Cephalaspideans (Cephalaspidea = Bullomorpha) are the most primitive opisthobranchs and they have traditionally been regarded as a transitional group between the prosobranchs and other opisthobranchs. There are more than 800 species distributed worldwide. Some recent phylogenetic studies have shown that cefalaspideans (sensu lato) are not a monophyletic group and so the group has been split in three, the Cephalaspidea sensu stricto, the Runcinacea and the Architectibranchia (also known by the name lower Heterobranchia, see Classification section). In the latter group, according to these studies, Acteonidae, Aplustridae and Ringiculidae families would no longer really be opisthobranchs, a group that they belonged to until recently.

Melanochlamys miqueli by Enric Madrenas

Cephalaspidean in wide sense (sensu lato) are typically testacean opisthobranchs, as many of these species have shells. For instance Acteon has a well calcified spirally wound outer shell, where the animal may withdraw into it completely, while in other species, such as Scaphander and Haminoea, the external shell, although calcified, is little spirallized and the animal can not withdraw completely into it. The shell consistency can also be fragile and could be partially covered by the mantle, as in the species of the Atyidae family, or little calcified and internal, having been completely covered by the mantle, as in the family Philinidae. In Runcinacea family there is a vestigial internal shell or it could have disappeared completely. The head of the cefalaspideans has a kind of head shield or disk (Cephalaspidea = head shield) that facilitates the animal’s burial in the soft substrate that conforms the usual habitat of the representatives of this group. Because of this, the head does not usually have tentacles or other sensory expansions. The mantle cavity is usually well developed and can be located in front of the animal, or in posterior position. A folding type gill lies within the mantle cavity. In the digestive tract there is a gizzard that has hardened plates to grind food. Radula could be missing in some species. About the reproductive system there is a genital opening located at some distance from the male copulatory organ and there is a ciliated seminal groove connecting them that allows the sperm to swim through in copulation, a trait shared with the Anaspidea. The foot is of the creeping type and differentiates, in some species, a pair of lateral lobes or parapodial lobules, as in Gastropteron rubrum, that could be laid on the shell when the animal is at rest and could be also used for swimming.

The cephalaspideans usually inhabit soft substrates, where they live buried several inches below the surface in search of food. Some species inhabit mud or gravel bottoms frequented by trawling fishing boats, so they usually appear among the discarded non-commercial fishes, such as Scaphander lignarius, which can reach about 80 mm in length and feeds on foraminifera, polychaetes, gastropods and small bivalves. In similar grounds lives Philine aperta and Ph. catena, which feed on polychaetes, foraminifera and bivalves. Retusa and Cylichna species live in sand and mud bottoms or within Posidonia oceanica meadows, feeding on small foraminifera and gastropods. The species of the genus Haminoea and Bulla are herbivorous and live inside muddy sea ports or shallow bays with seagrass bottoms, feeding on green, brown and red algae and phanerogams like Cymodocea nodosa cyanobacteria and diatoms. The species of the genus Navanax, Philinopsis, Aglaja and others from the Aglajidae family are known to be very active predators, preying upon flatworms, nemerteans, polychaetes and even nudibranchs, including other cephalaspideans. In different cephalaspidean species there have been found secondary metabolites involved in the chemical defense of the animal and also others that function as alarm pheromones for communication among different speciments, like in Haminoea species. Cephalaspideans are simultaneous hermaphrodites and after copulation they lay an egg ribbon with numerous eggs on the sand.

Cephalaspideans sensu stricto live in all kinds of soft substrates, from the intertidal zone to circalittoral bottoms. Several species inhabit warm and temperate waters of both hemispheres and even some are known to prefer polar waters, like Philine alata, from Antarctic waters. Scaphander has about twenty species distributed by deep soft bottoms of all the seas around the world, from Arctic to Antarctic waters. In the Iberian Peninsula, Balearic and Canary Islands there have been cited more than a hundred Cephalaspidea species s.s., which corresponds to 90% of all species known to live in European waters, according to the ERMS (European Register of Marine Species). About thirty of these species have been observed in Catalan waters.

According to recent phylogenetic studies using molecular data (Malaquias et al. 2009. A molecular phylogeny of the Cephalaspidea sensu lato (Gastropoda: Euthyneura): Architectibranchia redefined and Runcinacea reinstated) (see also the taxonomy section in this website), the opisthobranchs included in the traditional Cephalaspidea order in wide sense (sensu lato) could be divided into three groups or clades: Architectibranchia (=lower Heterobranchia according WoRMS) with “infraclass” category within the subclass Heterobranchia, Runcinacea and Cephalaspidea sensu stricto with the latter two of “order” category within the infraclass of the Opisthobranchia. This means that the families included within Architectibranchia would no longer be considered true Opisthobranchia despite the fact that by morphology and habitat some of them are related to the true cephalaspideans. In the classification that follows, however, we state those families within Architectibranchia that have been considered, at some point, within Cephalaspidea sensu lato. In the recent work of Jörger et al. (2010) Cephalaspidea s.s. and Runcinacea are included in the group or clade Euopisthobranchia.

