Period, biol. 79:65—68, 1977.

SYSTEMATIC POSITION AND STATUS OF THE HOMOLODROMIIDS (CRUSTACEA, , BRACHYURA)

Z. STEVCIC Laboratory for Ecology and Systematics, Center for Marine Research, Ruder Boskovic Institute, Rovinj, Yugoslavia

Received December 1, 1976. SUMMARY. The systematic position as well as the systematic status of the homolodromiids and some related taxa has been considered. By comparison with other Dromiacean taxa it has been established that homolodromiids form a separate family , which can­ not be included either in Homoloides or . The Homolodro- midae are most closely related to the families Eocarcinidae and Prosopidae with which they should form a separate superfamily Proso- poidea. This superfamily is the most primitive one within the , therefore it has to be retained at the beginning of the system of the Brachyura.

Although the homolodromiid idea. A. Milne Edwards and Bouvier (6, 14) have been much investigated (1, 5, 11, 13, considered them only as genera of the sub­ 16) their systematic position and status, as family Dromiinae. Balss (2), although giv with most brachyuran taxa, have been va­ ing a systematic review of the primitive riously considered and conclusions have Dromiacea according to Glaessner (9), varied from author to author. At first both treated them nevertheless as a separate fa­ homolodromiid genera Homolodromia mily. Finally, Pichod-Viale (17) considered and Dicranodromia were described in 1880 both homolodromiid genera to be a part by A. Milne Edwards (13) as members of of the family . the family . Alcock (1) placed As is obvious from this historical re­ these two genera in a separate family Ho view, these two homolodromiid genera molodromiidae, as a part of the superfa­ have had various treatments regarding mily Dromioidea. Such a classification their status, i.e. from genera to family, as was accepted by Borradaile (4), Gordon well as their systematic position, being (11), Gurney (12) and Rathbun (18), while included in the Dromiidae, Prosopidae or some authors, such as Beurlen (3) Monod Homolidae. As a consequence of such di­ (15) and Serene (19), treated them only versity of opinions, two questions could as a family of the Dromiacea. Glaessner be posed: what is the systematic position (9, 10) included these genera in the family of the homolodromiids in the Brachyuia, Prosopidae as the subfamily Homolodro and what is the systematic status of this miinae, but in the superfamily Dromio­ taxon? It is noteworthy that for these con- Reprint requests to: Z. Stevcic, Center for Marine Research, Ruder Boskovic Institute, Paliage 5, 52210 Rovinj, Yugoslavia. 66 Z. STEVCie siderations, only comparative morpholog­ hand there are many differences, because ical evidence from adults can be used, the homolodromiids have an elongate and because in these two genera free swimm cylindrical cephalothorax; their third ing larvae are not known and their devel­ maxilliped is pediform; 21 branchiae on opment is probably direct (7, 12). each side; epipodites on the second and The first point in considering the sy third pereiopods; sternal furrow very stematic position is to stress that the ge­ short; endoskeleton is discontinued (8) nera Homolodromia and Dicranodromia and the head is not condensed, i.e. the are very similar and form a natural taxon ocular segment is not invaginated into the clearly delimited from other brachyuran antennular one (17), so that there are taxa, which we have named conditionally neither orbits nor orbital and antennular homolodromiids. In order to establish the grooves. Because of these great differen­ systematic position of the homolodromida ces in important and distinctive charac­ it is necessary to establish the next higher ters it is not possible to include the ho­ taxon in which they can be included. In molodromiids into the superfamily Dro­ spite of the fact that many authors hold mioidea. widely differing opinions on this taxon, Comparing homolodromiaids with llo- they mostly agree that homolodromiids moloidea, whiach include two families Ho- are the most primitive living crabs and molidae and Latreillidae, one can see they are placed among the Dromiacea at that these two taxa have several charac the beginning of the Brachyuran system. ters in common: the endoskeleton is dis­ The homolodromiids correspond indeed continued, the head is not condensed; the to the Dromiacea in all diagnostic charac third maxilliped is pediform; the cephalo­ ters (antennal segments not fused; front thorax is elongate; the fifth pair of pe­ narrow; seminal ducts perforate coxae of reiopods is dorsal and subchelate. The dif­ the fiftht pereiopods; oviducts open in cox­ ferences are, however, also considerable: ae of the third pereiopods; greater num­ homolids do not posses sternal furrows; ber of branchiae; the first pleopod pre­ rudiments of uropods are absent; phylo- sent in females; epipodites on the first branchs are present and the linea homo- three pereiopods; the fourth and fifth pe­ lica is present. Because of these consider­ reiopods usually in dorsal position and so able differences the homolodromiids can­ metimes subchelate). However, the princi­ not be included into the superfamily Ho- pal problem is their position withm the moloidea. Dromiacea and their relationships with The third attempt at the classification other dromiid taxa. Before this considera­ of homolodromiids placed them in the fa­ tion it is necessary to point out that the mily Prosopidae as the subfamily Homolo- homolodromiids are the only crabs to pos dromiinae, along with the subfamilies Pro- ses such primitive characters as rudimen­ sopinae and Pithonotinae. Unfortunately tary antennal scalae and trichobranchs. the latter two taxa are known only as fos­ Considering the relationships with sils and therefore a complete comparison other Dromiacean taxa, we shall first exa­ is more difficult than with recent crabs. mine the relationships between homolo­ There are indeed similarities with both dromiids and the superfamily Dromioidea. prosopid subfamilies. For instance, they which is composed of Dromiidae and Dy- correspond in having an elongate and cy­ nomenidae. Between these two taxa there lindrical cephalothorax without orbits, an­ are several similarities, e.g.: linea dromi tennal grooves or a distinct lateral mar ca; abdomen incompletely folded agains^ gin, but with well developed cervical and cephalothorax: epipodites on the first pe- branchiocardiac grooves. Yet, prosopids reiopod; sternal furrows present; rudi­ differ in having the fourth and fifth pairs ments of uropods present. On the other of pereiopods neither dorsally placed nor SYSTEMATICS OF THE HOMOLODROMIIDS 67

