Marine invertebrate diversity in Aristotle’s zoology

The aim of this paper is to bring to light Aristotle’s knowledge of marine invertebrate diversity as this has been recorded in his works 25 centuries ago, and set it against current knowledge. The analysis of information derived from a thorough study of his zoological writings revealed 866 records related to animals currently classi ﬁ ed as marine invertebrates. These records corresponded to 94 different animal names or descriptive phrases which were assigned to 85 current marine invertebrate taxa, mostly (58%) at the species level. A detailed, annotated catalogue of all marine anhaima ( a = without, haima = blood) appearing in Aristotle’s zoological works was constructed and several older confusions were clari ﬁ ed. Some of Aristotle’s “genera” were found to be directly correlated to current invertebrate higher taxa. Almost the total of the marine anhaima were benthic invertebrates. The great philosopher had a remarkable, well-balanced scienti ﬁ c knowledge of the diversity of the various invertebrate groups, very similar to that acquired by modern marine biologists in the same area of study. The results of the present study should be considered as a necessary starting point for a further analysis of Aristotle’s priceless contribution to the marine environment and its organisms.


Introduction
Aristotle was the one who created the idea of a general scientifi c investigation of living things. Moreover he created the science of biology and the philosophy of biology, while his animal studies profoundly infl uenced the origins of modern biology (Lennox, 2001a). His biological writings, constituting over 25% of the surviving Aristotelian corpus, have happily been the subject of an increasing amount of attention lately, since both philosophers and biologists believe that they might help in the understanding of other important issues of his philosophy (Gotthelf and Lennox, 1987) and they may introduce a new generation of biologists to the richness of Aristotle's biological observations and the questions that motivated them (Tipton, 2006).
On the basis of his zoological works, he has been considered as "the founder of zoology" (Pellegrin, 1982) and "the father of zoological classifi cation" (Mayr and Ashlock, 1991). He was the fi rst who gathered information on species of animals, examined their similarities and differences, and attempted to classify them into groups although, as pointed out by various authors (Peck, 1965;Pellegrin, 1982;Mayr and Ashlock, 1991), his aim was not to present an orderly, fully consistent classifi cation of the animal kingdom. This did not prevent Darwin from considering him as "one of the greatest … observers that ever lived", and also as the ancient equivalent of the great systematist Linnaeus by saying, in his famous 1882 letter to W. Ogle, that "Linnaeus and Cuvier have been my two gods … but they are mere school-boys to old Aristotle" (Gotthelf, 1999). His contribution to the classifi cation of animals has been a subject of analysis and evaluation by philosophers such as Lloyd (1961) and Pellegrin (1982). Biologists, on the other hand, have greatly appreciated his contribution to various biological disciplines (Moore, 1987;Kiortsis, 1989;Mayr and Ashlock, 1991;Sofi anidou, 2004).
Around 500 animals are examined in his zoological works. During his stay for about 2 years in Lesbos Island, Aristotle devoted a considerable part of his biological research to marine animals (Thompson, 1913;Lee 1948;Solmsen 1978). Information on the morphology, anatomy, reproduction, development, habitat, diet and behavior of marine invertebrates, fi shes, cetaceans and pinnipeds is given in his zoological works and their fi rst classifi cation scheme is presented. Thus, he is fairly considered to be the fi rst marine biologist (Castro and Huber, 1997). Nevertheless, these data have not been paid special attention by modern researchers, with the exception of Aristotle's malakia, the current cephalopods (see Scharfenberg, 2001). A few attempts to examine Aristotle's marine animals are included in more general works by non specialists (Thompson, 1947;Louis, 1973) and can serve as a basis for a thorough analysis. However, many descriptions of marine animals have not been conclusively identifi ed, and there is scope for new and interesting discoveries in his work (Balme, 1970). We think that Aristotle's contribution to the knowledge of marine life needs to be studied in detail and evaluated under the scope of modern marine biology. As Voultsiadou and Tatolas (2005) pointed out, useful zoological information can be derived from the study of classical texts; this, among other benefi ts, may help historical zoogeographers as a supplement to paleontology, archaeology, and art in the reconstruction of faunas of older epochs. The aim of the present paper is to bring to light Aristotle's knowledge of marine invertebrate diversity as this has been presented in his zoological works 25 centuries ago and set it against current knowledge. This was achieved mainly by presenting a detailed, annotated catalogue of all animals appearing in Aristotle's zoological works, recognized nowadays as marine invertebrates.

