They have been replaced in Europa Barbarorum II (I see you took your inspiration from EB1), now the Parthians and the Seleucids have access to:
Payadag i Kardakan / Persian Heavy Spearmen
These men have been trained and carry uniform equipment, making them more reliable than other eastern infantrymen. Equipped with thureos shields and spears, they provide a strong infantry line, which levied men would not be able to hold against organised opposition.
Historically the Hakhamanishiya had always promoted a common education, in theory open to everyone, but only the nobility could truly afford it. All of this resulted in a comprehensive system, which provided future officials and administrators, but was also integral to the preparation for military life. Split in companies of 50 youths, led generally by the noblest of them, they followed a daily routine of exercises and studies. Specifically they were trained to increase their endurance through proper breathing techniques, but also how to resist the cold, heat and rains, to cross streams while keeping their clothing and armour dry, to tend to flocks and how to live outdoors all night, eating wild fruits like pistachios, acorns and pears. Moreover these youths ate and hunted together, while after their exercises they were instructed in the planting of trees, cutting and gathering of wood or roots and the making of weapons, hunting nets and linen clothing. All of this signified a rite of passage, because during this period the youths proved that they could be admitted to the adult part of society.
Even ancient authors noted the similarities to the Spartan Agoge and especially the Krypteia, however Strabon recorded how these youths were known as Kardaka, because Karda according to him meant manly and warlike spirit. This root word however, actually described those wandering or travelling, denoting the behaviours these youths had to learn. With the shortage of Hellenic mercenaries in the late 4th century BC, the Satrapal administration extended part of this system to young men in their dependencies, in order to develop a larger pool of trained infantry. This very infrastructure later allowed Alexandros Megas to muster and train Asiatikoi in Hellenistic warfare and indeed the practice was kept alive by the Seleukidai, who improved the Kardaka even further by furnishing them thureos shields.
Erin-mesh Uriki / Akkadian Elite Infantry
These men are the closer order infantry of the Akkadian peoples of Mesopotamia. Many of them wear some armour, helmets and light thorakes, and all carry aspides to go with their long spears. The spears give them good length when defending city walls, fending off cavalry, running down light troops, or challenging sarissa-equipped phalanxes. The Erin-mesh Uriki are drawn from the citizen rolls of Akkadian cities, and were customarily employed as guardians of cities and temples and as emergency militia during wartime.
Historically, the heyday of Akkadian arms was well past, although the monuments of Babylon, Uruk, and other places stand as testament to the Akkadians of the power their forefathers once held. The Akkadians were well-accustomed, for many years, to both pitched battle in close order formation and to skirmishes against lighter troops from the Arabian desert to the southwest and the highlands to the east. In the Persian Wars, the Akkadians were marshalled together with the Assyrians and Arameans, and even then carried concave round shields comparable to the aspis, lengthy spears, and variations of the machaira (Hdt. 7.63). Akkadians fought at Gaugamela as well under the satrap Mazaios, but soon after found themselves under Makedonian rule. Six thousand were trained by Macedonian instructors and joined Alexander's army in Bactria as pantodapoi, while others continued to serve, probably in traditional panoplies, in garrison duty roles. Babylonian tablets provide strong evidence that Akkadians continued to play limited, mainly regional military roles. Babylonian troops suffered heavy casualties against Ptolemaic phalangites in defence of their city in 245 BC due to their lighter equipment, but managed to hold a few key sectors of the city.
Nezagdar / Iranian Spearmen
These men represent the lower ranks of retainers to the Azads and nobles who come to the aid of the Shahanshah. They are not wealthy enough to possess their own horse, but are still able to possess enough equipment to fight as line infantry instead of as skirmishers. Armed with spear and reed shields, they can hold a line against lighter foes, but are not able to hold their own for long against more heavily armed opponents.
Most of the men in this unit are dressed in everyday clothes, including cloth jackets, pants and leather boots or shoes. Many wear a Kyrbasia, a hat with flaps which can be tied under the chin, or around the back of the neck of the wearer. Often, the flaps could be used to cover the mouth and nose, useful when in arid conditions, where dust clouds from marching would otherwise make breathing hard. Others wear simple cloth caps. Some of them wear tube and yoke armour corselets, made from leather or hardened linen, sometimes with padding added for extra protection. Their reed shields would be made from long pieces of reed on a leather base, where the reeds were fastened by being pushed through holes made in the leather. In this manner, it was possible to render impressive geometric patterns without the need for any paint or other decoration. They carry spears equipped with a ball-shaped butt, which helps to balance the weapon while fighting.
Historically, the armies of ancient Iran consisted of generally mounted noblemen, accompanied by their retinue, and levies from their lands. The more elite warriors were often funded by the nobleman himself: the rest were generally civilians who followed their local noble. Although the most prominent section of an Azad's retinue was the armoured cavalry, a larger portion was made up of less well trained and well equipped men. Those peasants and townsmen who could not afford a war horse, but were wealthy enough to purchase armour and weapons would serve as the line infantry. Men like these would have made up the majority of the armies faced by Alexandros, and still during the age of Parthian, and even Sassanian, hegemony, such men would be the mainstay of the infantry forces in Iranian armies.