الفهرس 
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Abstract
The warm tropical water of the Red Sea is home to some of the most beautiful coastal and marine ecosystems in the world and various wildlife. The shoreline of the Red Sea is considered one of the richest shores in the world, where it represents all major tropical marine ecosystems.
Although the importance of Red Sea marine algae, few investigations have been on Red Sea algae in different kinds of research especially the algal associations between each other and with its associated fauna. Also, the fauna and their biodiversity attracted many Egyptians and foreigners to study their ecological and biological aspects. The associated faunal biodiversity research was conducted on coral reef communities, mangrove communities and seagrass communities, but in the case of algal associated fauna, it is necessary to conduct more intensive studies on the faunal composition with algal communities and the diversity of these fauna.
Most of the previous amphipod research in the Red Sea covered all types of associated habitats like algae, seagrass, hydroids, sponge, corals, coral rubbles, and sandy bottom. Differences in the amphipod distributions along the depth gradients are due to their ability to deal with the physical/abiotic and biotic factors.
Regarding the abiotic factors, the distribution and abundance of amphipods in marine sediments are affected by the soft bottom grain size composition, sediment type, wave action and depth.
So, the aim of this study is to record all the recognized Ampithoid species within the targeted habitat (algae and sand), as well as revise the taxonomical characters of all assigned species in the Northern Red Sea during the period from July 2019 to April 2020. Samples were collected seasonally from 7 sites, which started from Hurghada to Halayeb.
The results of the present study showed that:
• Fifteen algal species were recorded from the 7 study areas red algae, Brown algae and green algae.
• A total of 1976 ampithoid individuals have been recorded from the Red Sea during the study period belonged to 9 species and 8 genera Amphithoides longicornis Kossmann, 1880, Ampithoe ramondi Audouin, 1826, Biancolina sp, Cymadusa filosa Savigny, 1816, Cymadusa setosa Haswell, 1879, Paradusa bilobata Ruffo, 1969, Paragrubia vorax Chevreux, 1901, Pleonexes kava Myers, 1985 and Sunamphitoe falsa Barnard, 1932.
• Algae habitat inhabited by the highest number of recorded species being, (1976 individuals) belonging to 8 genera while, sandy habitats consist of (23 individuals) belonging to genus Biancolina. All algae samples were collected from intertidal zones of the 7 sites, but sand samples were taken from all sites except in Shalateen site it was collected from intertidal and shallow sub-tidal depths.
• Data showed that families Sargassaceae, Dictyotaceae and Scytosiphonaceae (brown algae) are dominated by the highest number of ampithoid species, being 1088 individuals, followed by families Rhodomelaceae, Corallinaceae and Galaxauraceae (red algae) which are associated with 852 ampithoid individuals. The rest 13 ampithoid individuals recorded from green algae at Hurghada, El Quseir and Shalateen are dominated by the lowest number.
• Brown algae were recorded throughout all sites of study and represented by 3 species: Ampithoe ramondi Audouin, 1826, Cymadusa filosa Savigny, 1816 and Pleonexes kava Myers, 1985.
• Red algae are more diverse and lower density than brown algae, as well as are characterised by the presence of Ampithoe ramondi Audouin, 1826, Cymadusa filosa Savigny, 1816, Cymadusa setosa Haswell, 1879, and Pleonexes Kava Myers, 1985.
• Green algae are less abundant and diverse and were recorded by 3 species: Ampithoe ramondi Audouin, 1826, Paradusa bilobata Ruffo, 1969 and Pleonexes kava Myers, 1985.
• Although brown algae are the most abundant habitat, the amphipods; Cymadusa setosa Haswell, 1879 and Paradusa bilobata Ruffo, 1969 were not recorded so far.
• The present results indicated that the algae Galaxaura sp and Ulva sp are the most selected algae for Cymadusa setosa Haswell, 1879 and Paradusa bilobata Ruffo, 1969 respectively.
• The results revealed that the number of amphipods inhabiting soft bottom habitat was 23 individuals of Biancolina sp. Biancolina shows remarkable sexual dimorphism in the outer rami of uropods 1 and 2.
