The Cephalaspideans (CEPHALASPIDEA) are the most primitive opisthobranchs and have traditionally been considered as a transitional group between the prosobranchs and the rest of opisthobranchs. There are more than 800 species known around the world. Some time ago, phylogenetic studies were carried out that showed that classical cephalaspideans (sensu lato) were not a monophyletic group, so they split it into three: the Cephalaspidea sensu stricto, the Runcinidae (former Runcinacea) and the [unassigned] Heterobranchs  (former Architectibranchia). Within this last group, according to these studies, families such as Acteonidae, Aplustridae and Ringiculidae are no longer considered opisthobranchs, group where they belonged until very recently, although they are still classified as Heterobranchs.

Melanochlamys miqueli by Enric Madrenas

Cephalaspideans in the broad sense (sensu lato) are opisthobranchs typically testaceans since many of their species have a shell. Many species of Scaphander and Haminoea have an external well calcified shell but that is little spiralized and the animal can not retract completely inside. The shell can be very little calcified and be internal because it has been completely covered by the mantle, as in the family Philinidae. The head of the cephalaspideans has a cephalic disc or shield (Cephalaspidea = Shielded Head) that facilitates the burial of the animal in the soft substrate, common habitat of the representatives of this group. Precisely because of this, the head does not usually have tentacles or other sensory expansions. The pallial cavity is usually well developed and could be located anteriorly or posteriorly. Inside the pallial cavity there is a folded type gill. In the digestive tract there are hardened plates to crush the food and the radula could be missing in some species. In the reproductive system, the genital orifice is located at a certain distance from the male copulatory organ, so there is a ciliated seminal groove between them, as happens with the Aplysiida. The foot is of the crawling type and differentiates, in some species, a pair of lateral or parapodial lobes, as in Gastropteron rubrum, which are covering the shell when the animal is resting and can also be used for swimming.

The cephalaspideans are usually inhabitants of soft substrates, where they live buried several centimeters deep in search of food. Some species inhabit silt or gravel seabeds that are comercial trawlers fishing grounds, therefore they often appear as bycatch, such as Scaphander lignarius, which can reach 80 mm in length and feeds on foraminifera, polychaetes, gastropods and small bivalves. Philine quadripartita and Ph. Catena live on similar seabeds, feeding on polychaetes, foraminifera and bivalves. Retusa and Cylichna species live on sand and mud seabeds or Posidonia oceanica meadows feeding on foraminifera and small gastropods. The species of the genera Haminoea and Bulla are herbivorous and live in the muddy seabeds of ports or shallow bays with seagrass beds, feeding on green, brown and red algae and phanerogames such as Cymodocea nodosa, as well as cyanobacteria and diatoms. The species of the genera Navanax, Philinopsis, Aglaja and others (family Aglajidae) are very active predators of turbelarians, nemerteans, polychaetes and even nudibranchs and other cephalaspidedes. In different studies some cephalaspidean species have rendered secondary metabolites involved in the chemical defense of the animal and also others that function as alarm pheromones for communication between different specimens, as in Haminoea species. The cephalaspideans are simultaneous hermaphrodites and after the copula they produce a ribbon or cord with numerous eggs that they lay on the sand.

The Cephalaspideans live in all kinds of soft substrates, from the intertidal zone to circalitoral bottoms. Numerous species inhabit warm and temperate waters of both hemispheres and some are even known that prefer cold polar waters, such as Philine alata, from Antarctic waters. Scaphander has many species that are distributed on the soft seabeds of a certain depth of all the seas of the world, from the Arctic to the Antarctic waters. In the Iberian Peninsula, the Balearic and Canary Islands, more than one hundred species of Cephalaspideans have been reported, corresponding to 90% of all species present in European waters according to the ERMS (European Register of Marine Species). About 30 of these species have been observed in Catalan waters.

The current taxonomy of the Cephalaspidea, proposed by Bouchet et al. (2017) and published in WoRMS, is:

