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Crustaceans for Small Marine Aquariums: To Be Limited


By Bob Fenner

Small Marine Aquariums
Book 1:
Invertebrates, Algae
New Print and eBook on Amazon:
by Robert (Bob) Fenner
Small Marine Aquariums
ook 2:

New Print and eBook on Amazon: by Robert (Bob) Fenner
Small Marine Aquariums
Book 3:

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The arthropods (jointed-legged animals) we call crustaceans are iconic marine creatures. Crabs, lobsters, mantis and more on the “macro” side and many thousands of “micro” “pods”, skeleton shrimp, Mysids and oh so many other described “crusty” groups. Though they are so common in all marine habitats, biotopes, does this mean that we should keep them in our systems? My answer is decidedly not.

            IMO/Experience the use of most larger crustaceans, including the Anomurans called Hermit crabs is overrated… with most all crustaceans of size being at least opportunistic omnivores. Yes; there are no absolutely “reef safe” crustaceans; even Emerald/Mithraculus crabs will eat your fishes and other invertebrates given hunger and the chance.

            So; is this the end of the story here? Just say no to crustaceans? Far from it; there are set ups and mixes, even in volumes of less than a quart to tens of gallons where these insect-relatives can make wonderful displays. One just needs to have a working knowledge of their needs, dispositions and calculated odds of given species getting along; and understanding that keeping crustaceans is not an easy proposition of all getting along.


Macro-Crustaceans: for the most part, solitary species.

Crabs? No, Please:

            Decapods… “ten feet”… Crabs. Don’t get me wrong, I find them delicious cooked in soups and other ways… But all of them are to degrees omnivorous. If/when they get to large/r size, they can/will eat your other invertebrates, possibly fishes as well. IF you must keep them, or just end up with some as hitchhikers, DO your best to keep them small (i.e. don’t feed them directly), AND keep your eyes on the rest of your livestock.

Mithrax/Mithraculus sculptus, the Green/Emerald Crab. Tropical West Atlantic. Yes; even this  noted and frequently employed as algae eater (even Valonia), can turn into a fish eater... some references state to 2.5 others to a maximum of four inches carapace width. Now in its own genus Mithraculus. Family Majidae.


Stenorhynchus seticornis (Herbst 1788), the Caribbean Arrow Crab. Not to be trusted with small to medium fish tank-mates (may spear with rostrum, otherwise consume). Safe with hardy native corals and anemones. A small individual in Belize shown. Grows to about a foot in diameter.



Hermits? Maybe Some:

            My gripe with the false-crabs (Anomurans) called Hermits is several: For one, many are not really totally aquatic; that’s right, many species are amphibious. Second, they’re misunderstood as cleaner uppers. Most are opportunistic eater uppers who will cross the line given hunger and the chance to eat your tankmates (see below). Lastly, due to the above misunderstandings, and most regrettable is that too many people place way too many of these animals in their systems, expecting algae et al. Nirvana, and are disappointed. IF you must have Hermits, investigate and use the best species (some listed below), and avoid the outright predaceous species unless you’re housing one to a tank as your single specimen.



Never entirely "reef safe"... All hermits are to degrees opportunistic omnivores... they WILL eat your other livestock if hungry... Here two Paguristes cadenati are "riding" a snail in captivity.


A Couple of the Safer Hermit Species Commonly Offered in the Trade:

Clibanarius tricolor, the Blue-Legged Hermit Crab. To less than an inch in length. One of a few “reef-safer

” Hermits that stay small and almost exclusively feed on algae (and Cyanobacteria!). Good for aiding in aerating the substrate as well. Aquarium photo. 

Paguristes cadenati Forest 1954, the Scarlet or Red-Legged Reef Hermit. Tropical West Atlantic. To one inch in length. Red carapace and legs, eyes green, on yellow stalks. 


Some Suitable False Crabs; e.g. Porcelain et al. & Mutualistic “Real” Crabs:

            There’s actually a very large group of symbiotic crustaceans; including (yes) crabs that live in association with stony corals, soft corals and sea pens (Pennatulaceans) that can make really neat specialized displays. The way to purchase/acquire these is to be on super-look-out or ask your dealer, e-dealer to be so… As only the most carefully collected and shipped co-symbionts are shipped with good enough care ensuring survival of both.  A few shown here; there are MANY others. See below for shrimp examples as well. 

Anomurans Other Than Hermits: Squat Lobsters & Porcelain Crabs, Families Galatheidae & Porcellanidae

There are some bizarre (but neat!) squat lobsters on the worlds reefs, but these rarely make it into Western ornamental markets; instead of teasing you I’ll just present the two at-times available Anemone Crabs. If you’re keen to keep a carpet; you really should check these out and consider keeping them as well.

