Cladonema timmsii, Gershwin, Lisa-Ann & Zeidler, Wolfgang, 2008

Gershwin, Lisa-Ann & Zeidler, Wolfgang, 2008, Cladonema timmsii, a new species of hydromedusa (Cnidaria: Hydrozoa) from a salt lake in South Australia, Zootaxa 1826, pp. 59-68 : 60-65

Cladonema timmsii sp. nov.

Figures 1 , 2

Material examined. Holotype: SAM H1570, Blue Lagoon near Cactus Beach, via Penong, South Australia [approx. 32°05’S, 133°00’E], coll. by B. V. Timms, 11 October 2006; 2.16mm BH, 1.96mm BD, gravid female.

Allotype: SAM H1573, same locality as holotype, amongst the angiosperm Ruppia sp., coll. by B. V. Timms, 19 March 2007; 1.92mm BH, 2.20mm BD, mature male.

Paratypes: SAM H1571, same data as holotype; lot of 5 (1 male, 4 immature), 1.58–1.91mm BH, 1.54– 1.95mm BD. SAM H1572, same data as allotype; lot of 22 (10 female, 8 male, 4 immature), 0.67–2.06mm BH, 0.82–2.16mm BD.

Diagnosis. Cladonema with nine straight radial canals issuing directly from stomach; with dimorphic gonads, female gonad completely encircling stomach in upper half, lacking pouches, male gonad with 6 pouches; with 6 short oral tentacles with spherical knobs; with 9 tentacles, each bearing about 7 stinging branches and about 6 sucker branches, the median stinging branch with a double row of nematocyst warts and the side branches with clusters arranged in a single abaxial row; with dark red ocelli, each bearing a lens.

Description of holotype ( Figure 1 )

Body deep bell-shaped, with straight sides and evenly rounded apex; mesoglea evenly thin, without apical thickening ( Figure 1 A). Exumbrellar surface smooth, without apparent nematocysts or warts, but with indented regions between and tapering toward tentacle bulbs, defining the main radii, reminiscent of coronate scyphozoan pedalia.

Manubrium cylindrical, shallowly 9-rayed where connecting to subumbrellar surface; lacking a peduncle and apical chamber ( Figure 1 A, D). Gonads completely surrounding manubrium along upper half, without pouches, tapered above toward junction with subumbrella, ending abruptly on lower edge, leaving lower half of manubrium free. Lower half of manubrium narrow, cylindrical. Mouth edge rimmed with 6 spherical nematocyst knobs on very short stalks.

Radial canals 9, fine, straight, smooth-sided, one corresponding to each of the 9 shallow rays of the base of the stomach, without branching ( Figure 1 D). Ring canal very fine, difficult to discern.

Tentacle bulbs 9, one opposite each radial canal, of a characteristic bent cylindrical form, S-shaped in side view, hourglass-shaped in abaxial view; with numerous scattered short papillae, especially noticeable along lateral edges ( Figure 1 B, C). Endoderm of tentacle bulbs containing a very crowded mass of golden sparkly concretions. Ocelli 1 per bulb, positioned abaxially at top of tentacle bulb; comprising a whitish pit with a lens, surrounded with dark red pigment; some ocelli having a horizontal row of tiny dots below.

Tentacle branches approximately 13 per tentacle bulb, solid, emitting from bulb in a characteristic pattern ( Figure 1 B, C). Stinging tentacle branches 6–8, each with a row of abaxial nematocyst knobs, plus a terminal knob; the largest central tentacle continuous with brown endoderm of tentacle bulb, armed with double row of alternate knobs of nematocysts along entire length, with a few spaced knobs along the midline, plus terminal knob. Suctorial tentacle branches 5–7, adaxially-positioned, naked except for terminal knob.

Velum very broad, well defined. No evidence of marginal warts, statocysts, cirri, or other marginal structures.

Colouration in preservative 6 months: endoderm of tentacle bulbs rich brown, ocelli dark red, endoderm of tentacles dark red, vertical streaks on manubrium pale brown above and between nematocyst knobs; bell transparent and colourless, tentacle nematocyst clusters whitish, tentacle bulb papillae colourless.

Description of allotype ( Figure 2 )

Structurally identical to holotype except in the following respects: male specimen possessing 6 gonadal pouches ( Figure 2 A, B), similar in form to that described for C. radiatum and associated species; median tentacle branch similar to that described for holotype; side branches bearing a double abaxial row of nematocyst clusters, separated by a broad gap, with nematocyst clusters arranged mostly opposite, with some haphazard.

Variation from type specimen. Most of the paratypes are smaller than the holotype and allotype, and are believed to be younger than the types. Their characteristics are consistent with those that would be expected in immature specimens, e.g., smaller numbers of tentacle branches, less-developed gonads.

Female gonads appear as a swollen ball rather than as a set of pouches as in most other Cladonema species, whereas mature males develop the pouches. In smaller males, the gonad pouches are not as pronounced.

Some specimens with 1 or 2 canals forked near apex, resulting in 11 tentacle bulbs (female gravid, about 2.0mm BH, BD) or 10 tentacle bulbs (1 female, 2 males, and 2 juveniles, including one only 0.67mm BH, 0.82mm BD). The remainder have 9 tentacle bulbs. While in some species of Cladonema , branching of the radial canals is constant and diagnostic, the branches in a few specimens of C. timmsii appear to be aberrant, as they are uncommonly observed and irregularly arranged.

The tentacular nematocyst warts are noteworthy. In the holotype and the paratypes, the main branch has two rows, whereas the lateral branches have a single row along the crest; however, in the allotype, the lateral branches have two rows, separated by a broad gap along the crest.

