The mouthparts form a tubular sucking organ, the proboscis (from McAlpine 1981)
The mouthparts of most higher Diptera consist of a tube-like sucking apparatus, the proboscis. The main parts of the proboscis are the basal fulcrum, and the labium with the distal labella. The proboscis is connected to the head capsule by the clypeal membrane. The fulcrum is surrounded by this membrane. Anterolaterally at the distal end of the fulcrum are the maxillae. Cardo, stipes, and lacinia are fused to each other, but the cardo and stipes are enclosed within the clypeal membrane, while the lacinia is external. The stipes bears the maxillary palpus at its proximal tip and in most acalyptrate flies there is a ventral appendage at the middle of the stipes (Frey 1921).
The labium consists of the proximal prementum and the distal labella. The prementum forms a trough on the ventral side, in which the hypopharynx and labrum are situated. At its distal end it bears the paired labella. The inner surface of the labella is furnished with small sclerotised grooves, reminiscent of tracheae, which are called pseudotracheae. The pseudotracheae radiate from the terminus of the food canal and are used to distribute saliva and to suck up liquids. They are braced by a series of sclerotised rings, the tips of which can be of different shapes. Zaitsev (1982) distinguished two basic types of pseudotracheal ring tips: the dentate type (rounded or flattened tips) and the spinose type (elongated and pointed tips). Intermediate shapes of the ring tips are possible (Elzinga & Broce 1986).
Because the proboscis is short and not geniculate in most Schizophora and in the Acartophthalmidae, I think that this is also the shape of the proboscis in the stem-species pattern of the Chloropidae family-group. 
The proboscis of the Carnidae is apomorphically highly specialised: the prementum is strongly sclerotised and bulbous, and the labella are very short and inconspicuous.
An apomorphy for the Milichiidae+Chloropidae is a slightly elongated and geniculate proboscis, which means that the labella are folded back. I have not included this character in the cladistic analysis, because it is very difficult to decide whether a proboscis is slightly elongated or not elongated, and if it is only slightly elongated, whether it is geniculate or not. The geniculation is only easy to see in long probosces. In species with a strongly elongated proboscis, the labium with the labella and sometimes the fulcrum is elongated, but never the stipes (from Brake 2000)
In general there are two main types, the piercing and sucking type found in bloodsucking and predacious groups such as biting flies, Asilidae, and Empididae; and the lapping and sucking type found in the Anisopodidae, Tipulidae, Chironomidae, and Stratiomyidae and in most higher Diptera. However, both these types vary considerably. Typically, the proboscis consists of three unpaired and two paired elements. The three unpaired elements are the labrum, forming the dorsal wall of the proboscis; the labium, forming the ventral wall of the proboscis; and the hypopharynx, projecting between the other two elements. The two paired elements, also arising between the labrum and the labium, are the mandibles anterolaterally and the maxillae posterolaterally (from McAlpine 1981)
pl.: probosces