Immergentia suecica Silén, 1947, p. 41

Johnson, Mildred J., Saadi, Ahmed J., Kuklinski, Piotr, Smith, Abigail M., López-Gappa, Juan & Schwaha, Thomas, 2024, Digging into boring bryozoans: new characters and new species of Immergentiidae, Organisms Diversity & Evolution 24 (2), pp. 217-256 : 229-233

Immergentia suecica Silén, 1947, p. 41 , figs. 58, 60, 61

Material examined. NORTH SEA • extracted zooids and colony borings in bivalve shell; Skagerrak, Sweden, Gullmar Fjord, North of Flatholmen; depth: 45 m; 16 August 1946; L. Silén leg.; I. suecica in shell of Pseudamussium peslutrae Linnaeus, 1771 ; holotype: SMNH-Type-2366.

NORTH-EAST ATLANTIC – France • extracted zooids and colony borings in several bivalve shells; Stolvezen; 48º42.847’N 03º53.500’W, 48°40.000' N 3°52.999' W; depth: 15–25 m; 3 September 2021; ‘Neomysis’ cruise; characterized by bivalves, gastropods, algae (brown, red and green) and brown sediment, immergentiid colonies in bivalve shells: Lutraria lutraria Linnaeus, 1758 , Ensis sp. Schumacher, 1817, Pecten maximus Linnaeus, 1758 , and Anomia sp. Linnaeus, 1758; FR21– GP 21, FR21–A50, FR21–PF54, FR21–FP28, FR21– GP 28, FR21–A25, FR21– GP 25, FR21–A22, FR21– GP 12, FR22–72A, FR22–74A, FR23- A3, FR21-28; GenBank: SAMN 38786229 • extracted zooids and colony borings in bivalve shells; Stolvezen; 48º42.847’N 03º53.500’W, 48°42.846' N 3°53.5' W; depth: 15–25; 5 October 2021; ‘Neomysis’ cruise; FR21–D6/7 • extracted zooids and colony borings in bivalve shells; Térenéz; 48º41.532’N 03º52.075’W; depth: 10 m; 10 September 2021, 14 September 2021, 5 October 2021; ‘Neomysis’ cruise; characterized by rocks, living bivalves, red algae and dark sediment; FR21–A55, dried shells; GenBank: SAMN 38786228 • extracted zooids and colony borings in bivalve shells; Chateaux du Taureau, Roscoff; 48°40.2' N 3°53.12' W, 48°40.200' N 3°52.999' W; depth: 10–15 m; September 2020, 4, 5, 8, 12 September 2021, December 2022; ‘Neomysis’ cruise; FR19-6F, FR21-A6, FR22–33A, dried shells – Norway • one heavily bored shell; Trondheim Fjord, Norway; 63º51.479’N 11º04.354’E; depth: 12 m; 08 July 2014; P. Kukliński leg.; N19 gastropod 3.

Description - I. suecica (Holotype): Borehole apertures oval ( Fig. S1d ) with average width of 55 ± 9 µm. Autozooids typical vase shape, length 250 ± 11 µm and width of 68 ± 5 µm, with rounded or sometimes tapered basal tip, curved toward primary cystid appendage ( Fig. S1e ). Polypide with 9 tentacles ( Fig. S1f ) and lophophoral anus. Intercalary kenozooids may connect cystid appendages. Tubulets present. Presumed developing zooid length 131 µm and width 62 µm.

Description – Immergentia cf. suecica from France ( Figs. 3e, 3c , 7c, 8d, 9e and 10c): Borehole apertures oval or spindle shaped and enantiomorphic (Fig. 9e) with average width of 50 ± 9 µm. Colony not dense (Fig. 9e). Zooids irregularly and broadly spaced ( Figs. 3e and 9e) at intervals measuring 917 ± 175 µm. Autozooids typical vase shape, length 262 ± 48 µm and width of 74 ± 10 µm, with tapered or sometimes rounded basal tip ( Fig. 3c ), curved toward primary cystid appendage (Fig. 8d). Polypide with 9 tentacles (Fig. 10c) and low-positioned lophophoral anus (Fig. 7c). Opposite branching from the primary cystid appendage common (Fig. 9e). Up to three secondary cystid appendages form in middle sections of the zooids. Tubulets may be present or absent. Intercalary kenozooids may connect primary or secondary cystid appendages. Sac zooids typically bulb shaped and overall 1/3 size of autozooid.

