Bimeria lutea, Watson, 2016

Watson, Jeanette E., 2016, Two new species and a new record of hydroids (hydrozoa: hydroidolina) from Port Phillip, Australia, Memoirs of Museum Victoria 75, pp. 1-5 : 2-3

Bimeria lutea sp. nov.

Figure 2A-E

Material examined. NMV F228242 holotype, fertile colony alcohol preserved, epizoic on Sertularella eleganta , 1m deep, coll: J.E.Watson, 22/3/2016 . NMV F228243 , malinol mounted microslide from holotype colony .

Description. Colonies fertile, borne abundantly on lower branches of Sertularella eleganta . Hydrorhiza of tubular stolons reptant on host colony. Hydrocauli straggling, hydranths borne on single pedicels or on sparsely and irregularly branched stems to 4-5 mm long (rarely 8 mm long). Stems and pedicels monosiphonic, thick, of same diameter as stolons, deeply annulated above junction with stolon and above and below each branch, annulations often fading into corrugations before becoming smooth. Branching predominantly of first order, occasionally second order.

Hydrothecae terminal on pedicels of variable length, hydrotheca vasiform (preserved), a pseudohydrotheca covering body, hypostome dome-shaped with 10-12 finger-shaped tentacles arranged in an untidy whorl below hypostome (live material), the pseudohydrotheca continuing as a thin gelatinous pellicle over proximal region of tentacles.

Gonophores male, elongate oval, arising singly on a short annulated pedicel from stem and branches, enclosed in a thick gelatinous sheath, spadix central, leaf-shaped, opaque.

Cnidome (from live material) clusters of nematocysts of two categories in transverse bands along tentacles, none discharged: - microbasic euryteles, loaf-shaped, 4-5 x 8.5-9 µm, - desmonemes, droplet-shaped, 4 x 6 µm. Perisarc very thick on proximal stem region; hydrocaulus, hydranth and gonophores invested with very fine sediment. Colour of colony in life: stolons pale brown, hydrocaulus and tentacles white, hypostome yellow, spadix of gonophore brown.

Remarks. Bimeria is a genus of nine species ( Bouillon et al. 2006), two of which are known from Australia. Bimeria australis Blackburn 1937 (redescribed by Watson 1978) is from the same southern Australian locality as B. lutea , and Bimeria currumbenensis Pennycuik, 1959 is from tropical southern Queensland. The morphology of B. lutea fits with neither Australian species. Colonies of B. australis are not as abundantly rampant as those of B. lutea ; they are buff-coloured with a wrinkled hydrocaulus and the stems stand erect from the substrate. B. currumbenensis described from meagre infertile material by Pennycuik (1959) is a much larger species and lacks an annulated hydrocaulus.

Bimeria vestita Wright, 1859 is a known epizoite of sertulariid hydroids and has been described by Millard (1975), Calder (1988) and Migotto (1996); the type material was re-examined by Marques et al. (2000). Differences between the various descriptions are such that it is likely that more than one species may be involved. The type as described by Marques et al. (2000) is much larger and more branched than B. lutea , the number of tentacles is greater, the nematocysts are smaller (probably due to shrinkage), the pedicels widen distally and those of the gonophore are longer. Millard (1975) mentioned but did not figure a branching male spadix in B. vestita ; her material may be a different species, possibly more closely related to B. lutea than to B. vestita .

Etymology. The species is named for the yellow colour of the hypostome.