Friday, July 17, 2020

Keratella Sp Adalah; Klasifikasi, Morfologi, Habitat Dll




Keratella Sp adalah rotifera yang termasuk kelas Monogononta hidup di perairan tawar dan laut.

Klasifikasi Keratella Sp
Menurut Hauer (1963):
Kingdom : Animalia
Phylum : Rotifera
Class : Monogononta
Order : Ploimida
Family : Brachionidae
Genus : Keratella
Spesies : Keratella sp.

Morfologi Keratella Sp
Lorica spoon-shaped; with six spines in front; the medial pair curving strongly forwards: posterior extremity attenuated into a long slender spine, inclined forwards. From Ahlstrom (1943): Lorica terminates in a stout median posterior spine which usually varies in length from as long as the body proper to onethird as long but which may be even more reduced or completely wanting. Lorica oval shaped in dorsal view, depth of the dorsal plate is a little more than half the width; the greatest width of the lorica is slightly behind the middle of the body, although the lorica tapers but slightly anteriorward; the lorica is about two-thirds as wide as long (width varies from 0.56-0.71 of length of body exclusive of spines). Anterior dorsal margin with six spines: medians longest, curve ventrally, intermediates usually slightly divergent, somewhat shorter than lateral spines which are convergent at their tips and which arise at a slight angle toward the ventral. The lorica has the usual pattern of minute interlacing areolations on both plates. The ventral plate is usually pustulate on the upper third only, although this feature is somewhat variable. The dorsal plate is often somewhat pustulate, the small pustules being at the corners of areolations and scattered over the entire plate. The foundation pattern of the dorsum is characterized by a mediam line extending longitudinally from behind the median frontal area to the base of the posterior spine. Often there is but one pair of fully enclosed carinal plaques: the antero-carinal polygons (hexagons). Not infrequently, however, the postero-carinal polygons are fully formed; when this is the case there are two very small unenclosed carinal areas posterior to the two enclosed pairs of carinal plaques. There are two pairs of enclosed lateral polygons to the sides of the anterocarinal polygons; a third pair may be present to the sides of the postero-carinal plaques.

Keratella sp. has an oval lorica, a shell-like protective outer cuticle. At the anterior end are three pairs of spines. The central pair curve towards the ventral surface, the next pair diverge slightly and the outer pair converge. There is also a central funnel-shaped mouth and on either side of this are rings of cilia which twirl and help waft food particles into the mouth. They are also used for locomotion. There are two forms of this rotifer; some individuals have a long spine at the posterior end and others do not. Neither form has a foot.

Habitat Keratella Sp
Keratella Sp Hidup di perairan tawar dan laut.

Reproduksi Keratella Sp
Reproduction of rotifers is generally achieved parthenogenetically. For this to occur, the female produces a 2n egg via mitosis which will then hatch into a 2n clone of the mother. A noticable feature of the cloning of Keratella is the fact that the offspring may vary in body form from that of their mother.

Sexual reproduction occurs periodically in response to unknown stimuli. In sexual reproduction the female undergoes meiosis and produces 1n eggs, some of which hatch into 1n males. These males then undergo mitosis to create 1n sperm which will fertilize a 1n egg. The fertilized egg will hatch into a 2n female and sexual reproduction will be complete.

Keratellacochlearis is dioecious, with female specimens being larger than males. In the main, reproduction in this species is by parthogenesis. In this process, the female rotifer produces an unfertilised egg with a full set of chromosomes. This is carried around by the mother and hatches into a miniature adult. Whether the offspring has a posterior spine or not seems to depend on the number of predators in the body of water where the rotifer lives. If predation rates are high, spined "typica" forms are produced, but if low, spineless forms known as "tecta" develop. Tecta females can produce typica offspring and vice versa. It has also been found that different forms tend to predominate at different times of year. In the winter, most individuals have a long spine at the posterior end. As the spring advanced, the spine shortens and by July it is very short or non-existent. During the remaining months of the year it gradually lengthens once more. These changes take place over several generations as each individual rotifer has a lifespan of just a few days or weeks.

Periodically sexual reproduction takes place. It is not known why this occurs at some times and not others. The female undergoes meiosis and produces eggs with half the usual number of chromosomes. Some of these develop into male rotifers. Each of these is able to inseminate another of these eggs to restore the full complement of chromosomes in the offspring.

Keratella sp adalah dioecious dan bereproduksi secara seksual atau parthenogenetically. Mereka adalah seksual dimorfik, dengan betina selalu menjadi lebih besar daripada jantan. Dalam beberapa spesies, ini relatif ringan, tetapi di lain betina mungkin sampai sepuluh kali ukuran jantan. Dalam spesies partenogenesis, jantan dapat hadir hanya pada waktu tertentu tahun, atau tidak ada sama sekali.

