What is meant by the phrase, "in the shape of a leech, elongated," mentioned in Ibn Kathir's Tafsir for the noble verse (Then We made the Nutfah into an 'alaqah...)?

Ibn Kathir meant that the nutfah (sperm drop) became an 'alaqah (clot of blood), which is a thick piece of blood, and its shape is oblong, i.e., long. No scholar who commented on or explained his tafsir has clarified Ibn Kathir's intent in this regard.