Materials and methods
The fi rst step was to go carefully through Aristotle's zoological works searching for records of what we call today "marine invertebrates". The works studied, and their scope as defi ned by Aristotle himself, are the following: I. History of animals (HA) aiming "to determine fi rst of all the differences that exist [among animals] and the actual facts in the case of all of them" because "having done this, we must attempt to discover the causes" (HA 491a12). Here, a description of the observed diversity in animal structure, function and behavior is given.
II. Parts of animals (PA), the task here being "to consider what are the causes through which each animal is as I described it" [in Histories of Animals] (PA 646a10). Structure is herein examined in relation to function, and a long discussion is given on the scientifi c method and the principles of zoology. III. Movement of animals (MA), examining "the common cause of animal movement of whatever kind and how the soul moves the body and what is the origin of movement in an animal" (MA 698a4). The general mechanism of movement in animals is examined mostly theoretically. IV. Progression of animals (IA) discussing "the parts which are useful to animals for their movement… why each part is of the nature which it is and why they possess them … the differences in the various parts of one and the same animals and in those of animals of different species compared with one another" (IA 700b11). V. Generation of animals (GA) aiming "to describe those [parts] which subserve animals for the purpose of generation" and to deal with its "motive cause and to explain what it is" GA (715a12). This is a study on reproduction, embryology and development of animal characteristics. The publications of LOEB Classical Library, Harvard University (Peck, 1942(Peck, , 1961(Peck, , 1970Forster, 1961;Balme, 1991) were used for the study of the classical texts and their English translations for the quotations reported in the paper. Additionally, other editions of classical texts (Balme 2002) and translations of Aristotle's zoological works (Lennox, 2001b) were consulted. The results of the detailed examination of all the above texts were crosschecked using the searching machine offered by the Online Thesaurus Linguae Graecae database (TLG E, Edition 2000). TLG and the Liddel and Scott Dictionary of Greek language were used for the estimation of Aristotle's contribution to the nomenclature of modern zoology.
All animal names were carefully examined in order to be correlated to current marine invertebrate taxa. The identifi cation of animals encountered in the texts and their correlation to recent marine invertebrate taxa was not an easy task, since Aristotle's descriptions were very detailed and accurate in some cases, but fragmentary in others. Classical Greek names often proved very helpful, since they embodied information on their morphology or life history; this information was made available thanks to the continuity of Greek language. On the contrary, Latin scientifi c names inspired by Aristotle's animal names were sometimes confusing, such as holothourion, balanos and nautilos, which were given to animals other than the original, possibly due to misunderstanding of Aristotle's descriptions. Moreover, marine invertebrates are a very diverse group of animals including species not very well known, as for example other groups like mammals or birds. Their knowledge requires expertise in a number of totally different taxa belonging to almost all the known animal phyla. So, the personal experience of the authors on the Mediterranean, and more specifi cally Aegean, diversity of marine invertebrates such as decapod crustaceans (Koukouras et al., 1992), anthozoans (Vafi dis et al., 1994;, ascidians (Koukouras et al., 1995), gastropods (Koutsoubas et al., 1997), sponges (Voultsiadou-Koukoura et al., 1987;Voultsiadou, 2005), was critical, and their database of all literature on Aegean invertebrate fauna proved very useful. The construction of a complete catalogue was made possible thanks to the conclusive identifi cation of several descriptions for the fi rst time and the clarifi cation of various misidentifi cations and confusing points found in previous works, such as in the cases of sponges, anthozoans, crinoids, polychaetes, and echiurans. A series of zoological books (Ruppert et al., 2004), general zoological publications on Mediterranean invertebrates (Riedl 1963;Fischer et al., 1987;Weinberg 1993;Hayward and Ryland 1996), as well as more specialized ones (Ingle 1996;Delamote and Vardala, 1994), were really helpful in the evaluation of the collected information. For details on the identifi cation procedure see Voultsiadou and Tatolas (2005).