  • Infraclass Architectibranchia (lower Heterobranchia) Haszprunar, 1985
    • Family Acteonidae d’Orbigny, 1843
      • Genus Acteon
      • Genus Japonacteon
      • Genus Mexacteon
      • Genus Pupa
    • Family Aplustridae Gray, 1847
      • Genus Hydatina
      • Genus Micromelo
    • Family Bullinidae Gray, 1850
      • Genus Bullina
    • Family Ringiculidae Philippi, 1853
      • Genus Ringicula
  • Infraclass Opisthobranchia Milne Edwards, 1848
    • Order Runcinacea Burn, 1963
      • Family Runcinidae H. Adams & A. Adams, 1854
        • Genus Runcina
      • Family Ilbiidae Burn, 1963
        • Genus Ilbia
    • Order Cephalaspidea Fischer, 1887 (Cephalaspidea sensu stricto)
      • Superfamily Diaphanoidea Odhner, 1914
        • Family Diaphanidae Odhner, 1914
          • Genus Diaphana
          • Genus Newnesia
          • Genus Toledonia
          • Genus Colpodaspis
      • Superfamily Philinoidea Gray, 1850
        • Family Cylichnidae H. Adams & A. Adams, 1854
          • Genus Cylichna
          • Genus Acteocina
          • Genus Tornatina
        • Family Scaphandridae G. O Sars, 1878
          • Genus Scaphander
          • Genus Roxania
        • Family Retusidae Thiele, 1925
          • Genus Retusa
          • Genus Pyrunculus
          • Genus Cylichnina
        • Family Rhizoridae Dell, 1952
          • Genus Rhizorus
          • Genus Volvulella
        • Family Philinidae Gray, 1850
          • Genus Philine
        • Family Aglajidae Pilsbry, 1895
          • Genus Aglaja
          • Genus Chelidonura
          • Genus Navanax
          • Genus Philinopsis
          • Genus Spinoaglaja
        • Family Philinoglossidae Hertling, 1932
          • Genus Philinoglossa
        • Family Gastropteridae Swainson, 1840
          • Genus Gastropteron
          • Genus Siphopteron
      • Superfamily Bulloidea Gray, 1827
        • Family Bullidae Gray, 1827
          • Genus Bulla
          • Genus Hamineobulla
      • Superfamily Haminoeoidea Pislbry, 1895
        • Family Haminoeidae Pilsbry, 1893
          • Genus Atys
          • Genus Haminoea
          • Genus Phanerophthalmus
          • Genus Weinkauffia

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

Acteocina mucronata (Philippi,1849) @ Dubai (UAE) by Joop Trausel and Frans Slieker

Acteocina mucronata

Acteocina (Tornatina) crithodes by Melvill J. C. & Standen R. (1901)

Acteocina crithodes

Aglaja tricolorata

Aglaja tricolorata

Aliculastrum cylindricum by Monse Sanz Ortiz

Aliculastrum cylindricum

Atys blainvillianus

Atys blainvillianus

Atys jeffreysi @ Gnejna Bay, Mgarr, Malta by Constantino Mifsud

Atys jeffreysi

Atys macandrewii @ Malta by Constantino Mifsud

Atys macandrewii

Biuve fulvipunctata 1cm @ S'Algar, Menorca 5 m. 21-08-2015 by Enric Madrenas

Biuve fulvipunctata

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

Bulla arabica

Bulla striata @ Taranto, Italy 19-06-2016 by Enrico Ricchitelli

Bulla striata

Camachoaglaja africana by Enric Madrenas

Camachoaglaja africana

Colpodapsis pusilla (2) Quelhuit 24062009 by Jean Michel Crouzet

Colpodaspis pusilla

Cylichna alba @ Senja Island, Troms, Norway by Joop Trausel and Frans Slieker (Natural Museum Rotterdam)

Cylichna alba

Cylichna cylindracea @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Cylichna cylindracea

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

Diaphana globosa

Diaphana minuta by Klas Malmberg (Sweden)

Diaphana minuta

Gastropteron rubrum by Gilles Cavignaux

Gastropteron rubrum

Haminoea cyanomarginata by Alessandro Pagano

Haminoea cyanomarginata

Haminoea elegans @ Lake Worth lagoon, West Palm Beach, Florida, USA 21-07-2010 by Anne DuPont

