Interesting, this story is totally different than the Thiruthani story :-)
Thanikai Legend: Tharakasuran, takes Sudarshana from Vishnu when the battle is on, then apparently they agree upon a truce however Tharkasuran holds on to the sudarshana, when on battle with Murugan, he uses it and the sudarshana circles the lord and merges within him. Then Vishnu meditates on the lord at thanikai and gets back the sudarshana. Thats the depiction in Thiruthani...
Its what is said on the Puranam too, not sure about this loan...
The Murugan is atother side of raja gopuram - one side vinayagar and one side murugan.
The murugan has 12 hands and sitting on pea cock. ( visited first in 1996) . The Murugan was at that time was worshipped for cure of poisonus bites.
The Sundara Padikkasu was the only legend told to me at that time.
On enquired one fellow visitor l told that in Pallava nadu Murugan is more worshipped as brahma sasta ( later i visited Kacchi kandakottam, Padarivdeu, Siruvapuri) and in Chola desam Vishnu rupan and Pandya nadu as Siva rupan. ( Mostly called siva subramanian)
I did not remember he telling me any other temple where murugan is in vishnu roopam. Need to explore.
Is the Murugan with Bow and arrow is Siva's kiratha farm or Pinagapani. As of now it may be may not be. Even the common name of siva subramanian in T.veli can be only supportive but not conclussive.
If we have details of any murugan statue with deer, mazhu or agni, then the theory will be more logical if not conclusive.
The Thondai nadu is full of Brahmasata murugan, now 2 vishnu murugan in chola nadu and some more will add credentials. Theory is intresting and but need more evidences.
as pointed out earlier , taraka defeated Mahavishnu in the battle and usurped the chakra..
when taraka was defeated by Muruga, muruga took the chakra in his chest, the mark of the same can be seen on Tiruttani murugan. The same was handed over to MahaVishnu...
for the vel point, if iam not wrong, sashti kavacham , which is being sung by bala devaraya swamigal on Tiruchendur murugan, describes murugan with "pannirandaayudham", one of which might by bow...
one can also see the vigraham of "shanmugar" in most temples with one of the aayudham as bow..
also , murugan gets vel only at Sikkal from his mother , the all pervading mahasakthi... so vel is sakthi swaroopam handed over to him prior to the war....
may be A.P. Nagarajan wanted murugan to be associated with Vel always and has portrayed murugan with vel always...
So murugan is also with bow and arrow might be a possiblity before he acquired Vel and the depicted might be of the state before getting vel...
please also note that vishnu is with 5 weapons not necessarily chakram alone.. the five being, Chakra,sangu, bow, angusam and gadhai (ref. panchaayutha stothram) ...
anyways, Murugan is quitessential Form of Shiva - Kameswaran & Kameswari swaroopam... the form of supreme merger of Shiva and Shakthi... Murugan is the one who pervades all....
devargal request shiva to give a son who is equal to shiva himself..."ninnai nigarkka" is the word used by kachiappa sivacharyar.... hence murugan arose.. please note murugan was not created.. he arose .."ange udhithanan" murugan...
shiva has total six faces namely eesanam, thathpurusham,vamadevam, aghoram, sathyojatham and Adhomukham .. of the six faces only five are visible .. the adhomukham being invisible...
now murugan is all the six faces visible swaroopam of Sivan... more benevolent... though with lot of mystery around him, is very reachable to the devotees.. though he predominantly resides in the mountain... none of that is inaccessible to the devotees....all the abodes of murugan are very reachable...
Murugan is "guhan" who resides in the "gugai" the cave as mentioned repeatedly in the Upanishads..he is the brahman.. the all pervading....
Individual sirpa builders would do this based on their visions, but the concept of Skanda holding these weapons is different.
Shanmuka with 12 hands has various weapons in them (10 numbers) Bow, Chakra, Vajra, Soolam, Pasam, Ankusam,sword, shield (sometimes its the mala),Rooster Flag.
None of these are predominant weapons, only the Shakti Vel is, it again is a two fold thought in here, as Guru Arunagiri mentions in some of his songs, the Shakti could be a constituent of kundalini energy that brings about true knowledge (which is used against Sooran).
Other ways of Muruga's usage on that- more ground real - worldly - are in the human evolution where the spear was one of the most prominent hunting / battle weapons on ground.
A spear can Kill where as an arrow can make a terminal wound. Bow and arrow are more agile than a spear, which makes it a more lethal weapon inside the forests, but on the ground combat, a spear / sword combo is more powerful.
Bow and Arrows would be primarily used in forest areas - speed as primary need. Both spear and bows were out dated with the advent of guns ;), however, the spiritual concept still is very active.
Muruga using Bow and Arrow is seen as a God of the Forest and people who pray are dwellers from areas where they are not allowed into the mainstream of so called elites of society.
Other thoughts:
Pasam and Ankusam are specific to the Ganesha attribute of the Lord, they both are the same is the significance, Vajra is to say that he is the ruler of the devas, Chakra to say that he is none other than Vishnu himself,Sword / knife - Kali, Tirsul - Shiva, Bow is more symbolic to weapon of Kama(he knows how to romance:) ) and the Shaktivel - Very unique to him, only other God to possess the Vel is Maha Sudarshana murthy, the prominent weapon of Maha vishnu.
Thus the uniqueness of Muruga in displayed his Aarumugam pose.
The viswaroopa darisanam of Muruga is shown only to Sooran, one of the most interesting episodes of the puranam. He takes the position next to his uncle Krishna on the Viswaroopa display.
Now to the most interesting part, he is one of the very few who does not Kill the opponent but dissolves the material frame and takes the opponent into himself ( "thaduthaatkolluthal"), the energy is taken inside.
He also takes the form of supreme Guru and he also plays the role of Brahma when he arrests him, none of the Gods other than Muruga have done this role. The son of shiva,He is Shakti herself, when he bursts out of Shiva in an energy never seen before, that Agni himself could not hold. (Episode of Kama and Shiva becoming Arthanaareeswara is before Kumara sambhavam). As He is Shakti herself goes ahead to say Shakti is the one able to unify the 6 children into one.
Kandar Kalivenba quotes: For one so young and nothing more than a small child, Muruga, you are called as the oldest one, it is surprising.
Maha vishnu is also called as the Oldest one...
He has many shapes and has no shape, one of the very few gods who has a temple with no frame - Kathirgama.
He is so simple, yet probably the most difficult to understand and hence very discarded at many places due to the complex nature. At many places, if at all he is understood, it is for the wrong reasons. :)