Monotheca pulchella (Bale, 1882)

Watson, Jeanette E., 2011, Review of the genus Monotheca (Hydrozoa: Leptolida) from Australia with description of a new species and a note on Monothecella Stechow, 1923, Memoirs of Museum Victoria 68, pp. 71-91 : 84

Monotheca pulchella , measurements (µm)

Stem internode length 204–400 diameter at node 48–60 length of apophysis (adcauline wall) 52–64

Hydrocladium length of athecate internode 52–128 width at distal node (shoulder) 50–58 basal length of hydrothecate internode 164–200

Hydrotheca length of abcauline wall 100–148 diameter of margin 116–152

Gonotheca length (excluding bent pedicel) 560–696 maximum width 280–344

Nematotheca length of base 40–55 diameter of cup 32–50

Remarks. Stranks (1993) considered microslide NMV F59054 a probable syntype of Monotheca pulchella . I select this microslide as lectotype of Monotheca pulchella .

The submarginal lobate cusps mentioned by Bale are clearly visible in the gonotheca of the type. On present evidence, M. pulchella is associated only with brown algae. This is in contrast to M. flexuosa , which is a common opportunistic species occurring on a wide variety of red and green algal and invertebrate substrates.

The hydroid reported as Plumularia pulchella by Izquierdo et al. (1986) from the Canary Islands is probably Monotheca margaretta (see discussion in Calder, 1997), further supporting the contention that M. pulchella is endemic to Australia.

Type locality. Queenscliff , Victoria, Australia .

Known distribution. Victorian coastal waters.

Distinction between Monotheca flexuosa and Monotheca pulchella . Monotheca pulchella ( Bale, 1882) has often been confused by authors with Monotheca flexuosa ( Bale, 1894) . Although Bale clearly distinguished between the two species on the basis of M. pulchella having a robust septate stem, very short cauline internodes and hydrocladia midway along the internode, Totton (1930) reported infertile material from northern New Zealand as M. pulchella , presumably following Trebilcock (1928), who synonymised M. flexuosa in that species. Totton’s opinion was based on i) the specimens being twice the size of those described by Bale (for M. flexuosa ), some being half an inch in height (12 mm) and bearing 48 hydrocladia, ii) the trophosome of M. flexuosa falling well within the range of variation of M. pulchella and iii) there being only slight apparent differences in the gonosome. His figure (fig. 58, p. 221) is clearly that of M. flexuosa .

Later authors, such as Millard (1975) followed Totton but, with the exception of Millard, they did not provide figures of their specimens so the accuracy of their identifications cannot be confirmed. Watson (1973) examined Bale’s microslide specimens of both species in the collection of Museum Victoria, reporting the species to be markedly different and concluded that Totton was incorrect for the following reasons: i) height of the hydrocaulus is an unreliable character, ii) M. flexuosa has a more flexuous hydrocaulus than M. pulchella and iii) the gonothecae of the two species are markedly different. Medel and Vervoort (1995) misinterpreted Watson’s (1973) note on the submarginal gonothecal cusps of M. pulchella , and their description and figure is clearly that of M. flexuosa . Infertile material on green algae reported from New Zealand by Vervoort and Watson (2003) is also M. flexuosa .

On present evidence, M. pulchella is endemic to southern Australia where it is associated only with brown algae.