Malagazzia carolinae (Mayer, 1900)

Buecher, Emmanuelle, Goy, Jacqueline, J, Mark & Gibbons, 2005, Hydromedusae of the Agulhas Current, African Invertebrates 46, pp. 27-69 : 63-65

Malagazzia carolinae (Mayer, 1900)

Phialucium carolinae: Mayer 1900 a: 7 , pl. 3, fig. 9, pl. 4, figs 10, 11; Kramp 1959 a: 157, fig. 212; 1961: 185.

Malagazzia carolinae: Bouillon 1984: 77 , pls 1, 2, 6.

Description: Single specimen, damaged. Umbrella hemispherical, dome-shaped, slightly broader than tall, without apical projection; 4.6 mm in diameter. Exumbrella surface smooth. Mesoglea thickened apically. Velum narrow. Peripheral canal and four radial canals present; radial canals narrow, unbranched; without centripetal canals. Only five marginal tentacles visible (generally with up to 16–20), similar, connected to peripheral canal, arising from large, swollen, conical bulbs on umbrella margin. Tentacles short and thick, hollow, unbranched, filiform, with 3 small atentaculate swellings or rudimentary bulbs between tentacles. Marginal cirri absent. Marginal bulbs without spurs but with adaxial excretory papillae; lateral cirri absent. Manubrium flask-shaped, narrow, short and not reaching to velum, without perradial lobes, not connected to radial canals by mesenteries. Mouth simple, short, with four slightly crenulated lips. Gastric peduncle absent. With 64 closed statocysts. Without ocelli on tentacular bulbs. Four gonads, slightly sinuous, not surroundind completely the radial canals distally, not reaching to manubrium.

Material examined: H5071.

Comments: Six species are recognised as valid by Bouillon and Boero (2000 b), and two others have been recorded in the Indian Ocean: M. multitentaculatum ( Menon, 1932) was recorded by Bouillon (1988 a) off the Seychelles, whilst M. taeniogonia (Chow & Huang, 1958) has been recorded in the Mozambique Channel and off the

Seychelles (Bouillon 1978 b). Species can be distinguished by the number of tentacles, rudimentary marginal bulbs and statocysts, as well as by the arrangement of the gonads: M. multitentaculatum has 25–32 tentacles and 3–4 rudimentary bulbs between tentacles, and the gonads are found along almost the entire length of the four radial canals. M. taeniogonia generally has eight marginal tentacles and 3–8 rudimentary bulbs between successive tentacles, and the gonads are considered to be slightly twisted and ribbonlike near the umbrella margin.

Distribution: World-wide in tropical and subtropical waters. Previously collected from around the Seychelles (Bouillon 1978 b) and in the Mozambique Channel (Kramp 1965). Neritic.

DISCUSSION

The samples examined here have provided us with a rare opportunity to investigate the medusae from along the east coast of South Africa. Although they represent a first detailed examination of the fauna, it should be realised that the samples were not originally collected for their gelatinous zooplankton, but rather for ichthyoplankton ( Beckley & van Ballegooyen 1992). As a consequence, they were neither collected using appropriate techniques, nor fixed and preserved in the most suitable manner ( Petersen 1976). There was also a 12 year interval between collection and identification. During this period of time mechanical damage, distortion and shrinkage could occur ( de Lafontaine & Leggett 1989).All of these make identification difficult. Nevertheless, we were able to identify 93% of the individuals collected from a total of 4166 medusae. On average, each species was represented by 60 individuals (Table 1). However, the five species of Trachymedusae dominated the collection and made up nearly 88% of all the individuals identified. By contrast, the Antho- and Leptomedusae represented more than 90% of the diversity found during the surveys but each occurred in low densities (Table 1). For example, of the 30 new records for the region, half were Anthomedusae which occurred in low densities at less than four stations. The diversity and abundance of the different orders of hydromedusae is linked to their life-cycle (Bouillon & Boero 2000 b). Meroplanktic species tend to be more more diverse than holopelagic species.

The fauna appears to be characterised by cosmopolitanism. Such is to be expected for the holoplanktic forms, which can properly be described as panoceanic, but it is also obvious for many of the meroplanktic species. Some of these have long been known to be widely distributed though there is evidence that others might be more recent arrivals (e.g. Blackfordia virginica ). Clearly much of the fauna has an Indo-Pacific affinity, though only five species of Anthomedusae and one species of Narcomedusae are restricted to the Indian Ocean.

Most of the species have an affinity for warm temperate and tropical waters, which is no surprise given the subtropical nature of the warm Agulhas Current. It is interesting to note however that eight species are also known from polar waters. Most of these latter forms are again members of the holozooplankton, and those that are not ( Plotocnide incerta , Laodicea pulchra and Cosmetirella davisi ) provide some evidence to support the presence of cool water inshore along the east coast (as e.g. Thibault-Botha & Gibbons 2005).

In their review of zooplankton diversity around southern Africa, Gibbons and Hutchings (1996) noted that west coast assemblages are characterised by a low diversity and a high biomass that reflects the elevated productivity of the region. By contrast, east coast zooplankton assemblages were shown to have a relatively high diversity and low biomass, which mirrors the generally low levels of productivity. A total of 80 species of hydromedusae have been recorded from over 1500 samples collected at various times of year along the west coast of southern Africa between the Cape of Good Hope and Walvis Bay ( Pagès et al. 1992; Buecher & Gibbons 2000). By contrast, the 65 species found in this east coast survey were collected from 106 samples over a relatively short length of coastline. We can easily imagine an increase in the diversity of regional hydromedusae as observations get extended into neighbouring regions. The various studies that have hitherto been conducted on regional Hydromedusae suggest that a total of 112 different species (24 species are commune to the two coasts) can be found, which represents more than 14% of the world diversity. This proportion is less than has been noted for many other zooplankton taxa ( Gibbons 1999), and implies that many more species are likely to be recovered in the future.