Family Porcellanidae; Porcelain, Anemone Crabs. Live within Anemones tentacles. These will chase out Clownfishes if they can... or may be in turn chased out by them. Filter feeders (use modified, long third maxillipeds) that can do well in captivity. Movable abdomen aids them in rapid movement. Mainly Neopetrolisthes, Petrolisthes, Petrocheles. Typified as having flattened chelipeds, long antennae. 

Neopetrolisthes maculata (H. Milne Edwards 1837). Flattened, large chelipeds. White body with fine red spotting. Commensal with (and sometimes in the mouth of) anemones. West Pacific; Australia, Indonesia, Philippines.

Neopetrolisthes ohshimai Miyake 1937, the Spotted Anemone Crab. Indo-Australia; including Pacific Islands. Almost always found in pairs in the wild (have to be bought as such if keeping two). Chased from Anemones by Clownfishes. Large red spots on creamy white bodies.


Mutual Decapods for Specialty (Species Only) Set Ups:

Zebrida adamsii White 1847. Urchin Crab. Beautiful contrasting white, brown body banding; live on/in association w/ venomous Urchins. 

Achaeus japonicus Haan 1839, the Orangutan Crab. Bodies have long processes that the crab attaches algae et al. for camouflage/protection. Usually found in association with cnidarians: Plerogyra, Dendronephthya, Parazoanthus...

Lissocarcinus spp. Gorgeously marked little crabs. Found in association with soft corals, anemones. Indo-Mid-Pacific; South Africa to Hawai'i. To 3 cm. Here a tiny individual on an Alcyonacean in N. Sulawesi, another living on a Sea Cucumber and a third species living in a Tube Anemone!

Lybia tesselata (Latrelle 1812), the Pom Pom or Boxer Crab. 1-2 cm. Carries anemones of the genus Bunodeopsis on its claws. Indo-West Pacific; Mozambique, Seychelles, Indonesia, PNG, Philippines. Here in N. Sulawesi.



Specialty/Specimen Set Ups: Perhaps a Mantis?

            As stated re keeping larger decapods/crabs, lobsters to come, and some of the shrimps we’ll mention in passing; there are some really neat big/ger crustaceans that deserve (and require) their own small marine system… to not bother tankmates and to become more “outgoing”. One fave outstanding group here is the Stomatopoda; the too-often-feared Mantis “Shrimps”. There are many people I’ve met who became bored with their non-sharky sharks, too-large puffers and more… but NEVER one I’ve encountered who grew tired of their Mantis!

Beautiful, graceful creatures more often understood by loathing aquarists than kept, the Mantis "Shrimp" are more than loathsome marine pests. Making up four families of some 350 known species, the Order Stomatopoda can be welcome guests, even purposeful livestock!
The smashers protection and food-gathering appendage ends as a enlarged heel. These animals typically feed on hard-bodied creatures (snails, true crabs, hermits, mollusks) which they stun, break open with a sudden strike. Smashing type Mantis tend to live more out in the open. 
       Stomatopods can be bought (!) as pets, but more just "show up" as live rock hitchhikers. While many can be accurately blamed for fish losses and other predation, requiring elaborate baiting, trapping to even complete tear-downs to extract them, some of the larger, grander species can be considered excellent species for captive use.    As you might assume Mantis are solitary, territorial animals... one to a tank is the rule.
        Some examples of the more commonly encountered Mantis below: Lysiosquilla/Lysiosquilloides sp., and a couple of pix  (blue, yellow-green and red) of the most frequent hitchhiker with live rock from the Indo-Pacific,
Odontodactylus scyllarus (Linnaeus 1758), the Peacock Mantis Shrimp.
There are MANY more species; mostly “free” as hitchhikers on /in/with your live rock or from fellow hobbyists and stores from the same.  




Rock Lobster, Uh huh:

            Small reef lobsters are amongst my fave organisms… to encounter while underwater looking for photographic subjects; not so much in aquariums. Yes; the familiar refrain re large-enough crustaceans; they’re ready, willing and able to eat most any, all other invertebrate and fish life. That being stated; again these are beautiful, interesting animals; that although not super active during the day time, can make interesting specimen tank displays.

            Principally on offer are members of the genus Enoplometopus; there are others, but the two most commonly kept are shown below.

Enoplometopus daumi Holthuis 1983, Daum's Reef Lobster. East Indian, Western Pacific Oceans; imported from the Philippines, Indonesia. Common in the wild, but shy and reclusive. 

Enoplometopus occidentalis (Randall 1840), the Hairy or Red Reef Lobster. Found throughout the tropical Indo-Pacific. White emarginated spots all over the body. Nocturnal. 


Shrimps! Thank Goodness:

            Am reminded of the line from Forest Gump; “Jumbo shrimp, shrimp with grits, fried shrimp; shrimp and rice… “As with the movie, there ARE many kinds of shrimps; and several of these are suitable for small marine systems; some with additional life, and others best by themselves or at least no other edible tankmates. There are several smaller symbiotic shrimp species that live with various “corals, echinoderms and more that are especially attractive to me; for their grace, beauty and showing-offed-ness.

