97. The "Melon" Radical: 瓜
The "melon" radical 瓜 looks exactly like this non-Joyo kanji:
瓜 (うり: melon)
As a radical (also pronounced うり), this five-stroke shape has no variants and is on duty in no Joyo kanji. It does, however, serve as a component in these two Joyo characters:
孤 (1229: solitary), where 子 (radical 39: "child") is on duty
弧 (1230: arc), where 弓 (radical 57: "bow") is on duty
As in these examples, 瓜 almost always appears on the right side of a kanji, whether this shape serves as a radical or a mere component. The only exception is the non-Joyo 瓣, a variant of the Joyo 弁 (speaking). In 瓣, the 瓜 lies in the middle, so squished that it's hard to recognize.
According to Henshall's newer edition, the 子 in 孤 means "child," whereas 瓜 (squash, melon, gourd) serves as a phonetic conveying “nothing to rely on” or “suddenly separate, lone,” depending on which researcher you ask. Thus, the whole 孤 character represents "orphan."
Though his experts pay no attention to 瓜 as “gourd” and the like, Kanjigen does. That source says that the two halves of 孤 collectively refer to a solitary child that looks like a round gourd lying on the floor! The same source notes that because an infant's cry is referred to as 呱 (コ), an infant's wails came to be called 孤 (コ).
As for 弧, that combines 弓 (bow) with 瓜! Is this an odd twist on the William Tell story of shooting an apple balanced on someone's head?!
No, according to Henshall, this 瓜 phonetically contributes the associated sense "round, rounded," yielding "curved bow" as the overall meaning of 弧. Originally, this character likely referred to a "type of bow with a particularly pronounced and curved profile," he says, adding that this sense later generalized to "arc shape."
Kanjigen says much the same thing, calling 瓜 a pictogram of a "round gourd hanging down." Thus, 弧 represents a "curved bow."