Argyrotheca

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Argyrotheca is a genus of very small brachiopods, or lampshells, that reach up to about 5 mm in length. They live in oceans worldwide, from shallow waters to depths around 1300 meters, and they attach to hard surfaces with a short, thick stalk. The shells are biconvex and carry two high central ribs with additional radiating ribs. Inside, there are many coarse pits arranged in a diamond pattern. A large opening for the pedicle is toward the back of the ventral valve. Some species have red stripes radiating from the pedicle opening, a rare color pattern among living brachiopods that may help camouflage.

Reproduction is unusual. Argyrotheca species are hermaphrodites and brood eggs in enlarged nephridia that act as a brood pouch. Fertilization can occur with their own sperm or with sperm from the water. Early larval development happens inside the brood pouch, and the young spend only a short time free-swimming before settling as tiny fixed shells. In the Mediterranean, A. cordata and A. cistellula brood year-round, while A. cuneata tends to breed in autumn. These brachiopods are very small and short-lived, with life spans around a couple of years, which helps explain their rapid reproductive strategy.

Today Argyrotheca is found in the Atlantic, Pacific, Mediterranean, Red Sea, and Persian Gulf. In the Mediterranean three species occur: A. cordata, A. cuneata, and A. cistellula. A. cistellula is tiny (up to about 2 × 3 mm) and attaches to hard substrates at 20–100 meters, living off Norway, the United Kingdom and Ireland, and southern Italy (Sardinia and Sicily). A. cuneata has been found near Bermuda on coral and, farther south, off Brazil on shell fragments at 100–200 meters. A. jacksoni occurs in the Red Sea and Persian Gulf at 5–16 meters and is distinguished from A. cuneata by a pink-red wash between the ribs.

In taxonomy, Joania was recently separated from Argyrotheca. Argyrotheca has a brood pouch and hermaphroditism, while some related species like A. rubrocostata lack a brood pouch and have separate sexes, a difference that influences how scientists view their evolutionary relationships.