  • Order Cephalaspidea P. Fischer, 1883
    • Superfamily Bulloidea Gray, 1827
      • Family Bullidae Gray, 1827
        • Genus Bulla Linnaeus, 1758
        • Genus Hamineobulla Habe, 1950
      • Family Retusidae Thiele, 1925
        • Genus Pyrunculus Pilsbry, 1895
        • Genus Relichna Rudman, 1971
        • Genus Retusa T. Brown, 1827
        • Genus Sulcoretusa J. Q. Burch, 1945
      • Family Rhizoridae Dell, 1952
        • Genus Rhizorus Montfort, 1810
        • Genus Volvulella Newton, 1891
      • Family Tornatinidae P. Fischer, 1883
        • Genus Acteocina Gray, 1847
    • Superfamily Cylichnoidea H. Adams & A. Adams, 1854
      • Family Colinatydidae Oskars, Bouchet & Malaquias, 2015
        • Genus Colinatys Ortea, Moro & Espinosa, 2013
      • Family Cylichnidae H. Adams & A. Adams, 1854
        • Genus Adamnestia Iredale, 1936
        • Genus Bogasonia Warén, 1989
        • Genus Cylichna Lovén, 1846
        • Genus Cylichnania Marwick, 1931 †
        • Genus Cylichnella Gabb, 1873
        • Genus Cylichnoides Minichev, 1977
        • Genus Decorifer Iredale, 1937
        • Genus Mamillocylichna Nordsieck, 1972
        • Genus Paracteocina Minichev, 1966
        • Genus Semiretusa Thiele, 1925
        • Genus Sphaerocylichna Thiele, 1925
        • Genus Toledonia Dall, 1902
        • Genus Truncacteocina Kuroda & Habe, 1955
      • Family Diaphanidae Odhner, 1914 (1857)
        • Subfamily Diaphaninae Odhner, 1914 (1857)
          • Genus Diaphana T. Brown, 1827
      • Family Eoscaphandridae Chaban & Kijashko, 2016
        • Genus Eoscaphander Habe, 1952
        • Genus Pseudocylichna Chaban & Kijashko, 2016
      • Family Mnestiidae Oskars, Bouchet & Malaquias, 2015
        • Genus Mnestia H. Adams & A. Adams, 1854
    • Superfamily Haminoeoidea Pilsbry, 1895
      • Family Haminoeidae Pilsbry, 1895
        • Genus Aliculastrum Pilsbry, 1896
        • Genus Atys Montfort, 1810
        • Genus Austrocylichna Burn, 1974
        • Genus Bullacta Bergh, 1901
        • Genus Cylichnatys Kuroda & Habe, 1952
        • Genus Diniatys Iredale, 1936
        • Genus Haminoea Turton & Kingston [in Carrington], 1830
        • Genus Liloa Pilsbry, 1921
        • Genus Limulatys Iredale, 1936
        • Genus Micratys Habe, 1952
        • Genus Mimatys Habe, 1952
        • Genus Nipponatys Habe, 1952
        • Genus Phanerophthalmus A. Adams, 1850
        • Genus Smaragdinella A. Adams, 1848
        • Genus Weinkauffia Monterosato, 1884
    • Superfamily Newnesioidea Moles, Wägele, Schrödl & Avila, 2017
      • Family Newnesiidae Moles, Wägele, Schrödl & Avila, 2017
        • Genus Hocius Moles, Avila & Malaquias, 2017
        • Genus Newnesia E. A. Smith, 1902
    • Superfamily Philinoidea Gray, 1850 (1815)
      • Family Aglajidae Pilsbry, 1895 (1847)
        • Genus Aglaja Renier, 1807
        • Genus Biuve Zamora-Silva & Malaquias, 2017
        • Genus Camachoaglaja Zamora-Silva & Malaquias, 2017
        • Genus Chelidonura A. Adams, 1850
        • Genus Mannesia Zamora-Silva & Malaquias, 2017
        • Genus Mariaglaja Zamora-Silva & Malaquias, 2017
        • Genus Melanochlamys Cheeseman, 1881
        • Genus Nakamigawaia Kuroda & Habe, 1961
        • Genus Navanax Pilsbry, 1895
        • Genus Niparaya Zamora-Silva & Malaquias, 2017
        • Genus Odontoglaja Rudman, 1978
        • Genus Philinopsis Pease, 1860
        • Genus Spinoaglaja Ortea, Moro & Espinosa, 2007
        • Genus Spinophallus Zamora-Silva & Malaquias, 2017
        • Genus Tubulophilinopsis Zamora-Silva & Malaquias, 2017
      • Family Alacuppidae Oskars, Bouchet & Malaquias, 2015
        • Genus Alacuppa Oskars, Bouchet & Malaquias, 2015
      • Family Colpodaspididae Oskars, Bouchet & Malaquias, 2015
        • Genus Colobocephalus M. Sars, 1870
        • Genus Colpodaspis M. Sars, 1870
      • Family Gastropteridae Swainson, 1840
        • Genus Enotepteron Minichev, 1967
        • Genus Gastropteron Kosse, 1813
        • Genus Sagaminopteron Tokioka & Baba, 1964
        • Genus Siphopteron Gosliner, 1989
      • Family Laonidae Pruvot-Fol, 1954
        • Genus Laona A. Adams, 1865
      • Family Philinidae Gray, 1850 (1815)
        • Genus Globophiline Habe, 1958
        • Genus Hermania Monterosato, 1884
        • Genus Philine Ascanius, 1772
        • Genus Spiniphiline Gosliner, 1988
        • Genus Yokoyamaia Habe, 1950
      • Family Philinoglossidae Hertling, 1932
        • Genus Abavopsis Salvini-Plawen, 1973
        • Genus Philinoglossa Hertling, 1932
        • Genus Pluscula Er. Marcus, 1953
        • Genus Sapha Marcus, 1959
      • Family Philinorbidae Oskars, Bouchet & Malaquias, 2015
        • Genus Antarctophiline Chaban, 2016
        • Genus Philinorbis Habe, 1950
        • Genus Pseudophiline Habe, 1976
      • Family Scaphandridae G.O. Sars, 1878
        • Genus Alicula Eichwald, 1830 †
        • Genus Cylichnium Dall, 1908
        • Genus Kaitoa Marwick, 1931 †
        • Genus Maoriscaphander Dell, 1950 †
        • Genus Meloscaphander Schepman, 1913
        • Genus Micraenigma Berry, 1953
        • Genus Priscaphander Finlay & Marwick, 1937 †
        • Genus Roxania Leach, 1847
        • Genus Sabatia Bellardi, 1877
        • Genus Scaphander Montfort, 1810
        • Genus Taita Laws, 1948 †

Cephalaspidean superfamilies cited in the Mediterranean sea or around the Iberian Peninsula:

Bulla arabica by Baki Yokes @ 20081108 Kas, Turquia 15m on Cymodocea nodosoa+Halophila stipulacea, night dive, size 48.5mm


Diaphana globosa @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias


Weinkauffia turgidula by Lluís Toll


Philinopsis speciosa (60mm) @ Hekili Point, Maui, Hawaii 14-11-2008 by Cory Pittman