The suborder Thecata contains families in which the feeding and reproductive zooids as well as the stem and rooting system are protected by a chitinous perisarc in contrast to the Athecata, where the zooids are usually naked. Thecate hydroids in general are larger and more conspicuous than athecates, and the former suborder has the greater number of species. For this reason, the New Zealand thecate hydroids are being revised before the athecates. Elsewhere, for example, North America and Britain, thecate hydroids are well known and have been monographed either in toto, or at the family level. Such is not the case in New Zealand. Records of the known species are scattered throughout the literature. It is convenient here to review the literature of our hydroids, as the thecate hydroids make up by far the greater part of our hydroid fauna.
The pioneer era in this country coincided with the time when shore collecting was in vogue for the amateur naturalist as well as the professional scientist, and much hydroid material was classified in this early period, 66 species being described between 1843 and 1896. Hutton, Coughtrey, Hilgendorf and Farquhar wrote mainly for New Zealand journals, but a number of papers were written by workers outside New Zealand and published overseas.
In just over 100 years of publication only 2 check lists of the hydroids have been made, namely those of Farquhar (1896) and Hutton (1904). Bale (1924), however, briefly reviewed the literature, recognised 9 new species, reduced others to synonymy, and redescribed several species hitherto imperfectly known. Totton (1930) in the “Terra Nova” Reports, described 27 new species and also determined the status of other imperfectly known species, and Ralph (1953) gave a key to the species of athecate hydroids and their medusae.
The first account of New Zealand hydroids was by Gray (1843) in Diffenbach's “Travels in New Zealand”. Nearly ten years passed before Busk (1852) recorded Sertularia elongata Lamouroux in his report of the Polyzoa and Sertularians collected on the voyage of the H.M.S. “Rattlesnake”. No precise locality is given for this
species, but it is probable that it came from the Bay of Islands as the ship spent a week in this locality. Another twenty years passed before Hutton's paper (1873) appeared in the Transactions and Proceedings of the New Zealand Institute. In this period many papers by various authors appeared—viz., Carter (1873); Coughtrey (1875, 1876 and 1876a); Allman (1876, 1885 and 1888); Kirchenpauer (1864, 1872, 1876 and 1884); D'Arcy Thompson (1879); von Lendenfeld (1885 and 1886); Bale (1882, 1884, 1886 and 1889); Hamilton (1883); Marktanner-Turneretscher (1890) and Farquhar (1895). Of all these papers only those by Coughtrey, Hamilton and Farquhar exclusively concern New Zealand hydroids. All hydroid species and their synonyms, etc., known prior to 1896 are given in Farquhar's check-list of that year. Two years later Hilgendorf (1898) described “Hydroids from the neighbourhood of Dunedin,” and in 1901 Hartlaub reported species from various localities round the New Zealand coast in his “Hydroiden aus dem Stillen Ocean”. A paper by Dendy on Pelagohydra mirabilis, the only pelagic hydroid of the fauna, was published in 1902. This early period of relatively extensive research could be said to end with the publication of the hydroid section in Hutton's (1904) “Index Faunae Novae Zealandiae”.
Between 1904 and 1924 Bale referred briefly to some New Zealand hydroids in his papers on Australian hydroids in the Proceedings of the Royal Society of Victoria and in F.I.S. “Endeavour” reports from the same country, and Hilgendorf (1911) compares a few thecate species from the Kermadec Islands with New Zealand material. H. B. Kirk (1915) described a new species, Ascidioclava parasitica, from the pharyngeal region of a tunicate, and in 1917 Jaderholm noted 10 species from New Zealand in his “Hydroids from the South Seas”. Bale's 1924 paper is referred to above.
More recent publications are Findlay (1928) “Notes on New Zealand and Australian Gymnoblastic hydroids”; Fyfe (1928) on a variety of Cordylophora lacustris from Otago; Trebilcock (1928) “New Zealand Hydroids” in the Proceedings of the Royal Society of Victoria, and Jaderholm (1926) reported a small collection of New Zealand hydroids in his “Uber einige antarktische und subantarktische Meeren”.
Up to 1928 almost without exception hydroids are described from collections taken in the intertidal region, but in 1930 Totton described many new species and species new to New Zealand from dredgings made by the “Terra Nova” off Cape Maria van Diemen, North Cape and the Three Kings Islands. Percival (1938) briefly noted the finding of the second specimen of the unique Pelagohydra mirabilis. Reference to New Zealand hydroids more especially in relation to their distribution and possible relationship with other hydroid faunas are found in the papers of North American writers, notably Fraser (1946) and Australian writers Briggs and Gardiner (1931) and Blackburn (1937, 1938 and 1942). Vervoort (1946) discussed and described, together with hydroids from several other localities, some New Zealand material in the collections of the Rijksmuseum Natural Hist, and the Zoological Museum, Amsterdam. Three papers by Ralph (1947, 1953 and 1956) complete the literature on New Zealand hydroids.
The Campanulariidae and Campanulinidae were selected for Part 1 of the New Zealand thecate hydroids as they number between them some of the most widely distributed essentially cosmopolitan and consequently best known intertidal hydroids—e.g., Obelia geniculata and Clytia johnstoni. The campanulinids can be quickly distinguished from the campanularians as the former have an operculum, often pyramid-shaped, closing the mouth of the hydrotheca. This structure is most readily seen when the hydranth is retracted within the hydrotheca. Also, campanulinid hydrothecae are ovato-conic or tubular, not bell-shaped as are the majority of campanularian hydrothecae. In general, the species of both families have small, delicate, erect stems under 5.0 cm in height, but species with very tall, erect stems.
up to 60.0 cm are known. The stem is very variable in form. Frequently a genus will include species with three different stem habits, for example one species may have the hydrothecal pedicel arising directly from a creeping stolon as a simple structure with a single terminal hydrotheca (i.e., truly stolonal), another may have the stem slightly and irregularly branched, and yet another may show profuse and regular sympodial branching. Usually the stem is monosiphonic with a single central axis from which the hydrothecae and/or branches may arise. Some species are polysiphonic with two or more stem tubes from which hydrothecae and/or branches originate. In both families the reproductive zooid may produce a free medusa, or a fixed sporosac, or a reproductive body intermediate in organisational structure between these two extremes.
Differences of opinion exist on the limitation of genera in the two families. Particularly is this true of the F. Campanulariidae. Nutting, in his monograph of this latter family, gives a summary of the various classifications put forward before 1915, and concludes that none of them are entirely satisfactory. The same can be said of the two classifications in current usage, namely those based primarily on the characters of the erect stem (cf. Broch and others) and those based on the structure produced by the reproductive zooid (cf. Fraser, 1944, p. 110). As far as possible the characters of the erect stem and hydrotheca have been used here for separating the genera, as these structures are the ones most frequently found in collections of hydroids, but the genera Campanularia, Obelia, Gonothyraea and Clytia are distinguished from each other by the structure produced by the reproductive zooid, whether free medusa, or sporosac, etc.
From the above it will be realised that the erect stems of many species are strikingly similar in habit, form and hydrothecal structure and that the difficulties of separation met at the specific level will be very similar to those at the generic level. Therefore, just as generic status may be doubtful if the structure produced by the reproductive zooid is not known, so the specific status is frequently difficult to determine when the gonotheca is unknown. Keys to the genera and species in the F. Campanulariidae present greater problems than in most other families of thecate hydroids and for convenient and successful use it is often necessary for a genus or species to occur at several places in the key.