* Taxonomy and Phylogeny
The sea hake, also known as sand dollars, are named for their flat and oval. These animals belong to the phylum Echinodermata, a group which also include sea stars (asteroids), cucumber (holothurian), lilies (crinoids) and spiders, brittle stars (ophiuroids).
The previously mentioned organizations can live in all types of marine environments such as sandy bottom beaches, rocky shores, coral reefs, seagrass Thalassia among others. The sea hake can be found on sandy bottom beaches, in which feed on infauna (animals and microscopic plants) present in the background. At present there are an estimated 13 orders within the class Echinoidea of which five represent the irregular urchins.
Here are some figures highlighted the characteristics of a sea loach in this specific case Mellita quinquiesperforata.
Fig.1. View of the aboral surface of the sea hake (Mellita quinquiesperforata). 1. Previous Lune 2. Madreporic Plate 3. Anal Lune 4. Gonopore 5. Posterior lunula 6. Petaloid (Photo: Sylvia Grune).
Fig.2. View of the oral surface of the sea loach (M. quinquiesperforata) 1. Boca 2. Year 3. Periprocto 4. Ambulacral channel 5. Interambulacro 6. Fracture (failure) (Photo: Sylvia Grune).
Taxonomy and Phylogeny
Within the class Echinoidea includes regular and irregular sea urchins. These can be distinguished mainly by their external morphology varied. The regular sea urchins have a globular shape and can have very long spines, second irregular urchins may have a flat or cordate. Originally the order was divided into orders and Irregularia Regularia (Hyman 1955).
Organisms classified in this class (Echinoidea) have the following characteristics:
* Mobile Thorns
* Five ambulatory peristomium ranging from the sub-surface layer to the apex of the aboral surface.
* No arms or tentacles pose
* The mouth is retractable
Harlod and Telford (1990) collected all the synonyms of the species M. quinquiesperforata and concluded that the taxonomic history of this species is unclear. By phylogenetic studies compared the seven extant species of the genus Mellita sp. His cladogram supports that species and M. M.isometra tenuis are sister species. The type species M. quinquiesperforata is the sister species of all species in the Pacific.
For some years it was thought that gender Leodia sp. was a synonym of Mellita sp. or who were related, which according to the study of Harlod and Telford (1990) is not completely true. Mellita species sp. are related to Gender Leodia are M. isometric and M. tenuis.
The distribution of M. quinquiesperforata, specifically, is from the eastern United States (Delta Mississppi) along the coasts of Central America to South America, reaching the southern shores of Brazil. Including Puerto Rico, Jamaica, Dominican Republic and Trinidad.
Irregular urchins may have different ways of getting their food, as this group tends to bury urchins depending on environmental conditions and some remain buried constantly.
Irregular urchins remain buried build a cave with an entrance and exit channel for better flow of water and food to exert its function mainly spines, as are the food and place the tube feet dragging through the particles to ambulacral canals of the animal and these particles are transported through these channels and brought to the mouth. The particles are ingested in greater proportion, belong to the infauna (diatoms, plankton, benthic copepods among others) (Hyman, 1955).
Ghiold in 1979 determined by electron microscopy the presence of seven different types of spines in M. quinquiesperforata, whose functions are mainly for food and buried (locomotion).
These spines were classified by their shape and location in the following manner: a form of phosphorus (found along the aboral surface), miliary (oral and aboral surface), elbowed, locomotives (oral surface), margin terminal (it located on both surfaces along the outer edge of the exoskeleton) and lunulares (found around lunes) and opening margin (located along the openings (lunes) on the aboral surface).
Reproduction of irregular sea urchins is very similar to that of other sea urchins. There are male and female individuals, which expel their gametes into the water where the eggs are fertilized by sperm from here starts the metamorphosis of planktonic larvae initially (swimmers) to benthic (seated in the background.) Therefore, these organisms have external fertilization sexual (and that bind the gametes).
It is believed that there is some chemical interaction tells larvae where the patches of irregular urchins to settle and become recruits of this species. Not very familiar with the larval development of these irregular urchins.
However, parental care was observed in regular sea urchins and starfish, which are home to its young on its surface until they reach a size sufficient to find food and shelter from predators. Individuals of M. quinquiesperforata seem to not have this type of care.
According to a study conducted in 1980 by Lane and Lawrence is believed that populations of M. irregular sea urchins quinquiesperforata older individuals migrate to deeper waters, while younger individuals remain close to shore. The larvae of this species of sea loach seems to have cannibalism and sit on beaches far from the town of adults through the influence of currents.