Results
Overall 866 records corresponding to animals currently classifi ed as marine invertebrates were encountered in the studied texts. These records were unequally distributed in four of the studied works by Aristotle as follows: the majority -582 records-was found in History of animals, 195 in Parts of animals, 74 in the Generation of animals and 15 in Progression of animals. No specifi c animal records occurred in Movement of animals. All these records corresponded to 94 different animal names or descriptive phrases. Notice that Aristotle often needed to report animals that were not given a name up to his age. In such cases, he gave a short description of the animal's characteristic features or life history, e.g. γένος ἀστακοίς μικρὸν ὥσπερ καρκίνοι (a genus similar to lobsters, but small like crabs) or πιννοφύλαξ σπóγγων (pinna-guard of sponges), which is what we report here as "descriptive phrases".
A detailed identifi cation and assignment of all marine anhaima (a = without, haima = blood) to recent marine invertebrate taxa, as these are classifi ed in the groups defi ned by Aristotle himself, is given below. As is well known, Aristotle divided animals into anhaima (ἂναιμα) meaning bloodless and enhaima (ἔναιμα) meaning blooded, these two groups corresponding to what we call today invertebrates and vertebrates. Further on, he recognized four groups of bloodless animals: apart from entoma (insects) that do not fall into the scope of our study, these were ostrakoderma (having a hard shell surrounding the body), malakia (having a soft body), and malakostraka (having a soft shell) (Fig. 1).
The necessary documentation for the identifi cations were quoted from the classical texts and comments on etymology and other animal characteristics, helpful for identifi cation, are also cited. The extent of documentation depends on how well known or common an animal is. Therefore, we did not consider it necessary to quote and comment on the identity of animals such as the common edible sea urchin, which is frequently recorded and thoroughly described in the texts. On the other hand, the identifi cation of animals not very common or not easily recognizable was supported by detailed evidence. Animal names were transliterated in Latin for the convenience of the reader. Transliteration was made according to Brown (1979) and Lennox (2001b). All the records of each animal name in the examined texts are given. Superscript numbers in each name or descriptive phrase correspond to the taxa names listed in Table 2. Each number corresponds to one of Aristotle's animal names.
-Heledōnē 4 (ἐλεδώνη) or bolitaina 5 (βολίταινα) or ozolis 6 (ὄζολις): the musky octopus Eledone moschata (Lamarck, 1798). It is discriminated from other octopuses by its longer arms each "bearing one single row of suckers" (HA 525a19). The name ozolis (όζω = to stink) indicates its characteristic unpleasant smell. Scharfenberg's (2001) opinion that heledōnē and volitaena or ozolis are two different species does not seem to be valid. If such was the case Aristotle would not state that heledōnē is the only μαλάκιον with a single row of suckers.
-Nautilos 7 (ναυτίλος = sailor) or pontilos 8 (ποντίλος) or ōon polypodos 9 (ᾠὸν πολύποδος = the egg of the polypous): the paper nautilus Argonauta argo Linnaeus, 1758. Although the name has been given to the recent genus Nautilus, Aristotle's description indicates the paper nautilus: its shell is described as "a single, deep scallop valve not joining with another" (HA 525a21). The way it moves up and down in the water is described (HA 622b1-19).
-Polypous en ostrakō oion cochlias 10 (πολύπους ἐν ὀστράκῳ οἷον κοχλίας): the chambered nautilus, a species of the genus Nautilus spp. It is briefl y re-ported as "living inside a shell like a snail, sometimes protruding its tentacles" (HA 525a26). It is obvious that Aristotle had never seen a chambered nautilus; otherwise he would have been impressed by its appearance. It seems that he had rather been informed about its existence by somebody else, possibly someone accompanying Alexander the Great in his expeditions in the vicinity of the Indian Ocean, where the distribution of Nautilus species extends. Thompson (1947) suggested that Aristotle had in mind the species Janthina janthina (Linnaeus, 1758) and he must have mistaken for tentacles, the masses of eggs released by this fl oating species. Although J. janthina is common in the Aegean, it is very small in size and it could not be mistaken for an octopus.

