Family ROMANCHEINIDAE Jullien, 1888

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Family ROMANCHEINIDAE Jullien, 1888

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Romancheinidae was introduced by Jullien (1888), but has been little used subsequently. The similarities between the genera Romancheina, Exochella, Escharoides and Escharella, among others, has been demonstrated, for example by Gordon (1989) and by Hayward (1995). As a result, the families Escharellidae Levinsen (1909) and Exochellidae Bassler (1935) are included in the present concept of the Romancheinidae. The family includes the genera Allereschara, Escharella, Escharoides, Exochella, Hellerasca, Antarcticaetos, Lageneschara, Pseudosclerodomus (provisionally; Gordon 1988) and Romancheina (Gordon, 1989).

Colonies are encrusting or erect. The zooid frontal shield has either a single or a double row of marginal pores, and is generally imperforate centrally. The calcareous frontal shield is umbonuloid, with a hypostegal coelom between the outer surface of the calcified frontal and the cuticular external wall. The orifice is orbicular or semicircular, and usually lacks clear demarcation of the poster and anter; a flat proximal projection (lyrula) may be present in the primary orifice of some species. Several spines develop from the distal lip of the orifice. Secondary calcification around the orifice forms a well-defined peristome, which usually includes an internal central proximal tooth or projection. This may be confused with the lyrula seen in the primary orifice. The avicularia are lateral to the orifice (in Escharoides), or lateral to the zooid (in Exochella), or absent (in Escharella). Pore chambers are well developed in Escharella and Exochella, but have not been observed in Escharoides. In Lageneschara and Antarcticaetos zooidal budding occurs from multiporous mural septula (Hayward 1995). The ovicells are hyperstomial, either prominent or immersed in the distal zooid, and are imperforate centrally with a variable number of marginal pores.

The umbonuloid development of the frontal in Escharoides and Exochella was indicated by Hayward & Ryland (1979). Gordon subsequently (1989) demonstrated that species of Escharella also have umbonuloid development.

As is the case with many species which have small encrusting colonies, there is little distinction between early and later astogenetic stages. Ancestrulae that have been described are tatiform, with a ring of marginal spines. Fertile zooids appear in early stages of colony growth. In some species the colony may contain scattered fertile zooids, whereas in other species there may be a high proportion of fertile zooids. Zooid ontogeny is rapid, so that early stages of calcification are only seen in a few zooids at the growing margins of the colony. Frontal calcification, the growth of the peristome, and the complete development of ovicells is seen within one or two generations from the margin.

Secondary thickening by calcification of the frontal shield is minor, proceeding with rapid development of the paired lateral avicularia. Almost all zooids develop ovicells very early in the ontogeny of the zooid. The calcification is semi-transparent.

The entirely southern hemisphere genus Exochella is represented by five endemic Antarctic species, and rather more temperate or subantarctic species. E. conjuncta Brown is the only species with a temperate to tropical distribution, and ranges from New Zealand north to Queensland (Ryland & Hayward 1992). E. tricuspis (Hincks) has a wide distribution, including Bass Strait, encrusting shells. E. munita (MacGillivray) is also found in Bass Strait. This species has been placed in synonymy with E. tricuspis, but is distinct.

The earliest record of romancheinids from Australia was by MacGillivray (1860), who described Escharoides excavata (as Lepralia excavata) from Queenscliff. The accompanying illustration was not very accurate, and this has led to the erroneous identification of this species from many areas of the Indo-Pacific. Preliminary study suggests that E. excavata has a distribution restricted to the Port Phillip area; the identity of other samples described as E. excavata is not known at present. Levinsen (1909) may have had a sample of the same species. The tropical Escharoides longirostris Dumont occurs in the Great Barrier Reef (Hayward & Ryland 1995). The majority of Australian species encrusts hard substrata, particular bivalve shells, coral rubble, etc.

Escharella has a worldwide distribution, including polar seas. The genus is distinguished from the other romancheinids described here, principally in lacking avicularia. The peristome typically bears a prominent suboral mucro, and there is a conspicuous tooth, the lyrula, within the orifice, the size and shape of which is characteristic for each species. Oral spines are usually present and their number is again a good specific character. Three species of Escharella are known from Australia, including the widely distributed, cold temperate E. spinosissima (Hincks), described by Gordon (1989). E. diaphana (MacGillivray) is characteristically found encrusting flexible algal substrata, and the calcification between the zooids is deficient, allowing flexibility of the colony. Two species of Escharella, E. mamillata and E. watersi, are found on hard substrata from the Antarctic and subantarctic (Hayward 1995).

Two Antarctic genera, Lageneschara and Antarcticaetos, develop erect folded plates and twiggy, branching growths. L. lyrulata (Calvet) has a broad lyrula but lacks spines. Its very large zooids (1-2 mm long) form broad sheets or erect, brittle plates which may later develop compact coralline structures. A. bubeccata (Rogick) is a distinctive Antarctic endemic which has erect, narrow branched growths, dividing by regular dichotomy. Its most striking feature is its massive, hooked, lateral oral avicularia (Hayward 1995). On the other hand, two species of Romancheina are encrusting, forming small patches or thick, irregular crusts on hard substrata.

Fossil romancheinids are common in Australian Tertiary sediments, beginning in the Late Oligocene. The earliest species may be from the Santonian of Europe (Taylor 1993).

Diagnosis

Colony encrusting forming sheets, or erect, branched, moderately to well-calcified. Zooids with umbonuloid frontal shield and large, marginal areolae. Orifices with raised peristome, often with a proximal tooth and distal spines. Avicularia often oral, paired, sometimes large. Ovicells hyperstomial, with pores frontally, becoming immersed.