Cannot scan first part of a poem in the Satyricon

Question

I don't recognize the meter for the first part of this poem found in the Satyricon. I have scanned it as follows. The rest of the poem however seems to be in tetrameters as is shown at this website http://www.pedecerto.eu/public/scansioni/query

- u u - - - u - u - - -
artis sevērae sī quis ambit effectūs

- - u - - - u u u - - -
mentemque magnīs applicat, prius mōrēs

- - u u u - u u u u - - u
frūgālitatis lēge poliat exācta.

- - u - - - u u u - - -
nec cūret altō rēgiam trucem vultū

u - u - - - u - u - - u
cliēnsque cēnās impotentium captet,

- - u - - - u - u - - -
nec perditīs addictus obruat vīnō

- - u - - - u - u - - u
mentis calōrem, nēve plausor in scaenam

u u u u - u - u - u - - -
sedeat redēmptus histriōnis ad rictūs.

THE REST OF THE POEM SEEMS TO BE TETRAMETERS

sed sīve armigerae rīdent tritonidis arcēs
seu lacedaemoniō tellūs habitāta colōnō
sīrenumve domus, det prīmōs versibus annōs
maeoniumque bibat fēlīcī pectore fontem.
mox et sōcraticō plēnus grege mittat habēnās
līber et ingentis quatiat demosthenis arma.
hinc romana manus circumfluat et modo grāiō
†exonerāta† sonō mūtet suffūsa sapōrem.
interdum subducta forō det pāgina cursum
et fortūna sonet celerī distīnctā meātū:
dent epulās et bellā trucī memorāta canōre,
grandiaque indomitī ciceronis verba minēntur.
hīs animum succinge bonīs: sīc flūmine largō
plēnus pīeriō dēfundēs pectore verba.'

Answer 1

It's choliambic meter:

x — u — | x — u — | u — — —

I'll capitalize the long syllables so you can see it in action:

AR·TIS·se·VE|RAE·SE·quis·AM|bit·EF·FEC·TUS

Where you get three shorts instead of long-short-long, you have to remember that a long vowel can resolve into two short ones.

Starting from line 9, it's actually dactylic hexameter. Capitalizing again:

SED·SI·V'|AR·mi·ge|RAE||RI|DENT·TRI|TON·id·is|AR·CES