Mastigias (Page adapted from Dawson 2005)

 

Characteristics of the Genus (from Kramp 1961)

Mastigiidae with mouth-arms terminating in a naked, club-shaped extremity; mouths not only along the three edges of the mouth-arms, but also on their flat, expanded sides; numerous small clubs and filaments between the frilled mouths; intra-circular mesh-work of canals with 6-20 canal-roots in each octant, usually communicating with the rhopalar canals.

 

Meristics and morphometric features


Figure: The morphology of Mastigias. (A) Photograph of an approximately 15 cm [bell diameter] medusa from Goby Lake, Palau. (B) Sketch of a longitudinal section along the interradial axis of the medusa [i.e. through the plane of the paper after rotation of the medusa in A through approximately 30° to the left]. (C) Sketch of the subumbrellar surface of the bell, and (D) cross-section through the bell along line VWX. (E) Schematic of the oral disc, in oral aspect, showing two of the eight oral arms, and (F) cross-section through the oral disc along line YZ or its orthogonal. Features discussed below include the following. Bell colour (f1). Perradial and interradial canal colour (f2). The presence of pigmented flecks at the roots or along the length of radial canals (f3). Oral arm colour (f4; lower arrow points to the ‘fringe’). Terminal club colour (f5). Abundance (f6) and colour (f7) of spots on the exumbrellar surface. Bell diameter (f9). Ring canal diameter (f10). Length of the simple, unwinged, portion of the oral arm (f11). Length of the winged portion of the oral arm (f12). Shape (f13), number (f14), and length (f15) of the terminal clubs. Length (f16), width (f17), and depth (f18) of the oral pillars. Width of the subgenital ostia (f19). Diameter (f20) and depth (f21) of the oral disc. Presence of intermediate filaments on the oral arm and oral disc (f22). Number of velar lappets [i.e. all lappets bar the two at each rhopalium] (f23). Shape of the gastrovascular cavity (f24). Colour of the subgenital porticus (f25). The interradial (I. f26) and perradial (P. f27) diameters of the gastrovascular cavity. Bell thickness (f28). The number of perradial (f29), interradial (f30), and adradial (f31) canal origins at the gastrovascular cavity. The number of perradial (f32) and adradial (f34) anastomoses in the radial canals that are circumscribed by the ring canal. The number of sinuses originating at the gastrovascular cavity (f35), and interradial (f37) and adradial (f38) canals. Radial canals are named consistent with the phylogenetic hypothesis of Uchida (1926: 87). Five features are not indicated in the figure: the mass of the whole medusa (f8), the number of interradial anastomoses (f33), the number of sinuses originating at perradial (f36) and ring canals (f39), and the number of anastomoses leading to two sinuses (f40). bf, brood filaments which are found only on mature female medusae.

 

Methods

At least 40 meristic and morphological features (f; or indirect measurements thereof as indicated by ') can be measured on each medusae. Measurements should be made as soon as possible after collection.

While the medusa is in an holding tank of ambient salinity water, use a standard palette of reference colours to describe
(f1) Colour of the bell.
(f2) Colour of the perradial and interradial canals
(f3) Colour of the opaque flecks in the radial canals (if present)
(f4) Colour of the oral arms.
(f5) Colour of the terminal clubs.
(f6) Sketch, photograph,or otherwise describe the relative abundance [including the distribution pattern] of spots on the exumbrellar surface.
(f7) Colour of spots on the exumbrellar surface.

If mature, identify the sex of the medusa by the presence [female] or absence [male] of brood filaments on the oral arms and oral disk. Gonadal tissue also be biopsied and examined under a dissecting microscope to confirm the sex of the medusa.

(f8) Remove the medusa from the water, place it in a mesh [1 mm-sqr] bag, drain of water for 20 s and weigh to nearest 1g on an analytical balance.

Place medusa, flat, exumbrella surface down, on an horizontal transparent surface illuminated from below by a circular 40W fluorescent light. Place a thin mark [e.g. toothpick] snug against the manubrium, perpendicular to and at the base of each oral arm. Use 0.1 mm calipers to measure the following features.
(f9) Bell diameter [Db].
(f10) Diameter of the ring canal [Dc].
(f11) Length of the unwinged portion, as well as the total length, of four oral arms starting from the base of the arm at the oral disk (defined as the point at which the recumbent oral arm is creased).
(f12) Calculated the length of the winged portion of the oral arms was by subtracting the length of the unwinged portion from the total length of the arm.
(f13) Sketch or otherwise describe the shape of terminal clubs.
(f14) Record the number of terminal clubs.
(f15) Lengths of four [or as many as possible if less than four] terminal clubs.

Amputate the oral arms. Use 0.1 mm calipers to measure the following features.
(f16) Length of two oral pillars.
(f17) Width of two oral pillars.
(f18) Depth of two oral pillars.
(f19) Width of two subgenital ostia.

Amputate the oral disk and place it bell-facing surface down on a flat surface. Measure the following.
(f20) Diameter of the oral disk (Dd) across both perradial axes.
(f21a-d) Thickness of the oral disk at intervals of Dd/6 across one perradial axis using a mm-calibrated probe to determine disk-shape and thickness.
(f22) Note the presence of intermediate filaments [i.e. non-brood filaments] on (a) the oral arms and (b) the oral disk.
(f23) Record the number of non-rhopalar lappets in each of four, preferably adjacent, octants.
(f24) Sketch the shape of the gastrovascular cavity and the gastric and gonadal tissue and class as cruciform or not.
(f25) Note any colouration of the subgenital porticus, with reference to a standard palette of reference colours.
(f26) Measure the width of the gastrovascular cavity along one interradial axis.
(f27) Measure the width of the gastrovascular cavity along one perradial axis.

Remove the subgenital porticus from the bell.
(f28a-e) Measure the bell depth at intervals of Db/10 across one interradial axis using a mm-calibrated probe to determine bell-shape and bell thickness.

Inject the radial canal system of the medusa with food dye and photograph it. Use the resulting picture to enumerate the following 12 features of the canal system, per quadrant [delimited by consecutive perradial canals; see Notes below].
(f29) Number of originations of perradial canals.
(f30) Number of originations of interradial canals.
(f31) Number of originations of adradial canals.
(f32) Total number of anastomoses involving perradial canals [i.e. perradial-perradial, perradial-adradial].
(f33) Total number of anastomoses involving interradial canals [i.e. interradial-interradial, interradial-adradial].
(f34) Total number of anastomoses between adradial canals [i.e. adradial-adradial].
(f35) Number of sinuses originating at the stomach pouch.
(f36) Number of sinuses originating at perradial canal.
(f37) Number of sinuses originating at interradial canal.
(f38) Number of sinuses originating at adradial canals.
(f39) Number of sinuses originating at ring canal.
(f40) Number of anastomoses that give rise to two sinuses.

 

Notes:

Anastomoses of apparently ≥ 4 canals (c) may be indistinguishable from ≥ 2 very close anastomoses each involving 3 canals and are therefore interpreted as comprising c - 2 anastomoses separated by zero-length branches.

Sinuses are defined as canal branches that anastomose at only one end

The highly anastomosed canals marginal to the circular canal are too complex to enumerate reliably with the current methods and are therefore excluded.

 

 

Prepared by M. N Dawson