Description – Immergentia cf. suecica from Norway (Figs. 7d, 7e, 9b and 10d): Borehole apertures oval shaped and enantiomorphic (Fig. 9b) with average width of ◂ Fig. 6 Semi-thin histological serial sections of Immergentia stephanieae sp. nov. from Roscoff, France. a Apertural area of zooid (arrow) vestibulum and parieto-vestibular muscles. b Transition of the pharynx to oesophagus. Retractor muscles and caecum are visible. c Autozooids with ten tentacles. Transition into mid-gut. Arrow indicates circular muscles of cardiac constrictor. d Longitutinal section of autozooid. Cerebral ganglion at lophophoral base. e Same zooid as b & c. Caecum and intestine. Lateral cilia of tentacles. f Circular muscles of cardiac constrictor. g Autozooid with nine tentacles. Abbreviations: ap – aperture, bb – brown body, bc – body cavity, cae – caecum, cg – cerebral ganglion, cst – cardiac constrictor, cw – cystid wall, es – oesophagus, int – intestine, izs – interzooidal septum, lb- lophophore base, lc – lateral cilia, ph—pharynx, pm – parietal muscles, pvm – parieto-vestibular muscles, rm – retractor muscle, t – tentacles, ts – tentacle sheath, v – vestibulum

45 ± 9 µm. Zooids regularly and broadly spaced (Fig. 9b) at intervals measuring 952 ± 365 µm. Autozooids typical vase shape, length 303 ± 25 µm and width 100 ± 32 µm, with tapered or sometimes rounded basal tip, curved toward primary cystid appendage. Polypide with 9 tentacles (Fig. 10d) and low-positioned lophophoral anus (Fig. 7d, e). Up to three secondary cystid appendages form in middle sections of the zooids with thinner processes extending from primary appendages. Tubulets may be present or absent. Intercalary kenozooids may connect primary or secondary cystid appendages. Sac zooids typically bulb shaped and overall 1/3 size of autozooid.

Remarks: Direct measurements of I. suecica was done on 4 zooids, one of these zooids was small compared to the others and is presumably a developing zooid. These were embedded and sectioned for histological analysis. The presence of intercalary zooids is confirmed.

Silén (1947) described the colony morphology of I. suecica as an intermediate between that of I. californica and I. zelandica . Which means that I. suecica may have sections where zooids along the primary cystid appendage may occur at regular intervals as seen in I. cf. suecica from Norway (Fig. 9b) and lateral intercalary kenozooids/cystid appendages arise at irregular intervals in I. cf. suecica from France (Fig. 9e). Unfortunately, the colony morphology of I. suecica could not be determined because the substrate was fragile and eroded. The cystid appendages were also not visible from the shell substrate. DNA sequences were not recovered because material was fixed in Bouin’s and/or Flemmings’ solutions, that disrupt DNA. Therefore, we need to rely on the original descriptions and illustrations. Here, opposite and irregular branching patterns of lateral cystid appendages and/or intercalary kenozooids occur, differing from the type I. californica , where branching alternates in either direction (see Silén, 1947, p. 41, fig. 58).

In specimens from both France and Norway the primary cystid appendage may or may not bare tubulets. Similarly, intervals between zooids are up to two or three times greater than those in I. stephanieae sp. nov. Scaled drawings of I. suecica from Sweden (the type locality) by Silén (1947) permitted comparison of interzooidal intervals and zooid size with specimen examined here. Interzooidal intervals based on scaled drawings of I. suecica (five zooids) by Silén (1947, fig. 60) and reproduced by Prenant and Bobin (1956, p. 230, fig. 100, colony III) measured at 931 ± 177 µm, I. cf. suecica from France, 917 ± 175 µm and I. cf. suecica from Norway, 952 ± 365 µm.

