Spondoolies is a slang word for money: https://www.etymonline.com/word/spondulicks . I'd be surprised if there's any more to it than that, but according to the Wikipedia article, the shells were used as currency, so at least it's plausible as an etymology.
The title suddenly reminded me of this beautiful story [1] I read more than a decade ago, where spondylus plays a key role:
> [I]t was a sense of morbid attraction that led me to Diane Ackerman's newest book One Hundred Names for Love, in which she documents the stroke and subsequent language deficit suffered by her husband, novelist Paul West.
> [...]
> Oddly, it was often the most obscure words that were easiest to recover. He struggled with words like blanket or bed, or his wife's name Diane, words that you would think over time should have seeped into his genes. Nevertheless, he could recruit words like postillion or tardigrades to get an idea across.
> [...]
> At times, his speech sent even his verbally-endowed spouse scrambling for a dictionary. When trying to ask her whether she'd received a check as payment for some work done, he resorted to the word spondulicks, which prompted the following exchange:
>> "What's a spondulick?"
>> "Money."
>> "Really? Truly? Spondulicks?" In my mind's eye, I pictured a spastic duck.
>> "Yes," he said emphatically.
>> "Spondulicks?"
>> "Spondulicks. It's British."
>> Surely he was pulling my leg. I breezed into the library to look it up in an etymological dictionary, where I found this entry:
>> 1856, Amer.Eng. slang, "money, cash," of unknown origin, said to be from Gk. spondylikos, from spondylos, a seashell used as currency (the Gk. word means lit. "vertebra"). Used by Mark Twain and O.Henry and adopted into British English, where it survives despite having died in Amer.Eng.
Over time, West recovers:
> The intimate wordplay between West and Ackerman also eventually resumed, with West fashioning novel terms of endearment as gifts to his wife. The offerings were delightful. Deprived of the usual routes to language, and along with them, the common clichés that many of us struggle to shed, West bestowed on his wife exquisite pet names such as: My Little Bucket of Hair; Commendatore de le Pavane Mistletoe; Dark-Eyed Junco, My Little Bunko; Diligent Apostle of Classic Stanzas. And at one point, the man uttered what has to be the most searingly romantic sentence ever uttered in history, by anyone, in any language:
Mark Twain does in fact use it, it's in Huckleberry Finn,
- "“Yes,” he says, kind of pretty-well-satisfied like. “I’m the captain and the owner and the mate and the pilot and watchman and head deck-hand; and sometimes I’m the freight and passengers. I ain’t as rich as old Jim Hornback, and I can’t be so blame’ generous and good to Tom, Dick and Harry as what he is, and slam around money the way he does; but I’ve told him a many a time ’t I wouldn’t trade places with him; for, says I, a sailor’s life’s the life for me, and I’m derned if I’d live two mile out o’ town, where there ain’t nothing ever goin’ on, not for all his spondulicks and as much more on top of it. Says I—”"
[0] https://www.coindesk.com/tag/spondoolies-tech/