ABSTRAKEchinodermata termasuk komponen keanekaragaman hayati yang berperan penting dalam ekosistem. Penelitian ini bertujuan untuk mengetahui morfologi, anatomi, habitat, serta hubungan antara faktor fisika kimia perairan terhadap jumlah Holothuria atra di perairan Pulau Cemara Kecil Taman Nasional Karimunjawa. Metode dalam penelitian ini yaitu metode observasi dengan analisis statistik kuantitatif. Metode observasi merupakan metode yang digunakan untuk menganalisis sampel di lapangan serta di laboratorium. Penentuan stasiun secara systematic random sampling dengan mempertimbangkan keberadaan ekosistem padang lamun sebagai habitat utama teripang. Sampel teripang diidentifikasi dan sampel sedimen dilakukan analisis butir sedimen. Analisis kuantitatif dilakukan guna mengetahui pengaruh tutupan lamun terhadap kelimpahan teripang. Hasil penelitian menunjukkan bahwa ditemukan spesies Holothuria atra dengan tubuh berbentuk bulat dengan warna hitam terdiri atas mulut, tentakel, faring, esofagus, stomach, usus, gonad, cloaca, dan anus. Berat tubuh teripang yang ditemukan yaitu 192 - 411 gram, panjang tubuh 17 - 23 cm, lebar badan 4 - 7,6 cm, dan panjang ususnya 68,58 - 78,8 cm. Habitat dari teripang Holothuria atra berupa sedimen berpasir kasar (0,5 mm) yaitu sebesar 54 % dan pasir halus (0,125 mm) 44,9%. Hubungan antara kelimpahan teripang dengan nilai tutupan lamun didapatkan nilai koefisien determinasi sebesar 0,024 termasuk kategori lemah dan koefisien korelasi sebesar 0,15 termasuk kategori sangat lemah. Sedangkan parameter kualitas air optimal untuk pertumbuhan teripang dan lamun.Kata kunci: Echinodermata, Holothuria atra, Kelimpahan, Lamun, Teripang.ABSTRACTEchinoderms are one of components of marine biodiversity that play an important role in ecosystem function.This study aims to determine the morphology, anatomy, habitat, and relationship between physical, chemical factors in the waters and the number of Holothuria atra Cemara Kecil Island, Karimunjawa National Park. The method in this study is the observation method with quantitative statistical analysis. The observation method is a method used to analyze samples in the field and in the laboratory. Determination of stations by systematic random sampling by considering the the existence of seagrass ecosystems as the main habitat of sea cucumbers. Sea cucumber samples were identified and sediment samples were analyzed for sediment grains. Quantitative analysis was conducted to determine of seagrass cover influence on sea cucumber abundance.The results showed that the species Holothuria atra was found with a round body with a black color consisting of a mouth, tentacles, pharynx, esophagus, stomach, intestines, gonads, cloaca and anus. The body weight 192-411 grams, body length of 17-23 cm, body width 4-7.6 cm, and intestine length in the range of 68.58-78.8 cm. The habitat of the sea cucumber Holothuria atra is coarse sand (0.5 mm) sediment which is equal to 54% and fine sand (0.125 mm) 44.9%. The relationship between revealing sea cucumbers and the seagrass cover value obtained a determination coefficient value of 0.024 including the weak category and a correlation coefficient of 0.15 including the very weak category. Meanwhile, air quality parameters are optimal for the growth of sea cucumbers and seagrass.Keywords: Abundance; Echinodermata, Holothuria atra, Seagrass, Sea Cucumber.