Zooid size of I. cf. suecica from France resembles the sizes from the I. suecica measured here. However, this value is slightly smaller than those from illustrations of Silén (1947) and Hayward (1985). The autozooid size for I. suecica varies greatly between authors. Considering measurements from illustrations in literature, I. cf. suecica from France had a size range close to that of I. suecica by Hayward (1985, p. 105 drawing A) length 200 ± 18 µm and width 97 ± 13 µm but these measurements were based on two zooids. On the other hand, I. cf. suecica from Norway had a length range of 303 ± 25 µm comparable to the type I. suecica 310 – 340 µm illustrated by Silén (1947; see Table S5). According to illustrations from Prenant and Bobin (1956, p. 230) reproduced from Silén (1947, figs. 60 and 61) the measurements were as follows: five autozooids (image III) length 305 ± 43 µm and width 89 ± 13 µm; (image IV) length 444 ± 24 µm and width 141 ± 9. No zooids exceeding 400 µm has been observed here. It is important to consider that size differences can be attributed to improved precision with modern tools or the reproduction of images and scales from Silén’s original work as opposed to measurements of fresh material. In fact, the scale bar for the colony (image IV) varied from our measurements by about 50 µm.

The anus position of I. cf. suecica differs from that of I. suecica , which was reported to have a vestibular anus (see Schwaha, 2020c). It is important to note that the latter was based on the illustrations and descriptions from Silén (1947), which may not be completely accurate, as pointed out by Schwaha (2020c), and a lophophoral anus is confirmed for I. suecica in the analysis of the type material.

Reverter et al. (1995) collected immergentiids from Château du Taureau in Roscoff but were not able to assign a species because specimens were dry. In this study, material was collected from the same location and other subtidal locations around Roscoff, confirming the presence of immergentiids. Differences in zooidal size between the specimen from France and Norway can also be attributed to a high sampling of samples from France (the main study site) and only one shell from Norway, which probably influenced variability. Apart from the obvious size differences, other characteristics of specimen from both locations were quite similar.

Since the attempt to redefine all characteristics from the type material and genetic verification of the species were unsuccessful, the placement of I. cf. suecica from France and Norway remain inconclusive and are therefore tentatively

◂ Fig. 7 3D reconstruction of immergentiid polypides from histological serial sections. a–b Overview of autozooids of Immergentia patagoniana (Locality: Burdwood Bank, south-western Atlantic). a Oral view of polypide. b Close up of typical digestive tract shape.The low positioned lophophoral anus retracted tentacle sheath. c Side view of lophophore and digestive tract of Immergentia cf. suecica (Locality: Roscoff, France). d Autozooid of Immergentia cf. suecica from Trodheim Fjord Norway. e Close up of digestive tract of the same autozooid f–h Overview of autozooid and digestive tract of Immergentia stephanieae sp.nov. (Locality: Roscoff, France) with 9 tentacles. f Orientation of lophophore and gut in the zooid, oral view. g Same zooid, anal view of digestive tract, with brown body proximal to caecum. The anus terminates in tentacle sheath close to lophophoral base. h Digestive tract of same zooid. Foregut consist of the mouth opening, pharynx and elongated oesophagus. Midgut comprises the cardia, caecum and pylorus. The hindgut is comprised of the intestine and anus. i Oral side of lophophore indicating pharynx, lophophore base and tentacles in Immergentia stephanieae sp. nov. with 10 tentacles. j Anal view of the same autozooid. Abbreviations: a – anus, bb – brown body, ca – cardia, cae – caecum, cw – cystid wall, ds – diaphragmatic sphincter, es – oesophagus, int – intestine, lb – lophophore base, ph – pharynx, pm – parietal muscles, py – pylorus, rm – retractor muscle, t – tentacles, v – vestibulum placed as I. suecica . Considering the condition of the type material, a neotype needs to be assigned. In addition, more material from Norway would also need to be obtained and analysed.

Immergentia patagoniana Pohowsky, 1978

Figures 8a–c, 9a and 10a, b

Figures

Fig. 1 Immergentia stephanieae sp. nov (Type locality: Roscoff, France; MNHN-IB-2017-721). a Living gastropod shell heavly bored by the immergentiid. Regular arragement of colony with interconnecting cystid appendages. b Close up of the borehole apertures and cystid appendages connecting neighboring zooids. c Typical branching pattern of regularly spaced colony. Enantiomorphic colony struc-

Fig. 3 Zooidal plasticity of Immergentia. a–d Zooids of immergentiids after decalcification of substrate. a Autozooids and sac zooid of Immergentia cf. zelandica (Locality: Inner Otago shelf, New Zealand). Zooid with slightly narrowed mid-zooidal region and elongated rounded basal end (arrow). b Autozooids and sac zooid of Immergentia pohowskii sp. nov. (Locality: Taiaroa Head, New Zealand). Several zooids with slightly narrowed mid- region (arrow). c Autozooids of Immergentia cf. suecica from France. d Zooidal plasticity of