Panderevela hyllebergi K. R. Jensen, 2021

Location: Little creatures, Miyakojima, Okinawa, Japan
Date: 2026/04/30
Length: 4mm
Depth: 15.0m
Water temperature: 25.0℃

Description

A minute sea slug, only about 2 mm in body length when alive. The dominant ground color is intense black, covering the cerata, rhinophores, and lateral surfaces of the head. The anterior groove of the head, the tips of the cerata, the foot sole, paired patches around the eyes, and parts of the lateral head surface lack pigmentation and appear white.
Cerata are fusiform, each bearing a narrow sub-terminal orange band and a transparent tip with a black spot on one side.
Rhinophores are cylindrical with a slightly flattened base; the tips are white in most preserved specimens. The anterior face of the head bears black longitudinal bands flanking a pair of raised crests separated by a marked median cleft.
The pericardial prominence is short and ovoid, often marked posteriorly by a small white spot or stripe.
Preserved specimens measured 1–1.9 mm and live specimens reached only about 2 mm, making this one of the smallest sacoglossans known.

Distribution

Known only from the type locality at Rawai Beach, southern Phuket Island, on the Andaman Sea coast of Thailand. Specimens were collected only in November 1986 and November 1990; subsequent searches at the same site have failed to locate further individuals, suggesting the species is rare.
A morphologically similar but unnamed taxon from Guam (referred to in molecular studies as Costasiella sp. 4 in Krug et al., 2015) may be closely related, but differs in lacking the sub-terminal orange band and apical black spot on the cerata, and is treated as a distinct undescribed species.

Etymology

Named in honor of the late Prof. Jørgen Hylleberg, a Danish marine biologist who introduced the author (K. R. Jensen) to marine biology in Thailand, the Phuket Marine Biological Center, and the Tropical Marine Mollusc Programme.

Remarks

Found on thalli of the siphonalean green alga Avrainvillea spp., often inside the sand-encrusted stipes.
The genus Panderevela was established by Moro and Ortea 2015 for species previously confused with Costasiella. It is distinguished from Costasiella by having median eyes located behind (rather than between) the rhinophores, lacking pedal tentacles and protruding foot corners, and bearing rhinophores whose lateral extensions continue onto the front of the head to form crests separated by a marked median cleft. Panderevela hyllebergi is the first species of the genus to be described from the Indo-Pacific region.
All available specimens were fixed in formalin, so DNA analyses have not been possible.