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Loimia medusa (Savigny in Lamarck, 1818) 

Spaghetti-Worm or the Red-Spotted Worm


John McLaughlin (2014)

 


Fact Sheet

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Summary


Brief Summary


Classification


Names


Physical Description


General Body Plan


The Tentacles


Colouration


Ecology


Habitats


Crypsis


Larvae


Behaviour


Overview


Feeding


Predatory Defense Mechanisms


Survival Mechanisms


Reproduction


Reproductive Characteristics


Reproductive Strategy


Case Study


Ecological Role


Overview


Secondary Production


Sediment Processing


Biogeographic Distribution


Life History


Larval Development


Building of Sandy Tube


Early Benthic Development


Conservation and Threats


References & Links

General Body Plan



Being in the phylum Annelida, Loimia medusa has a number of physical characteristics it shares with other species of this phylum. Loimia medusa is a long, cylindrical, soft-bodied segmented worm. They are bilaterally symmetrical, triploblastic coelomates whose parapodia function as limbs. Internally, structures such as muscles, kidneys and nerves are repeated in each segment of the body. 

Loimia medusa have a particularly elaborate and complex body plan made up of two major body regions, the thorax and abdomen. The thorax is generally brick red and rather thick with dorsal bundles of setae and ventral pads whilst bearing hooked setae (Hutchings et al, 1995). The abdomen is much thinner, with reduced parapodia. Loimia medusa lacks prostomial eyespot patches, and thus has well developed features such as nuchal organs situated on the neck, which are chemosensors. They have multiple chetae per segment whilst parapodia function as limbs.  The first lateral lobe is directed anteriorly and ventrally, which forms a thin ventral structure receding to the midline which exposes the oral opening (Hutchings et al, 1995). These lobes are rather large and oval shaped, with the second pair giving the species a taller appearance as it directs anteriorly, but even more so dorsally. The upper lip is predominantly hidden by the species tentacle mass however is seen to project forwards, being longer than it is wide and far thicker basally, whilst the low lip appears swollen and covered by a membrane connecting the first pairs of lateral lappets in a ventral fashion (M. Londono-Mesa et al, 2005). The notosetae are viewed to have very narrow wings visibly only with the aid of a compound microscope. Uncini generally contain 5 teeth, increasing in thickness with depth. The pygidium, or the posterior end of the body, emits 7 papillae which are evenly spread around the organism’s anus (P. Hutching, 1977). With respect to colouring, the ventral thorax along setigers 1-7 is strongly stained, whilst the dorsum is stained more weakly to reveal very small dots, with the abdomen remaining unstained.
Whilst the parapodia, which are simply paired appendages on each body segment, can have a variety of roles across different polychaete species, in Loimia medusa they are reduced and used to hold onto and move about inside the tubes in which they reside. 
With regard to size, Loimia medusa varies with age, location and resource availability. Generally, the body of the worm reaches 5-6 inches long, and approximately 1 inch thick, however specimens of up to 12 inches have been documented (Waikiki Aquarium, 2013). L. medusa generally weighs about 300mg (ash-free dry weight) and can have a lifespan of up to 1 year (R. LLanso & R. Diaz, 1994). The body includes between 15-17 setigers, and possess three gill pairs. These three pairs of branchiae are branched on segments 2, 3 and 4, with the first and second pair slightly longer than the third. Branchiae themselves have long, think stalks with many short dendritic branches. The projection marking the opening of the excretory organ, the nephridial papillae, are absent, yet eleven ventral shields beginning from segment 2 are easily viewed (P. Hutching, 1977). Shields are predominantly equal in size, however the first, second, and third are fused and slightly wrinkled (M. Londono-Mesa et al, 2005). 
The abdomen is characterised by a midventral groove. Notopodia, one of the paired appendages of polychaete annelids which aid in locomotion and breathing, begin from segment 14 and extend through a further 17 segments. The notochaetae are long, smooth and narrowly bilimbate and gradually decrease in size whilst maintaining similar shapes (Hutchings et al, 1995). Neuropodia first appear on segment 5, and continue along until segment 10 in single rows, before appearing in double rows from segments 11-20, before returning to single row stature for the remaining segments leading toward the pygidium. 





source: http://cookislands.bishopmuseum.org/species.asp?id=7456

Classification

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Kingdom
Animalia
Phylum
Annelida
Class
Polychaeta
Order
Terebellida
Family
Terebellidae
Genus
Loimia

Synonyms

Terebella medusa (Savigny, 1822)

Common Names

medusa worm
spaghetti worm
Medusenwurm
Spaghetti-Wurm
Kingdom
Animalia
Phylum
Annelida
Class
Polychaeta
Order
Terebellida
Family
Terebellidae
Genus
Loimia
Species
medusa