Immergentia zelandica Silén, 1946, p. 3

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 : 235-237

Immergentia zelandica Silén, 1946, p. 3 , figs. 11, 12

Material examined. SOUTH-WEST PACIFIC OCEAN• heavily bored shell of Buccinulum littorinoides Reeve, 1846 with immergentiid colony and decalcified zooids in the extra cellular matrix of gastropod; New Zealand; North Island , Slipper Island, depth: intertidal; 20 December 1914; Mortensen’s Pacific exped.; holotype, SMNH-Type-3065 .

SOUTH-WEST PACIFIC OCEAN• dense colony in shell belonging to Buccinoidea Rafinesque, 1815; New Zealand; South Island, Otago inner shelf, 45º45.87’S 170º49.50’E; depth: 40 m; 05 November 2021; ‘PB Otago Shelf’ cruise; inner Otago shelf characterized by sticks, mud, molluscs, crabs; NZ21PB10, gastropods 1, 2 & 3; GenBank : SAMN38786232 .

Description – Immergentia zelandica (Holotype): Borehole apertures circular with an average width of 87 ± 14 µm ( Fig. S 1g ). Most zooids with typical vase shape with a length of 249 ± 29 µm and width 59 ± 12 µm, basal end mostly rounded, few tapered, and may curve strongly in the mid-zooidal area toward primary cystid appendage or not at all ( Fig. S1h ). Few zooids with short projections at the basal end ( Fig. S1h ). Autozooids with 9 tentacles ( Fig. S1i ). Description – Immergentia cf. zelandica ( Figs. 3a , 9c, 8e, h and 10f): Borehole apertures circular or oval shape (Fig. 9c) with average width of 52 ± 6 µm. Zooids in the colony densely packed and irregularly placed. Basal end of zooids rounded, few tapered, and slightly curved toward primary cystid appendage or not at all ( Figs. 3a and 8e). Few zooids slightly narrowed at mid-zooidal region and elongated rounded basal end ( Fig. 3a ). Average length of zooids is 284 ± 38 µm and an average width of 85 ± 11 µm. Autozooids with 9 tentacles (Fig. 10f). Sac zooids vase shaped and overall 2/3 size of autozooid (Fig. 8h). Up to four secondary cystid appendages form in the middle to distal sections of zooids with thinner processes extending from primary and secondary appendages ( Figs. 3a and 8f). Reproductive zooid with a bulge to one side of the zooid (Fig. 8f).

Remarks: Zooids of I. zelandica were in a degraded state, and few structures of soft body morphology, such as tentacles, could be distinguished. The borehole apertures (87 ± 14 µm) are comparatively larger than the width of the zooids (59 ± 12 µm) but almost the size of the zooidal width (80 µm) initially reported by Silén (1947). Colony is densely packed and difficult to distinguish cystid appendages and measure interzooidal intervals. The primary cystid appendage may or may not bear tubulets. More than two secondary cystid appendages commonly observed than that of any other species in this study. Thinner processes occur proximally beyond mid-zooidal region, not observed in any other species. Zooids pinched in mid-zooidal region are less common than in I. pohowskii sp. nov. Fewer individuals with tapered basal tip compared to I. pohowskii sp. nov. Position of anus difficult to ascertain (Fig. 11f–j).

The zooid size range of both I. pohowskii sp. nov. and I. cf. zelandica from southern New Zealand sometimes exceeded 100 µm. Here, colony morphology of I. cf. zelandica closely resembles the description of the type I. zelandica characterized as a dense, irregularly placed colony, zooids with 9 tentacles and numerous processes extending from the zooids making it difficult to distinguish primary and secondary cystid appendages (see Silén, 1947). Both I. zelandica and I. cf. zelandica here have a similar size range approx. 249 and 284 µm respectively, while I. zelandica var minuta was slightly smaller 207–218 µm (Soule, 1950). On the contrary, type of I. zelandica , described from the intertidal zone in Slipper Island (north of New Zealand) had a zooid length 310 and width 80 µm. Immergentia cf. zelandica was collected from the subtidal zone, further south near Otago inner shelf. Pohowsky (1978) reported a minimum length of 210–250 µm for the species (measured from Soule, 1950), taking the length and width of I. zelandica var minuta into consideration, 207 – 218 and 48 µm respectively (see Soule, 1950). DNA sequences were not recovered from I. zelandica and zooids for histology were in a mushy state; therefore, the soft-body components could not be differentiated. Another possible explanation for the size variation could be that the zooids (stored in a decalcified state) shrank but this is purely speculative.

The drawings of I. zelandica do not depict the shape of zooid aperture (see Silén, 1947 fig. 62, p. 43), nor is it explicitly mentioned (only the general zooidal aperture shape typical of immergentiids is described). In this study the borehole aperture is oval to spindle shaped (Fig. 9c) similar to illustrations of I. zelandica var minuta borehole apertures (Soule, 1950 pl. 2 fig. 4, p. 365) from the Philippine Islands. In contrast, that of the examined type material is circular to oval. In Immergentia pohowskii sp. nov. and I. zelandica , the autozooids may be pinched with an elongated projection extending proximally from the mid-zooidal region. Though there are similarities between the type I. zelandica and I. cf. zelandica , the difference in aperture size, uncertain soft-body morphology of the type material, and difference in location and depth of collection (intertidal vs subtidal) casts doubts on whether these two species are the same.

General morphological characters of Immergentiidae

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