Monostaechas quadridens McCrady, 1859

Watson, Jeanette E., 2011, New species, new records and redescriptions of Thecate hydroids (Cnidaria: Hydrozoa: Leptothecata) from Southern Australia, Zootaxa 3122, pp. 1-36 : 18-21

Monostaechas quadridens McCrady, 1859

Fig. 9A–J

Monostaechas quadridens McCrady, 1859: 199 .– Fraser, 1912: 380, fig. 46.– Jäderholm, 1919: 20. – Bedot, 1921: 6. – Stechow, 1923: 18.– Stechow, 1925: 252.– Leloup, 1937: 108, 117, fig. 10.– Fraser, 1938a: 10, 61.– Fraser, 1938b: 135.– Fraser, 1938c: 111.– Fraser, 1939: 161. – Fraser, 1943: 95.– Fraser, 1944: 40.– Fraser, 1944: 334 –335, pl. 71, fig. 323.– Fraser, 1945: 21.– Fraser, 1948: 274. – Pennycuik, 1959: 178, pl. 3 fig. 6.– Yamada, 1959: 81.– Mammen, 1965: 98.– Vervoort, 1968: 61. – Rho & Chang, 1972: 101, pl. 3 figs 12.– Millard, 1973: 30.– Millard & Bouillon, 1973. 206: 8, 85.– Hirohito, 1974: 35, fig. 16.– Millard & Bouillon, 1974: 9.– Rho & Chang, 1974: 148.– Millard, 1978: 195.– Watson, 1979: 234.– Ljubenkov, 1980: 50.– Calder, 1983: 17, fig. 9.– Hirohito, 1983: 65.– Park, 1992: 294.– Bouillon, Massin & Kresevic, 1995: 50.– Hirohito, 1995: 249, fig. 84a–g.– Migotto, 1996: 50, 123, fig. 9i. – Watson, 1996: 78.– Schuchert, 1997: 130, fig. 47.– Ansín Agís, et a l 2001: 171, fig. 71.– Galea, 2010a: 26 , fig. 6M.

Monostaechas fisheri Nutting, 1905: 959 , pl. 5, fig. 3, pl. 12, fig. 8.– Bedot, 1921: 6.– Bedot, 1921: 9.– Vannucci, 1949: 252, pl. 3, figs 51–54. – Vannucci-Mendes, 1950: 90, pl. 1, fig. 6.– Vannucci, 1951: 106, 108, 112, 114.– Von Schenck, 1965: 896, 910, 926, fig. 3d, 9.– Migotto, 1996: 123.– Schuchert, 1997: 127, fig. 46.

Material examined. NMV F171364, colony, and microslide from colony, Blairgowrie, Port Phillip, Victoria, large fertile colonies on pier pilings, depth 1–3 m, coll: J. Watson, 20/09/2007. Material alcohol preserved. Material in author’s collection: Mornington, Port Phillip, Victoria, infertile colony on mussels ( Mytilus galloprovincialis ) on pier pilings, depth 1 m, coll: J. Watson, 20/01/1999. Symonds Channel Port Phillip, fertile colony on sponge, depth 13 m, coll: J. Watson, 19/02/2007. Boat Rocks, Stradbroke Island, Queensland, infertile colony on red alga, depth 20 m, coll: J. Watson, 24/08/1975. Whitfords Reef, Perth, Western Australia, depth 12 m, coll: J. Watson, 22/11/ 1983.

Description. Colonies comprising bunches of many stems to 100 mm high. Hydrorhiza a tangle of stolons; stolons tubular, rugose, of same diameter as stems. Stems straight, monosiphonic, slender, lower stem region ahydrocladiate, internodes long, cylindrical, nodes transverse, varying from obscure to distinct, usually a slight tumescence below node; proximal internodes without nematothecae; internodes further up stem with up to six nematothecae in a double row.

Stems sparingly to much branched, primary branches opposite to alternate, distal on internode, arising from a long tubular, upwardly directed apophysis, distal node of apophysis transverse to weakly oblique, a nematotheca in axil and one cauline nematotheca below branch; primary branching from the stem dichotomous or trichotomous; when dichotomous, branches opposite, if trichotomous the third branch inserted between the first two; branches displaced towards front or back of stem.

Primary branch internodes long, slender, ahydrothecate, with a row of up to five nematothecae; secondary and tertiary hydrocladia (branches) given off from distal apophyses on internode, a nematotheca in axil; tertiary branching more common in distal stem region.

Proximal internode of hydrothecate hydrocladium with a long oblique proximal node passing below hydrotheca; secondary and tertiary hydrocladia usually beginning with a moderately long athecate internode with oblique distal node and two or three adaxillar nematothecae.

Hydrocladial internodes alternately hydrothecate and ahydrothecate; proximal node of hydrothecate internode strongly oblique, passing below hydrotheca, distal node transverse to weakly oblique, indistinct, athecate internode with one or two equidistant median nematothecae Hydrothecate internode short, with a centrally placed hydrotheca occupying much of internode, hydrotheca seated at an angle of c. 45° to internode, deep cup-shaped, adcauline wall straight, half wall free of internode, abcauline wall straight to weakly convex, slightly thickened, a small foramen connecting with internode at base of wall. Margin circular, transverse to hydrothecal axis, rim slightly everted, perisarc thin. Hydranth with c. 20 tentacles.

