Triphyllozoon regulare Silén, 1954

Martino, Emanuela Di, 2023, Scanning electron microscopy study of Lars Silén’s cheilostome bryozoan type specimens in the historical collections of natural history museums in Sweden, Zootaxa 5379 (1), pp. 1-106 : 76-78

Triphyllozoon regulare Silén, 1954

( Fig. 41 ; Table 36)

Triphyllozoon regulare Silén, 1954: 32 , fig. 14, pl. 2, fig. 10.

Material examined. Holotype by monotypy LUZM 55 , off NE of Rottnest Island, Western Australia; depth 18–46 m. Leg. Prof. T. Gislén , Australia Expedition 1951–1952, collected 27.11.1951.

Description. Colony erect, rigid, reticulate; holotype specimen fragment 2.5 × 1.5 cm; fenestrae oval, 0.70– 0.85 × 0.48–0.62 mm, and trabeculae consisting of 2–5 alternating autozooidal series, more commonly three ( Fig. 41A ).

Autozooids rectangular to flask-shaped, longer than wide (mean L/ W 1.87), distinct with boundaries marked by raised margins; frontal shield tubercular, flat to slightly convex, imperforate ( Fig. 41B ).

Peristome forming a raised collar around the orifice with a deep, median suture (90–120 µm long) terminating in a small, teardrop-shaped pseudosinus ( Fig. 41B, C ); peristomial avicularium (type 1) placed horizontally on one lobe, elliptical, with denticulate rostrum directed laterally ( Fig. 41D ); two lateral oral spines constantly present, an additional distolateral pair visible only in a few autozooids ( Fig. 41G , see arrow); spine diameter at the base about 30 µm, tapering distally (about 5 µm at the tip), ‘telescopic’-like ( Fig. 41D ), 60–65 µm long when complete; secondary orifice elliptical.

Frontal avicularia uncommon, two types recognizable: type (2) small, elliptical avicularium with slightly spatulate rostrum directed proximally, and mandible semielliptical, placed immediately below the pseudosinus and leaning more on one side ( Fig. 41B , see arrow); type (3) larger, pear-shaped avicularium with channelled rostrum directed proximolaterally, mandible triangular, cystid raised occupying the proximal half of the autozooid ( Fig. 41E, F ). The largest avicularium found adjacent to the fenestrae (type 4), either placed proximally and horizontally directed laterally or placed proximolaterally and obliquely directed proximolaterally, pear-shaped with bicuspid rostrum and triangular mandible with hooked tip pointing downward, slightly exceeding the length of the rostrum (mandible length 250 µm; rostrum length 220 µm) ( Fig. 41A see arrows, E, G). On the dorsal side a limited number of type (5) medium-sized avicularia, similar to type (2) on the frontal but with a more spatulate rostrum, usually placed near the fenestrae and randomly directed with spatulate mandible ( Fig. 41H–K ). All avicularia with complete crossbar.

Ovicells not observed.

Dorsal side coarsely granular (granules diameter 10–20 µm), with vertical and oblique vibices (10–25 µm wide), outlining irregularly polygonal sectors, and a limited number of avicularia as described above commonly adjacent to the fenestrae ( Fig. 41H ).

Remarks. Silén (1954) considered the small size of the fragment and the lack of ovicells as issues against the description of a new species. Eventually, the author decided to introduce the new species because of the unique set of avicularia observed. Similar giant avicularia at the bottom of the fenestrae were described in T. inornatum Harmer, 1934 , while similar peristome and secondary orifices were seen in several species of the genus such as T. mucronatum Harmer, 1934 and T. bimunitum Harmer, 1934 . As the other species of Triphyllozoon described by Silén (1943, 1954), Triphyllozoon regulare has never been reported in the literature since its first description. However, 12 occurrences of T. regulare are registered in GBIF (https://www.gbif.org/occurrence/map?taxon_key=1004915 accessed 31.10.2022) from six localities along the western and southern coast of Australia.

Figures

FIGURE 41. Triphyllozoon regulare Silén, 1954.Holotype LUZM55,WesternAustralia.A.General view of the colonyfragment. Arrows indicate the large avicularia adjacent to the fenestrae. B. Group of autozooids, one with elliptical frontal avicularium. C. Close-up of a secondary orifice lacking the peristomial avicularium. D. Close-up of a secondary orifice showing the peristomial avicularium with denticulate rostrum and two ‘telescopic’ lateral spines. E. Autozooids with large frontal avicularia. F. Closeup of the frontal avicularium. G. Close-up of the large frontal avicularium usually located at the fenestra. H. General view of the dorsal side. I. Close-up of a dorsal avicularium and tuberculation. J, K. Close-ups of dorsal avicularia with closed and open mandibles. Scale bars: A = 1 mm; B, G = 200 µm; C, D, I, J, K = 50 µm; E = 250 µm; F = 100 µm; H = 500 µm.