Fish identification archive / Costasiella arenaria

Costasiella arenaria

Costasiella arenaria

Fun facts for your next surface interval

Live and preserved specimens had different reported lengths. [source]
Its inflated cerata form several lengthwise rows. [source]
The corridor record is attributed to Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida. [source]

Florida and local context

Judy Townsend photographed Costasiella arenaria near Peanut Island on 15 January 2012; the page illustrates color variation.

A documented past record does not establish present abundance or guarantee an encounter.

Sources: Local occurrence record: Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida

How to recognize this animal

A small sacoglossan with closely spaced central eyes, a deeply notched head and inflated cerata arranged in three or four longitudinal rows on each side.

Sources: Biology reference for Costasiella arenaria

Size and life stages

The description records crawling animals 5–8 mm long and preserved animals 2–3 mm long. Preservation and live measurements must remain separate.

Sources: Biology reference for Costasiella arenaria

Habitat and where to look

The documented local setting is Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida. The source does not resolve a precise microhabitat or complete depth range; do not supply an exact reef or substrate that it does not name.

Sources: Local occurrence record: Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida

Range and local context

Corridor inclusion is based on Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida. Judy Townsend photographed Costasiella arenaria near Peanut Island on 15 January 2012; the page illustrates color variation. A historical record does not establish current abundance, and a Peanut Island record must not be relabelled as an exact Blue Heron Bridge observation.

Sources: Local occurrence record: Lake Worth Lagoon near Peanut Island, Palm Beach Inlet, Palm Beach County, Florida

What is on the menu?

The paper reports molecular analysis of pooled digestive-gland contents from four animals, identifying Bryopsis hypnoides and an unidentified pseudocodiacean alga. This is molecular food evidence, not a photographed feeding event or a complete diet.

Sources: Biology reference for Costasiella arenaria

Daily habits and behavior

The local record establishes presence at the stated place and time, not a daily activity schedule or encounter probability. Observe in place and record the animal’s substrate and posture; do not provoke a response for a photograph.

Mating and the next generation

The original description illustrates spawn with irregularly arranged egg capsules. The authors inferred planktotrophic development from egg-mass and capsule proportions; they did not demonstrate it by rearing larvae. The account does not establish a Florida breeding calendar.

Sources: Biology reference for Costasiella arenaria

Look-alikes and identification traps

Green cerata and close-set eyes do not establish the identity of every Costasiella. Several related species require finer anatomical or molecular comparison.

Sources: Biology reference for Costasiella arenaria; WoRMS: accepted identity

Observe without disturbing

Photograph the animal where it lives. Maintain buoyancy and keep fins, hands, lights and equipment clear of it and its substrate. Do not touch, feed, uncover, detach or reposition it. These observation practices do not grant permission to collect.

Harvest, protection and eating safety

Live collection only, where permitted

Listed marine-life group; live-only collection remains subject to location, gear and other restrictions.

This color is a qualified summary, not permission to collect or a guarantee that a particular animal is safe to eat.

Can it be hunted or harvested?

Costasiella arenaria maps to the FWC-listed marine-life group nudibranchs/sea slugs (FWC historical Opisthobranchia grouping). This is conditional live collection, not food harvest. Keep alive with adequate life support. Recreational saltwater license required; no recreational sale. Daily limit: five per species within 20 total marine-life organisms; possession: ten per species within 40 total. Use permitted collection gear only; do not remove live rock or damagingly detach a host. No annual season or trip clearance is asserted.

Florida seasons and areas

No year-round or current-trip clearance. Blue Heron Bridge mapped dive-site waters are closed to marine-life harvest; nearby Peanut Island records do not establish that exact location. Biscayne ornamental collection requires a superintendent permit. Its separate mapped fishing/possession closure is March 1–May 31, effective March 2026, with properly stowed continuous transit excepted. Key Largo Management Area prohibits collection of these invertebrates; lobster and commercial trap exceptions do not authorize their collection. Sanctuary Preservation Areas prohibit collecting. Check exact boundaries and current park requirements, including Pennekamp, before any take. General state rules do not override these areas.

Can it be speared?

Do not spear a live-only organism. State and federal jurisdictions differ. FWC location restrictions and NOAA Key Largo spearfishing prohibition must be checked independently. Pennekamp is not a spearfishing allowance.

Is it safe to eat?

No exact-species food-safety clearance, meal frequency, or dated species-matched local menu evidence was verified. Recipes remain disabled. Collection legality is not evidence of edibility.

This review covers the Vero Beach–Key Largo Atlantic corridor: Indian River, St. Lucie, Martin, Palm Beach, Broward, Miami-Dade and Monroe counties. Florida Atlantic state waters and South Atlantic federal waters are distinct jurisdictions. Do not extend a state-water season tag to federal waters or transfer Atlantic rules to Gulf-side Keys waters. Park and sanctuary boundaries can override a species allowance. FWC expressly states that its marine-life regulations apply in federal waters; this does not erase independent federal restrictions.

Before you act: Confirm the species, date, exact management area, state or federal waters, gear, licenses and current local closures. A local occurrence record never grants permission to take an animal.

Official rules and health guidance

Reviewed 2026-11-11. Rules and advisories can change; check the linked authorities before acting.

Identification and source cautions

All illustrated color forms count as one species.
The source names the Peanut Island / Palm Beach Inlet diving area, not an exact Blue Heron Bridge position. Do not relabel it as a BHB sighting.
This documents a past local record, not current abundance or a guaranteed encounter. Photographs remain copyrighted; no reuse rights are implied.
The exact local photograph is attributed to its source and has not been independently reidentified for this draft.
Biological source access varies: some records were accessible only as an abstract or indexed passage. Independent claim review is required.
No cited photograph is reproduced or licensed by this draft.

Sources and review

Reviewed 2026-11-11; biological claims and this representative illustration independently checked. Photographs on cited sites are reference material and are not reproduced here.

Make your next dive happen

Review current dates, availability, prices, inclusions and requirements on each listing before booking or buying.

Call us now

(772) 600-8288

Ask about marine life identification

Marine Life Identification

Ask about dates, prerequisites or your next step. An inquiry does not reserve a place. Please provide your own contact details; do not include medical, payment or a child's personal information.

We use these details to respond to your inquiry. This form does not sign you up for marketing.