Karaboi (κάραβοι)
Arktos 17 (ἄρκτος): the small European locust lobster Scyllarus arctus (Linnaeus, 1758), compared with karabos for its spawning season (HA 549b23). The name ἄρκτος (= a bear) indicates the shape of the second antennae which on dorsal view resembles the footprint of a bear.
-Karidon mikron genos 22 (καρίδων μικρὸν γένος): the small kind (HA 525b2), a species of Natantia Decapoda. It could be any group of small sized shrimps, since no description is given.
-Krangōn 23 (κραγγών): the mantis shrimp Squilla mantis (Linnaeus, 1758). The body structure of Stomatopoda is described in detail (HA 525b22-30); four plus three pairs of legs on the anterior part and a broad spiny tail (telson and two biramous uropods).
-Karidion 24 (καρίδιον): the shrimp Pontonia pinnophylax (Otto, 1821). The information given (HA 547b17) on the symbiotic relationship of this shrimp with the fan mussel (Pinna) indicates this species. Besides this specifi c meaning, the term karidion was used for a small karis.
-Hippos 28 (ἵππος = horse): the ghost crab Ocypode cursor (= O. hippeus) (Linnaeus, 1758) which is said to live in Phoenicia running fast on the beach (HA 525b7). It is a common species on the eastern coasts of the Levantine basin.
-Maia 29 (μαῖα = midwife): the spiny spider crab Maja squinado (Herbst, 1788). The information given for this crab is that it is "the biggest among all crabs" (HA 525b4), "it lives in the deep and moves little about" (PA 684a8), "has a very hard shell" (HA 601a19) and "owe its safety to it, having for this reason thin feet, considerably less effective for locomotion" (PA 684a10). Moreover, it is said to "have its eyes in the middle and close together", in contrast to most other crabs "in which eyes are placed a long way apart from each other" (HA 527b7). M. squinado has all the above characteristics.
-Pagouros 30 (πάγουρος): possibly the edible crab Cancer pagurus Linnaeus, 1778, according to older identifi cations (see Thompson 1947). No description exists but it is said to be "one of the biggest crabs in size" (HA 525b5).

Unclassifi ed malakostraka
Karkinion 34 (καρκίνιον): the hermit crab. A general name for Anomura Decapoda of the family Paguridae. It is considered to dualize (epamfoterizein, ἐπαμφοτερίζειν), since it looks like karabos but lives inside a shell like ostrakoderma do (HA 529b20-530a27), "carries it about with, feeds inside it, and as it grows it moves on again into a larger one" (HA 548a14-21). Besides this specifi c meaning, the term karkinion was used for a small karkinos (HA 547b17).
Kyllaros 35 (κύλλαρος): Paguridae sp. A species of Anomura living inside Nēreitēs, a small gastropod. It is characterized by having "the right pincer smaller than the left one" (HA 530a12). It is diffi cult to identify a certain species, since there exist some small sized common species of hermit crabs with obviously smaller right pincer.
-Genos mikron 43 (γένος μικρόν): the species Cidaris cidaris (Linnaeus, 1758). It is "a kind small in size, bearing large, hard spines … living in the area of Toronē, several fathoms deep, and some use it as a remedy for strangury" (HA 530b7). C. cidaris, which thrives in sandy bottoms deeper than 30 m, fi ts with the above description.
-Leukos echinos 44 (λευκὸς ἐχῖνος): the heart urchin Brissus unicolor (Leske, 1778). They are described as (HA 530b10) "white sea urchins -shells, spines and eggs are all white-longer than the ordinary ones, the spines neither large nor strong, but rather limp". The species B. unicolor, living in sandy bottoms, like in the area of Toroni mentioned in the text, is exactly as described above having a test diameter of up to 13 cm.
-Echinomētra 45 (ἐχινομήτρα = mother of sea urchins): the violet sea urchin Sphaerechinus granularis (Lamarck, 1816). It is "the largest of all in size" (HA 530b6). This common Aegean species is very similar to the common urchins but reaches 15 cm in test diameter. The species Echinus melo that has been suggested by some authors is yellowish in color and lives in deeper waters, characteristics which have been indicated by Aristotle for the discrimination of other sea urchin species.

Tēthya (Tήθυα)
Tēthyon 47 (τήθυον): the sea squirt (Ascidiacea, Chordata). It is described (HA 531a9-31) as "the most extraordinary of all these animals, being the only ones whose body is completely hidden inside the shell, the texture of which is between that of skin and shell, and consequently cut like hard leather. The animal clings to the rock by its shelly part and has two passages some distance apart". Two kinds are distinguished according to their colour.

Monothyra (μονόθυρα) (enclosed in one shell)
Lepas 50 (λεπὰς): the limpet Patella caerulea Linnaeus, 1758. It is described as a "univalve, having its fl eshy part exposed" (HA 528a14) "releasing its hold in order to search for food" (HA 528b1) and "living near the surface of the water with Nēreitēs" (HA 547b22).

