctulum reticulatum Golikov, 1986

Hasegawa, Kazunori, 2022, Bathyal Rissoidae (Gastropoda: Rissooidea) off the Russian Far East coast of the Sea of Japan, with redescription of Punctulum reticulatum Golikov, 1986, Ruthenica, Russian Malacological Journal 32 (2), pp. 85-92 : 90

Punctulum reticulatum Golikov, 1986

( Fig. 3 )

Punctulum reticulatum Golikov, 1986: 88–89 , fig. 4; Kantor, Sysoev, 2006: pl. 36, fig. J (holotype); Hasegawa, 2014: fig. 48 F–H (holotype).

Type material. Punctulum reticulatum Golikov, 1986, holotype, ZIN 36574 /3 (dried shell; Fig. 3 G–I); paratype, off Primorsky Krai, 380– 312 m, ZIN 36576 /5 (shell completely dissolved in preservative) .

Type locality. Off the coast of Primorsky Krai near Rynda Bay in the Sea of Japan (44°48’N, 136°40’E) at a depth of ca. 430 m on a silty ground with a sandy area .

Material examined. SoJaBio A 2-10, MIBM 39338 ( Fig. 3 A–D ); SoJaBio B 7-7, MIBM 39343 ( Fig. 3 E–F ) [depth range: 455–528 m].

Distribution. Off the coast of southern and middle Primorsky Krai, at depths from 240 to 880 m [ Golikov, 1986]. Because there have been no records of this species from Japanese territorial waters [ Hasegawa, 2014], it is probably endemic to the northern slope of the Sea of Japan.

Original description. “Раковина маленькаЯ, хрупкаЯ, с 4,5 выпуклыми, Закругленными оборотами, раЗделен- ными тонким вдавленным Швом. Периостракум тонкий, ШелуШаЩийсЯ, бледно-лимонно-желтого цвета. Заро- дыШеваЯ раковина иЗ 1,5 выпуклых Закругленных обо- ротов, покрыта тончайШей спиральной исчерченностьЮ, составленной 15 нитевидными ребрыШками. Последний оборот с Закругленной периферией и выпуклым основа- нием Занимает 0,77 высоты раковины. ОсеваЯ скульптура представлена тонкими линиЯми роста и уЗкими осевыми складками, расположенными с промежутками, примерно в 2 раЗа превыШаЮЩими их Ширину, распространЯЮЩи- мисЯ на всЮ высоту оборотов, но не ЗаходЯЩими на осно- вание раковины. На последнем и предпоследнем оборотах расположено по 28 таких складок. СпиральнаЯ скульптура состоит иЗ приподнЯтых, волнистых на осевых складках ребрыШек, расположенных с промежутками в 2–3 раЗа более Широкими, чем их толЩина. На последнем обороте расположено 10 таких ребрыШек, а на предпоследнем обороте их 5. Пупок не полностьЮ прикрыт отворотом внутренней губы. Устье с сомкнутым краем, почти окру- глое, слегка выступает у нижнего париетального краЯ. ”

[The shell is small, fragile, with 4.5 convex, rounded whorls separated by a thin, depressed suture. Periostracum thin, scaly, pale lemon yellow in color. The embryonic shell consists of 1.5 convex rounded whorls, covered with the fin- est spiral striation, composed of 15 threadlike ribs. The last whorl has a rounded periphery and a convex base that occupies 0.77 of the shell height. Axial sculpture is represented by thin growth lines and narrow axial ribs, located at intervals of approximately twice their width, extending over the entire height of the whorls but not to the base of the shell. On both the last and the penultimate whorls there are 28 such ribs. The spiral sculpture consists of raised cords that are made wavy by the axial ribs, spaced at intervals 2–3 times wider than their thickness. On the last whorl there are 10 such cords, and on the penultimate whorl there are five. The umbilicus is not completely covered by the folding of the inner lip. The aperture has a contracted margin, almost rounded, and protrudes slightly at the inferior parietal margin.]

Re-description (in accordance with Hasegawa [2014]). Shell minute, 2.7 mm shell length in holotype, moderately thick for genus, low conical in shape, with relatively small spire and covered by thick, rather smooth and light yellowish periostracum. Protoconch ( Fig. 3D ) dome-shaped, consisting of 1.5 whorls, with flat spiral cords, 15 in number at end of protoconch. Terminus of protoconch slightly thickened and clearly demarcated from teleoconch whorls. Teleoconch of ca. 2.0–2.5 convex whorls, with deeply constricted suture and weak angulation at shoulder. Relatively small spire occupying 25–28% of shell length. Surface rather smooth, with widely spaced axial and spiral sculpture of nearly same strength, forming rough lattice-like appearance. Axial sculpture consisting of straight, strong, round ribs that gradually appear on later part of first teleoconch whorl and persist to last whorl, and indistinct microscopic growth lines.Axial ribs reaching from suture to suture on spire whorls and from suture to umbilicus on last whorl; periostracum not fibrous on axial ribs. Spiral sculpture consisting of strong, rounded spiral cords and minute but distinct numerous secondary spiral threads. On initial part of first teleoconch whorl, very fine but distinct and somewhat granulate spiral threads present, gradually disappearing on later whorls. Spiral cords strongest below periphery, becoming slightly weaker and thinner toward suture and umbilicus. Last whorl large and inflated. Aperture oval to almost evenly rounded, only slightly angled at posterior end. Inner lip rather thin; outer lip slightly prosocline, with very weak apertural varix behind lip in mature specimens. Umbilical chink slit-like and only narrowly perforate.

Remarks. This species apparently belongs to the clade containing P. flavum and P. tanshumaruae Hasegawa, 2014 [Criscione et al., 2019] because of the close similarity in the morphology of the protoconch. However, it can easily be distinguished from other species by the teleoconch sculpture, and is probably endemic to the Russian Far East.

Figures

FIG. 3. Punctulum reticulatum Golikov, 1986. A-D. SoJaBio stn. A2-10 (455–456 m), MIBM 39338. E-F. SoJaBio stn. B7-7 (470–528 m), MIBM 39343.G-I. Holotype, ZIN 36574/3.All at the same scale, scale = 1 mm; except for D, scale, 200 µm.