ALBUNEIDAE STIMPSON, 1858

BOYKO, CHRISTOPHER B., 2002, A Worldwide Revision Of The Recent And Fossil Sand Crabs Of The Albuneidae Stimpson And Blepharipodidae, New Family (Crustacea: Decapoda: Anomura: Hippoidea), Bulletin of the American Museum of Natural History 2002 (272), pp. 1-396 : 54-56

ALBUNEIDAE STIMPSON, 1858

DIAGNOSIS: Carapace subquadrate; epibranchial spine absent. Gills phyllobranch; gill formula given below. Distal peduncular segments entire. Antennule with three seg­ ments; dorsal flagellum with 17–250 articles, ventral flagellum with 0–7 articles. Antenna five­segmented; acicle present; flagellum with one to nine articles. Proximal maxillar endites narrower than distal endites. Mandible with three­segmented palp. Maxilliped I with epipod. Maxilliped III with epipod; merus unarmed; crista dentata absent or weak; exopod slender or lamellar. Pereopod I subchelate; dactylus dorsal margin smooth or crenulate; propodus cutting edge smooth or with blunt teeth. Pereopods II–IV dactyli laterally compressed and dorsoventrally expanded; dorsal margins of carpi smooth (except Albunea speciosa ). Pereopod V reduced, chelate. Abdomen with pleura on somites II– IV or II–V. Uropods present. Telson entire.

Gill Formula (podobranch/arthrobranch/ pleurobranch): maxilliped I, 0/0/0; maxilliped II, 0/0/0; maxilliped III, 0/0/1; pereopod I, 0/2/0; pereopod II, 0/2/0; pereopod III, 0/ 2/0; pereopod IV, 0/2/0; pereopod V, 0/0/1.

DISTRIBUTION: Worldwide in tropical, subtropical, and temperate waters.

TYPE GENUS: Albunea Weber, 1795 .

INCLUDED SUBFAMILIES: Albuneinae Weber, 1795 ; Lepidopinae , n. subfam.

REMARKS: The family name Albuneidae Stimpson, 1858 (a correction of Albunidae ) is no. 242 on the ‘‘Official list of familygroup names in zoology’’ (ICZN, 1958). The family name Albunidae Stimpson, 1858 (invalid original spelling for Albuneidae ) is no. 276 on the ‘‘Official list of rejected and invalid family­group names in zoology’’ (ICZN, 1958). The ‘‘official’’ name for this family has been given as ‘‘mole crabs’’ and that of the Hippidae as ‘‘sand crabs’’ ( Williams et al., 1989). Unofficially, both names have been used essentially interchangeably in the literature. However, species of Hippidae bear a much more striking resemblance to moles (Mammalia) in the shape of their carapaces than do albuneids. I suggest that the ‘‘official’’ common names of albuneids and hippids be switched and that the Albuneidae be furthermore known as ‘‘sand crabs.’’

Although there has been much speculation about the use of the elongated antennules of albuneids as a feeding device (e.g., Williams, 1965), this seems unlikely. The antennules almost always have one long and one short flagellum ( Snodgrass, 1952, incorrectly cites a single long flagellum, which is only true of Leucolepidopa ), and the two long flagellae possess interlocking mesially directed setae on the dorsal and ventral surfaces along their length. The primary function of the antennules is to form a respiratory tube through the sand by means of the interlocking setae ( Snodgrass, 1952; Boyko, personal obs.). Water is taken in through the respiratory tube, but little material is transported along with it. This observation, combined with the fact that all albuneids have moderately welldeveloped mandibles, suggests that they are scavengers or predators, rather than any type of filter feeder. Observations of their burrowing behavior also support a detritivore lifestyle for these animals ( Howard, 1968). Although Hill (1979) suggested that at least one albuneid, Lepidopa websteri , switches between filter feeding and deposit feeding, no experimental data were given by him to support this. Observations of food scraping from the antennules by the mouth parts ( Pearse et al., 1942) were most likely antennule cleaning behaviors, not feeding. Benedict (1903) first hypothesized that the antennules are used in maintaining the flow of water to the branchial chambers, based on an ‘‘experiment’’ with a specimen of Albunea gibbesii . What is surprising about Benedict’s (1903) ‘‘experiment’’ is that it was done with a dead specimen in a beaker of sand and alcohol! Nevertheless, the idea of albuneids as filter feeders remains entrenched in the literature, especially nonsystematic works (e.g., Howard, 1968; Hill, 1979). The only record in the literature regarding stomach content in albuneids was given by Benedict (1903), who reported annelid setae, synaptid holothurian skin, and small crustacean flagellae in the stomach of a Lepidopa benedicti from Florida. It seems highly unlikely that the two specimens of Albunea steinitzi reported by Tirmizi (1978) would have survived 47 days in an aquarium if they were filter feeders.