Also refers to the reproductive cycles of these animals being this so biannually year classes are very rare. It refers to the ideal temperature for larval development this being 26 ^0 C for 7 to 9 days (Caldwell, 1973 in Lane & Lawrence 1980). The sea hake are gregarious organisms therefore remain together presenting a training patches in the funds.
Each agency is located in a food web indicating which is which prey and predator. In this case the sea hake are preyed upon by fishes and crabs. The dam is known by these infaunal organisms (benthic microalgae, copepods and other small animals) present back to the sandy beaches.
Fig.3. M. quinquiesferforata with signs of predation (Photo: Sylvia Grune).
The sandy bottom beaches in many countries (Venezuela, Colombia, Brazil and the United States among others) are exploited tourist, represented by the construction of hotels, ports of landing, restaurants, churuatas between some of the buildings for tourism purposes. The construction of jetties and piers alter the natural flow of longshore currents, which produce different effects such as alteration of the natural recovery of costs by the sea and coastal dynamics, which by the tides high trash discarded Tues
There is currently a legal protection of 80m from the high tide line and this is known as “protective zone” (Official Gazette of the Republic of Venezuela No. 4158).
(Conde and Carmona-Suarez, 2003)
Fig.4 View of the Punta Arena beach on the island of Margarita belongs to the state of Nueva Esparta, Venezuela (Photo: Sylvia Grune).
Some of the organisms in the supralittoral zone of sandy bottom beaches are: ghost crab (Ocypode quadrata), cirolanid isopods, amphipods talitridos. In the middle are polychaetes (Onuphis spp.) Crustaceans hiccups (such as Emerita brasiliensis) and the bivalve “Chipi-Chipi (Donax sp.). In the bottom of these beaches can be found as the Guacuco bivalves (Tivela mactroides) and Donax sp., Sea urchins and irregular as quinquiesperforata Mellita Encope sp, and stars (Asteroidea) as Astropecten marginatus. (Conde and Carmona-Suarez, 2003).
The coelomic fluid stains (blood) of the sea hake (M. quinquiesperforata) are considered indicators of environmental stress (Smith and Smith 1987). In the study of these authors relate the colors of serum (coelomic fluid) in the presence of environmental stress. Concluding that the serum of individuals with a lighter color indicate no environmental stress, and individuals with the amber-colored serum indicate the factor of environmental stress.
Another way to determine whether these organisms express stress due to environmental causes, by displaying osciculares plates on both surfaces (aboral and oral), can also account for the hyperactivity of the thorns or the contrast of the movement.
Fig.5. Sea loach (M. quinquiesperforata) expressing environmental stress, as you can see the plates in the aboral surface. (Photo: Sylvia Grune)
The sea hake have no direct economic importance as is the case of regular sea urchins, as they are grown and harvested by the gonads (roe). Irregular urchins however, their eating habits keep the funds from the sandy beaches free of periphyton (benthic algae) and prevent the beach becomes a sandy mud bottom. When these organisms die, their consistency being mainly calcareous, become part of the proceeds from the sandy beaches, like the dead shells of molluscs. This is important, as the sandy bottom beaches will not continue to be a tourist site used if they become a muddy bottom, so this can be considered an indirect economic impact for tourism use sandy beaches.
Conde, J. and Caromona-Suarez, C. 2003. Marine and Coastal Ecosystems. In Volume II of Biodiversity in Venezuela. Editors Marisol Aguilera, Aura Azocar and Eduardo Gonzalez Jimenez. Editorial ExLibris, Caracas, Venezuela: 862-883ppg.
Giold, J. 1979. Spine morphology and Its Significance in feeding and burrowing in the sand dollar, Mellita quinquiesperforata (Echinodermata: Echinoidea).
Bulletin of Marine Sciences. 29 (4) :481-491.
Harold, A and Telford, M. 1990. Systematics, phylogeny and biogeography of the genus Mellita (Echinoidea: Clyperasteroida). Journal of Natural History, 24: 987 – 1026.
Hyman, L.H. (1955). The Invertebrates. Vol.4. Echinodermata. McGraw-Hill, New York. 763pp.
Lane, J. & Lawrence, J. (1980) Seasonal variation in body Growth, density and distribution of a Population of sand dollars, Mellita quinquiesperforata (Leske). Bulletin of Marine Sciences. 30 (4): 871-882.
Smith, A & Smith, S. 1987. The sand dollar as a possible indicator of Environmental stress. Journal of Aq”uicultura & Aquatic Sciences. Vol 5 Nr.1.
Universidad de Oriente, N’ucleo Nueva Esparta, School of Applied Sciences of the Sea, Boca del Rio, Isla de Margarita.
Author’s note: the images shown here may not be disclosed without the permission of the author. It is recalled that this text was not arbitrated therefore not recommended the appointment of this manuscript.