Persistent ancestral feeding structures in nonfeeding annelid larvae.

Area of Science:

• Marine Biology
• Developmental Biology
• Evolutionary Biology

Background:

• Larval feeding structures in marine invertebrates often disappear with the loss of feeding requirements.
• Echinoderm studies indicate rapid larval evolution after feeding loss, but data from other groups are limited.
• Understanding evolutionary patterns across taxa is crucial for generalizing these findings.

Purpose of the Study:

• To investigate the retention of larval feeding structures in annelids (Sabellidae) despite the loss of feeding.
• To examine the functional state of particle capture systems in sabellid larvae.
• To propose a hypothesis for the evolutionary loss of larval feeding in annelids and other spiralians.

Main Methods:

• Comparative analysis of larval morphology in the Sabellidae family.
• Observation of particle capture and transport in *Schizobranchia insignis* larvae.
• Histological examination to assess gut functionality in larvae.

Main Results:

• Many Sabellidae species retain ancestral particle capture systems (ciliary bands) despite lacking functional guts.
• *Schizobranchia insignis* larvae concentrate and transport particles to the mouth, but reject them due to an absent functional gut.
• The persistence of these systems suggests recent feeding loss, low construction/operation costs, or alternative functions.

Conclusions:

• Larval feeding structures can persist even after the loss of feeding ability in annelids.
• The Sabellidae provide a model for studying the recent evolutionary loss of larval feeding.
• Retention of particle capture systems may inform hypotheses on the evolution of increased egg size and loss of larval feeding in spiralians.