One median nematotheca on ahydrothecate internode two-chambered, base stout, adcauline side of cup foreshortened and adpressed to internode, median inferior nematotheca same, cup not reaching base of hydrotheca, twin lateral nematothecae movable, tall, splayed outwards on a long pedicel; base of nematotheca conical, about same length as pedicel, cup just overtopping hydrothecal margin, shallow, wide, reduced on side facing hydrotheca; median superior nematotheca single-chambered, small, ovoid, scoop-shaped, dorsally convex, tucked below adcauline wall of hydrotheca. Cauline nematothecae on branch internodes and gonothecae, same as twin laterals but without pedicel, a smaller one, sometimes absent, in axil of branches and hydrocladia.

Male and female gonothecae borne prolifically on same stems and sometimes on same hydrocladium. Male much smaller than female, kidney-shaped, tapering to base, walls smooth, inserted in internode on a pedicel of two segments beside a hydrotheca, a nematotheca at base, aperture terminal, small, circular. Female gonotheca large, kidney-shaped, tapering to base, walls smooth, inserted in internode beside a hydrotheca on a pedicel of three segments, two nematothecae at base; aperture terminal, large, circular, oblique, closed by a slightly domed operculum that ruptures to release a single planula larva.

Cnidome of two categories of nematocysts:

i) large microbasic mastigophores, capsule oval, 18–20 x 7 µm, shaft 17–20 µm long, with large spines, tubule 45 µm long, moderately thick, with small spines; abundant in nematothecae.

ii) small isorhizas, capsule 7 x 3 µm, tubule c. 40 µm long; abundant in tentacles.

Perisarc of hydrocaulus moderately thick, walls of hydrotheca and gonotheca thin.

Colour of colonies dark purplish grey in life; male gonophore dark brown, female brown to creamy yellow.

Stem

internode length 1800–2500 width at node 136–224 length of apophysis 88–120 diameter of apophysis at distal node 136–144

Branch

adcauline length of internode 1020–2000

Hydrocladium

length of athecate internode 240–360 width at transverse node 80–96 length of hydrothecate internode (abaxial side) 264–336

Hydrotheca

length of free adcauline wall 128–160 length of abcauline wall 273–320 diameter of margin 256–280

Gonotheca

length of male 360–400 maximum width of male 216–224 length of female 900–1160 maximum width of female 520–600 length of pedicel (male and female) 110–112

Nematotheca

total length of median inferior 88–100 total length of median superior 58–80 total length of lateral 100–120 total length of others 140–160

Remarks. The present material agrees in most respects with Nutting’s brief description (1905) of Monostaechas fisheri and with dimensions given for both M. fisheri and M. quadridens by Schuchert (1997). Stechow (1925) and Vervoort (1968) found no clear differences between the two species and considered Monostaechas fisheri and Monostaechas quadridens conspecific. Migotto (1996) and Schuchert (1997) discussed the supposed differences, Schuchert pointing out that only the presence of a distinct caulus in M. fisheri separated the two species. Nevertheless he kept the two separate until such time as further material became available for examination. Calder (1983) identified branched specimens 8.5 cm high as M. quadridens from a South Carolina estuary but without explanation kept it separate from M. fisheri . I have examined a specimen of a female colony of M. quadridens from Sapelo Island, Georgia, USA (coll: M. Gray, 16 November, 1964, dredged, 18 m) loaned by the Royal Ontario Museum, Canada. Other than the Port Phillip colonies being much taller the specimens are identical.

Release of planula larvae of Monostaechas quadridens was observed in the laboratory. Near maturity the spadix of the female gonophore is displaced to one side to accommodate the growing planula. At release it is leechshaped, 1.5– 2 mm in length with strong muscular bands and a rounded anterior end. The body is amber-coloured with indefinite spots and lines and a paler border. It moves rapidly with a slug-like motion.

Distribution. Temperate seas; recorded in Australia from Queensland ( Pennycuik 1959) and Western Australia ( Stechow 1924, 1925; Watson 1996). Over the past decade the species has become moderately common in southern Port Phillip suggesting that it may be a recent introduction to Victorian waters.

FIGURE 9. Monostaechas quadridens . A, stem from colony. B, trichotomously and dichotomously branched stem. C, hydrothecate internodes and ahydrothecate internode. D, hydrotheca, anterior view, median superior and inferior nematothecae not shown. E, female gonotheca. F, male gonotheca. G, lateral nematotheca, H, median inferior nematotheca. I, median superior nematotheca. J, newly released planula larva. Scale bar: A, 50 mm, B, 1 mm, C–F, 0.5 mm, G–I, 0.2 mm, J, 2 mm. Family Kirchenpaueriidae Stechow, 1921