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THE VALENTINE GIFT FROM THE ATLANTIC - ECHINODERMS

On St Valentine’s day ie February 14 last year 2012, a group of fishermen doing their thing at Gbethrome, Badagry Local government, Nigeria, saw what none of them had never seen. It was a little creature that looked like a star. Did a star fall into the ocea? They beckoned on another fishermen who has been a regular collector off the same coast of the atlantic – Yusuf Usman, Lab Assistant in the Zoology Laboratory m Department of Zoology and Environmental Biology , Lagos State University, Nigeria. The illeterate fishermen were stunned when Yusuf told them – this is an animal? How can a star be an animal? Yusuf collected the animal and brought it into the laborratory with some sea water so that the animal will not die. In the lab it was identified as a Sea Star – a member of the Phylum Echinodermata.



Plate 1: Starfish

Echinodermata is a phylum composed of exclusively marine invertebrate species.. The adults are typically of radial symmetry, although the larvae are bilaterally symmetrical. They have a type of radial symmetry called pentamerous symmetry in which their body can be divided into five equal parts around a central axis.They include the  well-known animals such as starfish, sea urchins, sand dollars, and sea cucumbers. These animals are particularly intesting because they are considered to be the most closely related to chordates, and by extension, vertebrates when compared to all other invertebrate groups. Echinoderms are primarily bottom dwelling invertebrates and have a variety of feeding habits including filter feeding, scavenging, and predation. 

Yusuf

Echinoderms have an endoskeleton composed of calcareous ossicles. In sea stars and brittle stars, the ossicles articulate to form flexible structures. In sea urchins and sand dollars, the ossicles are fused together to form a rigid skeletal structure known as a test.

 

Classification:

         Kindom: Animalia
         Phylum: Echinodermata
         There are two subphyla with five clases altogether

      Subphylum I:  Pelmatazoa

      Members of this subphylum are primitive echinoderms that are attached to the substratum throughout life or only when they are still young. The podia are not used for locomotion, but rather for capturing food. Their life history includes a larval form called vitelaria larva. Most members of this subphylum are extinct except the crinoids.

     Class I: Crinoidea (feather stars and sea lillies). These are also called the crionoids. Members of this calls are the only living representatives of the Pelmatozoa sub-phylum. They are the most primitive of all living classes in the Phylum Echinodermata.

     Subphylum II:Eleutherozoa
      Class I: Asteroidea (sea stars and starfishes)
       Class II: Echinoidea (heart urchins, sand dollars, and sea urchins)
     Class III: Holothuroidea (sea cucumbers)
      Class IV: Ophiuroidea (basket stars, brittlestars, and snake stars)