Etymology. The specific name, timmsii , is in honour of Brian V. Timms, one of the pioneers of Australian limnology and the collector of the present material.

Distribution. Presently known only from the type locality.

Remarks. Cladonema timmsii is apparently the only species in the genus to display sexual dimorphism. The females are most similar to Cladonema pacificum Naumov (1955) from Japan, in having gonads that lack distinct pouches, but the males are most similar to Cladonema radiatum Dujardin (1843b) from European coasts in possessing a series of well defined radial sac-like gonadal protrusions or pouches. Cladonema timmsii further differs from all its congeners in number and form of the tentacular branches, and the papillae on the tentacle bulbs are apparently unique.

Like C. pacificum , C. timmsii possesses six spherical oral nematocyst knobs, but the two species differ in the length of the gonadal region and in the form of the radial canals. In C. pacificum , the gonads are along the entire length of the manubrium, whereas in C. timmsii the gonads occupy only the upper half, leaving the lower half free. The radial canals in C. pacificum are similar to those described for C. uchidae Hirai (1958) and C. mayeri Perkins (1908) in having both simple and paired radial canals, whereas in C. timmsii they are more similar to C. californicum Hyman (1947) in being entirely straight in most specimens.

In all other known species, the arrangement of nematocyst warts on the stinging branches of the tentacles is typically illustrated as being either alternate or haphazard. Indeed, Schuchert (2006) described and figured all tentacular branches in C. radiatum as having alternate clusters. In C. timmsii , however, they are of a peculiar and apparently unique pattern: on the median tentacle branch, the nematocyst clusters are arranged in two rows, mostly alternate, with a few clusters sparsely arranged down the midline; in the other (side) branches, the clusters are arranged in a single abaxial row, in an alternate or opposite, or even semi-haphazard arrangement. In addition, the conspicuous gelatinous papillae on the tentacle bulbs in C. timmsii are apparently unique, not being noted or illustrated for any other species.

Another specimen of Cladonema was found at Cowell, South Australia, over 400km away by the overland route, several years earlier (SAM H1225 (ex. GZ0518), Cowell Jetty, Cowell, South Australia [33°41’10.8”S, 136°55’47.3”E], coll. T. Laperousaz and L. Gershwin, 15 February 2002; about 0.5mm BH/BD, immature; Figure 3 ). Curiously, sketches made of this immature specimen while still alive indicate a 6-rayed stomach footprint, with straight and bi-forked radial canals in alternation; however, in the preserved specimen all nine canals are visible and appear to connect directly to the stomach. Furthermore, the stomach seems opposite to those from Penong, in that the swollen portion is distal in the Cowell specimen but midway in the Penong specimens. The significance of these features in this tiny specimen is not understood at this time, and we await additional material for further clarity.

Juvenile Cladonema specimens are also held in the Museum and Art Galleries of the Northern Territory (Darwin, NT: NTM C5963). The five specimens are about 0.5mm BH, and possess characters that one would expect for juveniles of C. timmsii , e.g., unbranched radial canals, unpouched gonads, and a lesser number of tentacle branches. However, given the geographic and ecological differences between Darwin and South Australia, it seems unlikely that they are the same species, but we reserve judgment pending the collection of mature specimens.

Similarly, specimens of an interesting form of Cladonema are held in the Australian Museum (Sydney: AM G14600; G16029). The four specimens are about 1mm tall, 0.6mm wide, and are characterized as follows: bell tall, narrow, with flat top; stomach on a gelatinous peduncle, with gonad in a continuous wide belt around the stomach; with 9 straight radial canals; with 6 sessile oral nematocyst knobs; with 9 tentacles, each bearing 12 alternate branches plus the terminus, and each bearing a lensed ocellus. The specimens, which were obtained from a private home aquarium, appear to be mature. Although this form may be unique, we are reluctant at this time to describe it as new, pending the study of wild-caught material. The above-mentioned specimens from different localities suggest that there may well be a cluster of Cladonema species endemic to Australia.

The species of Cladonema have undergone several rounds of lumping and splitting. At least 13 forms have been assigned to the genus ( Table 1 ). Haeckel (1879) recognized only C. radiatum at the species level, but named four subspecies based on meristic differences; subsequent authors have regarded these as identical to C. radiatum , as we do here. Only four species were considered valid by Kramp (1961), namely, C. californicum Hyman (1947) , C. myersi Rees (1949) , C. pacificum Naumov (1955) , and C. radiatum Dujardin (1843a) . According to Schuchert (2006), Stepanjants et al. (1993) recognized only two valid species, namely C. radiatum and C. californicum . Bouillon & Boero (2000) agreed with Kramp (1961), and further recognised C. uchidae Hirai (1958) . An excellent and thorough revision of the family and genus, and the historical taxonomy of C. radiatum , were given by Schuchert (2006); he concluded that it is likely that the highly variable nominal species C. radiatum comprises numerous distinct biological species. A synopsis of characters of all the nominal species of Cladonema is presented in Table 1 .

While only preserved material was available to us for this description, future study should include DNA analysis and elucidation of the life cycle, for a full revision of the family when this information becomes available for all species.

Figures

FIGURE 1. Cladonema timmsii, n. sp., holotype female. A. Whole animal, lateral view. B. Tentacle bulb and tentacle, abaxial view. C. Tentacle bulb and tentacle, lateral view. D. Bell, aboral view.

FIGURE 2. Cladonema timmsii, n. sp., allotype male. A. Whole animal, lateral view. B. Bell, aboral view.

FIGURE 3. Cladonema sp., immature. A. Whole animal, lateral view. B. Bell, oral view. C. Tentacle bulb and tentacle, lateral view. D. Bell, aboral view.