Haminoea elegans

Haminoea exigua by Sandrine Bielecki

Haminoea exigua

Haminoea hydatis @ Malta by Constantino Mifsud

Haminoea hydatis

Haminoea japonica by Gilles Cavignaux

Haminoea japonica

Haminoea navicula by Gilles Cavignaux

Haminoea navicula

Haminoea orbignyana

Haminoea orbignyana

Haminoea orteai @ Azores by Peter Wirtz

Haminoea orteai

Hermania scabra @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Hermania scabra

Laona pruinosa 5mm @ Sgeir Port A'Ghuail, Loch Fyne (Scotland) 6m 27-04-2013 by Jim Anderson

Laona pruinosa

Laona quadrata @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Laona quadrata

Melanochlamys miqueli by Enric Madrenas

Melanochlamys miqueli

Melanochlamys wildpretii @ Cap de Creus 11m 31-10-2015 by Enric Madrenas

Melanochlamys wildpretii

Philine angulata @ Artsdatabanken - Cephalaspids of Norway - by Lena Tina Ohnheiser

Philine angulata

Philine catena @ Costa Brava 3-05-2015 by Enric Madrenas

Philine catena

Philine lima @ Artsdatabanken - Cephalaspids of Norway - by Lena Tina Ohnheiser

Philine lima

Philine monterosati shell by Marion, A.F. Annales du Museé d'Histoire Naturelle de Marseille, Tome II, 1884-1885

Philine monterosati

Philine punctata 4mm @ Menai Strait, Wales. April 2011 by Ian Smith

Philine punctata

Philine_quadripartita 2 15mm @ Wied iz-Zurrieq, Malta 36m depth 27-08-1995 by Carmel Sammut

Philine quadripartita

Philine striatula. Colezzione malacologiche del Museo Civico di Zoologia, Roma

Philine striatula

Philine ventricosa @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Philine ventricosa

Philinoglossa helgolandica @ Cariño (Ría de Ferrol) 10.02.2004 by Victoriano Urgorri

Philinoglossa helgolandica

Philinopsis depicta by Luis Sánchez Tocino

Philinopsis depicta

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

Philinopsis speciosa

Pyrunculus fourierii (Audouin,1826) @ Mersin, Turkey by Joop Trausel and Frans Slieker (Natural History Museum Rotterdam)

Pyrunculus fourierii

Pyrunculus ovatus @ Artsdatabanken - Cephalaspids of Norway - by Lena Tina Ohnheiser

Pyrunculus ovatus

Retusa crossei (Bucquoy, Dautzenberg & Dollfus, 1886) 2mm from Malta in 35 m.

Retusa crossei

Retusa desgenettii @ Dahab, Egypt by Joop Trausel and Frans Slieker

Retusa desgenettii

Retusa leptoeneilema @ Vranjic, Croatia 3-12-2016 by Jakov Prkić

Retusa leptoeneilema

Retusa mammillata @ Cariño (Ría de Ferrol) 10.02.2004 by Victoriano Urgorri

Retusa mammillata

Retusa minutissima Monterosato, 1878 by Mouna Antit

Retusa minutissima

Retusa obtusa @ Artsdatabanken - Cephalaspids of Norway - by Lena Tina Ohnheiser

Retusa obtusa

Retusa truncatula 3mm @ Ibiza by Joop Trausel & Frans Slieker (Natural History Museum Rotterdam)

Retusa truncatula

Retusa umbilicata @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Retusa umbilicata

Ringicula auriculata (Ménard de la Groye, 1811) Specimen from La Goulette, Tunisia (soft bottoms 10-15 m, 19.01.2010), actual size 3.4 mm

Ringicula auriculata

Ringicula buccinea (Brocchi,1814) [MIOCENE]

Ringicula buccinea

Ringicula conformis Monterosato, 1877 Specimen from La Goulette, Tunisia (soft bottoms 10-15 m, 19.01.2010), actual size 3.1 mm

Ringicula conformis

Ringicula minutula

Ringicula minutula

Roxania utriculus @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Roxania utriculus

Scaphander lignarius @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Scaphander lignarius

Scaphander punctostriatus @ Artsdatabanken - Cephalaspids of Norway - by Manuel Malaquias

Scaphander punctostriatus

Mnestia girardi (Audouin,1826) @ Famagusta, Cyprus by Joop Trausel and Frans Slieker

Mnestia girardi

Volvulella acuminata @ Artsdatabanken - Cephalaspids of Norway - by Lena Tina Ohnheiser

Volvulella acuminata

Volvulella ovulina @ Japan by Tadashige Habe

Volvulella ovulina

Weinkauffia turgidula by Lluís Toll

Weinkauffia turgidula