Cockroach morphology: anal styles vs anal cerci, tegmina vs hindwings, and the mosaic vision thing
Diya Menon11th Sample
15 Oct 2026 · 1 min read
Doing cockroach (Periplaneta americana) tonight and omg the amount of tiny facts! 🪳
What I've written: body is divided into head, thorax and abdomen. Covered by a chitinous exoskeleton made of hardened plates called sclerites: dorsal tergites, ventral sternites, lateral pleurites, joined by arthrodial membrane. Head is triangular, with two compound eyes, antennae and mouthparts for chewing.
The parts I can't keep straight:
- Thorax has three segments with one pair of legs each. Wings: forewings are tegmina and hindwings are transparent, and which one actually works for flying?
- Abdomen has 10 segments. Anal cerci and anal styles? Male vs female? I wrote both are in both sexes and my sheet is crossed out in red by my own brain.
- Each compound eye has about 2000 ommatidia. What's "mosaic vision" and why is it called nocturnal vision?
- The female's 7th sternum, what about it?
7 answers & replies
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[+][–]Nisha Verma12thSample· 4d ago
Cerci and styles: anal cerci are a pair of jointed filamentous structures on the 10th segment in both males and females. Anal styles are a pair of short, thread-like structures that come from the 9th sternum of the male only. So "styles are for males, cerci are for everybody". The female doesn't have them. So you can sex a cockroach by looking for styles!
[+][–]Diya Menon11thSample· 4d agoAuthor
sexing a cockroach by styles is both gross and genius. thank you!!
[+][–]Lakshmi TripathiDropperSample· 4d ago
Wings: both pairs are on the thorax. Forewings (tegmina) arise from the mesothorax, they're opaque, dark and leathery and cover the hindwings when at rest, a protective role. Hindwings (on the metathorax) are transparent and membranous, and they're the ones used for flying. So tegmina are cover, hindwings are flight. Legs: one pair on each thoracic segment, prothorax, mesothorax, metathorax, giving three pairs total.
[+][–]Tanvi Deshmukh12thSample· 4d ago
Mosaic vision: the compound eye has about 2000 hexagonal ommatidia, and each one gets its own bit of the picture. The brain stitches several small images into a whole, like a mosaic. NCERT says it gives more sensitivity but less resolution, and that is common at night, so it's also called nocturnal vision. Nice for a night active animal that needs to catch faint light more than sharp detail.
[+][–]Rahul DubeyDropperSample· 4d ago
The 7th sternum in the female is boat-shaped and, together with the 8th and 9th sterna, forms a genital pouch (brood pouch) in which the egg capsules (oothecae) are formed. Both sexes have 10 abdominal segments in total, but the last segments are a bit reduced/tucked.
Mouthparts as a bonus: labrum (upper lip), a pair of mandibles, a pair of maxillae, labium (lower lip), and hypopharynx (the tongue-like structure acting as a salivary base). They're "chewing and biting" mouthparts. NCERT names them in this order.
[+][–]Aarav Kulkarni11thSample· 4d ago
quick doubt from class 11 as well: is the head at 90 degrees to the body? I read that the head is held "at right angles to the longer body axis" so it's a hypognathous head? Just trying to understand if I have to remember the term.
[+][–]Rahul DubeyDropperSample· 4d ago
Don't stress on the term. NCERT just says the head is triangular and lies anteriorly, at right angles to the longer axis of the body. Antennae, compound eyes in front. You don't need the word "hypognathous" for NEET.
