Surprising new information about aquatic invertebrates is uncovered every day…the following is a small sample, which I’ll add to from time to time. Please see Part I of this article as well.
Good and Bad Pets
The venom of the tiny blue-ringed octopus, Hapalochlaena maculosa, is one of the most toxic known, with the amount delivered in a single bite being sufficient to kill an adult person. Yet this creature occasionally appears for sale in the pet trade – learn to identify and avoid it!
Giant water bugs (Family Belostomatidae) can be collected throughout the USA and make interesting, if aggressive (they can inflict a painful bite), aquarium subjects. The males of many species carry the eggs about on their backs. A species I collected in Venezuela topped 4 inches in length, and regularly consumed small frogs. Another I came across at Japan’s Kaiyukan Aquarium easily subdued a 3 inch long minnow. Please look for my future article on aquatic insects.
Most corals rely upon minute creatures for their food and are difficult to maintain in aquariums. However, tooth coral (Cynarina spp.) accept pieces of shrimp and other large food items, and should be considered as a first choice by those new to coral-keeping.
Jellyfishes are not usually available in the pet trade, and are quite delicate in captivity. One exception is the upside-down jellyfish, Cassiopeia andromeda. In contrast to all others, it rarely swims but rather rests in a “head down” position, with the tentacles trailing above. Given intense lighting (it relies upon symbiotic algae) and plenty of brine shrimp, it often thrives in the aquarium.
Catching and Storing Food
Surprisingly, some spiders have adopted an aquatic lifestyle, and several of these adapt well to aquarium life. North America’s fishing spiders, Dolomedes spp., float on the water’s surface and dangle a leg below to lure small fish within reach. The European diving bell spider, Argyroneta aquatica, takes aquatic life a step further – it lives in a submerged, air-filled retreat from which it launches attacks on passing fish and invertebrates. Please look for my future article on these unusual creatures.
Several crabs have interesting ways of “planning for the future”. Atlantic spider crabs, Libinia emarginata, stuff marine algae into crevices on their shells, effectively camouflaging themselves and storing food at the same time (those I have kept abandon this habit when they reach 3 inches in size). The ever-popular arrow crab, Sterorhynchus seticornis, impales bits of food, to be consumed in the future, on the pointed end of its carapace.
How Big…How Old?
Crabs, lobsters and their relatives (Order Decapoda) are among the most important aquarium and food-trade invertebrates. The legs of the Japanese spider crab, Macrocheira kaempferi, the largest of the group, may span 13 feet. Both it and the American lobster, Homarus americanus (at 60+ pounds, the heaviest Decapod) may live for 100 years. The largest freshwater species is the 9 pound New Zealand crayfish, Astacopsis gouldi.
At 4.5 feet across and up to 750 pounds in weight, the South Pacific’s giant clam, Tridacna gigas, is the largest of the world’s 6,000+ bivalves (clams, oysters and relatives). It relies upon commensal green algae for much of its food, and produces the world’s largest pearls – one of which weighed in at 14 pounds!
Many mollusks (snails, clams and their relatives) lay down growth rings, which appear as irregularly-spaced lines on the shell. Much as with trees and turtles, these lines can often be used to determine these creatures’ ages.
Defense and Survival
Although largely aquatic, several species of North American crayfish, known as chimney crayfish, exploit terrestrial habitats. They live in wet meadows and dig tunnels, which may exceed 10 feet in length, to the water table. Recently, it was discovered that these water-filled retreats provide vital breeding sites for salamanders during droughts.
Sea urchins are interesting aquarium inhabitants, but most aquarists find them rather unresponsive. However, they react immediately to the shadow thrown by a hand or other object passing overhead by orienting their spines towards the disturbance. This is a defensive reaction, designed to direct the sharp spines towards an oncoming fish or other predator.
I look forward to hearing about your own observations concerning aquatic invertebrates, and to answering your questions. Thanks…until next time, Frank.
A great deal of interesting information concerning marine, fresh water and terrestrial in invertebrates of the Pacific Basin is available at the following web site: