title for learn-about section of A SNAIL'S ODYSSEY
  Life cycle & reproduction
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  Other species
  Topics on reproduction of hydroids include a section on other species, considered here, and a separate one on the well-studied PROBOSCIDACTYLA FLAVICIRRATA, considered elsewhere.
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Research study 1

drawing of planula larva of hydroid Corymorpha palmaphotograph of hydroid polyp Corymorpha palma being eaten by several nudibranchs Flabellina sp.; photo courtesy Kevin Lee, Fullerton, CaliforniaAn early study at UC Berkeley, California provides detail on larval development of Corymorpha palma. Unlike in many other hydroids, the medusa is not liberated.  Eggs are apparently released throughout the year.  The eggs sink to the bottom and are sticky.   Development is to an undifferentiated planula-like stage, which attaches to the sea bottom shortly after hatching, and is never free-swimming (see drawing upper Right).  Within a short time (the author does not provide a detailed time-line for development), the drawing of larva of Corymorpha palmapolyp elongates, and produces several distal and proximal tentacles (see drawing lower Right).  The author provides much detail on histological changes in the polyp during embryological development, but little on its behaviour.  Torrey 1907 U Calif Publ Zool 3: 253. Photograph courtesy Kevin Lee, Fullerton, California diverkevin.






Solitary hydroid Corymorpha palma being eaten
by several aeolid nudibranchs Flabellina sp. 2X

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Research study 2

drawing of medusa of hydroid Clytia gregaria with photos of gonadsLarge swarms of medusae of Clytia gregaria frequent the waters around San Juan Island, Washington throughout the summer. Observation in Friday Harbor Laboratories of gonad condition, and counts of sperm in water containing males, provide information on sexual reproduction. Rough counts from individual males indicate that 3 million sperm may be released each day, some as continuous dribble, but with larger releases at the same time as release of eggs from females.  Females release eggs readily in laboratory conditions, up to 50-70 at a time from fully grown and well-fed specimens.  Egg release mostly occurs 1-3h after sunset and/or 1h before sunrise, suggesting that change in light conditions may be a stimulating factor.  Cleavage begins about an hour after fertililsation (at 12oC) and the 32-cell stage is reached within 4h.  Roosen-Runge 1962 Pac Sci 16: 15.

NOTE  the author does not rear the embryos past this stage

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Research study 3

photograph of medusa of hydroid Clytia hemisphaericaLife cycles are known for only a few species of west-coast hydroids.  One of these is Clytia hemisphaerica (Phialidium hemisphaericum), collected as medusae from the dock of Friday Harbor photographs of feeding and reproductive polyps of hydroid Clytia hemisphaericaLaboratories, Washington and reared in plastic carboys in the laboratory at 12.5oC.  Settled planulae are collected on glass microscope slides placed at the bottoms of the carboys.  Most planulae settle within a few days and, by 4-5wk after fertilisation, growth of the colonies by stolons is vigorous (see photos on Left).   The first gonangia appear by 3wk and the first medusae are liberated by 4-5wk. 

The newly released medusae are about 1.3mm in diameter and have 4 tentacles (see photo on Right).  The medusae are capable of feeding while still attached to the blastostyle.  Within a few days the medusae have 8 tentacles and by 4wk they are sexually mature, with about 2 dozen tentacles and a diameter of 1cm).  A female in laboratory culture may produce 50 eggs per day for 60d, or about 3000 eggs in its lifetime.  Roosen-Runge 1970 Biol Bull 139: 203.

NOTE  the author uses a modified “Kreisel” apparatus in the carboys to ensure good water circulation, and self-siphoning to maintain constant water volume

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Research study 4

A researcher at Monterey Bay Aquarium, California provides details of life stages of the hydroid Mitrocoma cellularia.  Larvae are obtained from adult medusae and cultured in the laboratory at 11oC.  Life stages of polyp and medusa are shown below.  Life span of the medusa in the laboratory is estimated by the author to be 6mo, and perhaps twice that in the field.  Diet of medusae in the field consists of primary soft-bodied prey such as appendicularians and invertebrate eggs.  Widmer 2004 Mar Biol 145: 315.

NOTE  the author does not comment on habitat or depth preferences of the polyp-colony stage but, as the medusa stage is relatively large (10 x 5cm) and can be collected at the sea surface in dip-nets, the report is probably worth including here

early developmental stages in hydroid Mitrocoma cellularia polyp types of the hydroid Mitrocoma cellularia 16-tentacle medusa stage of hydroid Mitrocoma cellularia
Life stages: egg day 0, planula day1-3, hydroid colony 6wk.  Hydranths or feeding polyps (gastrozoids) are shown here along with 2 gonangia. The gonangia develop after about 6.5wk at 11o Hydranths (gastrozoids) begin feeding after about 5d.  Each gonangium liberates only a single medusa bud (shown on top of the polyp on Right) Medusae develop from 2- to 4- to 8- to 16-tentacle stage after 8wk in laboratory culture
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