''Janolus fuscus'' is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary ...

, or more accurately a

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to mat ...

, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is es ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Proctonotidae Proctonotidae is a family of sea slugs, nudibranchs, marine gastropod molluscs, in the clade Euthyneura.MolluscaBase (2018)Proctonotidae Gray, 1853.Accessed on 2020-10-20. Genera Genera in the family Proctonotidae include: * ''Caldukia ''C ...

Distribution

The species ''Janolus fuscus'' is found from the

Kenai Peninsula, Alaska The Kenai Peninsula ( Dena'ina: ''Yaghenen'') is a large peninsula jutting from the coast of Southcentral Alaska. The name Kenai (, ) is derived from the word "Kenaitze" or "Kenaitze Indian Tribe", the name of the Native Athabascan Alaskan tribe ...

central California Central California is generally thought of as the middle third of the state, north of Southern California, which includes Los Angeles, and south of Northern California, which includes San Francisco. It includes the northern portion of the San Jo ...

and also in northern Japan.

Habitat

This species of nudibranch is found in

intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species ...

and

subtidal The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...

zones. These areas are shallow and rocky, and Janolus fuscus do not inhabit spaces deeper than 30m.

Description

The bodies of

s in this species are semi-translucent and whitish-grey, and reach lengths of about 35mm. The body is covered in short

cerata :''The tortrix moth genus ''Cerata'' is considered a junior synonym of ''Cydia. Cerata, singular ceras, are anatomical structures found externally in nudibranch sea slugs, especially in aeolid nudibranchs, marine opisthobranch gastropod mollus ...

with brown cores, and the exterior fades to orange and then white at the tip. Its

rhinophore A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, marine gastropod opisthobranch mollusks such as the nudibranchs, sea ...

s have around 20

lamellae Lamella (plural lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * ...

and are also white tipped. The cerata in front of the rhinophores (as well on the standard back of them) are a distinguishing factor between it and other nudibranch species' that are similar in appearance.

Life habits

''Janolus'' species feed on

Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

, specifically ''Bugula californica'' and '' Tricellaria.'' The fuscus species live for approximately five months. Janolus fuscus

Predators

In California, ''

Navanax ''Navanax'' is a genus of sea slugs, marine opisthobranch gastropod mollusks in the family Aglajidae.Bouchet, P. (2012). Navanax. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=224591 ...

'' is a known predator of ''Janolus''. ''Navanax'' tracks the slime of ''Janolus'' by using

chemoreceptors A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecep ...

. When ''Janolus'' is about to be caught, it rolls into a ball, leaving its cerata exposed. If there is a water current, as if often the case, the sea slug may then be passively rolled away from the predator.

Parasitic Threats

Janolus fuscus can be infected with a parasitic

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

called ''Ismaila belciki.'' This is fairly common, and in some monitored populations of the nudibranchs such as

Coos Bay, Oregon Coos Bay (Coos language: Atsixiis) is a city located in Coos County, Oregon, United States, where the Coos River enters Coos Bay on the Pacific Ocean. The city borders the city of North Bend, and together they are often referred to as one ...

's, the rate of infection is up to 80%. When I. belciki is present in this species, it is covertly located inside the body cavity so the only portion that can be seen from the outside are egg sacs. The parasite does not interfere with the growth of its host, but it poaches off the sea slug for many functions including taking the nudibranch's resources that it uses for egg producution to use for I. belciki's own egg production, making reproduction slow for the host and the survival rate lower as a whole.

References

External links

* Sea Slug Forum info at

* SlugSite info

{{Use dmy dates, date=May 2017 Proctonotidae