Therenia peristomata, Berning & Tilbrook & Rosso, 2008

Berning, Björn, Tilbrook, Kevin J. & Rosso, Antonietta, 2008, Revision of the north-eastern Atlantic and Mediterranean species of the genera Herentia and Therenia (Bryozoa: Cheilostomata), Journal of Natural History (J. Nat. Hist.) 42 (21 - 22), pp. 1509-1547 : 1533-1535

Therenia peristomata new species

( Figure 7 )

Escharina hyndmanni: Norman 1909 , part: p. 302.

Differential diagnosis

This species differs from all other species in having a less densely perforated and slightly convex frontal wall, condyles that are more or less parallel to the proximal orifice margin and that do not extend beyond the shoulders of the sinus, and an avicularian crossbar with a thick, central, proximomedially directed columella.

Although T. porosa also has a peristome that encircles the entire orifice, it is rather flared and the exposed ooecium frontal is distinctly broader in T. peristomata . In contrast to T. cryptooecium , this species has a smaller primary orifice and especially aperture, while the ooecium is clearly visible at the colony surface. Primary orifice, aperture and avicularia are distinctly smaller in T. peristomata than in T. rosei .

Etymology

For its flaring peristome, which is especially well developed in early astogenetic autozooecia.

Material examined

Holotype: NHM 2007.10.9. 3, off Madeira, 75–90 m, on shell . Paratype: NHM 2007.10.9. 4, off Madeira, 75–90 m, on shell . Additional material: NHM 1911.10.1. 1203, off Madeira, 75–90 m, eight colonies on shells .

Measurements

ZL 632¡39, 567–718 (1, 19); ZW 535¡72, 437–651 (1, 19); OL 112¡7, 99–125 (1, 20); OW 132¡7, 114–143 (1, 20); ApL 119¡6, 103–125 (1, 12); ApW 149¡6, 140– 160 (1, 12); OvL 200¡16, 175–228 (1, 11); OvW 356¡23, 314–389 (1, 11); AL 133¡11, 118–152 (1, 20); AW 103¡11, 88–128 (1, 20); PD 7¡1, 5–9 (1, 15).

Description

Colony encrusting unilaminar, multiserial. Zooecia rhomboid, hexagonal or polygonal, separated by deep grooves; vertical walls with two small round communication pores per neighbouring zooid; frontal wall flat or slightly convex centrally, sloping towards zooecium margins, very finely granular, perforated by numerous small pseudopores and up to four larger but indistinct marginal pores. Orifice dimorphic, horseshoe-shaped, distolateral margin with a relatively broad immersed shelf; primary orifice in autozooecium slightly broader than long and widest at about mid-distance, proximal border slightly upturned and sloping towards sinus, which is shallow, widely U-shaped with rounded edges, and occupying little less than one-third of proximal margin, condyles as long as proximal orifice margin, narrowing and sloping at an increasing angle towards sinus; aperture in ovicellate zooecia slightly wider than in autozooecia, proximal border rather straight and slightly upturned, sinus shallow and distinctly U-shaped, comprising about one-fifth of proximal margin, condyles very narrow, sloping at an extremely acute but increasing angle towards sinus. Autozooecium orifice encircled by an orbicular and flared peristome, the relatively thin and low proximal wall rising and thickening distally, steeply sloping towards orifice; peristome in ovicellate zooecia reduced to a low and relatively thin proximal rim leading towards proximolateral ooecium edges.

Ooecium initially hemispherical, becoming largely immersed by frontal wall of distal zooecium and only slightly emerging from frontal plane; exposed frontal surface a curved, smooth, thickened rim sloping proximally.

Avicularium situated directly proximolateral to orifice and usually abutting the peristome on either left or right side, pseudoporous cystid level and continuous with frontal shield of zooecium; rostrum an orbicular to oval, broad, sloping band, laterally or distolaterally oriented, proximal opesium partly bounded by a very narrow, sickle-shaped, proximal shelf; crossbar thick and extending fairly deep into cystid, slightly curved and twisted along its axis, with a broad, thick, rounded and proximomedially directing columella.

An ancestrula was not observed, early astogenetic budding pattern may be similar to Herentia but periancestrular growth was disturbed and zooids were damaged in the only colony obtained.

Remarks

The original sample (NHM 1911.10.1.1203) contained specimens of both Therenia peristomata and H. andreasi , which Norman (1909) all identified as H. hyndmanni . Ironically, he did not notice the porous frontal wall in this species and instead considered the imperforate specimens as a curious variety of H. hyndmanni . Whether the species Cook (1968, p. 195) reported as Escharina porosa to occur at Madeira is, in fact, T. peristomata cannot be pursued at present because she neither figured nor described the specimens.

This species is remarkable in that it is the only one that has a rather convex frontal shield, indistinct condyles and an avicularian crossbar with a columella. These features make T. peristomata fairly distinct from the other species. On the other hand, the peristome, which entirely encircles the orifice, is also found in T. porosa , while the broad and slightly raised ooecium frontal is similar to that in T. rosei .

The only specimen with the periancestrular region preserved was unfortunately damaged during early astogeny ( Figure 7B ). Some proximal zooecia are overgrown or irregularly shaped, which makes it difficult to infer the early astogenetic budding pattern. However, the two 90 ° changes in growth polarity during early astogeny are shared with Herentia (see Figure 1B ).

As it has not been reported from any other region, T. peristomata seems to be geographically restricted to the archipelago of Madeira. The specimens were obtained from 75–90 m and encrust bivalve shells and other calcareous substrata .

Figures

Figure 1. Herentia hyndmanni (Johnston, 1847). (A, B) PMC.R.I.H.B-3c, Ionian Sea; (C, E, F) NHM 1899.5.1.1154, off Northern Ireland; (D) lectotype, NHM 1847.9.16.156, off western Scotland. (A) Kenozooidal ancestrula and first autozooecium; while the ancestrular gymnocyst is bored and damaged, we consider the central hole (arrow) as representing the remnant of an extremely reduced opesium; note the spine bases on the distal orifice margin of the autozooecium, the central pair of spines is already covered by the calcified rim encroaching the distal orifice margin; (B) ancestrula and early astogenetic colony; note the presence of a central hole in the ancestrula and the relatively proximally positioned avicularia in the autozooecia; (C) autozooecia and an ovicellate zooecium at the colony growth margin; note that in this and the other photos showing ooecia the vertical component, i.e. the distally raised ooecium hood, is understated; (D) general aspect of unbleached colony; (E) close-up of orifice and avicularium; (F) ovicellate zooecium; note slightly narrower condyles compared to those of autozooecia. Scale bars: 100 mm (A); 200 mm (B–D); 50 mm (E, F).

Figure 7. Therenia peristomata n. sp. Holotype, NHM 2007.10.9.3, off Madeira. (A) General aspect of zooecia at the colony growth margin; (B) early astogenetic zooecia showing a rather flared peristome; note that the ancestrula has been covered by the lowermost zooecia; (C) close-up of autozooecium orifice and avicularium; (D) ovicellate zooecium; note slight differences in condyle morphology to orifice of autozooecium. Scale bars 200 mm (A, B); 50 mm (C, D).