Speculation on the reason for the apparent rarity of albuneids in suitable habitats dates back as far as Benedict (1903), who suggested that they might live in higher densities in deeper waters, or perhaps deeper in the sand. Nearly 100 years later, all available evidence still suggests that albuneids are rarely common in any sandy beach habitat.

Chace and Kensley (1992) doubted the homology of the shallow incision at the posterolateral angle of the albuneid carapace with the cardiac notch of alpheid shrimp (Caridea). Indeed, these are certainly not homologous features and are likely not even in analogous positions on the cardiac region. Williams (1984) included the character ‘‘third maxillipeds without epipodites’’ in his diagnosis of the Hippoidea , but all albuneids possess these structures.

Ortmann (1892) presented a somewhat crude tree indicating his opinion on the relationships among the hippoids and between them and the galatheoids and paguroids, but most of his conclusions are unsupported by morphological evidence. Ortmann (1892) presented Blepharipoda as an intermediate between galatheids and the other hippoids, but both galatheids and the ‘‘higher’’ albuneids have phyllobranch gills, while Blepharipoda has trichobranch gills. It is difficult to envision a scheme by which the gill type easily transitions back and forth between these two states. Ortmann (1892) also indicated that Lepidopa is more derived than Albunea , but current analysis suggests that the opposite may be true (Boyko and Harvey, in prep.). Hippoids have generally been considered primitive anomurans (e.g., Ortmann, 1892; Martin and Abele, 1986), and, indeed, the characteristics of the spermatophores of hippoids are somewhat intermediate between those found in macrurans and those found in the higher Anomura (e.g., hermit crabs) ( Subramoniam, 1984; Tudge et al., 1999).

Digging behavior in hippoids has been postulated as a derived character uniting the Hippoidea (Faulkes and Paul, 1997b). However, it is equally possible that the similarities observed by Faulkes and Paul (1997b) in Blepharipoda , Lepidopa , and Emerita are due to convergence in morphology for a sand­dwelling lifestyle. Additional evidence showing that digging behavior is different in other sand­dwelling crabs (e.g., raninids) is needed to support any statement of this behavior as a synapomorphy for the Hippoidea .

Efford’s (1969) tree of evolutionary relationships in the Albuneidae is not highly informative. Although his basic groupings of taxa were sound (e.g., Albunea with Stemonopa , Lepidopa with Austrolepidopa ), his tree was based on rough ideas of relationships and is not a cladogram. His tree lacked resolution at the level of ‘‘ancestral Albuneidae ,’’ and some of his suggestions are untenable given additional evidence. For example, Efford (1969) placed Austrolepidopa and Leucolepidopa in a more derived position than Lepidopa , apparently on the strength of a single character (number of articles on the antennal flagellum), which he assumed should be reduced in the derived state. This logic, when applied to this one character, is not flawed, but when other characters, such as presence of leg membranes and flagellum on the exopod of maxilliped III, are examined, the overall pattern is reversed. It is unfortunate that this is the only tree of albuneid relationships available to date, particularly because it has been cited as if it were a true cladogram (e.g., Faulkes and Paul, 1997a).