Phallichtys fairweatheri
This livebearer is als known as "Banded merry widow" but also as "Picotee livebearer".
Phallichthys fairweatheri can be found in slowly flowing and standing marshy peripheral area of rivers in countries like Mexico to Guatemala, Belize and Honduras.

Best kept at water temperatures between 22°C - 25°C. 

It's a gray bodied livebearer with some yellow vertical markings on its body and also in the fin area there are some yellow markings to be noticed.  Both sexes are having a dark splotch on the lower part of the rear part of the body. Like most Phallichthys breeds, the male has got an extended gonopodium. One of the Phallichthys breeds that has a less extended gonopodium is the Phallichthys quadripunctatus. 

Above: An adult male.

After a gestation of approx. 3 - 4 weeks a number of 10 - 30 fry will be dropped. They'll size up to approx. 3 - 5cm.

Phallichthys quadripunctatus
This small livebearer is also known as the "Four spotted merry widow". "Four spotted" simply because there are in general four black (sometimes three or five) dots on both sides of the fish. And the number of dots can differ per side.
This species is endemic to Rio Sixaola in the eastern part of Costa Rica. It's not a very prolific livebearer for after a gestation of 4 weeks 5 to 20 fry will be born. From own experience the average number of fry will be 10-15.

They tolerate water temp rates between 18°C and 34°C. Which makes this species an easy fish to keep. But it's preferable to keep them between 20°C - 24°C. If kept higher they do well but won't grow up the max size they can potential reach. 
And because of their size, they can also be kept in smaller tanks. Furthermore, they're friendly fish. Even to their own newborn offspring.

Phallichthys amates pittieri
This livebearer is also called "Orange-fin merry widow", "Iridescent widow' and "Olomina"  and are to be found in inland and mountain streams in Costa Rica (Cahuita) and Northern Panama.

The species does look similar to the Phallichthys amates amates but is really smaller in size. They'll size up till 3 - 4cm in length. After a gestation of 4 - 5 weeks they'll reproduce a number of 10 - 30 fry.

Also with this Phallichthys breed the males have an elongated gonopodium.

Phallichthys tico
A small livebearer from Costa Rica is the Phallichtys tico also known as the dwarf merry widow. This species is to be found in still and turbid waters (mostly swamps and backwaters). Further on they occur in Rio Puerto Viejo and between the floating plants of the former Lago Arenal and Lake Nicaragua (mostly along the shoreline). Because they also live in Lake Nicaragua which is close to Nicaragua, it's possible to find them also in southern Nicaragua. And they're also known from the tributaries of Rio San Juan.

This is a peaceful small livebearer that can be kept at temperatures, ranging from 22°C - 30°C. They prefer neutral till hard water. They're timid fish and therefore, it's preferable to get some hiding spots for them.

The body is brown till greyish based with 8-10 vertical bars on each side. These bars are more present with males and young fish. In some way the bars disappears when a female comes to adulthood. And with both genders, the dorsal has got a black seam. They'll reach up max. 3,5 cm.