Sistem reproduksi betina terdiri dari satu atau dua ovarium, masing-masing dengan kelenjar vitamin A yang memasok telur dengan kuning. Bersama-sama, setiap ovarium dan vitamin A bentuk tunggal syncitial struktur di bagian anterior hewan, membuka melalui saluran telur ke dalam kloaka.

jantan biasanya tidak memiliki sistem pencernaan fungsional, dan karena itu pendek-tinggal, seringkali sudah secara seksual subur saat lahir. Mereka memiliki satu testis dan saluran sperma , terkait dengan sepasang struktur kelenjar disebut sebagai " prostat "(meskipun mereka tidak berhubungan dengan organ vertebrata dengan nama yang sama). Duktus sperma membuka ke gonopore di ujung belakang binatang, yang biasanya diubah untuk membentuk sebuah penis. gonopore ini homolog dengan kloaka betina, tetapi pada spesies yang paling tidak memiliki koneksi ke sistem pencernaan vestigial, yang tidak memiliki sebuah anus(Bender, 1988).

Fisiologi Keratella Sp
Keratella, like all rotifers are pseudocoelomates. This is a paedomorphic condition in which the blastocoel remains even once the animal has reached maturity. It is thought that this condition is secondarily derived (Brusca and Brusca, 1990).

Keratella is a footless rotifer which posesses a protective covering, or lorica. Keratella cochlearis occur in two body forms. The tecta form exists without the posterior spine displayed by the typica form. Generally, spines are present on those Keratella which are born in the presence of predators such as cladocerans, Asplanchna and cyclopoid copepods. The typica form can be born from a tecta mother and vice versa (Gilbert and Mac Isaac, 1989).

Karakteristik
Uraian
Bentuk tubuh
Ovari sebuah; jantan biasanya ada dan mengalami degenerasi.
(Pande,2012).
Dinding tubuh
Tubuh tertutup epidermis yang merupakan lapisan tipis dan sinsitial, dengan jumlah nuclei yang selalu tetap. Epidermis menghasilkan kultikula, tipis sampai tebal, tersgantung jenisnya, bahkan ada yang mengeras seperti cangkang disebut lorica. Lorica adakalanya dihiasinya galur-galur, duri yang pendek, atau panjang dan dapat digerakan, misalnya pada Filinia.
Dibawah epidermis terdapat susunan otot melingkar dan membujur, namun tidak terorganisir sebaik platyhelninthes. Antara dinding tubuh dan organ dalam terdapat pseudocoelom yang berisi cairan dan sel-sel ameboid bercabang-cabang yang tersusun seperti jala sinsitial.(Bender, 1988).
Ekskresi
Pada tiap sisi lateral terdapat sebuah protonephridium dengan 2-8 flame bul. Kedua protonephrida tersebut bersatu pada kantung kemih (bladder), yang bermuara pada bagian ventral kloaka. Isi bladder dikosongkan melalui anus dengan jalan kontraksi, dengan kecepatan satu sampai empat kali per menit. Pembuangan yang demikian cepat membuktikan bahwa fungsi protonephrida adalah sebagai osmoregulator, osmoregulator yaitu membuang kelebihan air didalam tubuh. Dalam beberapa menit dikeluarkan sejumlah cairan yang setara dengan berat tubuh rotifera tersebut. (Pande,2012).
         
Tingkah Laku Keratella Sp
The ciliated corona is the source of locomotion for Keratella,creating the appearance of spinning which gave rotifers their name. However, the main function of the corona is to provide the current necessary for highly efficient filter feeding. The cilia of the corona direct food particles into the buccal funnel and down into the mastax where they are crushed by the trophi. This feeding mechanism allows Keratella to eat a variety of shapes and sizes of food, primarily consisting of phytoplankton such as Cryptomonas and Chlamydomonas (Bogdan and Gilbert, 1982).

Pergerakan
Pergerakannya dilakukan oleh sekumpulan silia yang membudar di sekitar bagian kepala yang disebut corona (Pande,2012).

Peran Plankton Keratella Sp di Perairan
This species is easily cultured and it has been used as a model in order to quantify variation in size at different conditions. Keratella merupakan jenis plankton hewani yanng hidup di perairan litoral dan termasuk pakan larva ikan laut yang penting. Dalam percobaan pembenihan ikan laut,  diberikan sebagai pakan larva selama kurang lebih satu bulan.

Penulis
Rabella Septi Fauziah
Fpik Universitas Brawijaya Angkatan 2014

Editor
Gery Purnomo Aji Sutrisno
Fpik Universitas Brawijaya Angkatan 2015

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