Cockroach Anal Cerci and Anal Styles (Sexual Dimorphism)
Biology · Structural Organisation in Animals · NEET
Anal cerci are a pair of jointed, thread-like sensory structures on the 10th abdominal segment, present in BOTH male and female cockroaches. Anal styles are a pair of short, thread-like structures on the 9th abdominal segment found ONLY in the male, so they are the feature of sexual dimorphism. Memory hook: "Styles = 9 = boy only; Cerci = 10 = come in both."
Anal cerci sit on the 10th segment in both sexes; anal styles sit on the 9th segment in the male only, making styles the feature of sexual dimorphism.
Your doubts, answered
Are anal cerci present in both male and female cockroaches?
Yes. Anal cerci are present in BOTH sexes. They are a pair of jointed, thread-like (filamentous) structures on the 10th abdominal segment. Because they occur in both sexes, they do NOT show sexual dimorphism and cannot be used to tell males from females.
Which segment bears the anal styles, and who has them?
Anal styles arise from the 9th abdominal segment and are found ONLY in the male. They are short and thread-like. Females do not have anal styles, so the presence of anal styles is the chief external feature that distinguishes a male cockroach from a female.
What is the difference between anal cerci and anal styles?
Anal cerci: 10th segment, both sexes, sensory (detect air currents and vibrations). Anal styles: 9th segment, males only, part of sexual dimorphism. Remember: styles are on the smaller number (9) and belong to only one sex; cerci are on 10 and belong to both.
Which cockroach feature shows sexual dimorphism?
The presence of anal styles in the male shows sexual dimorphism (a structural difference between male and female). Anal cerci do NOT, because both sexes have them. Sclerites and body colour are also present in both sexes, so they are not dimorphic features.
Are anal cerci reproductive structures?
No. Anal cerci are SENSORY, not reproductive. They help the cockroach detect air movement and vibrations, useful for escaping predators. Do not confuse them with reproductive parts like the genital pouch.
Do female cockroaches have a genital pouch?
Yes. In females, the 7th, 8th and 9th sterna together form a genital pouch (brood pouch). This is a separate female feature, not related to anal styles, which the female lacks.
⚠️ The NEET trap ✗ Anal cerci are present only in the male and show sexual dimorphism. ✓ Anal cerci are present in BOTH sexes (10th segment) and do NOT show dimorphism; only anal styles (9th segment, male only) do. 🧠 NTA swaps cerci and styles. Cerci = both sexes = no dimorphism. Styles = male only = dimorphism.
Real NEET questions
NEET 2018
Which of the following features is used to identify a male cockroach from a female cockroach?
A · Forewings with darker tegmina
B · Presence of caudal styles ✓
C · Presence of a boat shaped sternum on the 9th abdominal segment
D · Presence of anal cerci
Solution: In the male cockroach, the 9th abdominal sternum bears a pair of short, thread-like anal styles (caudal styles), which are absent in females. This is the chief external feature used to tell the sexes apart. Anal cerci are present on the 10th segment in both sexes, so they cannot distinguish them.
NEET 2023
Which of the following is characteristic feature of cockroach regarding sexual dimorphism?
A · Dark brown body colour and anal cerci
B · Presence of anal styles ✓
C · Presence of sclerites
D · Presence of anal cerci
Solution: Sexual dimorphism is a structural difference between male and female. The male cockroach bears a pair of anal styles on the 9th segment, absent in females, so this shows dimorphism. Anal cerci (both sexes), sclerites (both sexes) and body colour are common to both, so they are not dimorphic.
NEET 2024
In both sexes of cockroach, a pair of jointed filamentous structures called anal cerci are present on:
A · 10th segment ✓
B · 8th and 9th segment
C · 11th segment
D · 5th segment
Solution: The abdomen has 10 segments. In both sexes, the 10th segment bears a pair of jointed, filamentous anal cerci, which are sensory (detect air currents and vibrations). The male additionally has anal styles on the 9th segment, which are the basis of sexual dimorphism.
Solved Structural Organisation in Animals NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Anal cerci are present on the 10th abdominal segment, in both male and female cockroaches.
On which segment are anal styles present and in which sex?
Anal styles are on the 9th abdominal segment and are present only in the male cockroach.
Are anal styles also called caudal styles?
Yes. Anal styles are also called caudal styles. Both names refer to the same male-only structures on the 9th segment, as seen in the NEET 2018 question.
What is the function of anal cerci?
Anal cerci are sensory. They detect air currents and vibrations, which helps the cockroach sense danger and escape quickly.
Why do anal cerci not show sexual dimorphism?
Because both males and females have anal cerci on the 10th segment. A dimorphic feature must differ between the sexes, so cerci cannot be used to distinguish them, but anal styles can.