subchelate in some examples; hepatic described the first. Since these three taxa grooves are absent in homolodromiids; are also mutually different in some details the rostrum projects in prosopids while it is necessary to consider them as sepa­ in homolodromiids there are two long rate families. Thus, the homolodromiids frontal spines. Also the sculpturing in the should be regarded as the family Homolo- prosopids is very prominent, especially in dromiidae, which with the Eocarcinidae the cervical and branchiocardiac furrows, and Prosopidae form the superfamily Pro- the last of which is stronger. Moreover, sopoidea. This superfamily, because of the in the Pithonotidae the fronto-orbitai most primitive organization, could be re­ margin is wide, not very projecting, and tained at the beginning of the Dromiacean there is an incomplete lateral margin in system, as the most primitive taxon. some forms. In spite of several similari­ By way of a summary here is the defi- ties, homolodromiids cannot be classified nition and classification of the superfa­ together with these taxa in the Prosopi- mily Prosopoidea including the subject of dae. our consideration — the family Homolo- Of the fossil Brachyuran families there dromiidae. The definition of the superfa­ is still the family Eocarcinidae, which is mily runs as follows: very similar to both the prosopids and to the homolodromiids. The homolodromiids Prosopoidea superfam, nov. and the eocarcinids have the following Cephalothorax elongate and usually cy­ characters in common: elongated and cy­ lindrical; front mostly narrow; rostrum lindrical cephalothorax; orbits and lateral present; true orbits absent; orbital groo­ margins absent; cervical and branchiocar­ ves present in some genera only: lateral diac furrows well developed; last pair ol margin usually absent; carapace frequent pereiopods in dorsal position. Differences ly strongly sculptured; cervical and bran­ are also present: in eocarcinids the inter­ chiocardiac grooves distinct; abdomen calated lateral platelets between; the sixth large in both sexes, with seven unfused and seventh somites (rudiments of uro- somites; chelae small and equal and can­ pods) are absent; the telson is small: the not be flexed against the carapace; fourth abdomen is not folded under the cephalo­ pair of pereiopods sometimes reduced and thorax (unless it is an artefact of fossili- dorsally placed: fifth pair of pereiopods, zation); the directions of the furrows on excluding some genera of the Prosopidae, the carapace are different. So the homo­ reduced and dorsally placed and subche­ lodromiids cannot be included in this tax- late. Predominantly fossil crabs. The Pro­ on. sopoidea includes the following families: Having considered all the possible re­ Eocarcinidae Withers, 1932; Prosopoidea, lationships between the homolodromiids von Meyer, 1860 and Homolodromiidae, and other Dromiacean taxa it is obvious Alcock, 1899. that they are most similar in form and structure to eocarcinids and prosopids, ACKNOWLEDGEMENTS. The author while they are less like the wishes to express his sincere gratitude to and Dromioidea. Moreover, the aforemen Dr. D. Williamson (Port Erin), Prof. L. tioned evidence permits the inference thai Holthuis (Leiden), Dr. R. Serene (Paris), the homolodromiids, the eocarcinids and Prof. B. Dulic (Zagreb) and M. Tiirkay the prosopids are not only on the same (Frankfurt) for their reading and critical organizational level, but also that they aie comments on the manuscript. Grateful related and therefore form a separate ta- acknowledgement is made to the Self-ma xon on the level of a superfamily. This naging Community of Interest in Scienti­ new superfamily could be named Proso- fic Research of the S. R. Croatia for the poidea because the genus Prosopon was support of this work. Z. STEVCIC

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SISTEMATSKI POLOZAJ I STATUS HOMOLODROMIIDA

SAZETAK. Polozaj u sistemu i sistematski status homolodromiida razlicito su shvaceni u proslosti, a misljenja karcinologa ni do danas nisu uskladena. Uvrstavali su ih u natporodice Homoloidea i Dromioidea i u porodicu Prosopoidae, a status im je kolebao od razine roda do po- rodice. Da bi im ustanovili sistematski polozaj a status, obavljena su po- redbena istrazivanja sa sistematski najblizim svojtama (taxa) unutar Dromiacea. Ustanovljeno je da se homolodromiidi zbog svojih specific- nih i izrazito primitivnih svojstava ne mogu uvrstavati ni u jednu od spomenutih svojti, vec da je rijec o posebnoj porodici Homolodromiidae, kao sto je to vec ranije utvrdio Alcock (1). Ta se porodica po svom ustrojstvu podudara s porodicama Prosopidae i Eocarcinidae, s kojima cini novu natporodicu Prosopoidea, koja je ovdje opisana. To je najpri- mitivnija svojta unutar Dromiacea te je stoga valja zadrzati na pocetku sistema kratkorepaca (Decapoda, Brachyura).