Strombōdē (στρομβώδη) (spiral-shelled)
Haimorrhois 54 (αἱμορροΐς): a gastropod species (Gastropoda, Mollusca). Its name, coming from haima (αἷμα = blood) and rheo (ῥέω = fl ow, spring) implies that it produces a purple dye. However, it is discriminated from porphyra, with which it is reported in a general description of spiral-shelled animals (HA 530a19). Possibly it was a separate name for one of the three species assigned to the name porphyra (see bellow).
Chēmē 63 (χήμη): the common Noah's arc shell Arca noae Linnaeus, 1758 and the related species. The name chēmē (χήμη from χάσμα = gap, chasm) indicates the space existing between the umbones which are far apart in dorsal view. They are reported once by Aristotle as "taking their rise in sandy places together with conchai, sōlēnes and ktenes" (HA 547a13). He does not give any further information of these animals, but Xenocrates in his work Περὶ τῆς ἀπὸ τῶν ἐνύδρων τροφῆς (xxxi) [on food from aquatic animals] writes that the coarser of them are "elongated, having a roughness when opened, just like the cup of the acorn", obviously indicating the straight hinge with the numerous small teeth and that "they are radially ribbed, with extra roughness, on their shell", just like Arca. HA 547a13.
Conchē 64 (κόγχη): a general name for smooth-shelled bivalves, such as tellins (Tellinidae), trough shells (Mactridae) or wedge shells (Donacidae). They are listed with razor shells and mussels as examples of ostrakoderma "having a smooth shell" (HA 528a21-27) and they are reported to "take their rise in sandy places" (HA 547a13). HA 528a22,530a11,547b13,b20,548a5,614a28,622b2. -Galax 65 (γάλαξ): a species belonging to one of the families Donacidae, Tellinidae and Mactridae. It is not possible to discriminate which of the three was known under this certain name, since it is just reported as "a kind of conchai, called by some galakes". The name itself indicates a milky white shell but such morphs exist in all the above groups which present a great variation in shell colour (HA 528a23).
(Holothurioidea, Echinodermata). It is mentioned along with aidoion and aspis as a "rare species not easily classifi ed, although observed by experienced fi shermen; … it is like a relatively long and stout bar, black, round and has the same thickness throughout its length" (HA 532b21). The description fi ts perfectly to this common Mediterranean species of sea-cucumbers, which may reach 40 cm in length.

HA 532b21.
Holothourion 83 (ὁλοθούριον): the soft coral species Veretillum cynomorium (Pallas, 1766) (Anthozoa, Cnidaria). According to Aristotle it is "an unattached, though not moving animal, not having any power of sensation, living like a plant unattached to the soil" (HA 487b14). Moreover, "it differs from sponges only slightly in being unattached" (HA 681a17). This description fi ts well with the above common species which resembles sponges actually in having a spongy internal structure and lives in sandy bottoms loosely held in the sediment. Its elongated shape and erect habit lies behind the name holothourion, ὁλοθούριον made of ὁλος (= whole, entire) and θούριος (= male, acute, fi erce).
Oistros o tōn thynnōn 84 (οἶστρος, ὁ τῶν θύννων): the parasitic copepods (Copepoda, Crustacea) of the genus Caligus commonly found on tuna fi sh. According to the description it is "found around the fi ns of tuna, it is like a scorpion and about the size of a spider" (HA 557a27). The species of the genus Caligus conform to this description.
Phtheir thalattia 85 (φθεὶρ θαλαττία): the isopods of the family Cymothoidae (Isopoda, Crustacea). Their description as "lices (φθείρες) found on fi shes, resembling woodlice, except that they have a fl at tail, and they are mostly found on the red mullet" (HA 557a21) indicates these common fi sh parasites. The most common species in the Mediterranean are Nerocila bivittata (Risso, 1816) and Anilocra physodes (Linnaeus, 1758). HA 537a5,557a22,a25,602b29. Pneumōn 86 (πνεύμων): the dead man's fi nger Alcyonium palmatum Pallas, 1766 (Anthozoa, Cnidaria). It is only mentioned once (PA 681a18) along with holothourion as "differing only slightly from sponges in being unattached. They have no power of sensation but they live just as if they were plants unattached to the soil". As mentioned for holothourion it has a spongy internal structure as well, justifying the name πνεύμων (= lung) and lives loosely held in sandy bottoms.
Psyllos thalattios 87 (ψύλλος θαλάττιος): the amphipods (Amphipoda, Crustacea). They are mentioned as attacking in great numbers the fi sh caught by the fi shermen when they are left in the water for a while before brought on the surface, or even crowding together around the bait, provided that it consist of fi sh, forming a ball around it (HA 537a8). The above information and the name ψύλλος (= fl ea), borrowed from the known insects, indicates the marine amphipods, which besides an external superfi cial similarity, share the ability of jumping (at least the littoral species of the group).

