Triphyllozoon mauritzoni Silén, 1943

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 : 70-73

Triphyllozoon mauritzoni Silén, 1943

( Figs 38 , 39 ; Table 34)

Triphyllozoon mauritzoni Silén, 1943: 89 , figs 1–10.

Material examined. Lectotype (designated here) LUZM 57 a, Great Barrier Reef, Heron Island , Australia. Leg. Dr J. Mauritzon 1936 . Paralectotypes: LUZM 57 b, c, same details as the lectotype . LUZM 57 a ( Fig. 38 , 2.2 × 2.4 mm, unbleached) correspond to the specimen on the right-hand side of fig. 1 in Silén (1943) ; LUZM 57 b ( Fig. 39 , 2.7 × 1.8 mm, bleached) and LUZM 57 c (not illustrated, 1.8 × 1.2 mm) seem to be the result of fragmentation of the specimen on the left-hand side of fig. 1 in Silén (1943) .

Description. Colony erect, rigid, reticulate, with a wavy surface; fenestrae oval ( Figs 38A, B, H , 39A, F ), 0.47–0.77 × 0.30–0.42 mm, and trabeculae consisting of 2–10 alternating autozooidal series, more commonly 4–5 ( Figs 38F , 39C, D ).

Autozooids rectangular to hexagonal, longer than wide (mean L/ W 1.51), either distinct, with boundaries marked by thin furrows and/or raised margins of smooth calcification ( Figs 38C, D, F , 39B, D ), or sometimes indistinct ( Fig. 39B ); frontal shield generally smooth ( Fig. 39B, C ) except for recently budded zooids at the tips of the branch ( Fig. 39D ) and areas around the fenestrae appearing finely granular to tubercular, flat to slightly convex, imperforate except for a few sparse, round, elliptical or slit-like pores along the lateral and proximal margins, 15–25 µm in diameter/length ( Fig. 39B, C ).

Peristome deep, forming a raised collar proximally and laterally almost completely hiding the orifice in frontal view, and with a deep (55–80 µm) drop-shaped pseudosinus proximally ( Figs 38D , 39B ); peristomial avicularium (type 1) present in each completely developed zooid, elliptical, embedded in the peristome and placed horizontally, rostrum slightly raised and denticulate, directed laterally, mandible semielliptical, crossbar complete ( Fig. 39C ); at least 1–2 oral spines always visible in each autozooid, even if ovicellate, 7–20 µm in diameter at the base, up to 4–5 spines visible around the distal margin of the orifice of autozooids placed at the growing tip of the branches ( Figs 38E , 39C, D ); secondary orifice subelliptical. Primary orifice visible on tilted autozooids with incomplete peristome at the growing tip, elliptical with denticulate anter, a pair of short triangular condyles, and a short, rectangular median process occupying most of the proximal margin and outlining two small indentations, 65 µm long by 90 µm wide ( Figs 38E , 39D ).

A medium-sized, adventitious, frontal avicularium (exceptionally two) developing in some autozooids, parallel-sided elliptical or with slightly spatulate rostrum (mean L/ W 1.72; type 2), placed on the proximal zooidal corner or medially and directed proximally, or placed at mid-length on one side and directed laterally, with a slightly raised, smooth rostrum and semielliptical mandible ( Figs 38D, F , 39B, C ), crossbar complete. Rarely, a type (3) larger avicularium, placed on the frontal of zooids adjacent to the fenestrae, with tricuspid rostrum directed proximally, and bicuspid mandible (mandible length 187 µm) ( Fig. 38C ). On the dorsal side adjacent to some of the fenestrae two types of avicularia are present, the same type (2) observed on the frontal shield of autozooids and a type (4) small, circular avicularium (mean L/ W 0.98), randomly directed with semicircular, denticulate rostrum and complete crossbar ( Figs 38H, I , 39F ).

Ovicell hyperstomial, prominent; ooecium flat frontally, almost as wide as long (mean L/ W 1.04), tubercular, with Y-shaped dentate suture ( Figs 38G , 39C ); relative length of the median and lateral sutures variable, with some ooecia having longer and others having a shorter median suture than lateral sutures; median suture 90–145 µm long, lateral sutures 65–115 µm long; lateral sutures of different length in the same ooecium, diverging at 125–130°. Labellum short and square.

Dorsal side evenly and densely granular (granules diameter 5–10 µm), with raised vertical and oblique vibices (10 µm wide) outlining irregularly polygonal sectors; avicularia rare, of two types (described above), and mainly on the inner areas around the fenestrae ( Figs 38H , 39F ); the dorsal side near the encrusting base characterised by smaller rectangular sectors with several areolar pores along the margins, and constantly at least one (often more) small circular avicularium ( Fig. 39E ); pillar-like kenozooidal, tubular projections developing perpendicular or obliquely from the dorsal side ( Fig. 38I ).

Remarks. Specimen LUZM 57a was designated here as the lectotype because of the unique presence, although rare, of the large frontal avicularia with tricuspid rostrum and bicuspid mandible, developed only on autozooids placed adjacent to the fenestrae. Those avicularia were not observed in the paralectotypes.

In the original description of this species, Silén (1943) remarked on the absence of oral spines. However, 1–2 spines are always present ( Figs 38C, D , 39B, C ), even in ovicellate zooids ( Fig. 39C ), while autozooids at the growing tip of the branches show 4–5 spines ( Figs 38E , 39D ) that are gradually covered by the calcification spreading from the areolar pores of the distal zooids.

Figures

FIGURE 2. Amphiblestrum crassispinosum (Silén, 1954). Lectotype (designated here) LUZM 50a, Western Australia. A. General view of the colony encrusting an alga. B. Close-up of the opesia, with the two robust distolateral spines, and the ooecium. C. Tilted view of ovicellate zooids showing the length of the spines and the aviculiferous suboral mucro, broken in some zooids. D. Frontal view of ovicellate zooids showing the suboral aviculiferous mucro of the distal zooid resting on the ooecium. Scale bars: A = 500 µm; B = 150 µm; C, D = 250 µm.

FIGURE 38. Triphyllozoon mauritzoni Silén, 1943. Lectotype (designated here) LUZM 57a (unbleached),Australia.A. General view of the frontal surface. B. Group of autozooids. C. Close-up of an autozooid with large frontal avicularium with bifurcate rostrum and mandible. D. Close up of an autozooid with elliptical frontal avicularium. E. Close-up of the primary orifice. F. Group of zooids, one ovicellate. G. Close-up of the ovicell in (F). H. General view of the dorsal side. I. Dorsal side with basal pillars. Scale bars: A = 1 mm; B, F, H, I = 500 µm; C = 200 µm; D, G = 150 µm; E = 50 µm.

FIGURE 39. Triphyllozoon mauritzoni Silén, 1943. Paralectotype LUZM 57b (bleached), Australia. A. General view of the frontal surface. B. Close-up of autozooids. C. Group of zooids, one ovicellate. D. Autozooids at the growing edge showing a denticulate anter and up to five spine bases. E. General view of basal kenozooids. F. General view of the dorsal side. Scale bars: A = 1 mm; B, D = 150 µm; C = 250 µm; E, F = 500 µm.