- merging s س with š ش and z ز with ž ج (this feature seems to have been emblematic, and was even extended to Jewish second language pronunciations of Berber)
- no -i- in the perfect forms of geminate-final verbs - thus dəqq-t دقّت "I knocked" instead of nearly universal dəqq-it دقّيت (also occasionally attested in Jbala dialects)
- relative marker di دي (similar to Jbala d), rather than li لي
- ama أما "which" - common in Algeria and Tunisia, but otherwise unknown in Morocco
- an allomorph -hu- of 3MSgAcc "him" when followed by a dative pronoun - common in Algeria and Tunisia, but otherwise unknown in Morocco
- ṛa را "see"
- qum قوم "get up"
- dnba دنبة "tail"
- skkin سكّين "knife"
- guf ڭوف "body", from Hebrew
- gaṛfu ڭارفو "fork", from Spanish
- ɣyyəṛ غيّر "eat breakfast"
However, far more of the features that made Jewish dialects distinctive in their 20th century locations are shared with a particular subset of Muslim dialects: the northern ones. Among the more striking features shared by Jewish dialects all over Morocco with Muslim dialects of the far north or the Jbala - and, in many cases, with "pre-Hilalian" dialects of old cities like Fez, or of coastal regions further east in Algeria or Tunisia or Malta - are:
- dual marker -ayn ـاين (an archaism)
- future marker maši ماشي
- bn بن "son" (an archaism)
- ħəbb حبّ "want"
- ʕməl عمل "do"
- ṣib صيب "find"
- ʕəbbi عبّي "take away"
- bzəq بزق "spit"
- fħal فحال "like", rather than bħal بحال
- Most Moroccan Jews originally came from northern Morocco, and they kept northern features when they emigrated.
- Most Moroccan Arabic speakers (at least in the towns, where most Jews lived) used to talk more like Northerners do today, and dropped these features in order to sound more like people from other regions.
There isn't much evidence for 1), so 2) is the most widely accepted explanation. That implies that mainstream (Muslim) Moroccan Arabic has been fairly heavily influenced by contact with Arabic dialects coming in later from further east. In fact - hard as it may be for students to believe - it means that mainstream Moroccan Arabic, even before TV, was already a compromise between the urge to maintain local forms and the urge to adopt trends coming in from the rest of the Arabic-speaking world.
So all of this is relatively clear for Morocco. What about Algeria?
For Algeria, nothing like Heath's religious dialect atlas exists or can be written, because almost all Algerian Jews had already abandoned Arabic well before independence in 1962. Algeria's Jews had received French citizenship in 1870, and all but the most isolated communities hastened to prove their loyalty to France by, among other things, adopting French as their home language. Then again, there isn't any dialect atlas of Algeria to begin with, so even where data on Jewish dialects exists, it's difficult to determine what features were distinctive or how they fit into a broader picture. Nevertheless, a few points can be gleaned. For western Algeria ("Oranie"), Cantineau (1940) paints a picture strikingly reminiscent of Morocco: all the Jewish dialects there shared phonetic and syntactic features specific among Muslim dialects to the mountainous coastal Trara region, around Nedroma and Ghazaouet. Unfortunately, he only mentions a handful of features, and gives very little specific data. For eastern Algeria ("Constantinois"), Cantineau reports elsewhere - again in rather general terms - that the Jews of Constantine and Annaba spoke sedentary dialects like those of the towns of Bejaia and Constantine and the mountains of Jijel and Skikda.
I haven't yet been able to see Cantineau's comments on central Algeria, but the vague picture he paints for these areas fits rather strikingly with the more detailed image given by Heath further west: in both Morocco and Algeria, the geographical dialect groups to which Jewish dialects belonged irrespective of location were eccentric "pre-Hilalian" ones spoken on the northern coast, at old ports and their mountainous hinterlands - even though those dialects do not themselves form a continuous territory. That raises a lot of questions about the region's linguistic history (which the label "pre-Hilalian" kind of sweeps under the rug), but those will have to wait for another time...