HA 537a6.
Scolopendra thalattia 88 (σκολόπενδρα θαλαττία): the fire-worm Hermodice carunculata (Pallas, 1766) (Polychaeta, Annelida). It is mentioned that "there exist marine scolopendras similar to the terrestrial ones but slightly smaller in size, occurring in rocky places" which "compared to the land millipedes, they are redder and have more numerous and more delicate feet" (HA 505b14). They are said to "bite, not with the mouth, but apparently with the whole body, like the sea anemone, and to turn its inside out when it swallows the hook, in order to expel it" (HA 621a6). This warm water polychaete, very common in the Eastern Mediterranean, but missing from the western basin, may reach 30 cm in length. It has numerous parapodia, bearing red gills at their base. It can easily extent and retract its pharynx and when touching the skin it causes a burning irritation.
Spongos 89 (σπόγγος): the sponges of the order Dictyoceratida (Porifera) including the commercial bath species. They are described as "living attached on the substrate, being black when alive, before cleaned and washed, providing home for animals like worms and crustaceans, being able to grow up again in case it gets broken off" (HA 548b1-549a13) as well as being the most primitive animals "resembling very much the plants" (HA 588b21), "having however, a sort of sensation" (HA 548b10) and "receiving food through the big passages on its upper part" (HA 548a30). Five different kinds are distinguished (HA 548b1-549a13). HA 487b9,548a23,a28,a32,549a7,a10,a10,a12,588b20,616a30,630a7,PA 681a11,a15, spongeis (σπογγείς = the sponge fi shermen) HA 620b34.
-Aplysias 90 (ἀπλυσίας): the black Ircinia Sarcotragus muscarum Schmidt, 1864, called "wild sponge" by the sponge fi shermen. The description given (HA 549a4) fi ts perfectly to this species, since it can not be cleaned and used as a bath sponge, though it looks very much like the common bath sponges while it is black and in cross section it has large canals, and dense skeleton. Moreover, "compared to the bath sponges it is stickier and more diffi cult to be torn, looking like a lung".
-Manos 91 (μανός): the honey comb Hippospongia communis (Lamarck, 1813). It is only mentioned by its name (μανός = loose) (HA 548b1) indicating the loose structure of this species which bears numerous and large canals, and for "reaching the largest size of all kinds" (HA 548b19), which is true for this species sometimes passing 30 cm in diameter.
-Pycnos 92 (πυκνός): the Greek bathing sponge Spongia officinalis Linnaeus, 1759. The name (πυκνός = dense, close-textured) and the comment that "they become the softest in the area around Lycia" indicates the best quality bath sponge of the species S. offi cinalis.
-Achilleios 93 (Ἀχίλλειος): the elephant ear Spongia agaricina Pallas, 1766. It is mentioned as "the fi nest, most closely textured and strongest and the rarest species of all, used for lining helmets and greaves for protection, deadening the noise of blows on them" (HA 548b1). This thin, cup -shaped, strong and delicate sponge fi ts well to the description.

Aristotle's major genera and higher taxa
All marine anhaima encountered in Aristotle's zoological works are correlated with current marine invertebrate taxa. As a result, a generalized correlation of Aristotle's major genera of marine anhaima ( Fig. 1) with current higher taxa was obtained (Table 1).
Obviously, there was not a direct correlation, since the main taxonomic character he used for their delimitation was the arrangement of the soft and hard parts in the animal body. However, he distinguished current cephalopods (his Malakia) and decapods (his Malakostraka) as separate groups (including stomatopods in the latter).
Malakostraka was not homogenous, including some major genera itself (PA 683b26), such as astakoi, karaboi, karides and karkinoi corresponding to the current Macrura Reptantia (the fi rst two), Natantia and Brachyura respectively. Echinoderms were not recognized as a group, since two of their classes (Echinoidea and Asteroidea) were put in Ostrakoderma and other two (Crinoidea and Holothourioidea) remained unclassifi ed. Several marine bloodless animals remained out of the three major genera; some of these unclassifi ed anhaima, i.e. the sessile sponges, anthozoans and ascidians were distinguished for their resemblance to plants and ranked at the early stages of "nature's transition from plants to animals" (PA 681a10-b9). Aristotle's principle of downward classifi cation, to which Linnaeus largely adhered, dominated in taxonomy up to the eighteenth century (Mayr and Ashlock, 1991).