• The numbers of ampithoid individuals in different sites were varied, and the highest number of individuals recorded at El Quseir site and Lahmy site being 632 and 405, respectively. On the other hand, the lowest numbers of ampithoid individuals were reported at Abu-Dabbab site and shalateen site being 28 and 50, respectively. While in the rest of the sites the number of ampithoid amphipods varied.
• The genus Amphithoides longicornis Kossmann, 1880 separated from almost all other ampithoids by having slender spine on the inner ramus of uropod 3 but is not setose and the outer ramus of uropod 3 has only one hook.
• Data showed that Ampithoe ramondi Audouin, 1826 was represented by (1226 individuals) 1206 mature males and 20 mature females, were collected from Hurghada, Safaga, El Quseir, Abu-Dabbab, Lahmy, Shalateen and Halayeb sites at intertidal macro-algae (Laurencia obtusa, Galaxaura sp, Dictyota dichotoma, Cystoseira crinite, Halimeda macroloba, Turbinaria triquetra, Digenea simplex, Sargassum dentifolium, Dichotomaria obtusata, Hydroclathrus clathratus, Jania rubens, Palisada Perforata and Padina Pavonica) during the study period.
• Biancolina sp represented by (23 individuals) 10 mature males, 13 mature females were collected from all study sites except in Shalateen it was collected from intertidal and shallow subtidal depths among sandy areas, biancolina shows remarkable sexual dimorphism in the outer rami of uropods 1 and 2 and the hypothesis that the transformed outer ramus of the male uropod 1 is related to reproductive behavior awaits observations of living animals.
• Cymadusa filosa Savigny, 1816 (464 individuals) 451 mature males and 13 mature females, were collected from Hurghada, Safaga, El Quseir, Lahmy, Shalateen and Halayeb at the intertidal macro-algae (Palisda perforata, Galaxaura sp, Dichotomaria obtusata, Padina pavonica, Cystoserira crinita, Digenea simplex, Laurencia obtusa, Turbinaria triquetra, Jania rubens, Hydroclathrus clathratus, Hydroclathrus clathratus, Ulva sp, Caulerpa Serrulata and Dictyota dichotoma) during the study period.
• Cymadusa setosa Haswell, 1879 represented by12 mature males was collected from Safaga at intertidal macro-algae (Galaxaura sp) during the study period.
• Paradusa bilobata Ruffo, 1969 represented by 2 mature males, was collected from El Quseir at the intertidal macro-algae (Ulva sp) during the study period.
• Paragrubia vorax Chevreux, 1901, Differing from most ampithoids by the gnathopod 1 is larger than gnathopod 2, the accessory flagellum is long, it consists of 4-5 articulated.
• Pleonexes Kava Myers, 1985 represented by (249 individuals) 234 mature males and 15 mature females, were collected from Hurghada, Safaga, El Quseir, Lahmy, Shalateen and Halayeeb areas at intertidal macro-algae (Palisda perforata, Galaxaura sp, Dichotomaria obtusata, Halimeda macroloba, Cystoseira crinite, Hydroclathrus clathratus, Jania rubens, Laurencia obtuse and Dictyota dichotoma).
• Sunamphitoe falsa K.H. Barnard, 1932 the presence and absence of a mandibular palp originally separated the genera Sunamphitoe Bate, 1857 and Peramphithoe Conlan & Bousfield, 1982 but in recent studies, the expansion of both basis and the merus of the pereiopods from 3 to 4 is focused on the diagnostic character for Sunampithoe differentiation.
• Data showed that the highest abundance of recorded species observed in algal habitat unlike the other habitats like seagrass bed, sand, hydroids, and coral rubbles.
• The results revealed that the number of amphipods inhabiting soft bottom habitat was 23 individuals of Biancolina sp., which considered low compared to Ampithoe ramondi was recorded (1226) by high densities in algal habitat.
• PCR amplification products generated by primers (Loc1490F and HCO2198R) targeting 631 Pb have been resolved by electrophoresis on a 1% agarose gel for the investigated species, and there was a total of 473 positions in the final dataset after pairwise deletion options.
• The evolution analysis was conducted using Tamura 3-parameter model for 13 nucleotide sequences being; 10101 for Ampithoe ramondi, 10102 for Pleonexes kava, 10103 for Cymadusa setosa and 10104 for Cymadusa filosa in addition to 9 gene bank sequences. The evolution tree confirmed the structure that was proposed in morphological study.