Thor amboinensis (de Man 1888), the Squat Anemone or Sexy Shrimp (in reference to its usually-raised and moving tail). 1/4-3/4" long. Common in all tropical seas. Found in association with Giant, Sun, Elegant Anemones. One on an anemone in S. Leyte 2013



Cleaner Shrimps

            Of all kinds can be kept without “customers”; i.e., fishes to clean. In small volumes, up to the limit here of forty gallons are really too little to have both; with the shrimp really bothering their hosts. Better that these symbiotic shrimps be kept by without fishes, in a group, one species to a tank.

Genus Lysmata: Shown; one of many choices

Lysmata amboinensis (De Man 1888), the Indo-Pacific White-Striped Cleaner Shrimp or Ambon Shrimp. Widespread in the tropical Indo-Pacific and Red Sea. Telson white, uropods with two white dots. Can be kept singly or in groups. A hardy Cleaner.


Genus Periclimenes: Many suitable species and wide range of hosts.

Periclimenes brevicarpalis (Schenkel 1902), the Pacific Clown Anemone Shrimp. Widely distributed in the tropical Indo-Pacific. Males smaller than females, both under an inch in length. Should be kept with a Sea Cucumber or better, an Anemone host, like this one here in a Pizza Anemone in S. Sulawesi (Wakatobi). Common in the wild within its range, easily kept. Accept all foods. 

Ancylomenes (was Periclimenes) pedersoni Chace 1958, the Caribbean Anemone Shrimp, Pederson's Shrimp. Should always be kept with Anemone hosts. A great cleaner of fishes, but ships poorly.  Here in a Bartholomea in Jamaica.


Boxer Shrimps; the family Stenopodidae: the most common species shown; there are others.

Stenopus hispidus Olivier 1811, Coral Banded Boxing Shrimp. Worldwide tropical distribution. Males smaller, more slender than females. Keep in reef settings with a cave of their own. May consume small fishes, other crustaceans. Eat most all meaty foods.  In N. Sulawesi here.


Pistol Shrimps (& Their Mutualistic Gobies): Family Alpheidae

Seldom seen, often heard... and the results of their "shooting" known far and wide... the Alpheids can be easily identified (if you can find them) by their very short eye stalks and one much larger "pistol" claw.  This specialized appendage is capable of punching holes in all crustacean exoskeletons, even many shellfish! Alpheus and Synalpheus species are the notable symbionts with Shrimp Gobies

Pistol Shrimp are the predominant crustaceans on the world's reefs... and so you are likely to run into them... they eat most all types of foods...

Shown above: a busy-as-usual Alpheid and Amblyeleotris symbiont… the fish keeping watch with its tunnel-mate in close antenna to body contact. Raja Ampat photo.

 Harlequin Shrimps: Beautiful, but…

            Boring; really… having to keep, chop up, or very regularly buy these echinoderm tube-feet strict dieters is wearisome. Yes, they’re beautiful, but… reclusive and not very active. Best to just watch on YouTube videos IMO. Two species:

Hymenocera elegans Tropical Indo-West Pacific; Red Sea to Australia. Here in N. Sulawesi (Lembeh Strait). Body spots are brown circled in Blue. Occur almost always in pairs. Live in shallow water feeding on echinoderms, principally seastars. 

Hymenocera picta Dana 1852, the Eastern Harlequin Shrimp. Anterior first pair of legs look like tweezers, second pair covering them. First antennae flap-like... waved around side to side. Live in pairs only.  Noted for their feeding exclusively on echinoderms; starfish and urchins. E. to Central Pacific. To about an inch and a half in length. A pair feeding down in Costa Rica.


Small Crustaceans Groups:

What about the many species of Mysids, Copepods, Amphipods, Caprellids, even Isopods ! And more smaller crustaceans? Of course these can make wonderful displays. Am reminded of the industry that is the “EcoSphere”, http://www.eco-sphere.com/ ; those sealed, self-contained worlds composed of a small air space, seawater, a gorgonian skeleton, bit of algae and Halocaridina rubra (a small red Atyid shrimp with the Hawaiian name ʻōpaeʻula).



            This is just a smattering of representative small marine systems possibilities involving the jointed legged animals called crustaceans. I hope I do not come off as being altogether too negative re their keeping in our aquariums. They do have their places; albeit in limited numbers, circumstances and with carefully selected tankmates. Many species, in fact whole groups are misunderstood as being “cleaner uppers” or benign toward other life. Symbiotic species in all groups are good choices, where/when you can acquire them in good health with their hosts; and cleaners work out fine in specialized set-ups, but most crabs, lobsters and Hermits are best left in the sea.


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