# Aplysia vaccaria
**Aplysia vaccaria** is a species of large sea hare, a shell-less marine gastropod mollusc of the family Aplysiidae, found on the Pacific coast of North America from [Monterey Bay](https://www.edgepedia.org/monterey-bay), California, to the [Gulf of California](https://www.edgepedia.org/gulf-of-california) and typically living in subtidal waters[1](https://www.marinespecies.org/aphia.php?id=568031&p=taxdetails). It is commonly called the California black sea hare or giant black sea hare, and it is the largest sea slug in the Eastern Pacific, reaching up to 99 cm in length[2](https://academic.oup.com/view-large/565038917) • [3](https://www.aquariumofpacific.org/onlinelearningcenter/species/california_brown_sea_hare/).
| Key fact | Detail |
|---|---|
| Scientific name | *Aplysia vaccaria* L. R. Winkler, 1955; type locality San Pedro, southern California[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797) • [1](https://www.marinespecies.org/aphia.php?id=568031&p=taxdetails) |
| Size | Up to 99 cm long, usually about 50 cm; up to 30 inches (76 cm) and 35 pounds (16 kg) by an earlier account[2](https://academic.oup.com/view-large/565038917) • [5](https://ncshellclub.com/wp-content/uploads/2025/07/1983-NCSC-BULLETIN-10.pdf) |
| Distribution | Monterey Bay to the Gulf of California; typically subtidal[1](https://www.marinespecies.org/aphia.php?id=568031&p=taxdetails) |
| Coloration | Black or dark brown, sometimes with fine white dots; Gulf of California animals with brownish spots[2](https://academic.oup.com/view-large/565038917) |
| Ink production | Absent, unlike inking species such as *Aplysia californica*[2](https://academic.oup.com/view-large/565038917) |
| Synonyms | *Aplysia cedrosensis* Bartsch & Rehder, 1939 (provisional); *Aplysia reticulopoda* Beeman, 1960[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797) |
## Description
The species was described by L. R. Winkler in 1955 from San Pedro, California, as a large purplish black animal with posteriorly fused parapodia, the wing-like lateral body extensions of sea hares, and a broad internal shell with a shallow sinus[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797). Adults usually measure about 50 cm and reach up to 99 cm, making it the largest species in the Eastern Pacific by a wide margin; its sister species *Aplysia nigra* reaches only 30 cm, and the well-known *Aplysia californica* usually reaches 30 cm with rare individuals to 75 cm[2](https://academic.oup.com/view-large/565038917).
The body is black or dark brown, sometimes with fine white dots, and animals from the Gulf of California show brownish spots[2](https://academic.oup.com/view-large/565038917). The parapodia are narrow and fused posteriorly, the mantle aperture is a medium oval-circular opening about one quarter of the mantle length, and the opaline gland is simple, with many tiny openings over a large area[2](https://academic.oup.com/view-large/565038917).
## Lack of ink
Unlike most sea hares, A. vaccaria does not produce ink[2](https://academic.oup.com/view-large/565038917). In inking species such as *A. californica*, the purple ink derives its color from pigments in the red-algae diet and is released together with the opaline secretion as a chemical defense against predators such as spiny lobsters and sea anemones[6](https://www.journals.uchicago.edu/doi/full/10.2307/25066645). The absence of ink in *A. vaccaria* is one of the diagnostic characters separating it from its inking relatives in the region[2](https://academic.oup.com/view-large/565038917).
## Taxonomy and synonymy
Since its description, *A. vaccaria* has been a well-established name for the California black sea hare, consistently regarded as a typical and common species in the region[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797). A 2026 systematic review of the genus in the Eastern Pacific, the first comprehensive revision combining mitochondrial and nuclear DNA markers, mitochondrial genomes, morphology, and re-examination of type material, confirmed *A. vaccaria* as a valid species and recognized six valid *Aplysia* species in the region[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797).
Two nominal taxa were placed in its synonymy. *Aplysia cedrosensis*, described by Bartsch and Rehder in 1939 from a single alcohol-preserved specimen from [Baja California](https://www.edgepedia.org/baja-california), closely resembles *A. vaccaria* in size, posterior parapodial fusion, and shell morphology, and its radular formula (118 × 80.1.80) and the presence of spiny warts at the base of the penis match; it is provisionally synonymized with *A. vaccaria*, though the holotype was not examined[7](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797?searchresult=1). *Aplysia reticulopoda* Beeman, 1960, from California and not reported again since its original description, was synonymized on morphological evidence from type material[4](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797).
Molecularly, *A. vaccaria* and *A. nigra* differ by 2.0% genetic divergence, less than half the 4.9% observed between *A. californica* and *A. lessonii*, supporting their recognition as sister but separate species[7](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797?searchresult=1).
## Distribution
The species ranges from Monterey Bay to the Gulf of California and is typically subtidal[1](https://www.marinespecies.org/aphia.php?id=568031&p=taxdetails). A single record is known from Tlacopanocha, Guerrero, Mexico, the only confirmed Tropical Eastern Pacific record and likely an isolated event[7](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797?searchresult=1).
## Biology
Like other sea hares, *A. vaccaria* is a benthic grazer on algae. Water-borne protein pheromones called attractins, first characterized in *Aplysia californica*, are also present in *A. vaccaria*, which aggregates with *A. californica* mating and egg-laying aggregations[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC406444/). Its respiratory protein, hemocyanin, has been the subject of biochemical study[9](https://pubmed.ncbi.nlm.nih.gov/7584828/).
## References
1. [WoRMS: Aplysia vaccaria L. R. Winkler, 1955](https://www.marinespecies.org/aphia.php?id=568031&p=taxdetails)
2. [Table 2, Diagnostic characters of the Eastern Pacific Aplysia, Zoological Journal of the Linnean Society](https://academic.oup.com/view-large/565038917)
3. [California Brown Sea Hare, Aquarium of the Pacific Online Learning Center](https://www.aquariumofpacific.org/onlinelearningcenter/species/california_brown_sea_hare/)
4. [Mendivil et al., The systematics of the genus Aplysia (Mollusca: Heterobranchia) in the Eastern Pacific, Zoological Journal of the Linnean Society 207(2)](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797)
5. [North Carolina Shell Club Bulletin 10 (1983)](https://ncshellclub.com/wp-content/uploads/2025/07/1983-NCSC-BULLETIN-10.pdf)
6. [Derby, Escape by Inking and Secreting, The Biological Bulletin 213(3)](https://www.journals.uchicago.edu/doi/full/10.2307/25066645)
7. [Mendivil et al., systematics of Aplysia in the Eastern Pacific (remarks section)](https://academic.oup.com/zoolinnean/article/207/2/zlag078/8703797?searchresult=1)
8. [Structural and functional analysis of Aplysia attractins, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC406444/)
9. [The hemocyanin of the Californian black sea hare, Aplysia vaccaria Winkler, PubMed](https://pubmed.ncbi.nlm.nih.gov/7584828/)
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*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Molluscs › Gastropods › Heterobranchia › Other opisthobranchs › Sea hares (Aplysiida)*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license