Mystacocarida

(Mystacocarids)

Phylum Arthropoda

Subphylum Crustacea

Class Maxillopoda

subclass Mystacocarida

Number of families 1

Thumbnail description
Very small, vermiform crustaceans with appendages behind those of the head strongly reduced or absent

Evolution and systematics

Mystacocarids have recently been grouped with, among others, Copepoda, Ostracoda, and Cirripedia, and in the class Maxillopoda. These groups all have in common shortened bodies with at most 11 trunk segments behind the head, of which six are thoracic segments. There are 13 known species of mystacocarids, which are grouped into a single family containing two genera. Some scientists now classify this group at the order level.

Physical characteristics

Mystacocarids have shortened, vermiform bodies, with about one-third of the total body length being taken up by the head. The trunk consists of a very short maxillipedal somite, followed by nine more-or-less similar somites, the first four of which bear reduced appendages. The last five trunk somites (abdomen) do not have appendages. The trunk ends in a large telson (=anal) somite, which has a pair of simple, terminal, furca-like appendages. All trunk somites and the posterior section of the head have dorsolateral toothed furrows of unknown function. The head appendages are the most conspicuous aspect of mystacocarids. The antennules are very long, about half the length of the body. The antennae, mandibles, and both pairs of maxillae are composed of large circular segments whose shape is maintained by fluid pressure. The antennae and mandibles are biramous, whereas both pairs of maxillae are uniramous. The maxillae are armed with long setae on their inner margin.

Distribution

Members of the genus Derocheilocaris are known from the coastlines of eastern North America, including the Gulf of Mexico, the Atlantic coast of southern Europe to the tip of southern Africa, as well as the Mediterranean. Species in the genus Ctenocheilocaris are known from the southern coasts of eastern and western South America, as well as Western Australia.

Habitat

All mystacocarids live among the sand grains of outer coastal beaches. Their distribution within one beach may be quite patchy, so they are often not found in areas where they were previously known to occur.

Behavior

Mystacocarids move among sand grains. They use the antenna and mandibles as well as the surface of the trunk to push against the sand grain surfaces. In order to move efficiently, they require sand grains both above and below the body.

Feeding ecology and diet

Mystacocarids most likely graze on microalgae and bacteria living on the surfaces of sand grains. The movements of the mouth appendages may also be responsible for capturing particles in the interstitial spaces.

Reproductive biology

Sexes are separate. Copulation has not been observed, but it is known that fertilized eggs are shed freely into the interstitial habitat. Development is direct, proceeding though a series of molt stages in which body somites and appendages are added in a gradual manner. Beyond the first three head appendages, body somites are always added, then limb primordia, and finally the definitive appendage.

Conservation status

No mystacocarid species are known to be threatened, even though some species are known from single localities. None are listed by the IUCN.

Significance to humans

These small animals are most likely only of intellectual interest, not being part of any food web leading directly to fish or other consumable marine organisms.

Species accounts

List of Species

No common name

Derocheilocaris typicus

order

Mystacocarida

family

Derocheilocaridae

taxonomy

Derocheilocaris typicus Pennak and Zinn, 1943.

other common names

None known.

physical characteristics

Very conservative body plan, with differences among them being in the details of the appendages and the sizes of trunk structures such as the toothed furrows. Has a large and robust maxillule with slight divisions of the precoxa, coax, and basis. The endites on the mouth appendages bear robust setulose setae. Caudal furca short, with terminal seta almost as long as basal article. (Illustration shown in chapter introduction.)

distribution

Found along the Atlantic coast of the United States from Cape Cod to southern Florida.

habitat

Lives deep in the beach, often several feet (meters) inland from the low-tide line where the seawater penetrates at high tide, but often individuals are above the water table at low tide.

behavior

Crawls with its antennae among the sand grains.

feeding ecology and diet

Feeds on small particles in the interstitial spaces on or microalgae and bacteria scraped from the surfaces of sand grains.

reproductive biology

Eggs are laid freely in the beach and development is direct, proceeding from a metanauplius with four post-cephalic

somites. Develops through six metanaupliar, and one juvenile stage before reaching adult size. One additional molt as an adult occurs.

conservation status

Not listed by the IUCN.

significance to humans

First mystacocarid species to be discovered; a new crustacean order was created to house it.

Resources

Periodicals

Lombardi, J., and E. E. Ruppert. "Functional Morphology of Locomotion in Derocheilocaris typica (Crustacea: Mystacocarida)." Zoomorphology 100 (1982): 1–10.

Pennak, R. W., and D. J. Zinn. "Mystacocarida, a New Order of Crustacea from Intertidal Beaches in Massachusetts and Connecticut." Smithsonian Miscellaneous Collections 103 (1943): 1–11.

Les Watling, PhD