Family PHIDOLOPORIDAE Gabb & Horn, 1862

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Family PHIDOLOPORIDAE Gabb & Horn, 1862

Compiler and date details

July 2001 - Dr Philip Bock

Phidoloporidae Gabb, W.M. & Horn, G.H. 1862. The fossil Polyzoa of the Secondary and Tertiary Formations of North America. Journal of the Academy of Natural Sciences of Philadelphia 5: 111-179.
Reteporidae Smitt, F.A. 1868. Kritisk förteckning öfver Skandinaviens Hafs-Bryozoer. IV. Öfversigt af Kongelige Vetenskaps-Akademiens Förhandlingar, Stockholm 25: 3-230.
Sertellidae Jullien, J., & Calvet, L. 1903. Bryozoaires provenant des campagnes de l'Hirondelle (1886-1888). Résultats du Voyage du S.V. 'Belgica', Zoologie. Expedition Antarctique Belge 1 23: 1-188.
Hippellozoonidae Vigneaux, M. 1949. Révision des Bryozoaires néogènes du Bassin d'Aquitaine et essai de classification. Mémoires de la Société Géologique de France, n.s 28: 1-153.
Schizoreteporinae Gregory, J.W. 1893. On the British Palaeogene Bryozoa. Transactions of the Zoological Society of London 13: 219-279.
Rhynchozooninae Vigneaux, M. 1949. Révision des Bryozoaires néogènes du Bassin d'Aquitaine et essai de classification. Mémoires de la Société Géologique de France, n.s 28: 1-153.

Introduction

The Phidoloporidae includes the forms with erect fenestrate colonies, known as 'lace corals' (with the exception of the cyclostome species Hornera foliacea ), and also a number of encrusting forms in the genera Rhynchozoon, Stephanollona, and Schizotheca (not known from Australia). There are no characters which define the entire family: characteristic characters include a denticulate distal margin of the orifice; a lip of the ovicell termed the labellum, and a variety of markings on the frontal of the ovicell Harmer (1934), Hayward (1999), Hayward (2000).

The family Phidoloporidae was introduced by Gabb & Horn (1862) for a Miocene fossil species from California, Phidolopora labiata. Curiously, these authors included two other genera in the family, both free-living lunulites, Oligotresium and Selenaria. The family has been known by other names in the past, and species have been commonly called reteporids, after the Lamarckian name Retepora. On the basis of its subsequently chosen type species, Retepora is actually a cyclostomatous bryozoan genus, but in any case the name is a junior homonym of a protozoan genus and cannot be used. Surprisingly, these details were largely overlooked and the names Retepora and Reteporidae have continued to be used, even as recently as the 1980's, partly because of their use in Bassler (1953). Other workers have used the names Sertella and Sertellidae, following Jullien & Calvet (1903), but Phidoloporidae has priority, and Sertella is here regarded as a junior synonym of Reteporella (Gordon 1989).

Phidoloporids are among the best-known and most easily recognised bryozoans. A phidoloporid was figured as 'Eschara marina' by Imperato in 1559. The most conspicuous and attractive species are erect and fenestrate, like stiff lace, and are often called 'lace corals' (Dakin & Bennett 1987). In addition, not all species are white, many being yellow, orange, pink and violet or deep purple (Bock 1982; Colin & Arneson 1995; Gosliner et al., 1996). Not all phidoloporids are erect or lacy, there being an increasing number of genera assigned to the family which are encrusting. The outstanding features that unite all phidoloporids are primarily zooidal, not colonial.

The zooidal frontal shield is typically smooth and porcellanous, although it may sometimes be mamillate, dimpled or otherwise textured. There are a few small septular pores marginally. The primary orifice in the vast majority of the genera has a distinctive 'beading' around the inner distal rim, beneath the edge of the closed operculum, which must be removed to see it. In erect genera, the orifice is usually concealed by a peristomial complex. Oral spines are present, and may be 'antenniform' (Harmer 1934), or entirely absent. One or more oral avicularia are usually present, as are larger adventitious avicularia elsewhere on the frontal shield. In fenestrate forms. very large avicularia may be associated with branch axils and fenestrae. After the beaded orifice, the second typically phidoloporid character is found on the frontal side of the ovicell. This is a descending process or tongue (the labellum), which overhangs the orifice. The frontal may also have a fissure, a suture, or even a broad opening. Ovicells and frontal shields can become covered over by secondary calcification, and all characters are best seen at the growing edge of a colony.

Frontal-shield development varies in the family. It appears that most genera have a lepralioid shield but two, Reteporella and Malleatia, are umbonuloid. The early astogeny of erect colonies has been described by Harmer (1934). Depending on the genus, the ancestrula is tatiform, with a circlet of spines around the opesia (eg. Reteporella), or has a calcified frontal shield and even a peristome (eg Iodictyum). The ancestrula becomes surrounded by primary and secondary autozooids, but by the time a young colony has about 20 zooids and is around 20 mm across, it buds kenozooids which start upward growth simultaneously at several loci, which when further developed, will form the base of a chalice-shaped colony. Alternatively, fewer loci will result in the development of open-branched colonies that grow mostly in one plane. Further growth includes proliferation of kenozooidal and multizooidal calcification round the base of the colony. Colonies can be up to 100 mm or more tall, and the basal side of branches are lined with a layer of kenozooids, some of which may bear avicularia (Banta 1977). The boundaries between the kenozooids have slightly raised lines, called vibices.

The erect phidoloporid colony represents a considerable degree of colonial integration, in which zooidal features are subjugated to those of the colony as a whole (Boardman & Cheetham 1973). The benefits of integrated behaviour are seen in enhanced channelling of incurrent and excurrent water flow. A chalice-shaped fenestrate colony, that may also be folded and scrolled, has incurrent flows through the inner, zooidal surfaces and excurrent flows through the fenestrate openings (Winston 1979; McKinney 1990). In colonies where the zooidal surfaces face outward, the flows are reversed (Cook 1977). In encrusting phidoloporids, colonies may be hummocky or mounded in such a way as to channel excurrent flows from areas of non-feeding zooids which form chimneys (Winston 1979).

Because of the similar colony form among erect forms on the one hand, and encrusters on the other, identifying phidoloporids can be very difficult, especially as zooids can be fairly small in erect forms and key taxonomic characters rely on details of the orifice, ovicells, and avicularia. In erect forms especially, the operculate orifice (primary orifice) tends to be concealed at the bottom of a peristomial shaft. The rim of the peristome is variously modified. It may be crenulated, with marginal spines, an anvil-like lyrula, and a labial groove and pore. The latter are formed when the proximolateral edges of the developing peristome grow towards each other and incompletely fuse. Avicularia are also very variable, and several different kinds can occur in a single colony. Some are small, and may be associated with the peristome or occur on the frontal shield and/or dorsal surface. Some are large, and may occur in the same locations and especially on the lateral faces of the fenestral slits in lacy colonies. Avicularia may be round, triangular, or linguiform in shape, or munitiform - oval with the rims like a pair of opposing lips. Crossbars occur on all avicularia, and the lateral edges of the rostrum onto which the mandible closes may be toothed. The mandible itself may be simple or forked.

Some phidoloporids are white (Phidolopora avicularis and some Iodictyum), but the majority of colonies have brilliant pigments, which are also found in skeletal tissue. Colonies tend to be free of epibiota, but some enter into close associations with other organisms. Thus some colonies can be heavily infested with commensal loxosomid entoprocts (Harmer 1934), whereas others have an intimate symbiotic relationship with zancleid hydroids. In the latter case, frontal calcification of the bryozoan can occur over the stolons to protect them (Hastings 1932; Ristedt & Schumacher 1985). Phidoloporids range from the intertidal, especially species of Rhynchozoon, to over 4000 m depth (e.g. Reteporellina); overall, most species occur in relatively shallow water to shelf depths. Colonies occur mostly on rock faces, molluscan shell gravel, and other hard substrata, less commonly on algal holdfasts and sea grasses.

The Phidoloporidae is a large family. There are more than 22 genera and some of these are very speciose, like Rhynchozoon. There are some 66 species in Australian waters, and the total is constantly increasing (Ryland & Hayward 1992, Hayward & Ryland 1995, Hayward 1999, 2000). Australian and other tropical and temperate species previously assigned to the boreal-arctic genus Hippoporella appear to require a new genus.

The genus Stephanollona, a senior synonym of Brodiella (Gordon 1984) has encrusting colonies with a broadly cleithridiate orifice with a beaded distal rim. The ovicell does not have a labellum but has a small triangular frontal area. There are one or two lateral suboral avicularia with a ligulate bar. Several species from southern Australia appear to belong to this genus, including the common form described as Hippoporella orbicularis (Hincks) by Bock (1982).

Plesiocleidochasma normani (Livingstone) is common on the reef flat at Heron Island (Hayward & Ryland 1995). It has characteristic porcellanous frontal calcification, a broadly cleithridiate, smooth-rimmed orifice, and large lateral avicularia. Its ovicell is clearly of the phidoloporid type, however, with a labellum, and it was referred to that family by Gordon (1993).

Species included in Sertella can be referred to Reteporella; the distinction, made on the basis of colony form, having no consistent correlation in zooidal and ovicellular characters.

Hayward (1995) described nine species of Reteporella from the Antarctic. One of these, R. frigida (Waters), has colonies more than 150 mm high and wide, and its maximum size is unknown.

The origin of the family is not known. The oldest records are doubtfully earliest Paleocene and certainly Upper Eocene (Taylor, 1993). Phidoloporids are an important component of the fossil fauna of the Upper Eocene to Miocene of southeastern Australia. On the basis of the two kinds of frontal shield occurring in the family, it probably originated from umbonuloid-shielded ancestors in the latest Cretaceous or early Paleocene.

Specimens in the QM thought to represent the genus Schedocleidochasma Soule, Soule & Chaney, 1991 have been found in Queensland, but have not been identified to species level.

Diagnosis

Colony well, sometimes heavily calcified, occasionally encrusting and mammiliform, usually erect, arising from a small encrusting base, unilaminar and fenestrate. The zooids are rigidly patterned in fenestrate colonies, and may be brightly pigmented. All frontal shields are lepralioid, and usually smooth, with a few marginal areolae. The primary orifice is often sinuate, and nearly always has a denticulate ('beaded') distal border. Avicularia are adventitious and oral, or very large and associated in position with a fenestra. The ovicell is prominent and hyperstomial, with a frontal suture or fissure, and a proximal tongue (labellum) overhanging the orifice.