Classical animal names and their assignment to current taxa
The 94 different animal names or descriptive phrases encountered were assigned to 85 current marine invertebrate taxa at different category levels (Table 2, Figure  2). The number of taxa is lower in comparison to the number of animal names mostly because some animals appeared in the texts with more than one name, e.g. heledōnē and nautilos. The majority of the animals (58%) were assigned to species level taxa and the remaining to supraspecifi c taxa. In malakia, a group including mostly incessant commercial species, species level taxa were almost exclusively identifi ed.
The fact that Aristotle himself did not undertake the task to name all animals he examined has been considered as a diffi culty for the construction of a full list of all animals he recorded by later researchers (Louis, 1971). However, although he did not purposely introduce new names or terms where they did not exist, modern marine biology owes to Aristotle a lot of names that appear for the fi rst time in his writings (

Aristotle's scientifi c knowledge of marine invertebrate diversity
It is clear that, with few pelagic exceptions, Aristotle's marine anhaima were benthic invertebrates. This seems quite reasonable since benthic organisms represent 98% versus 2% of the pelagic ones in the marine ecosystem (Gaston and Spicer, 1998). An estimation of the highly recorded animal names in Aristotle's works showed that they, unsurprisingly, included those of the three major genera (ostrakoderma, malakia, malakostraka) and some of the most common    (7,8,9) ναυτίλος*, ποντίλος*, ᾠόν πολύποδος* mautilos*, pontilos*, ōon polypodos* Cephalopoda (1) μαλάκια* malakia* Eledone moschata (4,5,6) ἐλεδώνη *, βολίταινα*, ὄζολις* eledōnē *, bolitaina*, ozolis* Loligo vulgaris (14) τευθίς teuthis Nautilus sp. (10) πολύπους ἐν ὀστράκῳ οἷον κοχλίας* polypous en ostrakō oion cochlias* Octopoda (2) πολύπους polypous Octopus vulgaris (3) πολυπόδων μέγιστον γένος* polypodōn megiston genos* Sepia offi cinalis (11,12) σηπία, σηπίδιον sēpia, sēpidion Todarodes sagtitatus (13) τεῦθος* teuthos* (Jackson et al., 2001). In an attempt to examine the general biodiversity pattern in the Aegean as illustrated in Aristotle's works, the only source of information for the status of marine fauna 25 centuries ago, and to evaluate his scientifi c knowledge of benthic diversity, a comparison of benthic taxa diversity given in his works with the relative current data for the Aegean Sea (as given by Chintiroglou et al., 2005a) was made (Fig. 4). The comparison showed that Aristotle had a remarkable, wellbalanced scientifi c knowledge of the diversity of the various invertebrate groups, very similar to the one acquired by modern marine biologists in the same area of study. Lennox (2001b) questioned the taxonomic purpose of the Aristotle's grouping of animals since "as one can see they differ widely in extension". However, on the basis of the above comparison, the difference in the extension of Aristotle's groups should be attributed to the uneven distribution of species inside higher groups. The differences existing between the number of taxa recorded by Aristotle and the number of current taxa inside groups (Fig. 4) only means that Aristotle had given to molluscs or cnidarians more attention than justifi ed by the number of species of these groups. On the contrary, he did not pay much attention to polychaetes possibly due to their not so obvious variety of form.
In conclusion, we can say that Aristotle's contribution to the knowledge of the diversity of benthic marine invertebrates is very high, taking into account the absence of any zoological background and the primitive facilities of his age. He had a balanced scientifi c knowledge of all the major benthic invertebrate groups. There have been diffi culties with the recognition of various marine animals recorded in his writings by previous researchers, as shown by several wrong identifi cations. This study, conducted by Greek speaking marine zoologists living and diving in the same area with the great philosopher, thus being very familiar with the objects of his inquiry, contributed to the clarifi cation of some confusing points. We think that it should be considered as a necessary starting point for any further analysis of the great philosopher's knowledge on the marine environment and its organisms.